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NASA NTRS1992

The thermal stability of water ice at the poles of Mercury

Recent radar observations of Mercury have revealed the presence of anomalous radar reflectivity and polarization features near its north and south poles. Thermal model calculations show that, despite Mercury's proximity to the sun, the temperatures of flat, low-reflectivity surfaces at Mercury's poles are not expected to exceed 167 kelvin. The locations of the anomalous polar radar features appear to be correlated with the locations of large, high-latitude impact craters. Maximum surface temperatures in the permanently shadowed regions of these craters are expected to be significantly colder, as low as 60 kelvin in the largest craters. These results are consistent with the presence of water ice, because at temperatures lower than 112 kelvin, water ice should be stable to evaporation over time scales of billions of years.

Paige, David A.↗

NASA NTRS2001

Integration of Lunar Polar Remote-Sensing Data Sets: Evidence for Ice at the Lunar South Pole

In order to investigate the feasibility of ice deposits at the lunar south pole, we have integrated all relevant lunar polar data sets. These include illumination data, Arecibo ground-based monostatic radar data, newly processed Clementine bistatic radar data, and Lunar Prospector neutron spectrometer measurements. The possibility that the lunar poles harbor ice deposits has important implications not only as a natural resource for future human lunar activity but also as a record of inner solar system volatiles (e.g., comets and asteroids) over the past billion years or more. We find that the epithermal neutron flux anomalies, measured by Lunar Prospector, are coincident with permanently shadowed regions at the lunar south pole, particularly those associated with Shackleton crater. Furthermore, these areas also correlate with the beta=0 circular polarization ratio (CPR) enhancements revealed by new processing of Clementine bistatic radar echoes, which in turn are colocated with areas of anomalous high CPR observed by Arecibo Observatory on the lower, Sun-shadowed wall of Shackleton crater. Estimates of the extent of high CPR from Arecibo Observatory and Clementine bistatic radar data independently suggest that approximately 10 square kilometers of ice may be present on the inner Earth-facing wall of Shackleton crater. None of the experiments that obtained the data presented here were ideally suited for definitively identifying ice in lunar polar regions. By assessing the relative merits of all available data, we find that it is plausible that ice does occur in cold traps at the lunar south pole and that future missions with instruments specifically designed to investigate these anomalies are worthy.

Nozette, Stewart↗

NASA NTRS2004

Drilling to Extract Liquid Water on Mars: Feasible and Worth the Investment

A critical application for the success of the Exploration Mission is developing cost effective means to extract resources from the Moon and Mars needed to support human exploration. Water is the most important resource in this regard, providing a critical life support consumable, the starting product of energy rich propellants, energy storage media (e.g. fuel cells), and a reagent used in virtually all manufacturing processes. Water is adsorbed and chemically bound in Mars soils, ice is present near the Martian surface at high latitudes, and water vapor is a minor atmospheric constituent, but extracting meaningful quantities requires large complex mechanical systems, massive feedstock handling, and large energy inputs. Liquid water aquifers are almost certain to be found at a depth of several kilometers on Mars based on our understanding of the average subsurface thermal gradient, and geological evidence from recent Mars missions suggests liquid water may be present much closer to the surface at some locations. The discovery of hundreds of recent water-carved gullies on Mars indicates liquid water can be found at depths of 200-500 meters in many locations. Drilling to obtain liquid water via pumping is therefore feasible and could lower the cost and improve the return of Mars exploration more than any other ISRU technology on the horizon. On the Moon, water ice may be found in quantity in permanently shadowed regions near the poles.

Stoker, C.↗

NASA NTRS2007

Beagle to the Moon: An Experiment Package to Measure Polar Ice and Volatiles in Permanently Shadowed Areas or Beneath the Lunar Surface

Near the beginning of the next decade we will see the launch of scientific payloads to the lunar surface to begin laying the foundations for the return to the moon in the Vision for Space Exploration. Shortly thereafter, astronauts will return to the lunar surface and have the ability to place scientific packages on the surface that will provide information about lunar resources and compositions of materials in permanently shadowed regions of the moon (1). One of the important questions which must be answered early in the program is whether there are lunar resources which would facilitate "living off the land" and not require the transport of resources and consumables from Earth (2). The Beagle science package is the ideal payload (3) to use on the lunar surface for determining the nature of hydrogen, water and lunar volatiles found in the polar regions which could support the Vision for Space Exploration

Gibson, E. K.↗

NASA NTRS2007

Prospecting Rovers for Lunar Exploration

A study of lunar rover options for exploring the permanently shadowed regions of the lunar environment is presented. The potential for nearly continuous solar illumination coupled with the potential for water ice, focus exploration planner's attention on the polar regions of the moon. These regions feature craters that scientists have reason to believe may contain water ice. Water ice can be easily converted to fuel cell reactants, breathing oxygen, potable water, and rocket propellant. For these reasons, the NASA Robotic Lunar Exploration Program (RLEP) sponsored a study of potential prospecting rover concepts as one part of the RLEP-2 Pre-Phase A. Numerous vehicle configurations and power, thermal, and communication options are investigated. Rover options in the 400kg to 530kg class are developed which are capable of either confirming the presence of water ice at the poles, or conclusively demonstrating its absence.

Graham, Jerry B.↗

NASA NTRS2007

Optomechanical Design and Analysis Considerations on the Lunar Orbiter Laser Altimeter

This paper presents the mechanical design and analysis work completed on the Lunar Orbiter Laser Altimeter (LOLA). LOLA is one of six instruments on the Lunar Reconnaissance Orbiter (LRO), scheduled to launch in 2008. LOLA's main objective is to produce a high-resolution global lunar topographic model to aid in safe landings and enhance surface mobility in future exploration missions. LOLA will also look for evidence of ice water in the permanently shadowed regions around the lunar poles. Beryllium was chosen as the primary material for the LOLA Optical Transmitter Assembly to take advantage of the material's low mass density for light weight optical instrument design and for CTE matching of the refractive optical components. In addition, the thermal conductivity and specific heat of beryllium minimizes thermal gradients and thermal excursions. Special consideration must be made for the planning and preparation to fabricate beryllium components, as well as the preparation and cleaning of the components for gold plating. Assembly challenges include handling, precision cleaning and integration and testing. Structural analysis considerations include following General Environmental Verification Specification (GEVS) guidelines for GSFC payloads. The GEVS random environment for LOLA has an acceptance level of 10.0 Grms, which was analyzed for higher frequency transients. The low frequency transients were analyzed using a Mass Acceleration Curve to obtain an equivalent static loading. In addition, Structural-Thermal-Optical analysis, commonly referred to as STOP analysis, was completed to predict optical performance under the instrument's operational thermal environment. This included stress and distortion analysis on the receiver telescope lens.

Schmidt. Stephen↗

NASA NTRS2008

Beagle 2 the Moon: An Experimental Package to Measure Polar Ice and Volatiles in Permanently Shadowed Areas or Beneath the Lunar Surface

NASA has announced the selection of several Lunar Science Sortie Concept Studies for potential scientific payloads with future Lunar Missions. The Beagle 2 scientific package was one of those chosen for study. Near the beginning of the next decade will see the launch of scientific payloads to the lunar surface to begin laying the foundations for the return to the moon in the Vision for Space Exploration. Shortly thereafter, astronauts will return to the lunar surface with the ability to place scientific packages on the surface that will provide information about lunar resources and compositions of materials in permanently shadowed regions of the moon (1). One of the important questions which must be answered early in the program is whether there are lunar resources which would facilitate "living off the land" and not require the transport of resources and consumables from Earth (2). The Beagle science package developed to seek the signatures of life on Mars is the ideal payload (3) to use on the lunar surface for determining the nature of hydrogen, water and lunar volatiles found in the polar regions which could support the Vision for Space Exploration.

Gibson, E. K.↗

NASA NTRS2006

Trajectory Design of the Lunar Impactor Mission Concept

The National Aeronautics and Space Administration (NASA) solicited proposals in 2006 for an opportunity to include a small secondary payload with the launch of the Lunar Reconnaissance Orbiter (LRO) scheduled for October 2008. The cost cap of the proposal was between $50 and $80M, and the mass cap was 1,000 kilograms. JPL proposed a Lunar Impactor (LI) concept for this solicitation. The mission objective of LI was to impact the permanently shadowed region of a South polar crater ultimately to detect the presence of water. The detection of water ice would prove to be an important factor on future lunar exploration. NASA Ames Research Center also proposed a similar concept, the Lunar Crater observation and Sensing Satellite (LCROSS), which was selected by NASA for the mission. However, in this paper, the trajectory design of the LI proposed by JPL is considered. Since the LI spacecraft was to be launched on the LRO launch vehicle as a secondary payload, its initial trajectory must be diverted at some later time from the LRO trans-lunar trajectory for the subsequent impact. Several such trajectories have been considered, where each trajectory option fields some specific values for the mission parameters. The mission parameters include the availability of LRO instruments at the time of impact for the observation by LRO, the mission duration, the impact velocity, the impact angle, etc. It is possible for the LI to be deflected with a relatively low delta-V to impact a South polar crater at a reasonable impact velocity and impact angle directly with no delay. However, the instruments on-board LRO may not be ready for observation. Thus, several delayed trajectory options have been considered further. The lunar phase at the time of impact may also play an important factor for observation, especially from Earth. Several lunar flyby trajectory maneuvers have been identified to arrive at the Moon for impact at the desired lunar phase. By using a combination of these successive lunar flyby maneuvers, the impact lunar phase may be adjusted to the desired location. A few such trajectories have been suggested. Also, some attempts have been made to maximize the impact velocity by converting the impact trajectory into a retrograde orbit with respect to Earth. Since these types of trajectories take advantage of the Sun-Earth three-body region to minimize the delta-V, the mission duration is relatively long. A few such trajectories are suggested. Also, an attempt has been made to adjust the lunar impact within a desired time period for the optimum Earth observation for the above trajectories. The mission parameters resulting from each trajectory option above are considered and weighed against the cost and robustness of the mission in a brief summary.

trajectory design↗

NASA NTRS2009

Fast Ray Tracing of Lunar Digital Elevation Models

Ray-tracing (RT) of Lunar Digital Elevation Models (DEM)'s is performed to virtually derive the degree of radiation incident to terrain as a function of time, orbital and ephemeris constraints [I- 4]. This process is an integral modeling process in lunar polar research and exploration due to the present paucity of terrain information at the poles and mission planning activities for the anticipated spring 2009 launch of the Lunar Reconnaissance Orbiter (LRO). As part of the Lunar Exploration Neutron Detector (LEND) and Lunar Crater Observation and Sensing Satellite (LCROSS) preparations RI methods are used to estimate the critical conditions presented by the combined effects of high latitude, terrain and the moons low obliquity [5-7]. These factors yield low incident solar illumination and subsequently extreme thermal, and radiation conditions. The presented research uses RT methods both for radiation transport modeling in space and regolith related research as well as to derive permanently shadowed regions (PSR)'s in high latitude topographic minima, e.g craters. These regions are of scientific and human exploration interest due to the near constant low temperatures in PSRs, inferred to be < 100 K. Hydrogen is thought to have accumulated in PSR's through the combined effects of periodic cometary bombardment and/or solar wind processes, and the extreme cold which minimizes hydrogen sublimation [8-9]. RT methods are also of use in surface position optimization for future illumination dependent on surface resources e.g. power and communications equipment.

McClanahan, Timothy P.↗

NASA NTRS2009

Epithermal Neutron Observations and Lunar South Pole Targeting for LCROSS Impact Planning using the Lunar Reconnaissance Orbiter (LRO), Lunar Exploring Neutron Detector (LEND)

LCROSS impact targeting and planning efforts included quantifying South Polar epithermal neutron flux depressions in early LEND mapped results to maximize the expected plume Hydrogen (H) yield. Epithermal neutron surface fluxes are a key geochemical indicator of surface Hydrogen (H) concentration inferred to be elevated in polar permanent shadow regions (PSR). LCROSS impact target regions were delineated as (PSR) using illumination modeling of polar topography. To quantify targets potential yield for LCROSS, LEND epithermal neutron flux observations were integrated over LCROSS targets of interest and compared to background observations. Discussion will define methods review impact prior estimates and contrast post impact results.

McClanahan, T. P.↗

NASA NTRS2010

South Pole Hydrogen Distribution for Present Lunar Conditions: Implications for Past Impacts

It has been known since the Lunar Prospector mission that the poles of the Moon evidently harbor enhanced concentrations of hydrogen [1,2]. The physical and chemical form of the hydrogen has been much debated. Using imagery from Clementine it was possible to roughly estimate permanently-shadowed regions (PSRs), and to perform image reconstructions of the Lunar Prospector epithermal neutron flux maps [3,4]. The hydrogen concentrations resulting from these reconstructions were consistent with a few weight percent water ice in selected locations. With the LCROSS impact, we now know that hydrogen in the form of ice does exist in lunar polar cold traps [5]. Armed with this information, and new data from LRO/Diviner, we can examine whether the pre-sent-day distribution of hydrogen in the form of water ice is consistent with a past large impact that delivered a large mass of volatiles to the lunar surface. These volatiles, mixed with solid impact ejecta, would then be lost from locations having high mean temperatures but would otherwise remain trapped in locations with sufficiently low mean annual temperatures [6]. The time scales for loss would depend on the location-dependent temperatures as well as impact history.

Elphic, R. C.↗

NASA NTRS2011

The Plasma Wake Downstream of Lunar Topographic Obstacles: Preliminary Results from 2D Particle Simulations

Anticipating the plasma and electrical environments in permanently shadowed regions (PSRs) of the moon is critical in understanding local processes of space weathering, surface charging, surface chemistry, volatile production and trapping, exo-ion sputtering, and charged dust transport. In the present study, we have employed the open-source XOOPIC code [I] to investigate the effects of solar wind conditions and plasma-surface interactions on the electrical environment in PSRs through fully two-dimensional pattic1e-in-cell simulations. By direct analogy with current understanding of the global lunar wake (e.g., references) deep, near-terminator, shadowed craters are expected to produce plasma "mini-wakes" just leeward of the crater wall. The present results (e.g., Figure I) are in agreement with previous claims that hot electrons rush into the crater void ahead of the heavier ions, fanning a negative cloud of charge. Charge separation along the initial plasma-vacuum interface gives rise to an ambipolar electric field that subsequently accelerates ions into the void. However, the situation is complicated by the presence of the dynamic lunar surface, which develops an electric potential in response to local plasma currents (e.g., Figure Ia). In some regimes, wake structure is clearly affected by the presence of the charged crater floor as it seeks to achieve current balance (i.e. zero net current to the surface).

Zimmerman, Michael I.↗

NASA NTRS2011

Isolation Effects on the Moon: High Topographic Slope Observations from the LRO and LOLA Instruments

The extremely low temperatures in the Moon's polar permanent shadow regions (PSR) has long been considered a unique factor necessary for entrapping volatile Hydrogen (H). However, recent discoveries indicate some H concentrations lie outside PSR, suggesting other geophysical factors may also influence H distributions. In this study we consider insolation and its resulting thermal effects as a loss/redistribution process influencing the Moon's near-surface < 1m volatile H budget. To isolate regional (5deg latitude band) insolation effects we correlate two data sets collected from the ongoing, 1.5 year long mapping mission of the Lunar Reconnaissance Orbiter (LRO). Epithermal neutron mapping data from the Lunar Exploration Neutron Detector (LEND) is registered and analyzed in the context of slope derivations from Lunar topography maps produced by the Lunar Observing Laser Altimeter (LOLA). Lunar epithermal neutrons are inferred to be direct geochemical evidence for near-surface H due to the correlated suppression of surface leakage fluxes of epithermal neutrons with increased H concentration. Regional suppressions of neutrons seen in LEND maps are considered localized evidence of H concentration increase in the upper 1 m of the Lunar surface. To quantify spatially localized insolation effects, LEND data are averaged from sparsely distributed pixels, classed as a function of the LOLA slope derivations.

McClanahan, T. P.↗

NASA NTRS2011

Insolation Effects on Lunar Hydrogen: Observation from the LRO LEND and LOLA Instruments

The Moon's polar permanent shadow regions (PSR) have long been considered the unique repository for volatile Hydrogen (H) Largely, this was due to the extreme and persistently cold environment that has been maintained over eons of lunar history. However, recent discoveries indicate that the H picture may be more complex than thc PSR hypothesis suggests. Observations by the Lunar Exploration Neutron Detect (LEND) onboard the Lunar Reconnaissance Orbiter (LRO) indicate some H concentrations lie outside PSR. Similarly, observations from Chandraayan-l's M3 and Deep Impact's EPOXI near infra-red observations indicate diurnal cycling of volatile H in lower latitudes. These results suggest other geophysical phenomena may also play a role in the Lunar Hydrogen budget. In this presentation we review the techniques and results from the recent high latitude analysis and apply similar techniques to equatorial regions. Results from our low latitude analysis will be reported. We discuss interpretations and implications for Lunar Hydrogen studies

McClanahan, T. P.↗

NASA NTRS2012

Topographically Induced Thermal Effects on Lunar Hydrogen Distributions: Correlated Observations from the LRO LEND and LOLA Instruments

The question of whether water exists on the Moon's surface has long been an enigma to Lunar researchers. Largely, this was due to the thermally extreme lunar surface environment that would seem to preclude any long term maintenance, manufacture, transport or accumulation of hydrogen (H) volatiles over most of the lunar surface. As a result, for many years the cold permanent shadow regions (PSR) in the bottoms of craters near the lunar poles appeared to provide the basic conditions at least for maintenance of lunar hydrogen. Importantly, recent discoveries indicate that there is some hydrogen at the poles. However, the picture of the lunar hydrogen budget may be more complex than the PSR hypothesis has suggested. This evidence comes from observations by the Lunar Exploration Neutron Detector (LEND) onboard the Lunar Reconnaissance Orbiter (LRO) that inclici1te 1) some H concentrations lie outside PSR and 2) though a few of the larger PSR's have high hydrogen, PSR does not appear to be an independent factor influencing the large-scale suppression of polar epithermals observed by LEND and the Lunar Prospector Neutron Spectrometer. In this research we investigate the possibility that the thermal contrast between pole-facing and equator facing-slopes is a factor influencing the surface distributions of lunar H. We perform this bulk correlated observation and study by developing a thermal proxy from slope data of the Lunar Orbiting Laser Altimeter (LOLA) digital elevation model (DEM) which is registered with the collimated LEND epithermal map. From the LOLA transforms we impose a thermal functional decomposition and systematic statistical analysis of the LEND epithermal map. Our hypothesis testing suggests in most high latitude bands studied> +/- 45 deg: Epithermal rates in pole-facing slopes are significantly lower than epithermal rates in equivalent equator-facing slopes. As a control study, we find that there is no statistically significant difference between equivalent east and west facing slopes. This finding suggests topographic modulation of insolation is a factor influencing the lunar H budget. Importantly, this result is consistent with observations in terrestrial, Martian research.

McClanahan, T. P.↗

NASA NTRS2012

Radar Scattering and Block Size Properties of Lunar Crater Ejecta From Mini-RF and LROC NAC Data

A major objective of the Mini-RF experiment is to distinguish lunar surfaces that may contain water/ice deposits [1,2]. Better understanding of the backscattering properties of craters of varying age and size is crucial for interpreting data received from the Mini-RF. The Mini-RF transmits a circularly polarized RF electromagnetic energy and coherently receives orthogonal linear polarization echoes [1]. The Mini- RF maps in two separate bands ( =12.6 and 4.5 cm) at a high resolution mode of 30 m/pixel [1]. Given the variables mentioned, the four stokes parameters are reconstructed. The Circular Polarization Ratio (CPR) is calculated for the purposes of understanding subsurface and surface roughness. The CPR is determined from reflections acquired from the ratio of power of the transmitted radio wave in same sense to the reflected radio wave in the opposite sense [1]. Ice in the permanently shadowed regions (PSRs) would be transparent to radar, but the inclusions of materials and imperfections would cause the radio wave to reflect multiple times [3], enhancing the number of same sense reflections and increasing the CPR. In addition, ice also displays the coherent backscatter opposition effect (CBOE), an interferrometric addition of same sense backscatter that further increases the CPR of ice targets [7]. High CPR values also correlate to multiple reflections and are typically associated with very rough surfaces [3]. The average dry lunar surface has a CPR in the range of 0.2-0.4 at 48deg incidence [3]. The purpose of this study is to begin to quantify degrees of surface wavelength-scale roughness with CPR and to understand how such surface roughness is created and gradually destroyed by erosion on the lunar surface. Another goal is to identify and isolate the possible causes of high CPR within the shadowed areas of anomalous polar craters [3]. All the studied craters are non-polar, so that we can see into their interiors in NAC images. The idea is to understand what controls blockiness in these craters so that we can rule out rocks (and rule in ice) for the anomalous polar dark ones [3].

Spudis, P. D.↗

NASA NTRS2012

Recent Results from the Lunar Reconnaissance Orbiter Mission and Plans for the Extended Science Phase

The Lunar Reconnaissance Orbiter spacecraft (LRO), launched on June 18, 2009, began with the goal of seeking safe landing sites for future robotic missions or the return of humans to the Moon as part of NASA's Exploration Systems Mission Directorate (ESMD). In addition, LRO's objectives included the search for surface resources and to investigate the Lunar radiation environment. After spacecraft commissioning, the ESMD phase of the mission began on September 15, 2009 and completed on September 15, 2010 when operational responsibility for LRO was transferred to NASA's Science Mission Directorate (SMD). The SMD mission was scheduled for 2 years and completed in September, 2012. The LRO mission has been extended for two years under SMD. The extended mission focuses on a new set of goals related to understanding the geologic history of the Moon, its current state, and what it can tell us about the evolution Of the Solar System. Here we will review the major results from the LRO mission for both exploration and science and discuss plans and objectives going forward including plans for the extended science phase out to 2014. Results from the LRO mission include but are not limited to the development of comprehensive high resolution maps and digital terrain models of the lunar surface; discoveries on the nature of hydrogen distribution, and by extension water, at the lunar poles; measurement of the day and night time temperature of the lunar surface including temperature down below 30 K in permanently shadowed regions (PSRs); direct measurement of Hg, H2, and CO deposits in the PSRs, evidence for recent tectonic activity on the Moon, and high resolution maps of the illumination conditions as the poles. The objectives for the second and extended science phases of the mission under SMD include: 1) understanding the bombardment history of the Moon, 2) interpreting Lunar geologic processes, 3) mapping the global Lunar regolith, 4) identifying volatiles on the Moon, and 5) measuring the Lunar atmosphere and radiation environment.

Vondrak, Richard↗

NASA NTRS2012

Results from the Lunar Reconnaissance Orbiter Mission and Plans for the Extended Science Mission

The Lunar Reconnaissance Orbiter spacecraft (LRO), launched on June 18,2009, began with the goal of seeking safe landing sites for future robotic missions or the return of humans to the Moon as part of NASA's Exploration Systems Mission Directorate (ESMD). In addition, LRO's objectives included the search for surface resources and the measurement of the lunar radiation environment. After spacecraft commissioning, the ESMD phase of the mission began on September 15, 2009 and was completed on September 15, 2010 when operational responsibility for LRO was transferred to NASA's Science Mission Directorate (SMD). The SMD mission was scheduled for 2 years and completed in September of 2012. Under SMD, the Science Mission focused on a new set of goals related to understanding the history of the Moon, its current state, and what it can tell us about the evolution of the Solar System. Having recently marked the completion of the two-year Science Mission, we will review here the major results from the LRO for both exploration and science and discuss plans and objectives for the Extended Science that will last until September, 2014. Some results from the LRO mission are: the development of comprehensive high resolution maps and digital terrain models of the lunar surface; discoveries on the nature of hydrogen distribution, and by extension water, at the lunar poles; measurement of the daytime and nighttime temperature of the lunar surface including temperature down below 30 K in permanently shadowed regions (PSRs); direct measurement of Hg, H2, and CO deposits in the PSRs; evidence for recent tectonic activity on the Moon; and high resolution maps of the illumination conditions at the poles.

Vondrak, Richard R.↗