LADEE Science Objectives LADEE Mission Concept Review (MCR) December 10, 2008 Greg Delory – Deputy Project Scientist Rick Elphic – Project Scientist Tom Morgan – Program Scientist

LADEE MCR Dec Summary Overview The top eleven science goals identified in the National Research Council’s report, “Scientific Context for the Exploration of the Moon” include: a.Determine the global density, composition, and time variability of the fragile lunar atmosphere before it is perturbed by further human activity b.Determine the size, charge, and spatial distribution of electrostatically transported dust grains and assess their likely effects on lunar exploration and lunar-based astronomy. The LADEE mission was designed to begin to address these objectives. 2

LADEE MCR Dec Lunar Exosphere/Dust Environment 3

LADEE MCR Dec Lunar Exosphere (1) 4 ALSEP-LACE Detections on Apollo 17 Post Apollo Ground-based The Exosphere is a collisionless atmosphere. Atoms due not collide with each other to thermalize the gas ̶ terms like temperature must be treated with care. Some of the exosphere is externally derived ̶ Solar Wind and Interplanetary dust ̶ but most is originated from the regolith and reflects composition. There are various source and sink mechanisms, dependent on species, location on the Moon, position of the Moon in its orbit, internal activity and external events (meteor showers, solar conditions) Remote observations of the Na exosphere (Potter & Morgan, 1998) Global distribution of Ar-40 at 30 km and 50 km (D. Hodges).

LADEE MCR Dec Lunar Exosphere (2) 5 Lunar Atmospheric and Composition Experiment (LACE) 40 Ar Measurements Identified Constituents are: 40 Ar, 36 Ar, 222 Rb, He, H, Na, K; the upper limit on density of the exosphere is a few times 10 7 atoms /cm 3 Upper limits established for most other species – but solid detections of important components such as C, N, O, CO 2, CH 4 + metals remain elusive

LADEE MCR Dec Lunar Dust 6 Based on mechanical techniques the accepted wisdom is that: 1.Regolith is fine-grained 2.Roughly: - 10% smaller than 10 mm - 20% smaller than 20 mm 3.Predictable physical properties (porosity, thermal conductivity, shear and bearing strength, angle of repose, tribology) 4.Notice the shape/surface area All size fractions are present, but the very smallest are difficult to collect or to adequately count. Plenty of dust, particularly in the size range below um for which electrostatic forces dominate over gravity. 100  m

LADEE MCR Dec Evidence of Dynamic Dust 7 Gene Cernan sketches from Apollo Command Module McCoy and Criswell, 1974 From lunar orbit… …and on the lunar surface Berg et al., 1976 Terminators Lunar Ejecta and Meteorites experiment (LEAM)

LADEE MCR Dec SDT Findings - Exosphere 8 Species that make up exosphere: 1)prevalent at 50 km altitude 2)maximize at sunrise terminator 3)peak densities at equator Species can be categorized by their sources, including solar wind, regolith and radiogenic Ar, He, H/H 2, OH, CH 4, CO, CO 2, Na, K, Si, Al, Fe all of interest No one instrument/technique can obtain all species of interest A NMS will likely detect Ar, He, H 2 but will have great difficulty with trace species requiring a supporting instrument Mission lifetime of a year is ideal, but new, interesting science can be done in 3 mo. Model km from R. Hodges for the LADEE SDT

LADEE MCR Dec SDT Findings - Dust 9 Two dust components: 1)Dust of Lunar Origin (DoLO) 2)Interplanetary Dust (IDP) DoLO: Electrostatically lofted or secondary ejecta DoLO may peak near terminator with densities at ~10 -4 /cc at 50 km IDPs/secondary ejecta detected at all longitudes Distinct Targets-of-Opportunity for improved dust observations: ˗ Known meteor shower/comet tails ˗ Magnetotail/plasma sheet crossings ˗ Solar storms DoLO single impacts very difficult to detect since grains are submicron and slow Remote sensing UV/VIS instrument will provide critical complementary data to in situ observations Stubbs et al., 2006

LADEE MCR Dec /21/ Baseline Science In order to accomplish the science objectives, the LADEE mission shall meet the following baseline science requirements: Measure spatial and temporal variations of Ar, He, Na, and K over time scales from several (3) lunar orbits to one lunation. Detect or obtain new lower limits for other species for which observations have been made. These include the following elements or compounds and the current limit * (part/cm 3 ); CH 4 (1  10 4 ), S(150), O(1  10 3 ), Si(48), Kr(2  10 4 ), Xe(3  10 3 ), Fe(3.8x10 2 ), Al(55), Ti (1), Mg(6  10 3 ), OH(1  10 6 ), and H 2 O(100). Search for other species (beyond those listed in the previous two bullets) or positive ambient ions of these species and other atoms or compounds in the Da mass range. Detect or set upper limits as small as dust particles /cm 3 from 1.5 to 50 km altitude for particles as small as 100 nm via occultation measurements. Detect or set upper limits on the dust population at 50 km. *Limits measured against Table 1.1, S. A. Stern, Reviews of Geophysics, 37, 453, (Stern states no limit for H 2 0)

Science Flowdown - Payload Dust Detector (DD) – TBD Detect sub-micron dust (size, charge) Neutral Mass Spectrometer (NMS) UV Spectrometer (UVS) Lunar Laser Com Demo (LLCD) To be selected 3 kg, 5W envelope Several well-understood candidates available LCROSS heritage MSL/SAM Heritage Dust and exosphere measurements In situ measurement of exospheric species Technology demonstration Science synergy: high data rates Mbps 300 Dalton range/unit mass resolution

LADEE MCR Dec Science Flowdown – s/c & Trajectory 12 Ideal orbit: Circular, retrograde, low inclination Most active science location: Periseline at < 50 km over sunrise terminator Retrograde orbit keeps instruments in ram but out of sunshine Equatorial orbit preferred over polar orbit: Densest portion of exosphere, don’t expect emitted polar water from cold traps. LADEE can contribute to search for water by “following the OH” and examining the terminator desorption processes Spacecraft is “dirty” and will have the potential to contaminate instruments via outgassing, thruster firings, and EMI

LADEE MCR Dec Science Flowdown - Operations 13 Guiding Considerations Spatial and temporal variations crucial to LADEE science objectives Science operations need to cover variations ranging from ~3 orbits to ~1 month or more. Spatial variations across noon- terminators-midnight important UVS: Sufficient time to achieve SNR ~5 for most species Occultation (dust) and limb (dust, exosphere) modes NMS: Sufficient time to resolve major species Ram, nadir, and rotisserie modes DD: Similar to NMS Operations Profiles 1UVS 2NMS/DD 3UVS 4Comm/PWR 5NMS/DD 6UVS 7NMS/DD 1UVS 2Comm/PWR 3UVS 4NMS/DD 5Comm/PWR 6NMS/DD Duty cycled profiles to optimize observations vs. bus resources NMS/DD: 40% duty cycle UVS: s integration times w/cycled occultations

LADEE MCR Dec Example Orbits 14 NMS/DD Orbit UVS Orbit LLCD Orbit Ram-pointing configuration Limb-pointing Sub-pointing

LADEE MCR Dec Follow-On Analysis Pointing w.r.t. lunar limb –Uncertainty in position of the Moon (lunar ephemeris) –Active trade underway examining slewing/coverage/SNR Altitude knowledge (ties into previous bullet) –3 km is current goal; 1 km desired –Part of larger trajectory/navigation trade analysis Continue orbit/science observation trade –Trajectory/fuel trade may lead to more variable orbits –OK with science with modified observation profiles –Potential coverage at low (20 km) altitudes very compelling from PSWG perspective 15

LADEE MCR Dec Summary Top level spacecraft and mission capabilities meet the baseline science objectives Current activities focused on optimization Implementation of baseline science remains flexible and can be responsive to changes in the mission design 16