Combined Pluto Orbiter and Kuiper Belt Exploration Mission. C.J.A. Howett 1 , S. Robbins 1 , H. Elliot 2 , C.M. Ernest 3 A.R. Hendrix 4 , B. Holler 5 , W.B. McKinnon 6 , F. Nimmo 7 , S. Protopapa 1 , S. Porter 1 , J. Radebaugh 8 , K. Sing- er 1 , J.R. Spencer 1 , S.A. Stern 1 , O.J. Tucker 9 , A. Verbiscer 10 , R.J. Wilson 11 and L.A. Young 1 , 1 Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80301 ([email protected]), 2 Southwest Research Insti- tute, San Antonio, TX, 3 Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 4 PSI Boulder, Boulder, CO, 5 Space Telescope Science Institute, Baltimore, MD, 6 Washington University in Saint Louis, St. Louis, MO, 7 University of California, Santa Cruz, CA, 8 Brigham Young Univ., Provo, UT, 9 Goddard Space Flight Center, Greenbelt, MD, 10 University of Virginia, Charlottesville, VA, 11 Colorado University, Boulder, CO. Introduction: Our Decadal Mission Study ad- dresses a first-of-its-kind mission to both orbit the Pluto system, and explore other dwarf planets (DPs) and small, primordial Kuiper Belt Objects (KBOs). This mission study has its roots in spectacular data returned by NASA’s New Horizons spacecraft that flew by the Pluto system in 2015 and the small, pri- mordial KBO (486958) Arrokoth (provisionally desig- nated 2014 MU 69 ) in 2019 [1,2]. New Horizons data led to a wide variety of surprising discoveries: the sev- en observed bodies are very diverse, Pluto has a cur- rently active surface, and Charon has had an active geologic history. These data also raised new questions that can only be answered by a return to the Pluto sys- tem with an orbiter, and yet the diversity of KBOs and other dwarf planets also beckons. We recently showed [3] that it is possible to study the Pluto system and explore the Kuiper Belt (KB) with a single mission: after orbiting through the Pluto system, a Charon gravity assist enables the spacecraft to leave that system with relatively little chemical pro- pulsion. Even the Dawn mission’s ion electric propul- sion system would be sufficient to accomplish this task. The craft could then go onto explore additional dwarf planets (DP) and KBOs, potentially even orbit- ing another DP. Such a mission opens up important new avenues of exploration, fulfilling the goals of mul- tiple planetary science communities. The aim of this mission concept study is to understand potential trajec- tories, instrumentation versus science goal trade-offs, and costs and risks associated with the long-duration, complex mission so that the next Decadal Survey will be able to weigh the costs and benefits of such a mis- sion. Why Return to the Kuiper Belt?: What we learned from New Horizons has provided a much deeper understanding of KBOs, and leads to deeper, more probing questions. Understanding the nature of the geological activity on Pluto, a moderately-sized world located in the Kuiper Belt, is an important goal of this mission concept, for it has profound implica- tions for the evolution of other bodies in our solar sys- tem (e.g., Triton). Understanding the Pluto system pro- vides critical information on heat and volatile transport mechanisms in the KB, and finally understanding the diversity of the KB would allow us to understand its complex evolution, and its context within the solar- system’s small body populations. Such a mission has been shown to have large support by the planetary sci- ence community. For example, the Committee on As- trobiology and Planetary Sciences (CAPS) suggested “a Pluto system orbiter and Centaur and/or Kuiper Belt object flybys” are important follow-on missions to study in advance of in the next planetary science deca- dal survey [4]. The conclusions of CAPS were sup- ported by the mid-term review of the planetary Deca- dal Survey, which suggested further study was re- quired to test the science value per dollar and technical and cost feasibility of such a mission [5]. Finally, the Roadmap to Ocean Worlds (ROW) also recommended that “mission studies should be performed to address technology advances enhancing exploration of the Kuiper Belt or a return to Pluto with an orbiter” [6]. Science Questions to be Addressed: The ques- tions to be addressed by the mission and their relative importance are still being explored. Under the three broad themes we expect the questions to be: Is Pluto an ocean world? How is Pluto’s internal heat maintained over 4.5 billion years? Are Pluto (and Charon) fully differentiated? What is the history of the Pluto System? What are the relative ages of Pluto’s and Charon’s surfaces and geologic activity? What is the history of atmospheric volatiles on Pluto and Charon? How is the internal heat expressed at the surface? What is the diversity of worlds in the Kuiper Belt? How similar targets in the Pluto system to other KBOs and their satellites, and what does this mean for accre- tion processes? How do other surface properties of KBOs vary? What is the cratering record on visited KBOs, and how does it inform the KB size-frequency distribution? What can binary fraction, density, and shapes of KBOs tell us about their formation and the collisional environment in the primordial KB? How do KBO compositions constrain giant-planet migration theories? What is the intrinsic magnetic field strength and overall magnetic field configuration around KBOs? Preliminary Payload: The preliminary mission payload includes ten instruments: a panchromatic high- 1342.pdf 51st Lunar and Planetary Science Conference (2020)
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Combined Pluto Orbiter and Kuiper Belt Exploration Mission. C.J.A. Howett1, S. Robbins1, H. Elliot2, C.M. Ernest3 A.R. Hendrix4, B. Holler5, W.B. McKinnon6, F. Nimmo7, S. Protopapa1, S. Porter1, J. Radebaugh8, K. Sing-er1, J.R. Spencer1, S.A. Stern1, O.J. Tucker9, A. Verbiscer10, R.J. Wilson11 and L.A. Young1, 1Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80301 ([email protected]), 2Southwest Research Insti-tute, San Antonio, TX, 3Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 4PSI Boulder, Boulder, CO, 5Space Telescope Science Institute, Baltimore, MD, 6Washington University in Saint Louis, St. Louis, MO, 7University of California, Santa Cruz, CA, 8Brigham Young Univ., Provo, UT, 9Goddard Space Flight Center, Greenbelt, MD, 10University of Virginia, Charlottesville, VA, 11Colorado University, Boulder, CO.
Introduction: Our Decadal Mission Study ad-dresses a first-of-its-kind mission to both orbit the Pluto system, and explore other dwarf planets (DPs) and small, primordial Kuiper Belt Objects (KBOs). This mission study has its roots in spectacular data returned by NASA’s New Horizons spacecraft that flew by the Pluto system in 2015 and the small, pri-mordial KBO (486958) Arrokoth (provisionally desig-nated 2014 MU69) in 2019 [1,2]. New Horizons data led to a wide variety of surprising discoveries: the sev-en observed bodies are very diverse, Pluto has a cur-rently active surface, and Charon has had an active geologic history. These data also raised new questions that can only be answered by a return to the Pluto sys-tem with an orbiter, and yet the diversity of KBOs and other dwarf planets also beckons.
We recently showed [3] that it is possible to study the Pluto system and explore the Kuiper Belt (KB) with a single mission: after orbiting through the Pluto system, a Charon gravity assist enables the spacecraft to leave that system with relatively little chemical pro-pulsion. Even the Dawn mission’s ion electric propul-sion system would be sufficient to accomplish this task. The craft could then go onto explore additional dwarf planets (DP) and KBOs, potentially even orbit-ing another DP. Such a mission opens up important new avenues of exploration, fulfilling the goals of mul-tiple planetary science communities. The aim of this mission concept study is to understand potential trajec-tories, instrumentation versus science goal trade-offs, and costs and risks associated with the long-duration, complex mission so that the next Decadal Survey will be able to weigh the costs and benefits of such a mis-sion.
Why Return to the Kuiper Belt?: What we learned from New Horizons has provided a much deeper understanding of KBOs, and leads to deeper, more probing questions. Understanding the nature of the geological activity on Pluto, a moderately-sized world located in the Kuiper Belt, is an important goal of this mission concept, for it has profound implica-tions for the evolution of other bodies in our solar sys-tem (e.g., Triton). Understanding the Pluto system pro-vides critical information on heat and volatile transport mechanisms in the KB, and finally understanding the
diversity of the KB would allow us to understand its complex evolution, and its context within the solar-system’s small body populations. Such a mission has been shown to have large support by the planetary sci-ence community. For example, the Committee on As-trobiology and Planetary Sciences (CAPS) suggested “a Pluto system orbiter and Centaur and/or Kuiper Belt object flybys” are important follow-on missions to study in advance of in the next planetary science deca-dal survey [4]. The conclusions of CAPS were sup-ported by the mid-term review of the planetary Deca-dal Survey, which suggested further study was re-quired to test the science value per dollar and technical and cost feasibility of such a mission [5]. Finally, the Roadmap to Ocean Worlds (ROW) also recommended that “mission studies should be performed to address technology advances enhancing exploration of the Kuiper Belt or a return to Pluto with an orbiter” [6].
Science Questions to be Addressed: The ques-tions to be addressed by the mission and their relative importance are still being explored. Under the three broad themes we expect the questions to be:
Is Pluto an ocean world? How is Pluto’s internal heat maintained over 4.5 billion years? Are Pluto (and Charon) fully differentiated?
What is the history of the Pluto System? What are the relative ages of Pluto’s and Charon’s surfaces and geologic activity? What is the history of atmospheric volatiles on Pluto and Charon? How is the internal heat expressed at the surface?
What is the diversity of worlds in the Kuiper Belt? How similar targets in the Pluto system to other KBOs and their satellites, and what does this mean for accre-tion processes? How do other surface properties of KBOs vary? What is the cratering record on visited KBOs, and how does it inform the KB size-frequency distribution? What can binary fraction, density, and shapes of KBOs tell us about their formation and the collisional environment in the primordial KB? How do KBO compositions constrain giant-planet migration theories? What is the intrinsic magnetic field strength and overall magnetic field configuration around KBOs?
Preliminary Payload: The preliminary mission payload includes ten instruments: a panchromatic high-
1342.pdf51st Lunar and Planetary Science Conference (2020)
resolution imager (e.g. New Horizons/LORRI); color imaging and near-infrared spectral coverage (e.g., New Horizons/Ralph); UV spectral coverage (e.g., New Horizons/Alice); thermal-IR coverage (e.g., Lu-cy/TES); Radio Science (e.g. New Horizons/REX); Ice penetrating radar (e.g., Europa Clipper/REASON); Mass Spectrometer (e.g., Europa Clipper/MASPEX); Laser Altimeter (e.g., Messenger/LOLA); Magnetome-ter (e.g., IMAP/MAG); and an instrument for making Plasma Ion Measurements (e.g., New Horizons/ SWAP). The feasibility of including such a large and diverse payload on such a mission is being investigated as part of this work. Other payload instruments are also under consideration instead of some of these. It is like-ly that the final mission concept study will only in-clude a sub-set of these instruments, and perhaps oth-ers, as required to fulfill its level one science goals.
Preliminary Tour: Our proposed tour was based on preliminary work done in house at SwRI [3], which has subsequently been refined [7]. The preliminary work indicated that the following tour was feasible: a launch in 2027, arrival in the Pluto system in 2039, a two-year orbital tour of the Pluto system, then breaking orbit in mid-June 2041 to encounter another large KBO dwarf planet, while investigating smaller distant KBOs along the way during post-Pluto cruise. Subse-quently we have discovered that the cruise period is significantly longer using current technology and launch vehicles. The result is that the most pressing trajectory trade/work is in reducing this cruise time. Since the Pluto system evolves slowly we expect the final Pluto-system tour to resemble the one we initially proposed [Figure 1], somewhat regardless of arrival time. However, the exact KBOs available to explore post Pluto-system are likely to change.
As Figure 1 shows, in the Pluto-system tour there are 59 close Pluto encounters (<100,000 km, with most between 3,000 and 10,000 km). During this time the spacecraft has multiple <3,000 km encounters with each of Pluto’s small satellites, and many more <20,000 km encounters. The tour begins near Pluto’s equatorial plane, but increases inclination to a polar orbit by using Charon. Polar coverage, combined with low periapse passes to allow in situ mass spectroscopy and ionospheric sampling.
After close Charon flybys are used to break orbit, our preliminary analysis shows we can reach multiple different types of dwarf planets (diameters >500 km) and small KBOs with a Δv of less than 8.4 km/s, and have low-speed (i.e., long duration) encounters with them. Assuming a post-Pluto ∆v limit of 10 km/s, the spacecraft could even be put in orbit around either of two targets: Ixion and 2017 OF69. During post-Pluto cruise, there is also the opportunity to perform flybys
of several smaller secondary KBO targets (diameter <500 km). The number of such secondaries depends upon the KBOs investigated, and should be considered a lower limit as more KBO objects are likely to be discovered.
Figure 1: Top left: spacecraft distance to Pluto for the entire Pluto-orbit phase, insert: intense pre-departure orbits. Bottom left: spacecraft distance to Pluto’s small moons. Right: global map of sub-spacecraft position every hour for spacecraft distances (r) <100,000 km for Pluto (top) and Charon (bottom). Distances given to New Horizons’ Pluto encounter distance (12,500 km).
Work to do: We are conducting trade studies aimed at refining the mission goals, science objectives, payload, trajectory, costs, and reducing flight times. Some of them will be conducted internally (e.g., refin-ing the science goals) and some of them require input from a NASA design lab (e.g. the costing, trajectory, and instrument integration). The science team has al-ready begun its trades, and we are working with APL to schedule the design lab work.
Conclusion: We are studying a small flagship class mission to return to the Pluto-system and the Kuiper Belt. The main goals of this concept study are to de-termine a realistic and feasible trajectory/tour, instru-ment suite and cost. Work has already begun in refin-ing the science question that drives this mission, and defining their relative importance.
Acknowledgments: This work was carried out un-der NASA grant 80NSSC20K0137 and with SwRI internal research funds. We thank both NASA and SwRI for their support.
References: [1] Stern S.A. et al. (2015) Science, 350, 292. [2] Stern S.A. et al. (2019) Science, 364, eaaw9771. [3] Finley T.F. et al. (2018) DPS meeting #50 workshop on Future Pluto and KB Missions. [4] CAPS (2017), NASEM, doi:10.17226/24843. [5] Vi-sion and Voyages for Planetary Science in the Decade 2013-2022: A Midterm Review (2018), doi: 10.17226/25186. [6] Hendrix A.R. et al. (2019) Astro-biology, 19, 1-27. [7] Stern S.A., et al. (2019) AIAA JSR, submitted.
1342.pdf51st Lunar and Planetary Science Conference (2020)
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