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Introduction

STUDY BACKGROUND

In 2023, the National Academies of Sciences, Engineering, and Medicine released Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023–2032 (NASEM 2023; hereafter, OWL). To maximize the advancement of the scientific fields under its purview, OWL outlined 12 priority science questions to guide planetary science and astrobiology within this decade (Box 1-1). To address these key questions, OWL proposed a recommended program that included a balanced portfolio of missions across ranges of both size and cadence.

The principal investigator (PI)-led New Frontiers (NF)-class (NASA n.d.-d) missions bridge the gap between the directed Large Strategic Science Missions (otherwise known as NASA flagship missions; NASEM 2017) and the smaller, but more rapidly responsive, PI-led missions under the Discovery program (NASA n.d.-a). The NF missions occupy a middle ground, having both a relatively longer timeline (nominally twice per decade) and higher budget (~$1 billion) than the Discovery program (nominally three times per decade, <$1 billion) although not as expansive as the NASA flagship missions. This allows more ambitious decadal survey science objectives to be accomplished by targeted missions that are smaller in scale than a NASA flagship.¹

NF mission selection occurs through an AO that provides the community a proposal mechanism to respond to priority mission themes recommended and specified by the decadal surveys. The scope of these mission themes can be broad—for example, the NF-4 mission themes ranged from target-specific missions to Saturn and Venus to a more open call to tour and rendezvous with multiple Trojan asteroids without mandating a specific target (NASA 2016). What unites these mission themes are the key decadal science objectives that the proposed missions are intended to address. Proposals to the NF program must address one of the mission themes, making selection of what themes to include in an AO an important strategic decision.

The planetary science and astrobiology decadal survey develops the list of NF mission themes for NASA based on scientific merit, programmatic balance, technical readiness and feasibility, and other factors. Because only three entities can manage an NF proposal (Johns Hopkins University Applied Physics Laboratory, NASA Goddard Space Flight Center, and the California Institute of Technology’s Jet Propulsion Laboratory), this list must maximize potential benefit to the field while bearing in mind the significant resources necessary to propose, implement, and manage an NF-class mission. OWL assumed that the NF-5 AO would be solicited prior to the decade covered by OWL and did not reevaluate the themes outlined for NF-5 in V&V. OWL recommended eight mission themes for the NF-6 and one additional mission theme for NF-7 to be included in the two AO’s anticipated to be solicited in the 2023–2032 decade.

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¹ Discussion with the NASA Planetary Science Division Director, Committee Meeting No. 1 on the New Frontiers Task, February 13, 2024.

OWL contained both a “Recommended Program” assuming a modest increase to the NASA Planetary Science Division’s (PSD’s) budget and a “Level Program” assuming a flat budget. However, various factors can motivate significant deviations from the decadal survey–recommended program. If these recommended programs were untenable, OWL provided a list of prioritized decision rules that

advise NASA on how to best accomplish the priority science questions. The fourth of these decision rules was to “Reduce the cadence of New Frontiers in the coming decade” (NASEM 2023). If this contingency came to pass, there would still be the outstanding question of which of these OWL mission theme lists to use for the next NF AO.

The National Academies’ Committee on Astrobiology and Planetary Sciences (CAPS) “monitor[s] the progress of implementing the priorities in the most recent decadal survey for the most important scientific and technical activities in that report and recommendations.”² In this role, NASA may request that CAPS undertake a report advising on how best to accomplish decadal scientific priorities, including “consideration of budget and programmatic aspects of the implementation of the decadal survey.”

Budget constraints have compelled NASA to delay the AO for NF-5 until no earlier than 2026. Because that timeframe approaches the expected timeframe for NF-6, it becomes necessary to consider which of the decadal survey mission theme lists to use for this next AO. Against this backdrop, the NASA PSD has requested this report via the statement of task below.

STATEMENT OF TASK

Then NASA PSD Director Lori Glaze requested that CAPS, as part of its role to “[monitor] the progress of implementing the priorities in the most recent decadal survey,”³ write a report evaluating potential mission themes for the next NF AO.

The statement of task for this activity, completed by the Committee on Proposed Science Themes for NASA’s Fifth New Frontiers Mission, was as follows:

It is noted here that the draft NF-5 AO cited in this statement of task was released on September 1, 2022. The committee corrects this editorial error here and uses the actual release date in the remainder of the report.

The committee received this task on January 25, 2024. CAPS held its first open session meeting to address these questions on February 13, 2024.

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² The Committee on Astrobiology and Planetary Sciences statement of task is reprinted in Appendix A.

³ See Appendix A.

Outline of the Report

This report is organized as follows: The remainder of Chapter 1 outlines a brief history of the NF program and its current state. Chapter 2 responds to the first item in the statement of task by succinctly summarizing each of the mission themes considered by this report and relevant science developments since the release of OWL. Chapter 3 addresses the second item in the statement of task, focusing on programmatic changes and balance issues that may justify the reconsideration of a mission theme (see Box 1-2). Last, Chapter 4 answers the final question posed in the statement of task and proposes a list of mission themes for NASA to use in its upcoming AO for NF-5, along with justifications as to why this list would best enable decadal-level science.

HISTORY OF THE NEW FRONTIERS PROGRAM

The NF program was developed by NASA and approved by Congress in 2002. With a cost cap of ~$1 billion, double that of the Discovery program, NF missions were designed to achieve more ambitious science objectives. The goal of the program was “to explore the solar system with medium-class spacecraft missions that conduct high-science-return investigations that add to our understanding of the solar system” (NASA n.d.-d). A summary of the missions included in the various NF AOs is included in Table 1-1 (found at the end of the chapter) and described in detail here.

The first NF mission was selected before the program existed and was grand sired in as its inaugural mission. The New Horizons mission (NF-1) was launched in 2006 with the goal of understanding the formation of the Pluto system and Kuiper belt objects through a close flyby of Pluto, a first in space exploration, and to continue on to perform reconnaissance of several additional Kuiper belt objects (NASA n.d.-e). It achieved its Pluto objective in 2015, and its second major science objective, a flyby of the Kuiper belt object Arrokoth, in 2019. The mission was further extended in 2022.

After NF-1, missions for the NF program were selected based on the objectives laid out in the planetary science decadal surveys or from follow-up reports by the Space Studies Board (SSB). In 2003, the decadal survey New Frontiers in the Solar System: An Integrated Exploration Strategy (NRC 2003; hereafter, NFSS) recommended five mission concepts as medium-class missions. A further five were considered high priority but were deferred for various reasons including mission sequencing, technological readiness, or budget.

Out of five recommended mission concepts in NFSS, four were included in the second NF AO. One was selected as the second NF mission in 2005: the Jupiter Polar Orbiter with Probe. This mission concept evolved into the Juno mission (NF-2) (NASA n.d.-c). The mission was launched in 2011 to develop a greater understanding of the composition, mass, and magnetic fields of Jupiter. Juno arrived at Jupiter in 2016 and has performed measurements since. Although originally designed to last only 33 orbits, Juno has been extended twice through September 2025.

In 2007, NASA asked the SSB to evaluate all of the unimplemented medium-size missions from NFSS in preparation for the third NF-class mission. The resulting report, Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement of Opportunity (NRC 2008), recommended that all three missions not selected for NF-2 as well as the five mission concepts considered “deferred” by NFSS be included in the third NF AO.

The resulting AO in 2009 included eight mission concepts, resulting in the selection of the Asteroid Rover/Sample Return concept. It should be noted that this particular mission concept was considered “deferred” by NFSS. This mission would become the OSIRIS-REx mission (NF-3).

OSIRIS-REx was launched in 2016 with the primary objective of collecting and returning a sample from the asteroid (101955) Bennu, a body with materials that can provide information on the early history of the solar system (NASA n.d.-f). OSIRIS-REx entered Bennu orbit in December 2018, surveyed for potential sample collection sites, successfully collected more than twice the required 60 g of sample in October 2020, and returned those samples to Earth in September 2023. At the time of this writing, sample analysis is ongoing. OSIRIS-REx was extended in April 2022 as OSIRIS-APEX, with the goal of studying the near-Earth asteroid (99942) Apophis shortly after its near-Earth encounter in 2029.

In 2013, the next decadal survey was published—Vision and Voyages for Planetary Science in the Decade 2013–2022 (NRC 2011; hereafter, V&V). V&V recommended a total of seven mission concepts as potential NF-class missions, including four mission concepts not selected for NF-3. Of these seven missions, one mission concept was added since the 2008 Opening New Frontiers in Space report and two were removed.

In 2015, the U.S. House of Representatives Committee on Appropriations released a report accompanying the Commerce, Justice, Science, and Related Agencies Appropriations Bill, 2016 (Congress.gov 2016). Although the language of this report was not reflected in the final appropriations bill, the report served as “an explanation of the accompanying bill making appropriations for Commerce, Justice, Science, and related agencies for the fiscal year ending September 30, 2016, and for other purposes.” This report directed NASA to “to create an Ocean World Exploration Program whose primary goal is to discover extant life on another world using a mix of Discovery, New Frontiers and flagship class missions consistent with the recommendations of current and future Planetary Decadal surveys” (Congress.gov 2016). In response, NASA announced via community announcement that “Ocean Worlds (Titan and/or Enceladus)” would be included as one of six possible mission concepts in the fourth NF AO.

The Ocean Worlds (Titan and/or Enceladus) mission theme was selected in 2017, becoming the Dragonfly mission (NF-4). Dragonfly is a rotorcraft designed for flight in the atmosphere of Titan, the largest moon of Saturn (NASA n.d.-b). Dragonfly will fly hundreds of kilometers in Titan’s atmosphere, sampling a wide variety of landing sites with its onboard science payload. This mission is expected to launch no earlier than July 2028.

CURRENT STATE OF THE NEW FRONTIERS PROGRAM

In 2020, NASA PSD requested a report from CAPS to evaluate four NF mission themes: Ocean Worlds, Trojan Tour and Rendezvous, Io Observer, and Lunar Geophysical Network. The resulting report, Options for the Fifth New Frontiers Announcement of Opportunity (NASEM 2020), recommended reconsideration of Ocean Worlds (Titan) and the Trojan Tour and Rendezvous as themes in light of the then recent mission selections, Dragonfly (NF-4) and the Discovery-class mission Lucy, respectively.

A community announcement in November 2020 gave advance notice for the upcoming AO for the NF-5 mission (NASA n.d.-g). This community announcement included the following mission themes as valid proposal targets:

• Comet Surface Sample Return
• Lunar South Pole–Aitken Basin Sample Return
• Ocean Worlds (Enceladus)
• Saturn Probe
• Venus In Situ Explorer
• Io Observer
• Lunar Geophysical Network

Note that this included four mission concepts not selected for NF-4. This community announcement stated that the estimated release of the draft AO would be October 2021, with the final version to be released in October 2022. This timeline was later delayed.

In September 2022, NASA PSD issued a community announcement removing Venus In Situ Explorer from the list of NF-5 proposal targets after two Venus missions were selected in the Discovery mission line (DAVINCI and VERITAS; NASA 2022).

The draft NF-5 AO was released on January 10, 2023 (NASA 2023b), estimating the release of the final version for November 2023. However, owing to budget uncertainty, the conversion of this draft AO to a final AO was delayed to no earlier than 2026 (NASA 2023a).

The delayed timing of the draft AO created an overlap with activities for NFSS. As stated in OWL (NASEM 2023, p. 586),

This delay stimulated NASA’s PSD request for CAPS to evaluate potential mission themes for the next NF AO in January 2024, which is the basis of this report.

TABLE 1-1 New Frontiers (NF) Recommended Target List Evolution

^a ONF5 and OWL recommended removal of Io Observer if Io Volcano Observer was selected in Discovery.

^b Grandsired into the NF program.

^c Program added by Congress.

^d Removed from 2023 NF-5 Draft Announcement of Opportunity (AO) by NASA’s Planetary Science Division after selection of Venus missions in Discovery.

NOTE: Each recommended mission can be found in one or more reports of the National Academies of Sciences, Engineering, and Medicine (published by the National Academies Press):

• NFSS, planetary decadal survey 1: New Frontiers in the Solar System: An Integrated Exploration Strategy (NRC 2003).
• NOSSE, New Opportunities in Solar System Exploration study: Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement of Opportunity (NRC 2008).
• V&V, planetary decadal survey 2: Vision and Voyages for Planetary Science in the Decade 2013–2022 (NRC 2011).
• ONF5: Report Series: Committee on Astrobiology and Planetary Science: Options for the Fifth New Frontiers Announcement of Opportunity (NASEM 2020).
• OWL, planetary decadal survey 3: Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023–2032 (NASEM 2023).

An “X” indicates that that mission was included in an NF AO, draft AO or, for NF-6, recommended in OWL.