Lunar Pits – Gateway To The Subsurface

Mark Robinson
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Lunar Pits – Gateway To The Subsurface
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Introduction: Lunar mare “pits” are key science and exploration targets. The first three pits were dis-covered in Selene observations [1,2] and were pro-posed to represent collapses into lava tubes. Subse-quent LROC images revealed ten new pits in lunar maria and showed that the Mare Tranquillitatis pit (MTP; 8.335°N, 33.222°E) opens into a sublunarean void at least 20 meters in extent [3,4]. Additionally, >200 pits were discovered in impact melt deposits [4]. Investigations using gravity [5] and radar [6] data sug-gest that kilometers-long intact lava tubes may exist within the maria. Landed elements are required to accurately deter-mine the scientific and exploration utility of pits. Re-quired measurements include decimeter scale charac-terization of the structure of wall materials, 5-cm scale imaging of the pit floor, determination of the extent of sublunarean void(s), and measurement of the magnetic and thermal environment. Bonus science could include geochemical and physical characterization of magmas and flows over time. Why Pits?: Rationale. Pits and sublunarean voids could provide a key first step in a sustainable architec-ture for lunar exploration [7,8,9]. Need: Enable sus-tainable crewed lunar exploration (reduce mass, cost, risk) Goals: 1) Investigate suitability of voids for ex-ploitation (radiation shield, micrometeorite shield, be-nign thermal conditions). 2) Technology demonstration (autonomous precision landing and hazard avoidance, flying payload with autonomous navigation). 3) Inves-tigate chemistry, thickness and physical properties of flows, and the nature of void spaces. 4) Engage the public (Explore the voids! What else can we find? What lies beneath?) Mission: We propose a small (~100-kg) yet capa-ble lander to explore the MTP, as it is one of the larg-est and least degraded of the known mare pits (n=13 [4,7]), and it was shown to extend at least 20-m back under the mare. Furthermore, the eastern floor of MTP is unique among the mare pits for having direct line-of-sight to Earth during parts of the lunar libration cycle, and this portion of the floor is smooth and relatively block free. Goals: 1) Investigate suitability of the void at MTP for exploitation (radiation shield, micrometeorite shield, benign thermal conditions). 2) Investigate na-ture of mare flood volcanism (thickness of flows, na-ture of void. 3) Engage the public in NASA explora-tion activities. We previously presented [8] a mission concept (“Arne”) that would place a <130-kg lander on the eastern floor of MTP, imaging the walls during de-scent. Once landed, three flying microbots (or pit-bots), each with mass of 3-kg [9], would launch in se-quence to explore the void. Each pit-bot flies for 2 min at 2 m/s for 100 cycles; recharge time is 20 min. The pit-bots can communicate directly with the lander, or act as pit-bot to pit-bot relays to explore beyond lander line-of-sight. The primary mission can be accom-plished in 48 hours after landing. Strawman Payload: Key to the landing success are autonomous precision landing and hazard avoid-ance hardware and software (critical feed forward technologies). Additionally the lander will carry a magnetometer, thermometer, two narrow angle camer-as, and six wide angle cameras. The pit-bots are equipped with a flash stereo camera, rangefinder, and obstacle avoidance sensors. Alternate Targets: An alternate (or perhaps se-cond) target is the Marius Hills pit (MHP); recent work [5,6] indicates there may be a large open lava tube in the vicinity, perhaps raising the probability that it con-nects to a significant void (relative to MTP). LROC off-nadir imaging does not indicate significant voids intersecting the MHP. Also, the Earth is not visible from the MHP floor, complicating data transmission during final stages of descent and science observations. Since the demonstration of autonomous precision land-ing and hazard avoidance is a critical objective we propose that MTP is the best first landing site. References: [1] Haruyama et al. (2010) 41st LPSC, #1285 [2] Haruyama et al. (2010) GRL, 36, [3] Robinson et al (2012) PSS, 69, j.pss.2012.05.008 [4] Wagner and Robinson (2014) Icarus, 237, [5] Chappaz et al. (2017) GRL, 44, [6] Kaku et al. (2017) GRL, 44, /2017GL074998 [7] Wagner et al. (2017) 48th LPSC, #1201 [8] Robinson et al. (2014) Annual Meeting of the Lunar Exploration Analysis Group, #3025 [9] Thangavelautham et al. (2012) IEEE ICRA
Robert V. Wagner