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Introduction

The National Academies of Sciences, Engineering, and Medicine established the Committee on Astrobiology and Planetary Sciences (CAPS) in 2012 to serve two major roles: first, to support scientific progress in astrobiology and planetary science; and second, to assist the federal government in integrating and planning programs in these fields by providing advice on the implementation of decadal survey recommendations. One of the primary means by which CAPS addresses its twin roles is by monitoring the progress in implementation of the recommendations of the most recent planetary science decadal survey, Vision and Voyages for Planetary Science in the Decade 2013-2022 (hereafter, V&V).¹ Planetary science decadal surveys evaluate the state of the field, identify the most important scientific questions and themes, and prioritize missions and activities for the decade in question based on scientific merit, technical feasibility, and anticipated cost. The need for careful monitoring is underscored by the fact that some of the decadal survey’s recommendations are triggered at specific programmatic decision points. This short report addresses one such decision point associated with the National Aeronautics and Space Administration (NASA) New Frontiers program.

THE NEW FRONTIERS PROGRAM

NASA’s Planetary Science Division (PSD) provides opportunities for individual investigators to propose, develop, build, launch, and operate small- and medium-class spacecraft missions for the study of solar system bodies. These so-called principal investigator (PI)-led missions fall under the aegis of the Discovery (≤$500 million) and New Frontiers (≤$1 billion) programs, respectively (note that launch vehicle and certain other costs do not presently count toward these cost caps). The ground rules for these two programs differ. Broadly speaking, PIs responding to an announcement of opportunity (AO) issued by the Discovery program may propose missions to any solar system body, whereas PIs responding to an opportunity in the New Frontiers program are restricted to a specific set of mission targets—or mission themes—identified in the most recent planetary science decadal survey. Once a specific New Frontiers target has been addressed by a mission, it is removed from the list of decadal survey-approved future-mission options.²

To date, three New Frontiers missions have been launched and are successfully operating. New Horizons has flown through the Pluto-Charon system and by a small Kuiper belt object (KBO) called Arrokoth and is currently outbound from the solar system. Juno is mapping the gravitational and magnetic fields of, and making numerous other measurements at, Jupiter. OSIRIS-REx is orbiting the near-Earth asteroid Bennu and will collect surface samples for return to Earth later in the 2020s.

V&V recommended that two missions be implemented between 2013 and 2022 through NASA’s New Frontiers program and identified seven possible mission themes. For the New Frontiers 4 (NF4)

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¹ National Research Council (NRC), 2011, Vision and Voyages for Planetary Science in the Decade 2013-2022, The National Academies Press, Washington, D.C., http://www.nap.edu/catalog/13117.html.

² See V&V, Table ES.2.

competition, there were five (in unranked order): Comet Surface Sample Return, Lunar South Pole-Aitken Basin Sample Return, Saturn Probe, Trojan Tour and Rendezvous, and Venus In Situ Explorer. For the New Frontiers 5 (NF5) competition, V&V recommended including the unselected mission themes from NF4 along with two additional themes: Io Observer and Lunar Geophysical Network (LGN).

Prior to the release of the NF4 AO, in response to scientific advances, programmatic considerations, and congressional direction,³ NASA added a sixth mission theme, Ocean Worlds (Titan and/or Enceladus), focused on the search for signs of extant life and characterizing the potential habitability of Titan and/or Enceladus (see Box 1.1). NASA does not prescribe how any missions or investigations responsive to a mission theme should actually be accomplished. However, NASA requires that any mission architecture achieve a preponderance of the science objectives listed.² After a competitive downselect, a rotorcraft mission to the surface of Titan, Dragonfly, was selected and is currently in development.

PSD plans to begin the task of drafting the AO for NF5 in the latter part of 2020 and is planning to release it to the community in its final form in the fall of 2022. This date is sufficiently late in the decadal cycle that NASA asked CAPS to evaluate any changes in scientific understanding and external factors,⁴ such as programmatic developments and/or technological advances, that would warrant a reconsideration of four of the identified New Frontiers mission themes—Ocean Worlds, Trojan Tour and Rendezvous, Io Observer, and Lunar Geophysical Network.⁵ Examples of programmatic developments include NASA’s selection of the Lucy multiple-Trojan-flyby mission in the small-mission-class Discovery program, the

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³ House Report 114-130 accompanying Commerce, Justice, Science, and Related Agencies Appropriations Bill, 2016, p. 59, https://congress.gov/114/crpt/hrpt130/CRPT-114hrpt130.pdf.

⁴ The next decadal survey in astrobiology and planetary science was formally initiated in March 2020 and is scheduled to release its report by the end of March 2022. As such, the findings and recommendations of the new decadal survey will be unable to impact the drafting of the announcement of opportunity for the fifth New Frontiers mission or community preparation for responding to it in any meaningful way.

⁵ Note: The committee was not asked to address other mission themes.

selection of Dragonfly as noted above, the selection in February 2020 of Io Volcano Observer (IVO) for a Discovery phase A concept study,⁶ and the renewed emphasis on lunar exploration within NASA’s Science Mission Directorate (SMD), Space Technology Mission Directorate (STMD), and Human Exploration and Operations Mission Directorate (HEOMD). Examples of technological advancements include developments in power and propulsion and the results of ongoing investments in instrument maturation, radiation hardening, communication, and other technologies. CAPS evaluates each of the questions posed in the statement of task below for Ocean Worlds (Titan and/or Enceladus), Trojan Tour and Rendezvous, Io Observer, and LGN.

The phasing of the various missions discussed in this report relative to the completion of the next planetary science and astrobiology decadal survey and the release of the AO for NF5 is outlined in Table 1.1.

STATEMENT OF TASK

Against the backdrop described above, PSD Director Lori Glaze requested that CAPS address the following task:

CAPS began to address this task by holding a committee-wide conference call on March 10, 2020. Detailed presentations, discussions, and deliberations were held during a virtual meeting on March 31 to April 2. Presentations heard by the committee included those on the relevant science goals for the exploration of Enceladus, Titan, Trojan asteroids, Io, and the Moon, together with details concerning the plans for Dragonfly, Lucy, and IVO.⁷ Committee discussions continued through the first half of April. The report’s conclusions were finalized during a committee-wide conference call on April 21, and the complete report was sent to seven external reviewers on May 1. The report was revised in response to reviewer comments during June and delivered to NASA in late-June. Details concerning the organization and principal conclusions of this study can be found in Box 1.2.

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⁶ The selection of missions in the Discover and New Frontiers programs proceeds via a two-step process: the initial (or Step 1) selection of a small number of proposed candidates for additional study, followed by the final (or Step 2) selection of the candidate selected for implementation and flight.

⁷ For more information about IVO, see, for example, University of Arizona Lunar and Planetary Laboratory, “IVO: Io Volcano Observer,” last update August 18, 2020, https://ivo.lpl.arizona.edu.

TABLE 1.1 The Phasing of the Various Discovery, New Frontiers, and Lunar (via the Commercial Lunar Payload Services [CLPS] Program) Missions Discussed in This Report Relative to the Timeline for the Selection of the Fifth New Frontiers Mission and the Release of the Scheduled Planetary Science and Astrobiology Decadal Survey

NOTE: All dates mentioned, including those associated with the announcement of opportunity (AO) for NF5, are based on current best estimates and are subject to change. The dates shown for the Io Volcano Observer assume that it is selected and launches at the earliest of its two possible launch opportunities.