LADEE Science Objectives LADEE Mission Concept Review MCR

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

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. LADEE MCR Dec 10 2008 2

Lunar Exosphere/Dust Environment LADEE MCR Dec 10 2008 3

Lunar Exosphere (1) ALSEP-LACE Detections on Apollo 17 Post Apollo Ground-based Remote observations of the Na exosphere (Potter & Morgan, 1998) Global distribution of Ar-40 at 30 km and 50 km (D. Hodges). • 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) LADEE MCR Dec 10 2008 4

Lunar Exosphere (2) 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 107 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 10 2008 5

Lunar Dust • All size fractions are present, but the very smallest are difficult to collect or to adequately count. 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 Plenty of dust, particularly in the size range below 10 - 20 um for which electrostatic forces dominate over gravity. LADEE MCR Dec 10 2008 100 mm 6

Evidence of Dynamic Dust From lunar orbit… …and on the lunar surface Gene Cernan sketches from Apollo Command Module Lunar Ejecta and Meteorites experiment (LEAM) Terminators Mc. Coy and Criswell, 1974 LADEE MCR Dec 10 2008 Berg et al. , 1976 7

SDT Findings - Exosphere • 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 Model results @50 km from R. Hodges for the LADEE SDT • Ar, He, H/H 2, OH, CH 4, 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 LADEE MCR Dec 10 2008 • Mission lifetime of a year is ideal, but new, interesting science can be done in 3 mo. 8

SDT Findings - Dust Stubbs et al. , 2006 • Do. LO 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 LADEE MCR Dec 10 2008 • Two dust components: 1) Dust of Lunar Origin (Do. LO) 2) Interplanetary Dust (IDP) • Do. LO: Electrostatically lofted or secondary ejecta • Do. LO 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 9

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(1 104), S(150), O(1 103), Si(48), Kr(2 104), Xe(3 103), Fe(3. 8 x 102), Al(55), Ti (1), Mg(6 103), OH(1 106), 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 2 -150 Da mass range. Detect or set upper limits as small as 10 -4 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, 1999. (Stern states no limit for H 20) LADEE MCR Dec 10 2008 9/9/2020 10

Science Flowdown - Payload Neutral Mass Spectrometer (NMS) UV Spectrometer (UVS) MSL/SAM Heritage LCROSS heritage In situ measurement of exospheric species Dust and exosphere measurements 300 Dalton range/unit mass resolution Dust Detector (DD) – TBD Detect sub-micron dust (size, charge) To be selected 3 kg, 5 W envelope Lunar Laser Com Demo (LLCD) Technology demonstration Science synergy: high data rates Several well-understood candidates available 51 -622 Mbps

Science Flowdown – s/c & Trajectory • Ideal orbit: Circular, retrograde, low inclination • Most active science location: Periseline at < 50 km over sunrise terminator • Retrograde orbit keeps instruments in ram but 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 10 2008 12

Science Flowdown - Operations 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 noonterminators-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 LADEE MCR Dec 10 2008 Operations Profiles 1 UVS 2 NMS/DD 3 UVS 4 Comm/PWR 5 NMS/DD 6 UVS 7 NMS/DD Duty cycled profiles to optimize observations vs. bus resources 1 UVS 2 Comm/PWR 3 UVS 4 NMS/DD 5 Comm/PWR 6 NMS/DD: 40% duty cycle UVS: 1500 -3000 s integration times w/cycled occultations 13

Example Orbits UVS Orbit NMS/DD Orbit Sub-pointing Ram-pointing configuration Limb-pointing LLCD Orbit LADEE MCR Dec 10 2008 14

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 LADEE MCR Dec 10 2008 15

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 LADEE MCR Dec 10 2008 16