6

Research Campaigns

In keeping with the move of the NASA Division of Biological and Physical Sciences (BPS Division) to the Science Mission Directorate (SMD), where large space missions operating over a decade or longer are the norm, and in keeping with the rapidly expanding presence of human activity in low Earth orbit (LEO), the statement of task for this decadal survey¹ included development of notional, proof-of-concept research campaigns. As tasked, these research campaigns were intended to address prioritized research activities as part of complex or multidisciplinary missions and to operate in the space environment as well as in appropriate ground-based research. Furthermore, these large-scale activities were to be considered in broad cost categories to “assist NASA’s understanding of the top-level scientific performance and resource options.” These research campaign activities emanated from over 100 input papers collected from the research community and discussion among the steering committee and the panels of the study. From those input papers and discussions, four distinct elements were developed and advanced for further technical risk and cost evaluation (TRACE). The TRACE process is described in Appendix E.

These four elements—comprising two research campaigns, one multi-agency opportunity, and one research infrastructure concept—are to be considered notional, to be pursued only when specific campaign-level investments above the current operating budget are available for the BPS Division.

Two research campaigns were identified that are coupled tightly to the key scientific questions (KSQs) and aligned with NASA needs and objectives, which scale to currently envisioned space platforms. These research campaigns directly address many of the recommended KSQs and directly target mission needs for future space exploration and habitation. They are designed to be accomplishable by NASA largely within the next decade.

Bioregenerative Life Support Systems (BLiSS) is a recommended research campaign to firmly demonstrate fundamental knowledge of the impact of the space environment on individual organisms and the dependencies on and synergies between organisms and the diverse populations that could serve as biological life-support systems in space—systems that could be self-sustaining. Manufacturing Materials and Processes for Sustainability in Space (MATRICES) is a recommended research campaign to develop a nonliving, self-reliant, sustainable, circular economy of materials and processes through better understanding of the attributes and fundamental characteristics of solid materials and complex fluids in space. There are no full-scale, closed-loop cycles for materials on Earth, yet they are essential for operating independent of Earth for long periods of time. Development of the

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¹ The statement of task is reprinted in Appendix A.

material systems, manufacturing techniques, and processing and reprocessing capabilities for intentional feedstocks and anthropogenic and natural source materials will not only enable living and working in space but would offer dramatic benefits to terrestrial sustainability.

Recommendation 6-1: NASA should pursue dedicated research campaigns that, through the coming decade, will drive resolution to specific groups of key scientific questions. Coordination beyond NASA, including other federal agencies and the private sector as well as public-private partnerships, should be considered for the dedicated new funding and materials to support the following two research campaigns:

• BLiSS (Bioregenerative Life Support Systems) to build and understand the systems that would provide high-quality food, refresh air and water, process wastes and enable the creation of space environments sustainable for long periods of time independent of Earth.
• MATRICES (Manufacturing Materials and Processes for Sustainability in Space) to understand and harness the physical processes by which materials and complex fluids can be repeatably used in space, to enable sustainable exploration and circular production life cycles for the built environment on Earth and in space.

Probing the Fabric of Space-Time (PFaST) is envisioned as a campaign-style, multi-agency opportunity that is only accomplishable through collaborative development between NASA and other U.S. government organizations and international partners. PFaST would use recent advances in atomic and optical clocks and spaceflight’s ability to span large distances and large variations in gravitational fields to seek both validation of purely theoretical models as well as previously unobserved features of spacetime. It is an extremely large-scale research and technology effort that scales well beyond the sole domain of NASA. The committee therefore determined that this is a multi-agency effort that would provide important data for multiple agencies’ technology needs that are derived from the biological and physical sciences (BPS) KSQs involving fundamental physics described in Chapter 5. This opportunity needs to be actively pursued, but only as a multi-agency effort where a substantial majority of the funding is provided by non-NASA sources.

Recommendation 6-2: NASA should pursue development of the Probing the Fabric of Space Time initiative in this decade only if it can obtain substantial (greater than 75 percent) funding from external (i.e., other than NASA) sources.

Polar Radiation of Model Organisms (PRoMO) is a notional concept of future research infrastructure that describes an opportunity for using a space vehicle not currently available to science—one that would allow a unique spaceflight experience that combines the effects of radiation and microgravity on mammals, plants, and cellular systems, thus underpinning the health risk–based decision process that is inherent in exploration beyond LEO. The PRoMO concept could enable crewless research investigations of physical systems, as well as on organisms including mammals, for extended exposure durations of interest to several KSQs described in Chapters 3, 4, and 5. This concept is presented for further study because of the long development time required to enable important BPS research, and the considerable unknowns in cost, especially as commercial spaceflight providers change the future cost landscape.

KEY TRACE ASSUMPTIONS

For the first time in the BPS in space research community planning, including the 2011 decadal survey, the committee utilized the TRACE process² to assess potential research campaigns. The Aerospace Corporation conducted the TRACE process under contract to the National Academies of Sciences, Engineering, and Medicine.

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² The TRACE process is described in Appendix E.

The committee provided input to Aerospace and worked with that contractor to develop TRACEs for several research campaigns, which the committee then used as input to its deliberative processes. In assessing the research campaigns, the committee used the following assumptions:

• NASA retains its key role in providing infrastructure and support to researchers. The International Space Station (ISS) Program Office support, with a segue to commercial LEO destinations (CLD) Program Office support to continue at least at present levels.
• NASA will continue to provide upmass, downmass, crew time, integration and support in preparation for launch, and so on, at levels similar to the present.
• Costs associated specifically with mission integration and operations (MI&O) and launch of BPS research are assumed to continue to be borne outside NASA or others’ funding of the BPS research activity itself. (See Chapter 7, Box 7-2.)
• Hosting and operations costs could be estimated from current NASA data, scaled by the number of experiments and projected crew hours. Some development reserves were included for phases B/C/D, but reserves for phases E/F were excluded under the premise that a research program is better managed by utilizing flexibility in the end date than by allocating dollar reserves to preserve the schedule.
• The current level of the core BPS Division research program is continued at least at the FY 2023 level, and so there is no break in research capability when the ISS is decommissioned. It is further assumed that the key facilities currently in use will be transitioned into the CLDs over time. If the current facilities are not transitioned, additional costs would be incurred for building, launching, and commissioning replacements.
• Crew time required to execute the core BPS Division research program and research campaigns can be estimated reasonably using NASA historical data. It is further assumed that, under the CLD model, crew time is an extensible resource (i.e., in principle, more crew time could be purchased if needed) and that arrangements will be made for private astronauts or civilian crews to use the NASA core facilities. These will enhance research productivity and may over time reduce NASA’s cost, but that could not be predicted with sufficient certainty for this effort.
• Technical risk (regarding timeline) and cost estimates can be based reasonably on both NASA’s historical costs (e.g., of crew time) and the best available published information from potential CLD providers.

A major new cost that has been considered is referred to as “Base CLD Facility Refresh” and represents the costs of moving some of the current facilities into a 51.6-degree orbit CLD and building fresh copies into a second CLD in another orbit. The costs of the proposed new facilities were estimated and scaled from the development of the legacy set, with an allowance for technology improvements. Note that the two research campaigns hold differing assumptions as to the transition time and implications of the transition from ISS to CLD capabilities. For example, the BLiSS campaign assumes experiments in parallel in the ISS and on the CLDs as they become available; the costs for continued ISS research and “copies” for research on the CLDs are included in the TRACE estimates for both the BLiSS and MATRICES campaigns.

Other considerations included strategic acquisition of multi-use infrastructure such as research racks, supporting space and resources for transport, environmental support, crew time, communication, and support for integration of experimenter-provided equipment and samples into launch transport facilities.

The research campaigns are described in the context of today’s rapidly changing space economy, and based on the best estimates of when and how capabilities will emerge and the business models of the various prospective providers. For example, Box 6-1 describes what happens when SpaceX’s Starship flies successfully.

MANAGING RESEARCH CAMPAIGNS TO ACHIEVE A STRATEGIC GOAL

The committee assumed that the core BPS research program will be managed similarly to recent practice. However, achieving the strategic goals of the two research campaigns will require a different way of managing the research efforts that goes beyond the standard Research Opportunities in Earth and Space (ROSES) open

announcements for BPS Division grants. Research campaigns will require development and evolution of research and technology roadmaps—building on and extending the body of knowledge and processes, selection criteria, and an alignment of proposed efforts to the roadmaps. Also, Research campaigns will require decision criteria such as when enough is known about a topic to focus resources elsewhere, continuity in research programs to allow commitment to longer-term sequences of experiments with a high cadence, and a fast decision cycle to quickly follow up to lessons learned.

NASA has learned much in exploring alternative models of pursuing strategic goals such as the SMD Heliophysics DRIVE Centers, the NASA SMD/HEO Solar System Exploration Research Virtual Institute (SSERVI), as well as the Space Technology Mission Directorate’s (STMD’s) Space Technology Research Institutes and The Lunar Surface Innovation Initiative. Lessons learned could be used to develop the best approach for strategic management to achieve the goals and balance considerations above. Chapter 7 includes recommendations in the context of the full decadal survey, with associated decision rules, and the lessons learned from the above institutes and initiatives may inform this management strategy specifically for research campaigns.

IMPACT OF THE RESEARCH CAMPAIGNS BY 2033

NASA has adopted a set of Moon-to-Mars objectives (NASA 2022c). The KSQs and the research campaigns directly support and are traceable to these objectives. Each campaign is intended to make major and transformative scientific contributions with recognizable impact to that mission space and to society. For example, the establishment of a robust bioregenerative life support system is a key contribution to Transportation and Habitation Goals TH-2 and TH-3. In addition to meeting Moon-to-Mars goals, the body of knowledge built through these campaigns will be critical to establishing a vibrant in-space economy. While it is always difficult to predict the applications of research, the increased body of knowledge of microbe, plant, and animal systems, and of biological systems-of-systems responses, to the stressing space environment will surely benefit terrestrial applications—including climate adaptations. Similarly, advances in efficient manufacturing and work to enable truly closed-loop production processes and habitats will inform advances in terrestrial systems, improving the management of waste stocks and reducing impact associated with mining and refining planetary resources.

RESEARCH CAMPAIGN: BIOREGENERATIVE LIFE SUPPORT SYSTEMS

The BLiSS research campaign is driven toward the following four high-level goals:

• Develop self-sustainable biological life-support systems that produce food, clean water, renew air, process waste, and create critical materials to meet the challenges of long-duration space missions.
• Harness beneficial properties of plants and microbes that will enable humans to live in space, independent of resupply from Earth.
• Create a highly functioning, robust, and resilient ecosystem and space environment that is self-sustainable under extraterrestrial radiation and gravity conditions.
• Enable long-duration (>3 years) exploration of deep space by providing a fully or partially closed–loop biological life-support system.

Future long-duration space missions of multiple years will require the ability to be self-sustainable without requiring resupply from Earth. (See Figure 6-1.) By harnessing the power of biological systems, the goal is to develop BLiSS for space exploration. Even while accepting that a full closed-system capability is unlikely to be achieved by the end of the decade, the BLiSS research campaign, as recommended, can provide appreciable offsets to resupply and quality-of-nutrient and quality-of-life benefits for the crews in that timeframe. The immediate benefits provided by BLiSS are production of vitamins and food, water purification, air revitalization, recycling of waste streams, and intangible mental benefits for crews living and working in space (Paradiso et al. 2014; Srinidhi and Turner 2021; Wheeler 2017). In addition, BLiSS can be a source of familiar biomaterials (e.g., plant fiber and wood) or more specialized materials such as drug precursors, specialty chemicals including epoxies, or bioplastics for three-dimensional (3D) printing.³

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³ See Aviles-Gaxiola et al. (2020), Buyel et al. (2021), Cestellos-Blanco et al. (2021), Haveman et al. (2023), Lu et al. (2020), and Shevtsov et al. (2023).

The NASA technology roadmap states that self-sufficient life support systems are crucial for sustaining life on long-duration missions (Kliss 2016). Several NASA needs assessments identify closed regenerative life support as an enabling technology for long-term, sustained human exploration, including the Lunar Human Exploration Strategic Knowledge Gap (SKG III-J-3), the Decadal Survey on Biological and Physical Sciences in Space Studies (DSBPS TSES6 and P3), the NASA 2020 Technology Taxonomy (TX06.3.5), and the Global Exploration Roadmap.

Earth is a worldwide BLiSS research campaign that is almost entirely self-sufficient and does everything from harvest energy from the Sun, renew the atmosphere, purify water, produce billions of different biomolecules, break down rock and inorganic and organic molecules, and produce the raw materials to build structures and feed future life cycles (Douglas et al. 2021; Drysdale et al. 2000). This is a system and capability needed to support life in deep space, at a vehicle scale, but that is currently not at a technology readiness level (TRL) that can be relied on in deep space. A BLiSS concept can be broken down in many different ways, but one approach involves modules or unit functions for primary production (e.g., plants), nutrient recovery and waste reprocessing, and secondary production to produce protein for consumption, or key biomaterials like drugs, bioplastics, biopolymers, or chemical feedstocks for other processes. Initially, some of these modules may be developed to augment or simplify functions that are currently done by the ISS environmental control and life support system (ECLSS), like water purification. As an example, plants can be watered with gray water, where a combination of plant microbiomes and plant roots recycle the nutrients and the water is transpired into the air. Recondensing the transpiration stream produces a water stream that could be fed into the final water polishing unit to make it potable rather than routing it through the entire ECLSS wastewater system. A square meter of plants produces about 5 liters of water a day, somewhat more than the allowance of an ISS astronaut. While it is not expected that a full, closed-system capability will be achieved by the end of the decade horizon described in this study (by 2032), the BLiSS campaign as recommended can provide appreciable offsets to resupply and quality-of-life benefits to exploration crews in that timeframe.

Research Thrusts

Overview

The major factors that impact crop systems and BLiSS for deep space are reduced atmospheric pressures with altered gas compositions, gravity, and radiation. Each factor needs to be considered in the context of a long-duration, multi-year mission. The first factor deals with the need to operate surface habitats at reduced pressures to reduce required prebreathing times for an extravehicular activity (EVA) in a space suit. These proposed atmospheres (e.g., the “exploration atmosphere” of 56.3 kPa atmospheric pressure and 34 percent oxygen) are not found anywhere on Earth. High carbon dioxide concentrations in spacecraft atmospheres can also be a challenge for plant performance (Burgner et al. 2020). The second factor relates first to gravity’s effect on water, helping it to move in familiar ways, rather than following any hydrophilic path. This has a big impact on how soils wet and drain, hydroponics, aeroponics, and root zone hypoxia (Heinse et al. 2009; Liao et al. 2004; Monje et al. 2003). Gravity also impacts gas exchange with the shoot zone necessitating higher air flow rates at reduced gravities (Poulet et al. 2018). Partial gravity or microgravity also impacts living systems in more indirect ways, such as causing increased virulence of some bacteria and increased disease susceptibility in some plants and animals (Taylor 2015). A related factor is extreme isolation on deep space missions. For microbial communities, this can lead to permanent loss of diversity over time, possibly endangering a mission by losing or altering critical species of a plant or soil microbiome. There is a similar risk for loss of crop genetic diversity. On the other hand, extreme isolation presents a mental stressor for crew function and performance that gardening may help to alleviate. Radiation, the fourth factor, is elevated outside of Earth’s protective magnetic field, with increased galactic cosmic ray (GCR) and solar proton events (SPEs) that degrade biological systems and materials over long periods of time. This can contribute to species loss, genetic damage, increased disease risk, reduction or elimination of seed germination, and destruction of the materials and hardware making up the BLiSS. Radiation exposure also increases the need for fresh foods, rich in antioxidants and vitamins, in the crew diet. The fifth factor is crop selection and optimization. Factors affecting crop choice include size of the hardware, ease of pollination, ability to produce relevant nutrition, crop hardiness in the relevant environment, and input needs of the crop. There may be other factors related to human responses over extended mission durations, particularly in helping with mental stress by establishing a sense of well-being with a familiar and tasty food, having colorful flowers, or producing food.

The BLiSS research campaign is designed to contribute answers to KSQs that are highlighted in Chapter 4, primarily under the second theme of living and traveling in space. That theme includes creating and maintaining safe, sustainable built environments and building a stable human presence. (See Table 7-1 for mapping to several KSQs.) Each KSQ could be explored using a learning cycle concept shown in Figure 6-2. Experiments need to be designed to test the concepts in meaningful and statistically relevant ways. This work can start with analogs or high-fidelity simulations on the ground more quickly and cost effectively than in space. Validated concepts can then be flown in LEO to gain an understanding of how space impacts the system, or to demonstrate that a solution works. Beyond LEO experiments are expected to be less available than LEO opportunities, so these could be used to add in the additional variables of a higher radiation environment and extreme isolation. Last, lunar environment (either lunar orbit or surface) opportunities will be least available but offer the opportunity to validate previous learnings under mission-relevant conditions (radiation, isolation, mission operations).

Objectives

BLiSS is designed to address KSQs and associated science and technology developments that lead to reliable bioregenerative life-support components. It is not designed to fully close the life-support loop in space. Therefore, key elements of BLiSS are considered to be primary production systems (e.g., plant or algae), nutrient recovery

systems (bioreactors using algae, bacteria, fungi or mixed systems; insect or hybrid systems, and potentially mammalian cell systems); and physical principle systems (e.g., plasma, combustion, heating, syngas production, and benefaction). Additional modules may include secondary production modules that produce protein, drugs, or specialized biomaterials (e.g., silk, biomolecules, vitamins, acetates, chiral chemistries) or feedstocks for manufacturing. Work has already been done on many of these.⁴ These systems could be fermenters, cell or tissue culturing systems, fungal production systems, or even plant-based, where the products could be varied through transformation or gene editing.

Bioreactors will be a critical part of any BLiSS because of the ability they provide to recycle nutrients. They offer the capability to help close the carbon, nitrogen, and water cycles while liberating critical locked-up minerals, including calcium, magnesium, potassium, and phosphorus. Additionally, bioreactors can be used to produce critical biomaterials or feed stock chemistries. Examples of types of products that can be produced include plastics made from poly-hydroxy alkanoic acid (PHA), poly-hydroxy butyrate (PHB), or polyethylene terephthalate (PET), used for high-strength plastics for spinning directly into fibers or solidified for later use. High-value chemistries or proteins include caffeine, aspirin, morphine, digitalis, insulin, taxol, or antibodies with therapeutic applications. Food waste and cellulosic materials may be converted to biofuels or used to produce high-value products. The type of bioreactor needed will be dependent on the nature of the starting material as well as the nature of the desired product and the gravity environment. In microgravity, bubbles do not float “up,” making it difficult to separate gases from the liquid eliminating most classic bioreactor. Bioreactors need to be designed for space. Initial experiments could be ground-based, focusing on obtaining the desired production and then looking at bioreactor designs that achieve the same or superior results in microgravity. Innovation is needed to develop bioreactors that work, can be cleaned, and that operate effectively and reliably in space.

Space Crop Production

The most immediate need for BLiSS is primary production—the ability to provide supplemental nutrition and a fresh element to astronaut diets (Douglas et al. 2021). A key goal for the BLiSS research campaign is to develop small-scale production systems that can supplement both of these for crews on long-duration missions while simultaneously laying the groundwork for larger BLiSS elements. The goal is to demonstrate how to do this, and to ensure that the food is safe to eat and nutritious (Haveman et al. 2021; Khodadad et al. 2020). Systems are currently being designed to fit into hardware analogous to the Veggie unit on ISS (Figure 6-3; Massa et al. 2017), although they could be made substantially smaller, potentially allowing demonstrations on CLPS missions (NASA 2020a) or testing in the Orion or human landing system space vehicles. Incremental technology steps include the following: development and testing of low-volume systems for microgreen (or other primary) production; understanding, modeling and optimizing how to produce safe nutritious foods from system inputs and outputs; demonstration of crop safety (plant and human pathogens) and vitamin production; and automation of microgreen production.

Infrastructure Enabling Research on Earth and/or Space Asset(s) Over the Decade

Moderately Sized Crop Production Systems

Moderately sized crop production systems (e.g., Veggie [Massa et al. 2017; NASA 2020b] and Advanced Plant Habitat [APH; Monje et al. 2020; NASA 2017] analogous hardware) are useful for developing cropping and microbiome models for a BLiSS. Crops of interest have already been produced in these types of systems, but current watering and growth systems are not suitable for 3-year missions. There are also knowledge gaps about preventing microbial biofilm production on spaceship surfaces, establishing and maintaining healthy plant microbiomes, integrating plant and human pathogen management plans (Khodadad et al. 2020; Liao et al. 2004;

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⁴ See Clauwaert et al. (2017), Gòdia et al. (2002), Hao et al. (2018), Massa et al. (2017), Miles and Lunn (2013), Poughon et al. (2020), Salisbury (1992), Schwartzkopf (1997), Taulavuori et al. (2017), Walker and Granjou (2017), and Yuan et al. (2019).

Monje et al. 2003; Schuerger et al. 2021), and understanding the interrelationships between the crop and the microbiome. In addition, there are questions about the effects of altered atmospheres and radiation environments in deep space on crops and the associated microbiomes, as well as the effects of years in space on microbiomes on seeds. Additional goals for crop systems involve developing and testing models for predicting, monitoring, and responding to plant health (Shevtsov et al. 2023). Experiments need to be conducted in ways that will generate data sets that will be useful to future investigators and that can be used to create models and train artificial intelligence (AI) for optimizing plant growth and system response to off-nominal events (Escobar et al. 2023). Veggie and APH sized systems may also be useful for developing and testing automation of plant growth systems as well as for improving ease of use, reliability, robustness, and ease of repair.

Integration and Development

The BLiSS research campaign represents a major effort that will benefit from focusing on developing and modeling individual modules or functions as well as from large, coordinated multi-national campaigns (Fu et al. 2016; Lang and Bamsay 2023; Salisbury 1992). Developing a functioning BLiSS requires developing primary production modules and integrating nutrient recovery modules and secondary producer modules and bioproducts such as medicines, plastics, epoxies, and foundation chemistries. Models based on the inputs, outputs, and

operations of these modules are needed so that they can be integrated into larger BLiSS designs. Additional testing and modeling of simple systems (e.g., a producing module and a nutrient recovery module) will uncover system dynamics and determine efficiencies. This will enable virtual testing of various designs to optimize systems before building and testing a larger BLiSS. Waste streams⁵ and nutrient recovery methods could be explored in parallel, including ones based on physical principles that include combustion, biochar, syngas, plasma, separations, and benefaction (Bubenheim and Wignarajah 1997) using bioreactors and physical chemical systems. Additional concepts include insects for breaking down bulk waste materials while also providing a source of protein (Fu et al. 2016).

Ground Testing and Development

Large ground versions of full BLiSS systems have been built, including BIOS-3, Biosphere 2, and Yuegong-1 (Lunar Palace 1) (Salisbury 1999). Lunar Palace 1 highlighted water and solid waste recycling (Liu et al. 2020; Zhao et al. 2022), impact on microbiomes (Hao et al. 2018; Yang et al. 2022), and element and energy cycling (Dong et al. 2017). The ESA has the MELiSSA project (Hendrickx et al. 2006; Paradiso et al. 2014; Verbeelen et al. 2021), which is focusing on various elements of a BLiSS, while DLR in Germany has developed EDEN ISS (Poulet et al. 2021; Zeidler et al. 2021) for understanding the requirements for operating a greenhouse in space. The University of Guelph in Canada offers large, sophisticated pressure chambers capable of simulating the reduced atmospheric pressures (75 kPa with elevated oxygen percentages) being planned for the lunar habitat (University of Guelph 2022). The Japan Aerospace Exploration Agency (JAXA) has the Ecology Experiment Facilities (EEF) for studying material cycles, particularly in plant modules. Ultimately, it would be beneficial to have one or more cooperative facilities of a scale capable of supporting two to six crew members where designs could be tested on Earth.

Biological Flight Hardware

There are three substantial pieces of hardware for plant biology on the ISS: Veggie, APH, and Spectrum. Veggie is a very basic, two-MLE-size growth system providing a light, a fan, a platform for growing, and bellows that can be pulled from the light fixture to the base to provide some isolation of the plants from the ISS environment. APH is four MLE-size payloads (1/2 Express Rack). It is a sophisticated growth chamber that provides a completely controlled plant growth environment (humidity, temperature, light, CO₂, and automated watering) requiring little oversight from the crew but is considerably more complex. Spectrum is a multifunctional piece of hardware for biological experiments that uses different lighting to measure properties of the biology. It is specifically designed to stimulate and record the most used florescent proteins. Its capacity is limited to four 10 cm × 10 cm petri dishes that are mounted to a carousel that can be rotated and monitored automatically or remotely. It can be used with small plants (Arabidopsis), microbes, and worms (C. elegans). These are valuable types of hardware to have available in the deep space environment. Veggie is the easiest to get to the lunar environment, owing to its comparatively lower mass, but this comes with the cost of crew time. Human factors will play a large role in identifying appropriate mission options for this hardware.

It is important to emphasize that biological research has been done in modular formats (mid-deck locker equivalents, or MLEs) that fit into the same mounting hardware onboard the space vehicle (the space shuttle or the ISS). This allows details of scientific experiments to be changed without major alterations to the spacecraft. It is critical that some level of portability be incorporated early into the designs of CLDs and across all vehicles so that hardware does not become unique to specific space vehicles and obsolete or unusable on others; this will require considerations of interoperability standards with participation of the public and private sectors. For example, Figure 6-4 provides an overview of possible locations for experiment infrastructure to support the BLiSS campaign.

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⁵ See Ashida (1994), Atkinson (1997), Garland et al. (1997), Guntur et al. (1999), Mackowiak et al. (1996, 1997), Pisharody et al. (1996), Saulmon et al. (1996), Strayer and Atkinson (1997), and Stutte (1996).

Sample Handling and Storage Infrastructure

Handling of biological samples is often similar regardless of the source of the sample (plant, animal, microbial). This is because biological responses are typically transient and degrade over time. Mission architecture plays an enormous role in the design of biological experiments primarily because the most sensitive and informative measurements are challenging or not currently possible to do in space. Free flying, no-return missions require measurements to be done on board the spacecraft, limiting the type of experiment and the data that can be recovered.

To understand biology, it is increasingly necessary to understand what is happening at the -omics level. Traditionally this includes sequencing capabilities (genome, transcriptome, metagenomics/transcriptomics, epigenetics) as well as the abilities to look at proteins (proteomics), enzyme activities and metabolites (metabolomics), and phenotypes (phenomics). Omics capabilities are a rapidly evolving technology space (Biteen et al. 2016). Unfortunately, the capabilities to do all of this in a fully automated manner in the deep space environment do not yet exist. If that can be done, this would reduce the need to return samples to Earth for analysis.

Missions offering the possibility of returning samples may require the samples to be preserved by chemical fixation, flash frozen, dry down (e.g., of seed, spores, plant materials) or other methods (e.g., lyophilization or freeze-drying). These techniques could be useful on commercial lunar payload services (CLPS) missions to the Moon where the samples might be preserved until they could be returned by a crew. Considerations need to be made for how the samples will survive long lunar day/night cycles in a passive or dead spacecraft until a crew arrives.

Shuttle and ISS experience shows that for crewed or fully automated missions, refrigerators and freezers (MELFI, GLACIER, POLAR, MERLIN, Glovebox Freezer) are valuable for preserving samples and increasing the science value. These can be used in combination with fixatives that preserve the samples suitability for omics studies, or directly if samples can be rapidly frozen. Samples need to stay frozen once they are frozen, while fixed samples are often more tolerant of temperature variations.

There are examples of flight hardware with built-in refrigerators or freezers such as the Space Automated Bioproduct Laboratory (SABL; Bioserve), TangoLab (Space Tango), BioCulture System (NASAAmes Research Center), Advanced Space Experiment Processor (ADSEP; Techshot), Multi-Use Variable-g Platform (MVP; Techshot), Science Taxi (Yuri), as well as others. These serve as models for most likely, smaller, more compact units that could be used in deep space. Ultimately, the real challenge is to have room for enough experiments to do a statistically valid experiment, as well as the ability to repeat it to establish the flight-to-flight variability required for impactful science.

Recommended Capabilities

Nucleic Acid Analysis

There is a high need for nucleic acid (DNA/RNA) analysis in space to reduce or eliminate the need for sample return, and to allow timely access to the data. This can be essential when scanning for or identifying human or plant pathogens and for monitoring microbiomes in the built space environment. Knowing early that there is a problem allows for corrective actions that can prevent serious consequences. In addition, the ability to monitor the environment for long periods of time informs understanding of the establishment and evolution of microbial communities in the space environment. This will be essential to long-term survival in space, because most organisms will be impacted by the high-radiation environment that increases genetic damage and the extreme isolation that can lead to loss of biological community and genetic diversity. Fields of related expertise would include fluid physics, nano-fluidics, and capillary electrophoresis for automated analysis. Better ways to capture DNA from dirty environments and clean it—that are compatible with automation—are also needed.

Automated Chemistry

Understanding what is happening in biology requires an understanding of the physical chemistry and biochemistry present. The field of “omics” is based on understanding the proteins and metabolites being produced in addition to the gene pathways leading to their production. On Earth, scientists have a wide array of tools available, including gas chromatography (GC), liquid chromatography (LC)-mass spectroscopy (MS), Fourier transformed infrared spectroscopy (FTIR), Rama spectroscopy, nuclear magnetic resonance (NMR), and so on. There are specialties and subspecialties of all of these techniques that help scientists uncover the complex chemistry of biological systems. While there is a strong desire to have all of these instruments in space, the constraints of spaceflight prevent most of them from flying. A research campaign is needed that calls for the development of automated, miniaturized versions of instruments that can be used in space.

Currently there are versions of chemical analysis instruments being developed for deep space studies such as microchip electrophoresis (ME)-LASER-induced fluorescence (LIF) or “chemical laptop” technology⁶ and capillary electrospray (CE)-MS and capillary electrospray ionization (CESI)-MS technologies being developed by the Jet Propulsion Laboratory⁷ and used in the European Molecular Indicators of Life Investigation (EMILI)

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⁶ See NASA JPL-CalTech Microdevices Laboratory, 2022, “Chemical Laptop: A New Twist on Life,” https://microdevices.jpl.nasa.gov/capabilities/in-situ-instruments-chemical-analysis/chemical-laptop.

⁷ See NASA JPL-CalTech Microdevices Laboratory, 2022, “CE-MS: Combining Two Powerful Approaches,” https://microdevices.jpl.nasa.gov/capabilities/in-situ-instruments-chemical-analysis/ce-ms.

(Brinckerhoff et al. 2022). While these devices are pushing back the boundaries on chemical detection in remote places, a recent review indicates that they are only able to detect some species and not others (Zhang and Ramautar 2021). Also, the table in the review indicates that many samples were extracted using reagents that are not usually allowed on the ISS owing to toxicity issues. Nonetheless, continuing to advance these types of analytic systems will advance researcher’s abilities to do chemical analysis in deep space and on Earth in remote places. There is a high need to detect and classify volatile organic compounds (VOCs) because some of these compounds (e.g., ethylene) are bioactive in parts per billion quantities, while others (e.g., siloxanes) cause problems for ECLSS systems currently in use on the ISS.

Data Requirements

A common element to many of the instrumentation systems above, but especially to genomics, transcriptomics, metagenomics, and to chemical analysis, is the need for large data libraries; these can easily be petabytes for genome analysis. Data sets from single crop experiments on Earth often exceed 5 TB. Typically, on Earth, genomics work is done on multi-core processor machines (hundreds of CPUs) or using “cloud computing” where the new data set is uploaded and then analyzed using petabyte-sized data libraries housed in data centers. The cloud can also provide thousands of processors and very large memory assets to support the analysis—reducing the analysis time to reasonable time periods (less than a day for most applications). In space, this is a challenge owing to limited computational and memory assets, telemetry, bandwidth, and latency or delay. Typically, the farther you get from Earth, the longer it takes to transmit a data set, increasing the strain on telemetry. One way to reduce these challenges is to have the computational, memory, and data resources available on the space vehicle. Basically, future space vehicles are going to need to take the cloud, or at least pieces of it, with them. Having this type of infrastructure available will also enable AI development in space, because machine learning and other forms of AI also benefit from cloud computing architecture.

Impact by 2033 If the Campaign Is Successful

As far as scientists understand currently, the land portion of Earth remained largely uninhabitable for billions of years until early forms of microorganisms produced oxygen and early plants evolved and began to colonize it, providing both an energy source and habitat for other creatures. Earth’s solar system is filled with distant worlds that are little changed and hostile to life for billions of years. The big idea of the BLiSS research campaign is to enable building fully functional biological support systems to support exploration of deep space. It is unlikely that this will be mastered or have the resources to build a functional habitat on Mars or the Moon by the end of the decade. Nonetheless, by 2033, the BLiSS campaign could deliver the science underpinning the modules of a bioregenerative life-support system that demonstrate augmentation, enhancement, or parallel replacement of portions of nonbiological ECLSS systems. Obvious areas are in partial purification of water so that it only requires final polishing to become potable, and in production of critical vitamins that are needed in high levels in space, such as vitamins and antioxidants that are very difficult to synthesize especially without raw materials. Small-scale BLiSS modules will provide data for mathematical models that enable building larger, more functional systems and substantially de-risk the substantial food and nutrient gaps in a multiyear, crewed mission to Mars. These systems will help recycle some food, pull carbon dioxide gas out of the atmosphere, and contribute to water purification, particularly of gray water. Ultimately, this will reduce the resupply requirements for any bases. More importantly, these systems will provide the knowledge for designing and building far more capable systems that are less vulnerable to the space environment. They further promise to help solve food issues posed by climate change or extreme environments on Earth by providing optimized, stable environments for production that are much less dependent on weather conditions.

Broad Costs of the Research Campaign, Including the Associated Facilities and Platforms

As illustrated in Figures 6-5 and 6-6, the total estimated cost of a BLiSS research campaign thus scoped would be $1.7 billion over 10 years, with the expenditure peaking in ~2029. The cost estimate for this campaign was driven

from a set of specific goals to meet a set of capabilities needed to enable a bioregenerative life support system. For example, one such experiment series termed “Supplemental Crop Selection/Verification” was laid out as a series of 60–70 experiments in Veggie and expected to take ~4.5 years if there were two Veggie facilities available.

• BLiSS Campaign Level (red)—includes the costs of all crosscutting and ground-based activities to support the campaign including the ground-based experiments serving as controls for the flight experiments and science support to prepare for and build on the results of the space-based experiments. (See Figures 6-5 and 6-6 item in red.)
• BLiSS LEO (blue)—the total cost of executing the sets of experiments in space required to meet the campaign goals including support costs (crewtime, upmass, etc.) beyond those in the base support. (See Figures 6-5 and 6-6 item in blue.)
• Total BPS@FY 2023 level (yellow)—the total cost of the current BPS portfolio. To keep the campaigns separable, items 1 and 2 were not suballocated to each campaign. (See Figure 6-6 item in yellow.)

• Refresh/host Biofacilities (green)—the total of the transition cost current capabilities to the CLD era. It is assumed that the CLD versions are new copies and may operate in parallel with those in the ISS. (See Figures 6-5 and 6-6 item in green.)
• ISS PO + CLD PO CLD Contribution (yellow)—a ROM estimate of the allocation of launch and return vehicle services, crew time, and integration and operations services provided for the total BPS program. (See Figures 6-5 and 6-6, items in yellow.)

For each of the top-level goals, the series of experiments was defined to include the location (e.g., ISS/CLD, Artemis or ground), the facilities to be used (e.g., Veggie, APH, OHALO, etc.), and the number of experiment repetitions or iterations. The calendar time was estimated, and crew time and upmass/downmass were then scaled using relevant NASA-provided cost estimates for LEO research based on the NASA Commercial Use Pricing Policy,⁸ including midsize (1–4 MLE, EXPRESS rack) research payloads; EXPRESS rack payloads typically range from 25–150 kg, requiring power, data, and video links/storage and thermal management. Crew time requirements range from 1 hour for simple initiation/shut down operations to 200 hours for experiments requiring rodent maintenance and on-orbit dissections. A range was determined for each type of experiment. Launch and recovery costs were estimated at ~$20,000/kg for unpowered upmass, ~$45,000/kg for conditioned/late load upmass, $60,000/kg for powered upmass, $40,000/kg for downmass (unpowered, unconditioned), $45,000/kg for conditioned downmass, and $60,000/kg for powered downmass. Crew time is estimated at ~$130,000/hour. Estimated cost of integration, mission planning and operations, ground facilities and maintenance, and refresh of commercial LEO destination facility outfitting of repurposed/transitioned ISS

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⁸ See NASA Space Station, 2021, “Commercial and Marketing Pricing Policy,” https://www.nasa.gov/leo-economy/commercial-use/pricing-policy.

equipment or equivalent capabilities (CLD refresh) were estimated in broad categories. No specific estimate was made for data transfer costs.

RESEARCH CAMPAIGN: MANUFACTURING MATERIALS AND PROCESSES FOR SUSTAINABILITY IN SPACE

The MATRICES research campaign is driven by an overarching aim with four goals, together enabling circular life cycles for materials in space and on Earth. The overarching goal is to develop a sustainable ecosystem that allows materials and materials-enabled devices to have circular life cycles, thus reducing resource use and waste and harnessing materials in space via better understanding of the attributes and fundamental characteristics of the constituents and processes in the space environment. The component goals achieving this overarching aim are to

• Learn how materials and energy interact in the non-terrestrial environment and use that knowledge to design the infrastructure for space exploration.
• Enable a sustainable in-space economy by learning to make and build much of what is needed in space.
• Develop the nonliving aspects of sustainable circular systems of materials and processes via better understanding of the attributes and fundamental characteristics of its constituents and their formation.
• Understand and exploit the synergies of living and non-living systems for production of needed materials.

Throughout the era of human and robotic operations in space, the materials life cycle has been composed of carefully manufacturing finished items on Earth while ensuring they can withstand the harsh launch environment. Materials are used in space for a given lifetime and afterward are declared waste. The waste is either lost as debris or destroyed via burning in Earth’s atmosphere upon reentry. Future long-term human activity in space and future sustainable behaviors on Earth could redefine our relationship with materials. MATRICES seeks a paradigm shift in the way space missions approach the use of materials by asking whether waste can be eliminated, as inspired by work by organizations such as the National Institute of Standards and Technology (NIST) on circular economies. Can all materials be selected for a multi-use life cycle that allows inputs to be formed, used to provide value, and then converted into another form for reuse? In addition, long-term human and robotic activity in space will be enabled by effective and well-thought-out use of resources available in locations beyond Earth, such as the Moon, asteroids, and Mars. To use celestial resources well implies having the science and engineering to adopt them while also understanding the limitations of the supplies in the locations where humans and robotic systems will operate. The research that is required to enable that future state of a circular economy of materials in space affords the opportunity to learn from the centuries of Earth-based failures and successes in extracting, processing, using, reprocessing, and wasting terrestrial resources (Figure 6-7) and to create transformative processes and materials that also benefit Earth.

To create a future with circular materials life cycles, effective and well-rationed use of in situ resources and a gradual elimination of waste in space and on Earth, specific research is needed that characterizes the performance of materials, manufacturing, recycling, and processing in space. This campaign shows how work done in the period of this decadal survey can bring value by demonstrating initial capabilities for partial manufacturing of space systems, additive manufacturing, recycling, and in situ resource management and processing.

The high-level vision of a circular economy outlined by NIST in Figure 6-7 is made even more concrete in Figure 6-8. To eliminate waste and develop methods to reuse materials on Earth and in space, methods need to be invented for space operations that allow life extension of products, distribution of products to the location and user that needs them, and reuse of products that reach the end of one life stage and need to be converted into another. Creating such a life cycle for products in space requires planning from the design phase of materials selection, logistics, and energy access. The remaining discussion highlights examples of research that could enable progress in achieving this vision. The space environment brings unique challenges to implement the circular economy while considering the effects of microgravity; the radiation environment; and limited access to power, volume, and water that may support manufacturing.

Research Thrusts

Future human activity in space will be shifted by the capability to both manufacture raw materials into useful products and to reuse material via recycling and reprocessing. Future exploration can be greatly enhanced by identifying ways to use all or nearly all material as inputs to value creation and avoiding the creation or designation of materials as waste products. The pursuit of manufacturing will gradually enable humans to overcome traditional limitations of exploration that assume all materials are brought from Earth. In the process of making this feasible, fundamental discoveries about material properties, dynamics of manufacturing processes, and characteristics of in situ materials will be achieved.

The space environment is also an important context in which to phase out waste production and work toward a circular material life cycle; these capabilities will be impactful to change operations both on Earth and in space. This section discusses several facets of this experimental research that can be pursued within the coming decade to advance the capabilities for circular material life cycles and in situ resource processing. The work includes both non-living and biologically based material processes.

The MATRICES research campaign is designed to contribute to answering KSQs that are highlighted in Chapters 4 and 5, leveraging the opportunities of space-based experimentation to observe phenomena hidden by gravity and with an emphasis on creating and maintaining safe, sustainable built environments. (See Table 7-1 for mapping to several KSQs.) The work can begin by building on experience with additive manufacturing, circular material life cycles, material reclamation, and recycling on Earth. While additive manufacturing is not the only type of manufacturing that is relevant to space, it has a specific connection to recycling and reduced material waste. In both additive manufacturing and recycling, a material is processed into a feedstock that is often a limited set of pure ingredients that can be converted using various combinations of heat, binding, and mechanical force. There are several primary approaches to performing additive manufacturing on Earth. Some of these capabilities have been demonstrated in space and others are theorized to be feasible. Some of the key processes that enable additive manufacturing include heating and sintering or binder-based approaches. The research questions that inform progress in additive manufacturing depend in part on which process is under question.

Likewise, recycling is pursued on Earth with various approaches based on the materials. The methods used for glass, polymers, metals, paper, and other core ingredients each differ and may inspire distinct streams of research. For this discussion, consider the example of plastics recycling, which seeks to reuse engineered polymers. In this practice, the level of purity of the materials stream plays a role to influence the effort required to achieve recycling. When ingredients such as dyes, plasticizers, and antioxidants are used within a plastic product, it increases the challenge of separating materials to aid in recycling. Some sectors on Earth have developed standards for producing materials streams with limited ingredients; for example, this is done in the medical device industry, and the result is that products are easier to recycle. One consideration when designing a recycling process is whether the resulting output of the process seeks to maintain the same properties of the original feedstock or allows degradation. When degradation is allowed, the term “down cycling” is sometimes used to note that the mechanical properties of the next-generation product may have changed. Research to determine how to increase the number of times a product or feedstock can be reused in space would be valuable to enable circular value chains. During the plastic recycling process, one design decision is to consider whether the bulk material is broken down into polymers or monomers. The choice influences the energy requirements for the process and the options for products that can be created in the next generation. Molecular weight of the constituent materials is known to influence features such as stiffness, viscosity, and degradation temperature. Each of these factors needs to be considered when designing the process, and work is needed to determine whether aspects of the space environment may influence this.

Another category of recycling focuses on fluid management. This builds on past design approaches that reuse wastewater sources to create potable water for astronauts. In order to expand to larger-scale wastewater management, capabilities such as supercritical combustion to oxidize hydrocarbons in wastewater at low temperature need to be explored in the space environment.

The gravity environment, vacuum environment, and thermodynamics may each play a role to determine the performance of additive manufacturing. For example, in the area of thermodynamics, radiation is a key form of heat transfer and natural convection does not occur. The role of thermal radiative transfer is highly important for heat transfer in metals and plays less of a role in polymers, although the material influences the thermal options.

Owing to the lack of convection, heat will be retained within systems for longer periods relative to the case on Earth. The gravity environment influences the processing and handling of the media used in additive manufacturing. For example, if materials are in the form of powders or other loose small ingredients, these can be challenging to handle in the orbital gravity environment. Thus, uncertainties of these processes in the space environment include the following: How do thermodynamics in the space environment create obstacles or opportunities for additive manufacturing and recycling? What approaches to additive manufacturing and recycling are effective in a vacuum or near vacuum state, especially to reduce combustibility of feed stock that typically oxidize? What approaches leverage the microgravity environment to manage and process media for additive manufacturing?

The planetary surface environment brings new opportunities and questions for additive manufacturing. Further research is needed to characterize potential input materials from the surface of moons, asteroids, and rocky planets such as Mars. Work is needed to ask how the raw materials can be processed into new formats for manufacturing. Additionally, work is needed to design and engineer the processes that can be built, maintained, and fueled on a planetary surface to perform additive manufacturing and, eventually, recycling of planetary materials.

Limited technology demonstrations have pursued capabilities in this area. Made in Space (now owned by Redwire [Redwire 2020]) sent a 3D printer to the ISS in 2014 and demonstrated that a fused filament fabrication process could be performed with no significant defects on the products compared to Earth (Gaskill 2019). Later work included using ABS (acrylonitrile butadiene styrene), Green PE (polyethylene), and polyetherimide/polycarbonate as inputs for the Additive Manufacturing Facility operated by Made in Space. A 3D bioprinting facility was added to the ISS in 2020 (Sertoglu 2020), with anticipated future capabilities to print biologically generated materials (bioinks) as well as living cells within natural or synthetic bioinks.

Building on the current experiments, additional work could be done on the ISS to attempt new forms of manufacturing. As the ISS is retired, additional experiments on the scale of a benchtop module could be applied in commercial LEO systems that are either crewed or uncrewed. In later evolutions of the microgravity ecosystems, experiments could be included on research facilities in cis-lunar orbit or on planetary surfaces. The gravitational environment does impact the behavior of ingredients, and both microgravity and planetary gravity are of interest. Any facility needs to be able to record temperature, perform structural measurements, and enable video documentation. Current experience on the ISS allows the experiments to be designed to be autonomous; thus, crew are not required for manufacturing processes. There may be a need for crew to support the material characterization, such as with atomic force microscopy (AFM) and X-ray diffraction (XRD). In this case, launch cadence will be partly driven by crew availability. It will be valuable to gradually print larger objects, noting that large-scale, powder bed printers on Earth are on the scale of approximately 3 m × 1 m × 1 m, although some manufacturing technologies allow printed objects to extend far beyond the manufacturing platform. Expansion of this research thrust also includes the opportunity to compare different manufacturing approaches and materials. Future research will extend to robotic systems that can build additional manufacturing capability and expand or provide maintenance with some level of autonomy. The experimental system can be shared with other research topics such as cryogenic fluids.

Part of the research agenda to enable a circular material life cycle and the design of materials processing in space is to progress in knowledge about the behavior of materials in a setting outside the Earth environment. The fundamental principles for organizing the structure and functionality of materials are obscured by gravity. Traditionally, thermodynamics has used an approach based on equilibrium to predict potential results from chemical reactions and molecular rearrangements. However, many processes have significant gradients and/or rapid changes that deviate far from equilibrium conditions. The ability to “suspend” particles or fluid elements, such as bubbles and droplets, in their continuous medium allows for the investigation of other forces or field effects to manipulate the motion and orientation of these particles and fluid elements. This capability can produce structures and even chemical compounds by “building” the one element or molecule at a time. Conversely, the ability for targeted removal of portions of a structure or chemical compound can be used to either harvest desired products, degrade toxic compounds, or recycle waste.

The MATRICES research campaign will cover a wide field of fluid topics, including but not limited to colloids, gels, granular media, polymeric fluids, melts, and supercritical fluids. The operational concept for a research facility to support experiments in this area could be like that found in an academic or industrial research laboratory and

conduct the iterative process of research that includes the ability to either synthesize or adjust sample composition on-orbit based on real time diagnostic measurements. As such, capabilities could include the ability to generate or alter the composition of fluid samples, to alter the experiment and analysis simultaneously, have real-time or near real-time interaction with the investigator, either remotely or in person. The instrumentation could include microscopes, high-speed cameras, hyperspectral imagers, extensional and rotational rheometers, gas-chromatographs, mass spectrometers, and devices with the ability to measure reactant and product properties.

Several examples from existing experimental facilities provide models for future capabilities to advance knowledge of the fundamental characteristics of materials beyond Earth to support manufacturing and recycling. A work volume similar to the Microgravity Science Glovebox (MSG) (Spivey et al. 2008) would provide the functionality of a chemical fume hood, fluid containment, and test cell cleansing to provide sample preparation and extraction/separation after testing. A second volume similar to an ISS ExPRESS Rack (Pelfrey and Jordan 2008) would house the instrumentation listed above. The Shear History Extensional Rheology Experiments (Hall et al. 2006; Jaishankar et al. 2012; Soulages et al. 2010) (SHERE⁹ and SHERE-II¹⁰) were conducted in the MSG and examined flows and forces as a Boger fluid was stretched across an open volume. Similarly, the Observation and Analysis of Smectic Islands in Space (OASIS)¹¹ (Clark et al. 2011; Klopp et al. 2019) was conducted in the MSG and examined the behavior of defects on liquid crystal films to various perturbations. The Light Microscopy Module (LMM) in the Fluids Integrated Rack has been utilized to conduct the Advanced Colloids Experiments (ACE) Series,¹² the follow-up to the preceding Binary Colloidal Aggregation Test (BCAT) Series.¹³

Progress in this series of experiments will benefit from a semiautomated facility that can manipulate many samples, preferably simultaneously, in the desired environment. Specialized researchers operating both on Earth and in space will benefit from the ability to interpret results in near real time and adjust sample composition and manipulation parameters as necessary. Depending on phenomenological residence time, ground-based experiments may be used to refine techniques and test parameters prior to in-space testing.

Enabling long-duration space exploration independent of resupply from Earth will require not only establishing the biological knowledge and capabilities described in other sections, but also that of all of the physical systems interacting with and supporting the biological systems. Closed systems will require using physical/chemical systems to create and control the environments for the biological systems. Developing the understanding and methods to create the most efficient and effective end-to-end closed systems will require the ability to choose physical, chemical, and biological methods to execute steps in the subprocesses and create the right outputs and outcomes for successive steps. Doing so will require fundamental knowledge of pure materials and mixed systems, with a wide range of concentrations and parameters. For example, what are the changes in the physical parameters and behavior of water in microgravity when containing various kinds and concentrations of dissolved materials? How does the absence of gravity-driven convection and sedimentation affect the behaviors of waste in flow systems and reaction vessels? In microgravity, buoyancy forces are reduced, resulting in a reduction of sedimentation and natural convection. Consequently, diffusion and electrostatic and capillary forces increase in importance and allow larger 3D structures that are not possible on Earth. Are there as yet unidentified opportunities not available on Earth to process waste streams? A better understanding of fluid behavior to maximize fluid uptake in plants for developing the next generation of crop production and cell respiration is critical (Poulet et al. 2022). Similarly, if there is a need to recycle materials used for vessels, structures, and packaging, how is this best done? Going further, how can by-products of one reaction be utilized to feed into other critical processes? Some will fit into

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⁹ See NASA Glenn Research Center, 2023, “Shear History Extensional Rheology Experiment (SHERE),” https://www1.grc.nasa.gov/space/iss-research/msg/shere.

¹⁰ See NASA Glenn Research Center, 2023, “Shear History Extensional Rheology Experiment-II (SHERE-II), https://www1.grc.nasa.gov/space/iss-research/msg/shere-2.

¹¹ See NASA Glenn Research Center, 2021, “Observation and Analysis of Smectic Islands in Space (OASIS),” https://www1.grc.nasa.gov/space/iss-research/msg/oasis.

¹² See NASA Glenn Research Center, 2023, “Advanced Colloids Experiments (ACE),” https://www1.grc.nasa.gov/space/iss-research/iss-fcf/fir/lmm/ace.

¹³ For example, NASA Glenn Research Center, 2020, “Binary Colloidal Alloy Test-3 (BCAT-3),” https://www1.grc.nasa.gov/space/iss-research/mwa/bcat-3.

well-established bio-pathways supported by physical systems. Others may require classical chemical engineering approaches or hybrid processes with both. To remove otherwise intractable materials (such as per-and polyfluoroalkyl substances) via processes such as supercritical combustion need more study before becoming part of the “standard” repertoire.

A logical progression of research at the intersection of biological and physical sciences could be responsive to the questions derived from the KSQs in Chapters 4 and 5. One KSQ asks what physical properties and behaviors of biologically important materials affect how they participate in and affect biological processes. This work also asks how these behaviors may differ in the space environment. This work is partly motivated by the fact that biofilms have been discovered within the ISS Water Processing Assembly (Prakash et al. 2003), raising questions about the methods of generation, agglomeration, and attachment to solid surfaces in an aqueous environment. Further work is needed to understand the mechanisms of growth and promulgation.

Another KSQ asks about the fundamental characteristics of the non-equilibrium behavior of complex fluids, such as suspensions and slurries. This is of particular interest for those with water as the base fluid. This work explores whether there may be key physical states and conditions not exploitable on Earth that are important in the space environment. The work could investigate the surface physics and interactions with materials of interest under microgravity or low gravity conditions. In the space environment, it may be possible to differentiate between direct and indirect gravity effects, and to distinguish these from mechanical effects unrelated to gravity. Furthermore, studies could examine the chemical and molecular mechanisms that underlie the formation of functional subdomains in cells. This topic also considers the distribution of water flow among the evapotranspiration, plant growth, and fruit production. In the area of plant growth, other topics include the strategies to adequately hydrate and aerate plant roots while providing sufficient nutrition. This work may give insight into how the energy and mass balance can be optimized for fruit production and plant vitality. Another example for investigation in this area considers that in microgravity, buoyancy forces are reduced, resulting in a reduction of sedimentation and natural convection. Consequently, diffusion and electrostatic and capillary forces increase in importance and allow larger 3D structures that are not otherwise possible.

A third KSQ prompts studies of the detailed properties of in situ-acquired space materials and asks how the space environment affects their ability to be used directly by biological systems or processed into usable forms. For example, how does their microstructure affect water retention in plants and cells, root formation, microbial activity, cell respiration, and internal or skin effects on more complex organisms? A related question asks what physical, chemical, or biological processes create other useful materials.

Some of the research progress needed to advance this field includes exploring how to manufacture in space the supportive equipment such as pipes, tanks, and vessels to contain biological experiments. There may be opportunities for biologically based systems to enable the maintenance and repair of the non-living components of sustainable space environments to support long-duration missions. Biologically based systems may also contribute to recycling by participating in the conversion of a product into the base stock materials that can be manufactured. Both chemical and biological processes have been shown on Earth to assist with converting waste into reusable stock material. There is also potential to manufacture finished or intermediary products from bio-supplied base materials.

The types of experiments that explore the relationship between biological and mechanical materials processing will need a variety of equipment. For example, characterization and evaluation may be supported by Fourier-transform infrared spectroscopy (FT-IR spectroscopy), with libraries and software that helps the user to take a spectrum and capture the output. This tool could include multi-component search (MCS) algorithms. Other tools include systems to perform ultraviolet spectroscopy, shear rheology, nuclear magnetic resonance, and gas chromatography. Additional tools include a scanning electron microscope and mass spectrometers. For each of these systems, the capability could include automated sample acquisition and handling.

Infrastructure Enabling Research on Earth and/or Space Asset(s) Over the Decade

Two CLDs are assumed to provide platforms for continuing BPS research in space. A baseline assumption is that one of these CLDs will be in an ISS-like orbit (51.6 degree) and the other at a different inclination. For the purposes of cost profiles, it is assumed that research capabilities begin to become available as follows: one in 2026

TABLE 6-1 Overview of Legacy Facilities That Support the BPS Research Program in Materials-Related Studies

and the other in 2029. TRACE of the BLiSS research campaign assumed experiments in parallel in the ISS and on the CLDs as the latter access becomes available; cost estimates included continued ISS-based research capabilities and adapted “copies” for CLD-based research. TRACE of the MATRICES research campaign includes similar assumptions, specifically the assumption in these cost estimates that the high-mass, high-cost physical sciences facilities (Fluids and Combustion, EXPRESS Rack for Microgravity Science with Glovebox, Materials Science Research Rack, the light microscopy module, and the Cold Atom Laboratory) are transferred into the 51.6-degree orbit CLD from the ISS. These facilities were and will be expensive to build and are large and thus expensive to launch. Rebuilding and launching these to some other CLD would incur >~$1.5 billion in additional costs.

The legacy facilities that underpin the BPS physical sciences basic research program are well known and described in detail at the related sources. Table 6-1 provides reference material to further describe each legacy facility.

The facilities above are key and underpin the work of the MATRICES research campaign as well, but there is also a need for new capabilities to enable a more exploratory, highly interactive environment for rapid learning and repeat experiments. It is envisioned that these would be used by a combination of privately funded and government funded astronauts with the goal of maximum utilization for discovery and iterative development. The committee has identified a need for three new capabilities. All three of these are only described in concept and will require formulation studies and inputs from the scientific and commercial communities to define the base capability and evolutionary path. The first facility is designed to enable research on manufacturing in space. This capability builds on the concept of operations used in the EXPRESS Rack for Microgravity Science with Glovebox, but it is focused on enabled manufacturing processes. It is envisioned that a fully evolved facility could handle a wide variety of feedstock (ceramics, metals, plastics, wood, bioprinting, etc.). The second facility is a highly interactive wet laboratory and characterization facility to allow for experiments in a wide range of soft matter, fluids, suspensions, and slurries. In addition, the instrumentation could allow characterization onsite of a variety of samples. The third facility is designed to allow combined biological, chemical, and physical processing of multiple inputs. The inputs may include wastes, in situ resource utilization (ISRU) or other feedstocks to produce materials suitable for reprocessing into needed forms. Ideally, such a facility could handle waste or ISRU material and convert them into forms suitable for the manufacturing facility. Experiments in this facility would likely be synergistic with the wet laboratory to understand systems at different scales.

Impact by 2033 If the Campaign Is Successful

The combined vision for use of materials found in space and circular life cycle for materials in space proposes a capability that is vital to enable Earth-independent, long-duration exploration, especially beyond the Earth–Moon system. During the coming decade, the progress is expected to be uneven in disparate areas. For example, as observed on Earth, recycling is less complex when materials streams have a small set of pure ingredients. This implies that early demonstrations of recycling in space may occur on specific sets of objects that can be composed of a well-defined materials list. The campaign will also show the distinctions in complexity, cost, and effectiveness of additive manufacturing with different material classes, such as metals and polymers. The work will encompass both basic research and demonstrations of pilot capabilities, with low and medium TRLs (2–6). As this series of

exploratory studies and demonstrations concludes, it will enable subsets of the materials management tasks for future human missions to be designed with additive manufacturing and recycling as part of the typical life cycle. This lays a foundation for a long-term path toward closed-loop material life cycles.

The biological aspects of the research agenda outlined in this campaign are expected to contribute to the design of life support systems for long-duration human exploration capabilities, such as those needed to travel to Mars or uses in situ materials from the Moon. The progress that is feasible by implementing the proposed campaign is targeted to demonstrate a variety of disparate capabilities that illustrate the potential for future designs. By 2033, further research will be needed to prepare fully designed systems; however, substantial uncertainty will be reduced by showing what may be feasible when combining mechanical, chemical, and biological properties of materials to create new life cycles. While fully closed-loop sustainable space habitats are unlikely within the decade, the research in biophysical systems could provide major advances in waste recycling to reduce replenishment from Earth and in-space disposal needs. Advances in understanding and technology for converting complex waste in a combined biological-chemical engineering environment into manufacturing feedstocks would be highly beneficial to terrestrial recycling and reducing impact on the environment.

Broad Costs of the Research Campaign, Including the Associated Facilities and Platforms

As illustrated in Figures 6-9 and 6-10, the total estimated cost of a MATRICES research campaign thus scoped would be $3.7 billion over 10 years, with the expenditure peaking in ~2029. The cost estimate for the MATRICES campaign was based on the overall goals to advance the science and technology to enable circular, sustainable space systems. Because these goals are more general than those for the BLiSS campaign, the experimental goals and cadence were defined using analogies to the existing program but at levels projected to deliver significant results over the decade.

• MATRICES Campaign Level (red)—includes the costs of all crosscutting and ground-based activities to support the campaign including the ground-based experimetns serving as controls for the flight experiments and science support to prepare for and build on the results of the space-based experiments. (See Figures 6-9 and 6-10 item in red.)
• MATRICES LEO (blue)—the total cost of executing the sets of experiments in space required to meet the campaign goals including the new facilities plus support costs (crewtime, upmass, etc.) beyond those in the base support. (See Figures 6-9 and 6-10 item in blue.)
• Refresh/host Physics facilities in CLD (green)—the total of the transition cost current capabilities to the CLD era. (See Figures 6-9 and 6-10 item in green.)
• Total BPS@FY 2023 level (gold)—the total cost of the current BPS portfolio. To keep the campaigns separable, items 1 and 2 were not suballocated to each campaign. (See Figure 6-10 item in gold.)
• ISS PO + CLD PO CLD Contribution (yellow)—a ROM estimate of the allocation of launch and return vehicle services, crew time and integration and operations services provided for the total BPS program. (See Figures 6-9 and 6-10 item in yellow.)

The cost drivers for the MATRICES campaign have similarities to and key differences from those for the BLiSS campaign. In comparison to the biological sciences facilities, the core physical sciences space facilities underpinning both the BPS base physical sciences program as well as this campaign were very expensive to develop originally. They are also large, driving up launch costs. It was assumed that NASA will sponsor activities in two CLDs and that one of these will be in an ISS-like orbit (51.6 degree) and the other at some other inclination. To avoid approximately ~$1.5 billion in the cost of building and launching new versions, it is assumed that the Fluids and Combustion, EXPRESS Rack for Microgravity Science with Glovebox, Materials Science Research Rack, the add-on light microscopy module, and the Cold Atom Laboratory are transferred into the new 51.6 inclination CLD (see Figure 6-11). For the purposes of cost profiles, it is assumed that research capabilities begin to become available as follows: one in 2026 and the other in 2029. This campaign is exploratory in nature and is expected to benefit greatly from the opportunities for more interactive experimental settings. Again, by analogy to the previous interactive facilities, concepts are described and costed for the three new facilities described above. The crew time and upmass/downmass were then scaled using from relevant NASA-provided cost estimates

for LEO research based on the NASA Commercial Use Pricing Policy,¹⁴ including midsize (1–4 Middeck Locker Equivalent, EXPRESS rack) research payloads; EXPRESS rack payloads typically ranging from 25–150 kg; requiring power, data, and video links/storage; and thermal management. Crew time requirements range from 1 hour for simple initiation/shut down operations to 200 hours for experiments requiring rodent maintenance and on-orbit dissections. A range was determined for each type of experiment. Launch and recovery costs are estimated at ~$20,000/kg for unpowered upmass at ~$45,000/kg for conditioned/late load upmass, $60,000/kg for powered upmass, $40,000/kg for downmass (unpowered, unconditioned), $45,000/kg for conditioned downmass, and $60,000/kg for powered downmass. Crew time is estimated at ~$130,000/hour. Estimated cost of integration,

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¹⁴ See NASA, 2021, “Space Station: Commercial and Marketing Pricing Policy,” https://www.nasa.gov/leo-economy/commercial-use/pricing-policy.

mission planning and operations, ground facilities, and maintenance were estimated in broad categories, and no specific estimate was made for data transfer costs.

The opportunities to pursue the research described above are enabled by an expected ecosystem in LEO that includes several additional years of ISS operations, CLDs, and planetary space experimental platforms. The vision assumes that both public and private sector resources will combine to enable new science and engineering outcomes. For example, government funds may serve as an anchor tenant for commercially operated orbital science laboratories; both government-selected and private-sector astronauts may contribute to scientific work; and research facilities may be multi-use, perhaps combined with facilities used for tourism and commercial manufacturing. Many types of space experiments can be carried out in multiple space regimes, regardless of orbital altitude or distance from Earth. Some experiments are uniquely suited for a specific planetary context, such as the surface of the Moon. As technology matures, new options for research may be available, owing to the availability of increasingly automated and reusable laboratory facilities. More research will be feasible if the need for crew time is reduced by increasing the autonomy of experimental systems and allow remote operation and monitoring. The research needed to enable future circular material life cycles will involve a variety of dissimilar experiments. Within the areas of in situ resource use, in-space manufacturing, recycling, and bio-assisted materials, there is a wide variety of research needs. For this reason, establishing and using modular laboratories in this research campaign that can be adapted to support other research in fluids, materials, and biological sciences are efficient investments.

MULTI-AGENCY OPPORTUNITY: PROBING THE FABRIC OF SPACETIME

In addition to the two research campaigns recommended above, the committee also considered a multi-agency opportunity that would ultimately include research campaign–related efforts important to NASA’s BPS contributions to fundamental physics, and resulting in data and capabilities of interest to several other parts of the U.S. government and to society.

The goal of PFaST is to exploit the distance and gravitational characteristics unique to spaceflight to advance knowledge of fundamental physics leading to novel approaches for energy, communications, and computation challenges. Initial R&D thrusts are to develop space-rated, quantum technology optical lattice clocks (OLCs) to enable ultralong baseline measurements and develop optical time transfer (OTT) techniques and technology to enable space-space and space-ground synchronization of ultra-high-performance clocks.

Achieving the overall goal, including deployment of OLC and OTT into space missions, and creating an inter-comparative network will require not only completing the technology development but also fully space qualifying units of low enough size, weight, and power (SWAP) to allow their incorporation into any medium-sized to large science mission. That work will require more than this decade, and this opportunity could be pursued only through a U.S. interagency, and potentially international, consortium to develop the spacefaring units.

While basic scientific research has led the way to great advances in technology, vastly improving the human condition, many fundamental questions remain to be explored. For example, the formation of galaxies and the accelerated expansion of the universe cannot be understood by currently known physics. Explaining them requires the existence of dark matter and dark energy, respectively, neither of which have ever been detected in the solar system. Some argue that the fundamental theory of gravity and the universe, Einstein’s general relativity, may have to be modified. Besides being a paramount scientific question in and of itself, fundamental physics can also become instrumental in studying the universe in new ways. This is certainly true of detection of gravitational waves, which were long known to be a prediction of general relativity, but which had not been observed directly until 2015. Since then, they have opened up new windows into the universe. For example, next-generation gravitational wave observatories will be able to detect gravitational waves emitted at greater “redshift” (and thus much earlier in time, and hence closer to the Big Bang) than the electromagnetic sources that can be detected by using the James Webb Space Telescope (JWST). Gravitational waves are thus opening new windows into the cosmos, and are already challenging our fundamental understanding of stars, black holes, as well as galaxies. We live at the beginning of an era of quantum technology changing the way we live and think. The development and deployment of space mission–rated ultra-high-performance clocks with commensurate OTT techniques can provide new windows into the fundamental nature of the universe.

Scientific Landscape: Quantum Sensing and Fundamental Physics

Historically, the return on investment from exploring what is not fundamentally understood has been huge; ultimately, harnessing the effects of quantum mechanics (within transistors, communication technologies, and a myriad of other technologies) has led to the digital age, and engineering quantum effects are leading to a quantum age.

Effects like quantum tunneling, where particles can traverse barriers that they could never pass classically, were initially controversial but are now underlying everyday technologies like flash memory (which is used everywhere from USB sticks and smartphones to solid-state drives in computers) to Josephson junctions. Josephson junctions, which permit quantum sensing at levels that are often more than 10 million times more precise than ever before and have revolutionized military sensors, geologic exploration, and medicine, and are now one of the prime contenders for developing large-scale quantum computing. Josephson junctions are the quantum bit, or “qubit” in major quantum computers today (e.g., those developed privately by IBM, Google, and other companies).

Quantum technologies quietly made their way into the mainstream. Atomic clocks, and thus the Global Positioning System (GPS), are early successes of quantum physics that are now taken for granted. These clocks were first-generation quantum devices, based on the quantum physics of individual particles and atoms. Meanwhile, pioneering “experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science” (the 2022 Nobel Prize in Physics) opened the door to “quantum 2.0,” where intricate properties of multi-particle systems lead to groundbreaking applications. Examples include quantum cryptography (like the Chinese QUESS project), LIGO (which is now using a non-classical “squeezed” quantum state of light to detect gravitational waves arising from sources that are further away than what would otherwise be possible), and quantum computing (which is being rapidly advanced by researchers in academia and industry). Quantum computing is both a huge opportunity and a substantial threat, because it may be used in the future to crack advanced encryption, which is essential.

While unpredictable, advances in fundamental science are seldom accidental; “chance favors only the prepared mind,” as Louis Pasteur said.¹⁵ Preparing minds requires steadfast development and deployment of advanced technology, pushing to reach new technological heights, so that scientific discovery is favored. The noted science fiction writer Arthur C. Clarke’s second law is, “The only way of discovering the limits of the possible is to venture a little way past them into the impossible” (Clarke 1962).

The Justification for Space-Based PFaST

This profound journey of discovery continues. Quantum physics is now enabling investigations that leverage the space environment in multiple ways.

The proposed research requires solar system distance scales to accumulate measurable signals from weak gravitational waves, dark matter and dark energy, or as-yet-unknown physics. Operations in deep space provide distance scales of literally 100 million miles (comparable to the Earth-Sun distance) over which tiny effects from gravitational waves, dark matter and dark energy, or as-yet-unknown physics can stack up to generate a measurable signal. For example, a pair of ultraprecise clocks that use “quantum 2.0” effects to gain unprecedented precision, one in LEO and one in a solar orbit trailing Earth (at the L5 Lagrange point), may be used to search for low-frequency gravitational waves that are currently undetectable, and that may provide clues about the origins of the universe. These clocks can also detect when stars, neutron stars, and/or black holes are on a collision course, long before an actual collision occurs. Earth-based detectors are often not capable of this task.

Weightlessness in space enables quantum effects to be scaled up in duration and spatial extent, beyond terrestrial boundaries. Fundamentally, in any quantum technology, a quantum process would be accomplished before unwanted interactions with the environment destroy the quantum states. The weight of particles in Earth-based laboratories produce background forces, making it hard to isolate the quantum process from Earth’s environment. Operating quantum systems in space avoids the need to hold a system against Earth’s gravity. This will enable

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¹⁵ During an 1854 lecture at the University of Lille, French microbiologist and chemist Louis Pasteur said, “In the fields of observation chance favors only the prepared mind.”

minutes-long or even hours-long quantum processes, well beyond what can be achieved on Earth, as well as superposition states that span large spatial distances (Xu et al. 2019). One application may be finding out whether the gravitational interaction is itself a quantum effect (Carney et al. 2021).

Access to large variations in gravitational potential or space-time curvature allows the use of gravitational potential hills, present in the solar system, for the curved spacetime (gravity wells) that exists around massive objects, such as planets, and the Sun. In this environment, relativistic effects of curved spacetime can be probed in ways that are simply unavailable on Earth. This can be used (in combination with 1 and 2) to probe for dark matter or dark energy.

As the accuracy and resolution of time and distance measurements improve, seismic activity on Earth masks the fundamental physics details that scientists want to observe. Deployment of an optical clock on a free-flier orbital platform, or even possibly on the lunar surface, would greatly reduce these adverse effects of vibration.

Research Thrusts

Overview

The ultraprecise quantum sensing network proposed here will provide the collective “prepared mind” of the advanced physics communities to be able to discover new science that will undoubtedly become the basis for the development of the most advanced engineering systems in decades to come. PFaST is about harnessing the power of quantum technology to search for dark matter and dark energy in the solar system to probe the origins of the universe by listening to gravitational waves of currently unmeasurable frequencies, and to explore if the gravitational field—described by space-time curvature in Einstein’s theory of general relativity—is fundamentally a quantum entity unto itself. More generally, it is also about developing U.S. leadership in quantum technologies, which is essential to many breakthrough technologies in quantum computing and in quantum sensing.

The approach is centered on deploying an advanced quantum sensing network whose performance will be many orders of magnitude better than previously thought possible, enabled by scientific discoveries that occurred only recently and that will be continuously refined throughout the decades to come. Establishing space-based OLCs for ultraprecise quantum sensing will enable breakthrough science for probing the fabric of spacetime in the following ways:

• Precisely measuring the curvature of spacetime, and thus testing the understanding of fundamental physics at levels of precision that are 100,000 times what is possible in terrestrial experiments. This includes testing relativistic gravity by measuring the curvature of spacetime near planets and other massive objects, searching for violations of fundamental symmetries, searching for additional fundamental forces, and searching for time-variations of the fundamental constants.
• Probing the hidden nature of the universe by searching for dark matter and dark energy and other exotic low-mass fields. In the same way that relativistic physics revolutionized our perspective of the world (and is now instrumental in the engineering of GPS and in many other advances in technology), a future understanding of dark matter and dark energy may produce models that similarly impact our worldview, and those refined and verified theories of nature may also have unexpected engineering benefits.

  A quantum network of OLCs may permit an early detection of gravitational waves produced by massive inspirals (such as neutron-star and black-hole collisions). The currently unmeasurably mid-band (mHz to 10 Hz) gravitational waves may provide an early warning of major cosmic events (e.g., stellar-mass binary in-spirals, intermediate-mass black hole binary mergers, and intermediate mass ratio in-spirals) long before terrestrial detectors can pick them up; combined with the solar system baseline, mid-band sensing allows precise localization of the events (Kolkowitz et al. 2016). This network will be sensitive to gravitational waves that have been emitted much sooner after the Big Bang than the associated electromagnetic signals detected by the JWST, which allows this network to probe the dynamics of the universe in the epoch after matter condensation.

• Testing whether the gravitational field has quantum aspects. Perhaps the most fundamental open question of fundamental physics is whether the gravitational field itself is a quantum entity. While this question has long been regarded as being beyond the reach of current experiments, the rapidly developing field of quantum information has opened doors for answering the question by testing whether the gravitational field can be in a superposition state and mediate quantum entanglement (Carney et al. 2021; Kumar and Plenio 2020). The basic time-scale needed for such experiments is given by the gravitational constant G and the density of available materials ρ as 1/(G ρ)^1/2, which is about 15 minutes. Maintaining the required quantum state over such times is impossible on Earth, but is possible in weightlessness (Panda et al. 2022).

Numerous societal benefits are already linked to technology developed for space exploration, ranging from solar panels to cancer therapy. PFaST would be at the forefront of developing quantum technologies with a huge indirect Earth benefit, notably quantum sensing, computing, and quantum information processing. In addition, the quantum network of OLCs will allow a “solar-system GPS” for autonomous spacecraft tracking and navigation, including true one-way ranging and doppler; space-based synchronization/comparison links for high-precision optical clocks on Earth; and master clocks in gravitationally unperturbed reference frame for a redefinition of the SI unit of time (the second). Developing mastery in optical and microwave time-transfer, which is important in geodesy, navigation, and time-keeping, and the development of quantum sensors in deep space will enhance understanding of the behavior of quantum gases.

Key Steps

Atomic clocks and atom interferometers are two basic building blocks of quantum sensing. The quantum sensing network proposed here involves precise inter-comparisons of advanced, optical clocks that will eventually be deployed throughout the solar system. Clocks based on atoms held by radiation forces within laser beams (OLCs) have reached differential instabilities of better than 10⁻¹⁸ in 1 second of averaging time and better than 10⁻²⁰ with averaging over longer time-scale (Bothwell et al. 2022; Zheng et al. 2022). The first goal of this multi-agency opportunity is to make such technology available for space-based operation by ground-based research. At the same time, optical lattices have also proved instrumental in generating the longest coherence times in atom interferometers, and observed scaling shows that these coherence times can be strongly extended by operation under weightlessness in space (Panda et al. 2022; Xu et al. 2019). Another goal of this multi-agency opportunity is to develop optical-lattice technologies for use in space-borne atom interferometers.

While these developments are under way on the ground, space-qualified clocks based on a different technology are already available. These are ion clocks with a 10⁻¹⁴ stability in 1 second, such as the Deep Space Atomic Clock (DSAC; a miniaturized, ultraprecise mercury-ion atomic clock). Flying such a clock—perhaps on a slightly improved version—in a highly elliptical Earth orbit will be an initial demonstration of highly accurate OTT as well as exploring the ultimate performance of microwave timing links. Such a mission will probe the fabric of spacetime by testing relativistic gravity at accuracies up to 30,000 times that of current work, enhance searches for dark matter and drifts in fundamental constants, and establish a high-accuracy international time scale and geodesic reference. The mission would also demonstrate space-based operation of optical frequency combs, as needed for OTT to the ground. Recent results from the Defense Advanced Research Projects Agency’s (DARPA’s) Micro-Mercury Trapped-Ion Clock (M2TIC) suggest that this technology may continue to improve dramatically over the next decade, achieving very low size, weight, and power.

By suspending atoms in an optical lattice made of the mode of an optical cavity under conditions of weightlessness, atom interferometry can reach coherence over much larger stretches of space and time. Ground-based experiments have shown that reducing the depth of the optical lattice as well as the sample temperature can extend coherence. However, doing so on the ground is impossible, as it causes the atoms to fall out of the lattice. In space, reaching coherences over time scales of 15 minutes to hours is expected, enough to show whether the gravitational field is quantum mechanical and consists of gravitons. Even with a lower-performing instrument, a mission could be searching for dark energy in the solar system.

Ultimately, a pair of ultraprecise clocks that use “quantum 2.0” effects would be used to gain unprecedented precision. Such clocks will be able to achieve the grandest goals of this multi-agency opportunity, with detection of mid-band gravitational waves and a search for dark matter and dark energy at unprecedented sensitivity. Several deep-space trajectories are interesting for such a mission. Going to the L4 or L5 Lagrange points offers long baselines with minimal variation of the relative position relative to Earth, which is beneficial for time transfer. This is favorable for gravitational-wave detection as well as many types of dark matter and dark energy searches.

Infrastructure-Enabling Research on Earth and/or Space Asset(s) Over the Decade

Reaching PFaST objectives requires two key capabilities: space-qualified stable and precise high-resolution clocks—operating at atomic microwave or optical frequencies—and a time transfer system capable of synchronizing (or comparing) these accurate clocks from spacecraft to Earth, or from spacecraft to spacecraft, without loss of stability, accuracy, or resolution. The specific campaign elements selected attempt to balance risk and usefulness of the achievements.

Space-Capable Optical Clocks

There have been significant improvements in the implementation of microwave, space-capable, trapped-ion atomic clocks (Burt et al. 2021). Their performance level, however, is below that of demonstrated optical ground-based clocks, which are currently quoted as having a fractional frequency instability (FFI) of 1 × 10⁻¹⁶ τ^−1/2 and fractional inaccuracy of 1 × 10⁻¹⁸ (Abdel-Hafiz et al. 2019; Ludlow et al. 2015; Sanner et al. 2019).

Space-qualifying optical clocks is not easy; challenges include not only the size, weight, and power, but, among others, radiation resistance of the electronics, robotic vacuum maintenance, and reloading of ion sources (when used) and packaging to survive and resist launch environments and loads.

Opinions on the required performance of a space-based optical clock range (looking only at FFI as an example) from 1 × 10⁻¹⁴ τ^−1/2 to that of the ground-based clocks mentioned above (Derevianko et al. 2022). A possible compromise is to use the intermediate value 1 × 10⁻¹⁵ τ^−1/2 as an achievable goal.

Furthermore, there is an irreducible sensitivity to vibrations owing to the mechanical nature of several components, including optical paths. This complicates (but not totally eliminates) deployment in a crewed spacecraft, such as the ISS, where a close-proximity free-flyer or magnetically coupled “remora” platform may be required.

But perhaps the greatest challenge to a space-qualified optical clock is the ability to operate for its desired lifetime without the periodic maintenance that current Earth-based optical clocks require. For Earth-based clocks, maintenance limits the length of experiments, but maintenance is possible; for a spacecraft-based unit (with a possible exception of the ISS, which has other problems such as vibration and crew-induced seismic disturbances), human-tended maintenance is impossible, and “self-maintenance” could be a design feature.

For developing such a clock, this multi-agency opportunity could pursue one or two alternative approaches: (1) deployment to the ISS (with “analytical” corrections for the ISS environment) or (2) a small dedicated 1-year lifetime LEO platform with an OTT as described below.

If option 1 is pursued, then it will be possible to systematically develop long-term functionality in the lattice optical clock by developing new control technology that seldom requires crew intervention in the weightless laboratory environment of space. The crew will be available to intervene when necessary to service the clock, but the time between such crew interventions will become a measure of the effectiveness of newly designed systems to stabilize the clocks for long-term unsupported missions in space. New methods will need to be developed to correlate and compensate for the effects of vibrations, especially below 10 Hz, where an effective ability to passively and actively vibration-isolate the clock from the ISS vibrational environment is not readily available. Vibration in this low frequency regime may be measured by an accelerator, such as the Space Acceleration Measurement System (SAMS) on the ISS and correlated with deviations in the OLC stability. The effects of the ISS vibrational environment have been studied at length on other human spaceflight missions that supported ultra-sensitive experiments on the quantum fluids. (See the Lambda Point Experiment [LPE] and Confined Helium Experiment [CheX]

experiments on the space shuttle.) Also, see the Science Requirements Document for the Critical Dynamics in Microgravity (DYNAMX) experiment that was prepared for the ISS (Science Requirements Document, JPL Document Number D-18698). Systematic variation of the clock’s performance with steady acceleration may be determined experimentally. These data may be useful to estimate the systematics of uniform acceleration in future lattice optical clock designs. Such an OLC facility on the ISS may be operated later within this program and compared against a free-flyer optical clock to further characterize the effects of vibrations, and other aspects of the crewed space environment on optical clock stability and systematics.

Deep-Space Atomic Clocks

It is essential to develop ruggedized OLCs in space during this decade, in order to start the process that will achieve the advantages listed above. This is a top priority. But the development of space-qualified OLCs will likely take until 2030, and possibly beyond. Currently, “Quantum 1.0” clocks, also known as microwave atomic clocks (Burt et al. 2021), have already been miniaturized, ruggedized, and deployed in deep space, and less-accurate atomic clocks are an integral part of the GPS constellation of satellites that are deployed in 12-hour, medium Earth orbits. This DSAC is currently being prepared for a second deep-space deployment (DSAC-2), and while the performance of these already space-deployed DSAC devices is about 100 times less precise and accurate than the anticipated performance of OLCs, the DSACs are immediately ready for launch, and hence may be deployed on upcoming missions to the outer planets, such as the mission to Uranus (which was the top priority from the recently published planetary science decadal survey). This will permit the less-capable DSACs to be deployed on a very long baseline within this decade. The committee proposes this as a less-expensive, more immediate opportunity, but again, it considers this to be a lower priority than the development of the space-based OLCs over this decade.

One scientific advantage of a long-baseline deployment of less-accurate DSACs will be the ability to test time transfer back to terrestrial or Earth-orbital clocks over very long baselines, and this will permit the identification of technical challenges that will be encountered when space-based OLCs become available to be deployed over much larger baselines in the future. While the fundamental physics scientific return from DSACs is not expected to be high, the engineering advantage of such clock deployments on long-baseline planetary missions—for example, as a “rider” that requires low-size, weight, and power—will likely provide future engineering and deployment advantages. Furthermore, the measurement accuracy and size, weight, and power of DSAC technology continues to improve at a rapid rate, but this rate of improvement will definitely pale in comparison to the capabilities that future space-based OLCs are anticipated to provide. DARPA’s M2TIC, for example, has provided Alan Deviations of about 10⁻¹⁴ in a volume of less than 10 L, and with a power requirement of less than 20 W. This miniature space-based clock is scaling with volume in a manner that is similar to OLCs, which suggests that miniature mercury trapped ion clocks may show dramatic improvements over the coming decade.

Some scientific return may be realized in a DSAC-like clock deployment over long baselines. The size of the dark matter signature, if it exists at all, is unknown, so the better OLCs performance will provide a better chance for major scientific discovery. This is why the committee places top priority on the systematic development of OLCs in space, as discussed below. But the variation of the density of dark matter in the solar system may depend strongly on the distance from the Sun, and on the distance from large massive planets, because dark matter is thought to interact only gravitationally. If so, then any detected signature from less-precise DSACs that are distributed over a large baseline of a few astronomical units would be a major discovery of its own, and it would strongly motivate the future deployment of OLCs over these long baselines in the future. But a null scientific result over these long baselines would also motivate similar dark matter searches using much more accurate OLC deployments over large baselines in the future.

Optical Time Transfer

The next element is the time transfer capability (Ashby 2003). There have been recent demonstrations of OTT in the atmosphere at distances of about 30 km (round-trip). This provides confidence that at least a surface to LEO OTT (LOTT) can be developed and implemented within the decade. Such a LOTT can enable synchronization of

two distant Earth-based optical clocks in co-visibility with the platform hosting the LOTT. This co-visibility has an inherent low duration, thus limiting the time available for synchronization, averaging, and comparison.

The next step would be to extend the range capability to geostationary orbit (GEO), therefore enabling GEO OTT (GOTT) capability. This not only increases the maximum co-visibility distance between the Earth clocks, but also allows long synchronization and averaging times.

The two next steps in the development of time transfer capabilities are deep-space OTT (DOTT) and space-to-space OTT (SOTT). DOTT increases the maximum distance between the spaceborne optical clock and an Earth-based one, enabling very long baseline measurements. The main difficulty of achieving this capability is the combination of the large (1/r²) signal loss and the atmospheric losses. It is questionable if this capability could be developed in the next decade unless major breakthroughs occur in the development of LOTT and/or GOTT. Similarly, SOTT has “only” the 1/r² problem to handle and many be feasible in the next 10 years. Of course, one could conceive of a relay system whereby a spacecraft-to-spacecraft link is relayed from a GEO platform to Earth.

Practices to Manage Technical Priority and Risk Over the Decade

As mentioned, there have been significant recent advances in Earth-based optical clocks and trapped-ion space-capable clocks by non-NASA organizations, such as NIST. In addition, the Department of Defense (DoD) has considerable interest in precision space clocks for communications and cryptographic applications.

The first step in managing the development risk is to set reasonable expectations; as mentioned above, an FFI of 1 × 10⁻¹⁵ τ^−1/2 seems a reasonable compromise between improving the state of the art and an unrealistic 10-year goal. Along these lines, deployment at the ISS or its commercial replacements seems to reduce the risk by simplifying launch and hosting costs, but at the expense of having to cope with the relatively high-vibration environment inevitable in a crewed spacecraft. Two possible avenues of managing this risk are using the ISS deployment as a development and validation step, correcting the results for the effects of vibration, or developing a suitable vibration-free deployment, such as a proximity co-free-flyer.

Another risk mitigation approach is to host in the ISS the LOTT system, using it as a short-duration relay between co-visible ground optical clocks. This would both demonstrate the performance of the LOTT (and OTTs in general) and enable Earth-based experiments.

Last, NASA’s development could coordinate closely with both the Earth-based clock developers and DoD efforts in this area to avoid duplication and take mutual advantage of the other partner’s advances.

Impact by 2033 If PFaST Is Successful

Of the various benefits, the capability of GPS-like autonomous navigation throughout the solar system and space-based synchronization of Earth-based optical clocks are very likely to be achievable by 2033. In particular, an ISS-based “relay” OTT would be useful and relatively straightforward to deploy on the ISS, because it would not be affected by the ISS environment the way an optical clock would.

Detection and measurement of dark matter or dark energy within the solar system does depend on achieving effective OTT beyond LEO or developing the clocks to the suggested performance goal. The risk of achieving this objective is higher but is nevertheless within reach of a 2033 target date. Another possible 10-year result enabled by a GEO OTT or deep space OTT would be to demonstrate deep-space quantum links. The speed of achieving either approach with U.S. leadership and anchorship participation depends strongly on collaborative interagency progress on the base clocks. But more importantly, a millihertz to 10 Hz gravitational wave observatory within the next 20 years can only be possible if this opportunity is started now.

Potential Use of PFaST-Critical Infrastructure to Others

PFaST infrastructure could benefit national security-related communications and cryptography and space exploration navigation and timing (e.g., on the Moon). “GPS-equivalent” navigation (i.e., by measuring time of flight of coded signals) outside of the near-Earth environment, such as the Moon and Mars, can be greatly simplified

using high-precision, low-drift clocks on the navigating spacecraft. Specifically, the need for multiple linearly independent measurements to estimate local clock bias can be reduced by implementing true one-way ranging and precision Doppler, which, combined with a suitable gravitational model, would allow autonomous, on-board, real-time position and velocity estimation in the cis-lunar, Mars, and solar system environments for future space missions. For example, Figure 6-12 shows an overview of locations for the PFaST elements with key hardware elements denoted with a green star.

Broad Considerations of PFaST, Including the Associated Facilities and Platforms

While the DSAC-2 elements and needed technology developments were assessed as low to medium risk, those associated with the OTT link and high-performance OLC were mostly assessed as medium to high. While the fundamental concepts support BPS science, development of the technological capabilities and system integration required for flying a DSAC-2 on a deep space mission is more properly within the realm of one of the other NASA SMD divisions or STMD. The schedule risks and challenges of developing OLCs and the OTT link to the required performance and durability level lend themselves better to a mostly ground focus in the near term, coupled with in-space experiments to be done on the ISS or a CLD, depending on timing. For example, overcoming the effects of atmospheric disturbances and Doppler closing rates of kilometers per second are serious challenges, and it is difficult to predict how quickly they will be overcome. Other government agencies, notably the Air Force Research

Laboratory (AFRL) and NIST, have long-standing R&D programs relevant to their own needs. In addition, there are several potential international collaborations.

Opportunities exist today for collaboration and mission cost-sharing within the international scientific community and between U.S. federal research programs, and they may substantially reduce the costs of the recommended fundamental physics research campaign to place OLCs in space. Because the results of fundamental physics research is typically published in journals with an international distribution, and because the results of fundamental physics research involves international scientific collaborations already, and builds human knowledge that spans across national boundaries, a strong commitment exists to cooperate and share expenses between nations in support of fundamental physics research.

The Space Optical Clocks (SOC) project is one example of such international collaboration, which is funded by the European Space Agency (ESA) and the German government. This program includes subcomponents of OLC that are suitable for later space use, such as all-solid-state lasers, low-power consumption, and compact dimensions. These components have been developed and validated. This included a demonstration of laser-cooling and magneto-optical trapping of strontium atoms in a compact breadboard apparatus and demonstration of a transportable clock laser with 1 Hz linewidth. Non-destructive detection of atom excitations and minimization of decoherence effects have achieved a fractional frequency stability of 10⁻¹⁶. Furthermore, ESA operates the SOC project with the goal of installing and operating an OLC on the ISS with improved frequency stability of at least one order of magnitude over more conventional cesium-based atomic clocks. The payload is planned to include an OLC complete with an integrated frequency comb and the additional equipment and infrastructure necessary to support Two-Way Optical Time and Frequency Transfer (TWOTFT) to enable accurate comparisons of the ISS clock with ground clocks located in several countries and continents. To this end, the EU-FP7-SPACE-2010-1 Project No. 263500 (SOC2) operated from 2011 to 2015. It developed accurate transportable OLC demonstrators on the ground, having fractional relative frequency stability of 1 × 10⁻¹⁵ in a 1-second integration time, and relative fractional accuracies better than 5 × 10⁻¹⁷. The devices were based on trapped neutral ytterbium and strontium atoms. This ESA development demonstrates the importance of an extensive terrestrial technology effort to ensure that OLC ground-based technologies are subjected to extensive environmental testing early in their development cycle, to ensure that they can continue to perform at these advanced levels following launch loads, and in the radiation environments and weightless conditions of space. It is much easier to de-risk the technical design and to contain costs if such flight qualification is done well before the new OLC technologies enter the flight campaign.¹⁶

Another opportunity for collaborative cost reduction for a future NASA-based space OLC program may be achieved through joint project agreements with DoD and the Departments of Energy and Commerce. Many government agencies have been effective in developing commercial off-the-shelf (COTS) technologies that are delivered through industrial and academic consortiums. One such consortium, called the QED-C, was mandated in the National Quantum Initiative Act, and was established with support from NIST within the Department of Commerce.¹⁷ Another is Q-NEXT, which is a Department of Energy (DOE) National Quantum Information Science Research Center led by DOE’s Argonne National Laboratory. The AFRL has led the development of programs in photonic integrated circuits to miniaturize and ruggedize these once huge and vulnerable photonic benches for flight operations, in cooperation with national laboratories, industrial partners, and universities. Given the potential cost savings from such collaborations, it appears that it is worth exploring this possibility.

NOTIONAL CONCEPT: POLAR RADIATION OF MODEL ORGANISMS

The committee also considered PROMO, a notional concept that provides a capability to conduct research on biological and physical samples to better understand their response to the harsh space environment of microgravity and giant cosmic ray space radiation for extended periods of time not suitable for crewed scientific research.

At present, the plans for Artemis missions have few opportunities for research prior to dispatching crew into extended beyond-LEO missions. The research opportunities that are envisioned to exist within cis-lunar space are

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¹⁶ See Schiller (2015).

¹⁷ See QED-C, 2020, “The Quantum Consortium,” https://quantumconsortium.org, for more details.

expected to be severely limited in volume and frequency. This sets an interesting conundrum where some critical research cannot be met with the current deep space platforms, yet they would richly inform human exploration beyond LEO during the Artemis missions. Of particular concern in deep space are radiation effects from high atomic number and high-energy cosmic rays that are both highly damaging to biological systems and difficult to shield (Cucinotta et al. 2011; Giovanetti et al. 2020). Moreover, extremely limited data exist on the combined effects of radiation and microgravity. Therefore, there exists a strong need for laboratory science with animals, organs on chips, plants, and other model systems in vehicles that sample both microgravity and space radiation for extended periods of time.

Missions that experience high levels of radiation and microgravity by traveling completely outside the Van Allen belts are extremely expensive and well beyond current funding concepts. However, there exists a tractable approach that builds on the notional concept known as the “Rodent Mission of Unusual Size,” a concept studied by NASA (Robinson 2017). In this concept, a crew capsule, such as Dragon or Starliner that had passed its rated life for human flight, would be retrofitted with suitable rodent habitats and could potentially support tens of rats for up to a 90-day mission in a polar orbit similar to that used for weather satellites (800 km, ~90-degree inclination). Such an orbit passes through the polar regions effectively unshielded by Earth’s magnetic field and thus with the higher radiation flux. One central goal would be to get larger numbers of intact mammals, including genetically diverse populations, into the combination of high radiation and microgravity to gauge the response of intact mammals in the deep space environment. Figure 6-13 shows the polar orbit of the proposed notional concept freeflyer that accesses a wider range of radiation and microgravity than typical orbits used currently for BPS research.

Preliminary assessment indicates that the avionics and reentry systems are adequate with minimal changes. Return of fixed samples and living mammals, recovered on timelines similar to returning crews, would provide a rich set of samples and data for assessment.

The costs of a repurposed crew capsule polar freeflyer mission are highly dependent on acquisition strategies and the extent to which NASA and the potential providers, including those with strategic objectives of interplanetary flight, can find common interest and approaches to achieving the goals at low cost. Acquisition with traditional models shows potential cost of approximately $1 billion. However, there are good reasons to believe that acquisition approaches finding common interest between NASA and the potential systems partners, and flexibilities to leverage low-cost approaches and manage risks, could result in a mission cost at 25 to 50 percent of the traditional approaches. As more vehicles become available, either dedicated science vehicles or potentially after serving as human-rated systems, the opportunities for innovative deployments will expand.

SUMMARY

The proposed research campaigns, multi-agency opportunity, and notional concept for BPS research platforms offer transformative opportunities for sustained, coordinated science that advance the knowledge needed for extended space missions and return benefits to society. Such ambitious efforts will require investment in the human capital—including broadened participation by more talented scientists inspired by such team-based, multiyear, mission-focused research—and in the physical capital and collaboration within and beyond reach of U.S. federal agencies (see Figures 6-14 to 6-16). Chapter 7 closes this decadal survey report with recommendations to maintain strategy and address challenges for disciplinary balance, infrastructure, and access, and the vibrantly sustained space science community required to realize the promise of this research and to achieve answers to the KSQs in BPS over the coming decade.