E
Planetary Science Division Missions
The committee requested data on several planetary missions including Cassini, Mars Science Laboratory (MSL)/Curiosity, the Mars Exploration Rovers (MER), the Mars Reconnaissance Orbiter (MRO), Juno, and Dawn. The committee sought to evaluate the Cassini and Curiosity large strategic missions compared to the medium-size Juno and MER (which consisted of two rovers), as well as the medium-size Mars Reconnaissance Orbiter and smaller (Discovery class) Dawn. NASA could not produce sufficient data on Cassini for the committee to conduct an assessment. This may be due in part to the fact that Cassini was initiated in the early 1990s and launched in 1997, long before NASA implemented full cost accounting in the early 2000s. NASA did not provide information on Juno. Although NASA did provide information on MER, the committee sought to include representative examples of large, medium-size, and small missions and did not want its examples to be dominated by Mars missions. Therefore, the committee included Curiosity (large), MRO (medium) and Dawn (small).
MARS SCIENCE LABORATORY/CURIOSITY
The Mars Science Laboratory (MSL), also known as Curiosity, is a strategic mission in the Mars Exploration Program designed to answer the question of whether Mars ever had the right environmental conditions to support primitive (e.g., microbial) life. Curiosity is a car-size rover equipped with state-of-the-art imaging cameras and laboratory-quality instrumentation for characterizing the mineralogy and chemistry of the Martian surface and atmosphere, as well as the local environmental conditions. MSL was slated to launch in 2009, but due to technical challenges associated with spacecraft hardware systems the launch was delayed until 2011, and the spacecraft successfully landed in Gale crater on August 6, 2012. Curiosity currently is in its second extended mission, embarking on an ascent of the mound at the center of Gale crater, informally known as Mount Sharp.
Scientific Productivity
Through geological, chemical, and isotopic analyses, the MSL mission has found evidence of a sustained, habitable environment at a location in Gale crater called Yellowknife Bay. Preserved rocks indicative of past water-related environments have been identified and characterized, such as those deposited by or in streams, alluvial fans, deltas, and lakes. Further evidence for the persistence of groundwater is the alteration of some of these formations. Organic molecules have been detected in multiple drilled samples, and measurements of methane abundance sug-
gest that this atmospheric component varies seasonally. Measurements of solar radiation have helped to constrain the impacts on the preservation of organic material and the radiation risk to future human explorers.
Impact on the Current and Future Health of the Relevant Scientific Communities
The MSL mission has been a key part of the Mars Exploration Program, collecting data sets from the Martian surface with unprecedented accuracy and precision. The diversity of science enabled by the MSL instrument suite, which includes imaging, alpha particle X-ray spectroscopy, X-ray diffraction analysis, laser-induced breakdown spectroscopy, mass spectroscopy, and temperature, wind, and UV measurements, has led to the involvement of a large segment of the Mars science community in the analysis of MSL data—the entire science team consists of 485 people at the time of this writing, approximately 40 percent of whom are non-U.S. investigators. Of these, 146 are team members (instrument principal investigators, co-investigators, participating scientists, and the project scientist) and 339 are collaborators (research associates, postdoctoral researchers, students, and technical staff). Personnel rotate on and off the project each year, with an average of about 40 people leaving and 57 people joining. Of the current science team, 62 percent have been on the mission since landing.
A number of team members are supported by nonproject funds. Participating scientists are funded from resources outside the project (including non-U.S. organizations such as foreign space agencies, research institutes, and universities), and many more scientists (including students and postdoctoral researchers) have worked on the project and/or analyzed MSL data through fellowships and the Mars Data Analysis Program. The Radiation Assessment Detector instrument and team (eight scientists) are funded by NASA’s Human Exploration Operations Mission Directorate.
Data collected by MSL have been published regularly and integrated by the science community with data collected at Mars by orbiters and prior landers. Since landing, the number of peer-reviewed science papers first-authored by members of the MSL team has increased steadily from 20 in 2013 to 49 in 2014, to 47 in 2015, to 68 in 2016, and to 7 in 2017 (through January 20). (See Figure E.1.) Additional papers using MSL data or results have been published by members of the scientific community who are not MSL team members: 1 in 2013, 19 in 2014, 58 in 2015, 49 in 2016, and 3 in 2017 (through January 20).
Contributions to Development and Demonstration of Technology Applicable to Future Missions
One of the most significant and highest profile developments associated with the MSL mission is the Sky Crane technology for safely depositing the rover onto the Martian surface. Airbag technology used for the Mars Pathfinder and Mars Exploration Rovers missions was not scalable to a rover of the size of MSL. The Sky Crane system was specifically designed to allow MSL to land on Mars directly on its wheels. The Sky Crane was recommended for reuse with future landers in the planetary science community’s decadal survey, and NASA has adopted this system for the Mars 2020 rover currently in development.
Many of the Mars 2020 rover instruments and technologies are directly derived or can point to heritage from MSL, including test beds, spare parts, hardware designs, and personnel (engineering, management, and science). Lessons learned have carried forward into new designs, such as a redesign of the rover wheels that will make the Mars 2020 rover wheels more resistant to punctures/damage. Operational lessons learned feed forward into advances in operational efficiency in terms of operations tools, spacecraft system and performance modeling, and tactical planning procedures.
Conclusions
As part of a balanced program of large-, medium-, and small-class Mars missions, MSL has demonstrated the power that large strategic missions have in terms of their ability to make many diverse but complementary scientific measurements that can address scientific questions that are broad in scope and have far-reaching implications for our understanding of Mars and its geologic and climatological history—and by extension the search for life in our solar system. Making such measurements requires ambitious technological approaches to scientific instrumenta-
tion as well as spacecraft hardware and operations. Many of these investments are paying off beyond the MSL mission proper as the technologies are carried forward into the next generation of flight hardware and processes.
MARS RECONNAISSANCE ORBITER
The Mars Reconnaissance Orbiter (MRO), a medium-class mission in the Mars Exploration Program, was designed to map the Martian landscape at high resolution for both scientific and programmatic applications. The orbiter carries a suite of moderate- and high-spatial-resolution cameras and a visible to near-infrared spectrometer for characterizing the geology and mineralogy of the Martian surface, a radar instrument for characterizing subsurface structure (with emphasis on the polar ice caps), and an atmospheric sounder for measuring Mars’s weather. Imaging data from MRO have aided and continue to aid in the selection of landing sites. MRO also functions as a high-data-volume telecommunications relay, having monitored the entry, descent, and landing events of several missions, and is the primary data relay for the MSL rover. MRO was launched in 2005 and entered Mars’s orbit in 2006. After completing its 2-year primary science phase, MRO entered an extended science phase (through 2010), has subsequently been extended four times, and continues to operate as of this writing.
Scientific Productivity
The very high spatial resolution of several MRO instruments has augmented the scientific community’s understanding of the geology and mineralogy of Mars. Key results include the following: (1) the discovery and monitoring of seasonally appearing features known as recurring slope lineae that are associated with hydrated salts and suggest some role for water in their activity; (2) details of localized deposits of water-bearing clay minerals; (3) evidence that the north polar cap is geologically young (<~5 My) and contains layered dust and ice indicative of obliquity-driven climate change; (4) observations of dynamic processes such as sand dune movement; and (5) the identification of a three-event pattern of dust storms initiating in the southern spring and summer.
Impact on the Current and Future Health of the Relevant Scientific Communities
The MRO mission continues to play a significant role in the Mars Exploration Program, both scientifically and programmatically. As with many planetary missions, MRO engages a large segment of the Mars science community, primarily through the analysis of MRO instrument data sets. The MRO science team proper (not including postdoctoral researchers and students) consists of 88 people, 15 of whom are foreign nationals. In addition, co-investigators on the Italian-supplied Shallow Radar instrument are appointed by the Italian Space Agency. Over the life cycle of the mission, approximately a dozen people have left the team or are inactive, and 28 new co-investigators have been added (9 of whom were originally appointed as Participating Scientists).
Scientific results from the MSL mission have been published regularly by the mission team and the broader science community. (See Figure E.2.) From 2007 to 2016, the MRO team published 335 papers, and non-team members published another 681 (note that team publications were funded by the MRO project and other sources such as the Mars Data Analysis Program).
Contributions to Development and Demonstration of Technology Applicable to Future Missions
Vertical profiling of the atmosphere has helped to improve databases for engineering models that are used to design and implement entry, descent, and landing activities for other missions. The MRO spacecraft was a new design that became the basis for subsequent missions (OSIRIS-REx and MAVEN) and Discovery-class proposals.
Conclusions
The MRO science team is one of many successful examples of how NASA works to integrate U.S. and foreign scientists, as well as engage the broader scientific community. Orbiters like MRO can provide a synoptic view of a planetary body, as well as acquire targeted data at very high spatial resolutions (e.g., tens of centimeters to tens of meters) that support science analyses and programmatic needs. Whereas landed spacecraft can explore a small area of Mars in great detail, medium-size orbiters contribute to the broader context.
DAWN
Dawn is the ninth mission in the Discovery program of relatively small, principal investigator (PI)-led missions. Indeed, of the planetary missions for which this committee received data from NASA, Dawn had the lowest development cost. The total life-cycle cost is slightly greater than that of Gravity Recovery and Interior Laboratory (GRAIL) because of Dawn’s unusually long prime mission duration of nearly 9 years. (Only the larger Cassini and New Horizons had longer prime mission phases.) Dawn was designed to conduct detailed investigations of Vesta and Ceres, the two largest bodies in the main asteroid belt between Mars and Jupiter. Dawn was developed before NASA instituted key decision point date tracking. The project completed its preliminary design review in September 2003 but was canceled the following December. It was restarted in February 2004 and completed its critical design review in June 2004. Development work was put on hold in October 2005, and Dawn was canceled for a second time in March 2006. Later that month NASA restarted the project, and launch took place in September 2007. Dawn’s capability to accommodate significant schedule changes was a direct result of its use of solar electric propulsion, which can provide planetary launch periods of years instead of weeks. The project completed its prime mission in June 2016, having met or exceeded all its original requirements, and at the time of this writing is conducting an extended mission at Ceres.
Scientific Productivity
Dawn’s first target was Vesta, which the spacecraft orbited from July 2011 to September 2012. Vesta was the first object in the main asteroid belt to be studied from orbit, allowing a detailed investigation. Dawn thoroughly mapped Vesta in visible and near-infrared wavelengths; acquired extensive stereo images for topographical mapping; collected a rich set of gamma-ray, visible, infrared, and neutron spectra; and measured the gravity field (allowing the interior structure to be inferred). Dawn’s data showed that Vesta, with a mean diameter of 525 kilometers, is more closely related to the terrestrial planets than to typical asteroids. Dawn entered orbit around Ceres in March 2015. Ceres was the first dwarf planet discovered (January 1801) and the first dwarf planet to be explored by a spacecraft. Dawn performed the same measurements as at Vesta. The mission revealed a world of rock, ice, and salt. Ceres may have had a global ocean early in its history, and Dawn provided evidence of geologically recent activity, including a cryovolcano.
Impact on the Current and Future Health of the Relevant Scientific Communities
Dawn has been vital to the scientific vigor of the small-body community, providing the only orbital data on objects in the main asteroid belt and the only data on objects of such large size (sometimes described as protoplanets). Moreover, Dawn is the only spacecraft to reach a main belt object during a period of nearly 15 years and the only spacecraft to reach large ones in a span of 20 years. When Dawn arrived at Vesta, the previous spacecraft to
fly by an object in the main asteroid belt was 4 years earlier, when the European Space Agency’s Rosetta conducted a brief encounter with Lutetia in July 2010. No other missions are scheduled to main belt asteroids until NASA’s Lucy mission flies by the 4-km-diameter Donaldjohanson in April 2025. The next mission to a large object in the asteroid belt is currently planned to be NASA’s Psyche, which will arrive at the ~250-km-diameter asteroid of the same name in August 2030. Therefore, Dawn has been vital in providing data to the extensive community of scientists studying main belt asteroids, especially large ones. In exploring Ceres, Dawn also has provided the most detailed view of a world with a substantial inventory of water ice, displaying some similarities to the moons of Jupiter and Saturn that have been investigated only with flyby missions.
Contributions to Development and Demonstration of Technology Applicable to Future Missions
Dawn has advanced the state of the art in the use of solar electric propulsion (SEP), implemented as an ion propulsion system (IPS). The IPS was inherited from Deep Space 1 (DS1). From a hardware standpoint, compared with DS1, Dawn used three ion engines instead of one, two digital control units instead of one, and two power processing units instead of one. Dawn launched with 425 kg of xenon, compared to 81.5 kg on DS1. Therefore, the Dawn project extended the system design. Dawn used the new system engineering principles developed on DS1 that are now recognized to be essential for any SEP mission. The Dawn project also developed methods of operating an SEP spacecraft in orbit around planetary bodies, whereas DS1 remained in orbit around the Sun. The new operational methods Dawn developed will reduce cost and risk on future SEP missions. Dawn maintained NASA’s unique expertise in designing and flying SEP missions, for the subsystem, system, and mission. That expertise was developed and brought to an operational capability on DS1, maintained and enhanced on Dawn, and will be applied on subsequent missions, including Psyche.
Conclusions
Despite being one of the smaller planetary missions, Dawn yielded a wealth of valuable scientific data on two previously unexplored worlds. In orbiting two targets beyond Earth, it also accomplished a mission unique in the history of planetary exploration, even among large strategic missions. Dawn obtained a significant benefit from international collaboration, with foreign partners investing about 12 percent of NASA’s cost. Dawn clearly demonstrates that small missions can achieve impressive results and represent an important element of a balanced program.
