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Impact on New Frontiers 5 Mission Theme Considerations

The science objectives and overall goals of each New Frontiers (NF)-5 and NF-6 mission theme summarized in the Chapter 2 set the stage to evaluate the second item in the statement of task:

The following sections identify those mission themes that fall into this category, and those that do not, with specific emphasis on those aspects of the mission theme that have changed to warrant reconsideration. In those cases where no significant developments warrant reconsideration, the committee encompasses these mission themes into a single finding.

LUNAR SCIENCE

As the nearest neighbor and Earth’s only satellite, the Moon remains one of the most accessible bodies within the solar system to elucidate Earth’s early planetary evolution as well as early solar system dynamics. The growing national and international focus on lunar missions, including the National Aeronautics and Space Administration’s (NASA’s) Artemis program, India’s Chandrayaan-3 mission, and China’s Chang’e-6 sample return mission, is evidence of the importance of lunar science to broad planetary exploration.

Lunar science and exploration directly address at least 3 of OWL’s 12 priority science questions, including Q3: “Origin of Earth and inner solar system bodies”; Q4: “Impacts and dynamics”; and Q5: “Solid body interiors and surfaces.” Furthermore, lunar exploration for both scientific and resource utilization was highlighted in 2017 as part of Space Policy Directive-1 (White House 2017). In 2019, NASA instituted the Lunar Discovery and Exploration Program (LDEP), which is funded through PSD and managed between the Planetary Science Division (PSD) and the Exploration Science Strategy Integration Office (ESSIO). Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023–2032 (NASEM 2023; hereafter, OWL) explicitly recommended that NASA focus a lunar exploration program that prioritized lunar science objectives:

Within this framework set out by OWL, the committee considered the two lunar missions contained in the comprehensive NF-5 and NF-6 mission themes: Lunar South Pole–Aitken (SPA) Basin Sample Return and Lunar Geophysical Network (LGN).

The SPA Basin Sample Return mission theme has remained a planetary science exploration priority for the past three decadal surveys because it targets the chronology of lunar basin-forming impacts and early solar system impact dynamics, lower crust and upper mantle composition, as well as lunar differentiation. As such, this mission theme is directly responsive to Q3, Q4, Q5, as well as Q9 and Q10. OWL studied two mission concepts, Endurance-R and Endurance-A, and concluded that this high-priority science was more likely accomplished through an Endurance-A mission framework in which a single, medium-class mission concept would return ~100 kg of lunar samples through a robotic–human partnership. Given the high priority of lunar science and the 2019 establishment of the LDEP to coordinate lunar exploration, OWL recommended that an SPA sample return mission would be better suited within LDEP. The committee concluded that no new scientific discoveries or technological developments have negated these findings.

Finding 1: Endurance-A, identified in Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023–2032 (NASEM 2023) as the highest-priority medium-class mission for the Lunar Discovery and Exploration Program (LDEP), addresses multiple decadal survey priority science questions. Because the Endurance-A mission scope encompasses the objectives outlined in the New Frontiers (NF)-5 draft announcement of opportunity (AO) Lunar South Pole–Aitken Basin Sample Return mission theme, the absence of this theme from the next NF AO is warranted.

The LGN mission theme has been identified in the past three planetary decadal surveys as high-priority science. The last LGN mission concept study was conducted in 2011, and the mission concept was last reviewed in full in Vision and Voyages for Planetary Science in the Decade 2013–2022 (NRC 2011; hereafter, V&V). The 10-year mission proposes an array of four seismic stations, each with a seismometer, heat flow probe, retroreflector, and magnetotelluric sounder. Direct mission objectives include determining the size, structure, composition, and heterogeneity of the Moon’s interior, its relation to surface characteristics, and the current seismo-tectonic and thermal state of the interior. Also informing understanding of the evolution of terrestrial planets, the LGN mission is directly responsive to priority decadal science question themes Q3, Q4, Q5, and Q8.

Although not included in the NF-4 solicited mission themes, V&V did recommend the inclusion of LGN in the next NF AO. The science proposed by the mission is still important, and there has not yet been a mission to address these particular lunar science questions despite advances by both GRAIL and LRO as discussed in Chapter 2.

This mission does present several challenges that preclude it from other existing mission lines such as Discovery or Commercial Lunar Payload Services (CLPS). A single station with a seismometer, heat flow probe, retroreflector, and magnetotelluric sounder is insufficient to fulfill the science objectives. Rather, four stations are required to achieve the stated science objectives, exceeding the Discovery mission cost cap.

Furthermore, the 4-seismometer array must be deployed together and survive for at least a full lunar tidal cycle of 6 years to achieve its primary science objective: determining the distribution and origin of lunar seismic activity. While LDEP’s ongoing CLPS Program shows promise, delivering an array of seismometers, simultaneously or in quick succession, that can survive a full lunar tidal cycle is currently outside the CLPS capability scope. Work is under way to extend lifespans of CLPS landers and associated payloads (Lunar and Planetary Institute 2022); the Lunar Farside Seismic Suite is packaged as a self-sufficient payload with thermal control to enable survival through the lunar night, and it is designed to operate for at least 4.5 months. However, no discussion so far has proposed the 6-year lifespan required to achieve the decadal objectives addressed by LGN.

In sum, owing to the lower cost cap of Discovery and the inability of CLPS landers to survive long enough to accomplish the science goals of this mission theme, the committee finds that there are no programmatic avenues that can accomplish LGN other than the NF program. Furthermore, the mission still meets decadal survey–level science objectives. Therefore, the committee finds that there has not been a significant change in scientific understanding or programmatic developments to warrant the reconsideration of this mission theme for inclusion.

The committee continues to support NASA’s focus on lunar science with the establishment of LDEP during the end of the past decade. However, priority lunar science, including LGN, must continue to be prioritized across NASA mission programs while LDEP and ESSIO capabilities are expanded.

Finding 2: The science proposed by the Lunar Geophysical Network (LGN) addresses multiple decadal survey priority science questions. There are currently no programmatic avenues, including the NASA Lunar Discovery and Exploration Program (LDEP) and the Commercial Lunar Payload Services, that could accomplish LGN other than the New Frontiers (NF) program. Therefore, the inclusion of LGN as a theme in the next NF announcement of opportunity is warranted.

SMALL BODIES

Three orbiter, lander, and sample return missions to small bodies were included in the OWL report NF-5 and NF-6 mission theme lists. Comet Surface Sample Return (CSSR) has been included in New Frontiers mission target lists since NF-2, and both Centaur Orbiter and Lander (CORAL) and Ceres Sample Return were added to the NF-6 list during the OWL process as part of a planetary mission concept study (PMCS). OWL concluded that each of the three small body mission themes was unique and addressed high-priority decadal science. Collectively, these mission themes address 11 of the 12 priority science question topics, with the most significant contributions to Q1: “Evolution of the protoplanetary disk”; Q2: “Accretion in the outer solar system”; Q3: “Origin of Earth and inner solar system bodies”; Q5: “Solid body interiors and surfaces”; and Q10: “Dynamic habitability.”

CSSR has been a community and decadal priority since the early formulation of the New Frontiers program. The related Comet Astrobiology Exploration Sample Return (CAESAR) mission was one of two finalists in NF-4, evidence of both community prioritization and mission feasibility. Samples returned by a CSSR-themed mission would represent some of the most primitive materials of the early solar system and protosolar nebula. Ceres Sample Return targets the only dwarf planet within the asteroid belt. Ceres Sample Return would represent the first cryo-preserved sample and the first sample return from a candidate Ocean World, making this mission and the Enceladus Multiple Flyby (EMF) mission theme the only two that could result in breakthrough science addressing Q10: “Dynamic habitability.”

Chemical and physical observations from Dawn (McCord et al. 2022) suggest that Ceres’s internal structure and surface are the outcome of extended water–rock–organic compound interactions, which could be further explored by this orbiter/lander/sample return mission. Centaur Orbiter and Lander (CORAL) represents a second cometary target, but specifically targeting a Centaur provides an opportunity to investigate nebular volatiles in primordial, ice-rich planetesimals that originated in the primordial Kuiper belt. CORAL addresses 10 of the 12 priority science questions, with the most significant potential for questions Q1, Q2, and Q3.

All three small body mission targets would provide key reference measurements for ground- and space-based observations and expand applicability of these observations across the solar system. Furthermore, the current NF timeline could allow for upcoming observations from the Vera C. Rubin Observatory, NEO Surveyor, and James Webb Space Telescope (JWST) to improve target selection for these missions. Recent successes in small body sample return from Ryugu and Bennu can only improve sample return, curation, and analysis protocols from small bodies, and may provide mission cost savings. Results of the Autonomous Navigation Demonstration Relevance Assessment (ANDRAT) chartered

study (NASA 2024) could also result in reduced operation mission costs. The committee concluded that these scientific, mission, and technological developments only support the continuation of small body mission research.

Finding 3: Comet Surface Sample Return, Centaur Orbiter and Lander, and Ceres Sample Return address multiple decadal survey priority science questions. Inclusion of these missions in the next New Frontiers announcement of opportunity is warranted.

OUTER SOLAR SYSTEM PLANETS AND MOONS

The saturnian moon Enceladus has been identified as high-priority science in both V&V (NRC 2011) and OWL (NASEM 2023). In V&V, Enceladus Orbiter was listed as the fourth-priority target for flagship missions, and the Ocean Worlds theme (with a focus on either Titan or Enceladus) was then included in the NF-4 AO by NASA. Following the selection of Dragonfly for NF-4, the NF-5 Draft AO included Ocean Worlds (Enceladus only). OWL subsequently completed the PMCS for an EMF mission theme. EMF addresses at least two of OWL’s 12 priority science questions, Q10: “Dynamic habitability” and Q11: “Search for life elsewhere,” while also contributing to Q5: “Solid body interiors and surfaces” and Q12: “Exoplanets.” The committee concluded that no additional scientific, technological, or programmatic changes impact the evaluation of EMF in OWL.

Saturn Probe was first added to the New Frontiers missions themes list for NF-4 in V&V, and has subsequently been included in the NF-5 draft AO as well as recommended for inclusion in NF-6 by OWL. V&V noted that this mission concept was the only one to address giant planet science questions within the cost cap of the NF program (NRC 2011). The Saturn Probe mission theme will explore the structure of Saturn’s atmosphere, the abundance of noble gases, and the isotopic ratios of hydrogen, carbon, nitrogen and oxygen. It is responsive to Q1: “Evolution of the protoplanetary disk” and Q12: “Exoplanets.” Importantly, Saturn Probe is the only recommended NF concept that addresses Q7: “Giant planet structure and evolution.”

The only other mission concept in any mission program reviewed in OWL to address Q7 was the Uranus Orbiter and Probe (UOP), which was determined in OWL as the highest-priority flagship mission for the coming decade. V&V noted that “When a Saturn Probe mission is combined with a Uranus Orbiter and Probe mission, the understanding of planetary formation will be greatly advanced in the next decade” (NRC 2011), and OWL maintained Saturn Probe in the NF-5 and NF-6 mission themes. The committee concluded that selection of UOP for the next flagship, whose start is already delayed, did not pose a significant impact on programmatic balance.

Finding 4: Enceladus Multiple Flyby and Saturn Probe address multiple decadal survey priority science questions. Inclusion of these missions in the next New Frontiers announcement of opportunity is warranted.

Io Observer was first evaluated in the 2003 decadal survey New Frontiers in the Solar System: An Integrated Exploration Strategy (NRC 2003; hereafter, NFSS) and was included in NF-3 AO and the NF-5 draft AO. A mission concept study for Io Observer was part of the V&V review and included in the V&V NF-5 priority list. Io Observer was also reviewed in Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement of Opportunity (NRC 2008) and maintained on the NF-5 list in OWL. Each review maintained the importance of addressing the science objectives of the Io Observer mission concept.

The Io Volcano Observer (IVO) mission was a finalist for Phase-A Concept Study in the 2019 Discovery Program but was ultimately not selected for flight. The 2020 Committee on Astrobiology and Planetary Sciences (CAPS) report reiterated the importance of the science objectives of Io Observer and asserted that the mission theme should be maintained on the NF-5

mission theme list if IVO was not selected. The Io Observer mission concept was not included in OWL’s priority science question matrix but would cover major themes including Q5: “Solid body interiors and surfaces”; Q6: “Solid body atmospheres, exospheres, magnetospheres, and climate evolution”; and Q8: “Circumplanetary systems.” The committee reaffirms the importance of Io as a unique body for understanding active volcanic, tectonic, and plasma processes, and for providing a potential analogue to certain exoplanets and young terrestrial planets. Furthermore, while Juno observations of Io are contributing to Io science, the Juno instrument package cannot address all 7 of the science objectives outlined for Io Observer in V&V.

Finding 5: The broad objectives of Io Observer continue to address multiple decadal survey priority science questions. Recent advances in Io science, including those from the Juno flybys, do not warrant reconsideration or removal of Io Observer from the next New Frontiers (NF) announcement of opportunity (AO). Therefore, inclusion of Io Observer in the next NF AO is warranted.

The concept of a Titan Orbiter was included as part of the Flagship-class Titan Saturn System Mission in V&V (NRC 2011). While the science objectives were deemed important, the cost estimate was well outside the NF cost cap and, therefore, not included in V&V’s recommended NF mission themes. However, Titan was added to the NF-4 AO by NASA as part of the Ocean Worlds—Titan or Enceladus theme, and the Titan Orbiter Oceanus was proposed but not selected in NF-4.

With science targets that include the exploration of Titan’s dense atmosphere, potential for atmospheric prebiotic chemistry, a unique methane hydrological cycle, and subsurface ocean, the Titan Orbiter mission theme directly addresses OWL’s Q5: “Solid body interiors and surfaces” and Q6: “Solid body atmospheres, exospheres, magnetospheres, and climate evolution.” Titan Orbiter is also responsive to Q8, Q10, Q11, and Q12. In evaluating Titan Orbiter within the NF program, OWL cited the previous CAPS report (NASEM 2020), which suggested that the mission theme remain in the NF-6 concept list but be removed from the NF-5 theme owing to the selection of Dragonfly in NF-4. The OWL steering committee concluded that Titan Orbiter provides important and complementary science to Dragonfly and prioritized it for the NF-6 list. OWL assumed that Titan would not be included in the next NF AO while making this prioritization. The committee affirms that there is no new significant science or technological changes that counter the conclusions in OWL.

Finding 6: Titan Orbiter addresses several decadal survey priority science questions that are distinct from the Dragonfly mission to Titan selected in the New Frontiers (NF)-4. However, to maintain programmatic balance, the absence of Titan Orbiter from the next NF announcement of opportunity is warranted. Titan Orbiter remains a high priority for future NF mission opportunities as recommended by Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023–2032 (NASEM 2023).

VENUS

The Venus in Situ Explorer (VISE) mission has been recommended as a New Frontiers mission in each of the three planetary decadal surveys. VISE proposals reached Phase-A in NF-3 and received development funding in NF-4. VISE was included in the NF-5 list of V&V. As stated earlier, OWL did not comment on the NF-5 mission candidates. Therefore, OWL prioritized VISE for NF-6 and NF-7 but did not directly address VISE with respect to NF-5.

VISE was included in the “Second Community Announcement: Advance Notice Regarding New Frontiers 5 (NF-5) Announcement of Opportunity” (NASA n.d.-g) but was removed from the “Fifth Community Announcement: Advance Notice Regarding Forthcoming Release of the New Frontiers 5 (NF-5) Announcement of Opportunity (AO)” (NASA 2022) by the PSD after the selections of DAVINCI

and VERITAS in Discovery and the ESA EnVision mission (which includes a NASA-supported radar). NASA decided to remove VISE from the draft NF-5 AO for reasons of programmatic balance. Since then, budgetary turbulence has delayed the launches of VERITAS and DAVINCI, but they (and EnVision) have not changed their scientific objectives. A private company (Rocket Lab) continues to plan to launch a small, low-cost probe to Venus, focused on astrobiology. Other national space agencies have discussed new Venus missions but have not revealed any finalized plans.

When NASA removed VISE from the NF-5 draft AO in early 2023, after the then-recent selections of DAVINCI, VERITAS, and EnVision, programmatic balance was the most significant driver for omission. As per this committee’s charge, when considering the scientific, technical, and programmatic changes in the past 2 years since VISE was removed from the 2023 NF-5 draft AO, the science remains compelling and the programmatic landscape is unchanged. The committee asserts that it would be challenging for NASA to demonstrate programmatic balance of principal investigator (PI)-led missions if three Venus missions are selected in a row.

Finding 7: Venus In Situ Explorer (VISE) addresses several decadal survey priority science questions that are distinct from those addressed by recently selected missions (DAVINCI, VERITAS, and EnVision) to Venus. However, to maintain programmatic balance, the absence of VISE from the next New Frontiers (NF) announcement of opportunity is warranted. VISE remains a high priority for future NF mission opportunities as recommended by Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023–2032 (NASEM 2023).