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David E. Smith

Publications and source records attributed to David E. Smith.

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

Constraining the Structure under Lunar Impact Basins with Gravity

The lunar gravity field is used to estimate and constrain the depth of mass anomalies under 19 major lunar impact basins. We use radial gravitational spectra, consisting of accelerations computed either per spherical harmonic degree or cumulatively, at surface locations to obtain the distribution of the gravity signal with spherical harmonic degree and, by implication, to the likely depth below the surface. The results provide estimates for the maximum likely depths of the primary component to the mass anomalies under 19 basins. We find that the maximum depths of the primary source of mascon gravity on the lunar nearside are deeper than the depths for those on the farside when South Pole–Aitken (SPA) is excluded. All basin mass anomalies on the lunar nearside are in the mantle. The maximum depth of the primary source of the mass anomalies is 200 km beneath the surface. The upper 20 km under all basins is largely devoid of anomalies, reflecting predominantly mixing and relaxation associated with impact melt combined with ejecta fallback, as well as homogenization associated with post-basin formation impact bombardment. Except for SPA, all basin anomalies merge with the deep interior at ∼150 km or below, indicating the depth penetration of disruption of the density structure of the lunar interior associated with impact bombardment.

Lunar gravitational field↗
NASA NTRS2023

A New View of the Lunar South Pole from the Lunar Orbiter Laser Altimeter (LOLA)

Upcoming missions to the lunar south pole require detailed maps over large areas to fully characterize landing sites locally and regionally and to place their data into proper geologic context. To that end, we enhanced the Lunar Orbiter Laser Altimeter (LOLA) altimetry dataset for the south polar region, from which we produced new maps of topography, topographic roughness, and permanently shadowed regions (PSRs). The roughness maps reveal a diversity of terrains characterized by hectometer-scale roughness which is controlled in this region primarily by cratering and downslope mass transport. The south polar region is littered with linear roughness features of order ~1 – 10 km wide and ~10s – 100s of km long hypothesized to be secondary impacts within extended ejecta rays. Non uniformities in these features could reflect variations in secondary impactor properties and/or target terrain properties. Poleward of 80° S, the PSR cumulative size-frequency distribution (CSFD) shows an approximately power-law behavior whose exponent has a spatial variation of ~10%. PSRs with areas < 1 km2 contain 15 ± 5% of the total PSR area. Finally, we studied the effect of false positives and false negatives on the accuracy of the measured PSR cumulative size-frequency distribution (CSFD) and on the area for any individual PSR. The new maps presented here have many applications in the science and exploration of the lunar south polar region, such as geologic mapping and traverse planning.

Michael K. Barker↗
NASA NTRS2020

Optical Characterization of Laser Retroreflector Arrays for Lunar Landers

Laser Retroreflector Array for Lunar Landers (LRALL) is a small optical instrument designed to provide a target for precision laser ranging from a spacecraft in lunar orbit, enabling geolocation of the lander and its instrument suite and establishing a fiducial maker on the lunar surface. Here we describe the optical performance of LRALL at visible and near-infrared wavelengths. Individual corner cube reflectors (CCRs) within LRALL were tested for surface flatness and dihedral angle values. We also imaged the far-field diffraction patterns of individual CCRs as well as the entire retroreflector array over the range of possible incident angles to extract the optical cross section as a function of viewing angle. We also measured the optical properties of one of the CCRs over the lunar temperature range (100 K to 380 K) and found no significant temperature-dependent variance. The test results show LRALL meets the design criteria and can be ranged to from elevation angles above 30° with respect to the instrument base from an orbital laser altimeter such as the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO). This work summarizes the test data and serves as a guide for future laser ranging to these retroreflector arrays.

Daniel R Cremons↗
NASA NTRS2017

Evidence for Surface Water Ice in the Lunar Polar Regions Using Reflectance Measurements from the Lunar Orbiter Laser Altimeter and Temperature Measurements from the Diviner Lunar Radiometer Experiment

We find that the reflectance of the lunar surface within 5 deg of latitude of theSouth Pole increases rapidly with decreasing temperature, near approximately 110K, behavior consistent with the presence of surface water ice. The North polar region does not show this behavior, nor do South polar surfaces at latitudes more than 5 deg from the pole. This South pole reflectance anomaly persists when analysis is limited to surfaces with slopes less than 10 deg to eliminate false detection due to the brightening effect of mass wasting, and also when the very bright south polar crater Shackleton is excluded from the analysis. We also find that south polar regions of permanent shadow that have been reported to be generally brighter at 1064 nm do not show anomalous reflectance when their annual maximum surface temperatures are too high to preserve water ice. This distinction is not observed at the North Pole. The reflectance excursion on surfaces with maximum temperatures below 110K is superimposed on a general trend of increasing reflectance with decreasing maximum temperature that is present throughout the polar regions in the north and south; we attribute this trend to a temperature or illumination-dependent space weathering effect (e.g. Hemingway et al. 2015). We also find a sudden increase in reflectance with decreasing temperature superimposed on the general trend at 200K and possibly at 300K. This may indicate the presence of other volatiles such as sulfur or organics. We identified and mapped surfaces with reflectances so high as to be unlikely to be part of an ice-free population. In this south we find a similar distribution found by Hayne et al. 2015 based on UV properties. In the north a cluster of pixels near that pole may represent a limited frost exposure.

Emily A Fisher↗
NASA NTRSDate not supplied

Optical Characterization of CLPS MiniatureLaser Retroreflector Arrays

Laser retroreflector arrays (LRAs) consisting of corner cube retroreflectors (CCRs) can act as fiducial markers for decades of laser ranging on the Moon and other planetary bodies. Upcoming lunar lander missions from government space agencies and commercial partners offer a unique opportunity to support lunar science and exploration through the deployment of small LRAs on lander decks. Placement of an LRA on the deck of a lander or rover enables tracking with an orbital laser altimeter to aprecision on the order of centimeters. When mounted alongside a suite of scientific instruments the LRA enables precise geolocation of those instruments in the lunar geodetic frame. Finally, optical markers such as LRAs can support precision autonomous navigation and landing regardless of lighting conditions, an especially valuable capability for lunar polar exploration where long shadows complicate terrain relative nagivation using imaging methods.

Daniel R. Cremons↗
NASA NTRSDate not supplied

APRES Prototype Mission Planner System Demonstration

Activity Planning with Resources for the Exploration of Space (APRES) is a mixed-initiative mission planning system for ground operations. APRES has been designed to support multi-spacecraft missions. The APRES Interface is browser-based and includes a plan editor, a timeline plan display, a temporal constraint editor, display of the state and numeric chronicles, and a violation resolution manager. Automation support is supplied by the APRES Service, which includes components that provide the following capabilities:(1) plan simulation, which determines the state and numeric chronicles (values of the model variables over time) and determines when "processes" are triggered and terminated based on world states in the execution trace, (2) violation detection of constraints and flight rules encoded in the domain model, and of the temporal constraints created by the user, (3) violation resolution suggestions as to how to fix the plan's violations via rescheduling. The user controls when and how to utilize the automation support. Demo video included with paper, runtime 8:54 in color with sound.

John L. Bresina↗