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NASA NTRS2017

Advanced Stirling Convertor Control Unit Testing at NASA Glenn Research Center in the Radioisotope Power Systems System Integration Laboratory

Future NASA missions could include establishing Lunar or Martian base camps, exploring Jupiters moons and travelling beyond where generating power from sunlight may be limited. Radioisotope Power Systems (RPS) provide a dependable power source for missions where inadequate sunlight or operational requirements make other power systems impractical. Over the past decade, NASA Glenn Research Center (GRC) has been supporting the development of RPSs. The Advanced Stirling Radioisotope Generator (ASRG) utilized a pair of Advanced Stirling Convertors (ASC). While flight development of the ASRG has been cancelled, much of the technology and hardware continued development and testing to guide future activities. Specifically, a controller for the convertor(s) is an integral part of a Stirling-based RPS. For the ASRG design, the controller maintains stable operation of the convertors, regulates the alternating current produced by the linear alternator of the convertor, provides a specified direct current output voltage for the spacecraft, synchronizes the piston motion of the two convertors in order to minimize vibration as well as manage and maintain operation with a stable piston amplitude and hot end temperature. It not only provides power to the spacecraft but also must regulate convertor operation to avoid damage to internal components and maintain safe thermal conditions after fueling. Lockheed Martin Coherent Technologies has designed, developed and tested an Engineering Development Unit (EDU) Advanced Stirling Convertor Control Unit (ACU) to support this effort. GRC used the ACU EDU as part of its non-nuclear representation of a RPS which also consists of a pair of Dual Advanced Stirling Convertor Simulator (DASCS), and associated support equipment to perform a test in the Radioisotope Power Systems System Integration Laboratory (RSIL). The RSIL was designed and built to evaluate hardware utilizing RPS technology. The RSIL provides insight into the electrical interactions between as many as 3 radioisotope power generators, associated control strategies, and typical electric system loads. The first phase of testing included a DASCS which was developed by Johns Hopkins UniversityApplied Physics Laboratory and simulates the operation and electrical behavior of a pair of ASCs in real time via a combination of hardware and software. Testing included the following spacecraft electrical energy storage configurations: capacitive, battery, and supercapacitor. Testing of the DASCS and ACU in each energy storage configuration included simulation of a typical mission profile, and transient voltage and current data during load turn-on/turn-off. Testing for these devices also included the initiation of several system faults such as short circuits, electrical bus over-voltage, under-voltage and a dead bus recovery to restore normal power operations. The goal of this testing was to verify operation of the ACU(s) when connected to a spacecraft electrical bus.

Dugala, Gina M.↗

NASA NTRS2018

Solar Sail Propulsion for Interplanetary Small Spacecraft

NASA is developing solar sail propulsion for use by small robotic interplanetary spacecraft. Solar sails use sunlight to derive useful thrust by reflecting solar photons from a large, mirror-like sail made of a lightweight, highly reflective material. Using reflected sunlight to obtain thrust instead of relying on the use of reaction mass has many advantages for exploring the inner solar system, including extremely large total delta V (velocity difference) and significant launch window flexibility.

Asteroid↗

NASA NTRS2018

Radioisotope Power Systems to Enable Extended Lunar Science and In-Situ Resource Utilization Missions

The Moon's surface environment offers a significant challenge for most space systems and, particularly, for power technologies. First, the Moon's rotational synodic period is 27.3 days long because it is tidally-locked with Earth and thus matches its orbital period. However, for a point on the lunar surface with respect to the Sun returning to the same position in the sky, called a synodic day, is 29.5 days or 708 hours. Therefore, a lunar day is 354 hours of sunlight and 354 hours of darkness. Equatorial diurnal temperatures range from about 400K at noon to 100K during the night. Within craters and permanently shadowed regions (PSRs) temperatures can be a constant 40K or below. Sunlight in the lunar polar regions can range from total darkness in deep polar craters and at higher elevations, potentially nearly continuous conditions are possible. However local topographical features such as outcrops or more distant mountains and ridges would obscure the Sun even in these extended sunlit areas and thus create intermittent shadowed periods depending on seasonally varying Sun angle and the obscuring topographical features. Thus, the power system technology that a mission selects becomes a critical trade.

radioisotope↗

NASA NTRS2018

Advanced Stirling Convertor Control Unit Testing at NASA Glenn Research Center in the Radioisotope Power Systems System Integration Laboratory

Future NASA missions could include long-duration flyby, orbital, lander, or rover applications where generating power from sunlight may be limited. Radioisotope power systems (RPSs) provide a dependable power source for missions where inadequate sunlight or operational requirements make other power systems impractical. Over the past 16 years, NASA Glenn Research Center has been supporting the development of RPSs. The advanced Stirling radioisotope generator (ASRG) utilized a pair of advanced Stirling convertors (ASCs). Although flight development of the ASRG has been canceled, much of the technology and hardware continued development and testing to guide future activities. Specifically, a controller for the convertor(s) is an integral part of a Stirling-based RPS. For the ASRG design, the controller maintains stable operation of the convertors, regulates the alternating current produced by the linear alternator of the convertor, provides a specified direct-current output voltage for the spacecraft, and synchronizes the piston motion of the two convertors to minimize vibration as well as manage and maintain operation with a stable piston amplitude and hot-end temperature. It not only provides power to the spacecraft but also must regulate convertor operation to avoid damage to internal components and maintain safe thermal conditions after fueling. Lockheed Martin Coherent Technologies, Inc., has designed, developed, and tested an ASC control unit engineering development unit (ACU EDU) to support this effort. GRC used the ACU EDU as part of its nonnuclear representation of a RPS that also consists of a Dual advanced Stirling convertor simulator (DASCS), and associated support equipment to perform a test in the Radioisotope Power Systems System Integration Laboratory (RSIL). The RSIL was designed and built with flexibility to evaluate hardware utilizing RPS technology. The RSIL provides insight into the electrical interactions between as many as three radioisotope power generators, associated control strategies, and typical electric system loads. The first phase of testing included a DASCS that was developed by Johns Hopkins University Applied Physics Laboratory and simulates the operation and electrical behavior of a pair of ASCs in real time via a combination of hardware and software. Testing included the following spacecraft electrical energy storage configurations: capacitor, battery, and supercapacitor. Testing of the DASCS and ACU in each energy storage configuration included simulation of a typical mission profile and transient voltage and current data during load turnon and turnoff. Testing for these devices also included the initiation of several system faults such as short circuits, electrical bus overvoltage, undervoltage, and a "dead bus" recovery to restore normal power operations. The goal of this testing was to verify operation of the ACU(s) when connected to a spacecraft electrical bus. The results of these tests are presented here.

General↗

NASA NTRS2018

Surface Reconstruction of a Challenging Region with Permanent Shadows on the Moon

As the Earth is orbiting the Sun, there is the region a sunlight can't be reached on the Moon, a satellite of the Earth. Usually, the permanent shadows are located near a pole area and the surface reconstruction in the permanent shadows region is challenging because of the lack of sunlight.In this research, the reconstruction method containing the permanent shadows is suggested. To apply this method, the time-varying shadow region and a permanently shadowed region are needed to be separated. In the time-varying shadow region, the pixel intensity of the image can be composed of the albedo and the reflectance model. Using the light source direction from ISIS3 of USGS, the shape of the region can be extracted from the reflectance model. Though this region is visible in the camera, the change of illumination is quite large in this region, it is hard to reconstruct the shape using stereo-photogrammetry or SfS. So, it is needed of collecting more surface normal information from several pixel level-aligned images. In this process, the albedo information can be initialized and enhanced easily from many images.In the middle of permanent shadows, the high-resolution DEM is generated by LOLA DEM. The LOLA DEM is generated by interpolation between measured data point strips, the actual scene of the permanent shadows. Using the sensor like DIVINER, the Imaginary scene generation via a trained network between the sunlight sensor and other kinds of a sensor is suggested.

Moon, Sunghyun↗

NASA NTRS2018

Comparison of the MODIS and VIIRS On-Board SD and SDSM Performance

The MODIS reflective solar bands (RSB) are calibrated on-orbit using a solar diffuser (SD) with its on-orbit degradation, or change in the bi-directional reflectance factor (BRF) monitored using a solar diffuser stability monitor (SDSM). By performing alternate observations of direct sunlight via an attenuation screen and of sunlight reflected diffusely off the SD, the SDSM monitors the on-orbit degradation of the SD. The MODIS SDSM has 9 detectors, covering wavelengths from 0.41 to 0.94 microns. Both Terra and Aqua MODIS instruments have successfully operated for more than 16 years on-orbit, with the SD experiencing significant degradation at the shortest wavelength (about 50 percent for Terra MODIS and about 20 percent for Aqua MODIS at 0.41 microns). The first VIIRS instrument on the Suomi NPP spacecraft was launched in October 2011 and the follow-on instrument was launched in November 2017 on the JPSS-1 spacecraft (now NOAA-20). Both the VIIRS instruments carry a MODIS-like SD and SDSM system with an improved design based on the lessons learned from MODIS. Unlike MODIS, the VIIRS SDSM collects data using 8 detectors covering a similar wavelength range as MODIS. A similar wavelength dependent SD degradation pattern is also observed in both VIIRS instruments. This paper provides a comparison of the on-orbit performance of the four instruments in terms of the on-orbit changes in the SDSM detector responses and on-orbit degradations of their SDs. The NOAA-20 VIIRS instrument is still in its first year of operation and hence the early performance of the Terra and Aqua MODIS and SNPP VIIRS is discussed to provide a perspective comparison.

VIIRS↗

NASA NTRS2015

Lunar Plant Experiment: Testing Plant Germination in Lunar Gravity and Ionizing Radiation

We present an open design for a first plant growth module on the Moon (LPX). The primary science goal of lunar habitat is to investigate germination and initial plant growth when subject to the combined effects of lunar gravity and lunar surface radiation. The LPX module has been designed to be a flexible base unit that can be adapted to fly to the lunar surface on a variety of landers and rovers. LPX has size and shape of a 1 Unit CubeSat (10 centimeters on a side) and a total mass of 0.3 kilograms. The base will contain a seed module holding around 50 Arabidopsis seeds and provide approximately 0.5 liters of normal air at standard pressure. By the action of a small pump, water will be released after landing to initiate germination. Images will document the germination, initial growth, phototropism, and circumnutation of the small plants while sunlight remains available. A CO2 sensor tracks the release of CO2 during germination and the subsequent uptake of CO2 by photosynthesis. Simulations indicate that the CO2 peak level will be an increase by 2250 parts per million after 2 earth-days and then decline to about 1000 parts per million after 7 earth-days. The camera and CO2 sensor interfaces are USB. The water pump initiation requires a 5-volt signal. After initiation of germination by the addition of water, the habitat must be maintained above 22 degrees Centigrade to allow for plant growth and below 27 degrees Centigrade to prevent damage to the plants. This relatively tight temperature tolerance will require thermal control systems using reflecting surfaces and insulation that must be specifically designed for each lander or rover. The plant growth unit will function to tilt angles of 20 degrees along any axis. Total image data volume required to gauge the plant growth rate and leaf area is 1 megabyte (minimum data required) to 40 megabytes (preferred data). The lid of the habitat will allow adequate sunlight for plant growth. To provide for optimum growth, light levels in the plant growth stage need to be between 75 and 150 micromoles per meter squared per second interval.

first plant growth↗

NASA NTRS2019

Outgassing From the OSIRIS-REx Sample Return Capsule: Characterization and Mitigation

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft launched on September 8, 2016, beginning a seven-year journey to return at least 60 g of asteroid material from (101955) Bennu to Earth. During the outbound cruise, Doppler tracking of the spacecraft observed a small but measurable acceleration when the sample return capsule (SRC) was first placed in sunlight. Subsequent analysis determined that outgassing from the SRC is the most likely cause for the acceleration. This outgassing received combined engineering and scientific attention because it has potential implications both for spacecraft navigation performance and for contamination of the collected samples. Thermal modeling, laboratory studies of SRC materials, and monitoring of the acceleration are all consistent with H2O as the main component of the outgassing. Dedicated, in-flight campaigns continued to expose the SRC to sunlight until the acceleration dropped to the acceleration noise floor. Any residual amounts of H2O outgassing are not considered to be a hazard with regards to mission operations or pristine sample acquisition. The sample stow procedure has been updated to ensure that no direct line of site exists between any residual outgassing and the samples during future operations. Similar outgassing of the Stardust SRC probably also occurred. No adverse contamination of Stardust samples was observed that could be associated with this process. Future missions that use similar reentry vehicles should consider procedures to test for and, if necessary, mediate such outgassing after launch.

Origins, Spectral Interpretation, Resource Identif↗

NASA NTRS2019

Outgassing From the OSIRIS-REx Sample Return Capsule: Characterization and Mitigation

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft launched on September 8, 2016, beginning a seven-year journey to return at least 60 g of asteroid material from (101955) Bennu to Earth. During the outboundcruise, Doppler tracking of the spacecraft observed a small but measurable acceleration when the sample return capsule (SRC) was first placed in sunlight. Subsequent analysis determined that outgassing from the SRC is the most likely cause for the acceleration. This outgassing received combined engineering and scientific attention because it has potential implications both for spacecraft navigation performance and for contamination of the collected samples. Thermal modeling, laboratory studies of SRC materials, and monitoring of the acceleration are all consistent with H2O as the main component of the outgassing. Dedicated, in-flight campaigns continued to expose the SRC to sunlight until the acceleration dropped to the acceleration noise floor. Any residual amounts of H2O outgassing are not considered to be a hazard with regards to mission operations or pristine sample acquisition. The sample stow procedure has been updated to ensure that no direct line of site exists between any residual outgassing and the samples during future operations. Similar outgassing of the Stardust SRC probably also occurred. No adverse contamination of Stardust samples was observed that could be associated with this process. Future missions that use similar reentry vehicles should consider procedures to test for and, if necessary, mediate such outgassing after launch.

Scott A Sandford↗

NASA NTRS2020

Solar Contamination in Extreme-precision Radial-velocity Measurements: Deleterious Effects and Prospects for Mitigation

Solar contamination, due to moonlight and atmospheric scattering of sunlight, can cause systematic errors in stellar radial velocity (RV) measurements that signiﬁcantly detract from the ~10 cm/s sensitivity required for the detection and characterization of terrestrial exoplanets in or near habitable zones of Sun-like stars. The addition of low-level spectral contamination at variable effective velocity offsets introduces systematic noise when measuring velocities using classical mask-based or template-based cross-correlation techniques. Here we present simulations estimating the range of RV measurement error induced by uncorrected scattered sunlight contamination. We explore potential correction techniques, using both simultaneous spectrometer sky ﬁbers and broadband imaging via coherent ﬁber imaging bundles, that could reliably reduce this source of error to below the photon-noise limit of typical stellar observations. We discuss the limitations of these simulations, the underlying assumptions, and mitigation mechanisms. We also present and discuss the components designed and built into the NEID (NN-EXPLORE Exoplanet Investigations with Doppler spectroscopy) precision RV instrument for the WIYN 3.5m telescope, to serve as an ongoing resource for the community to explore and evaluate correction techniques. We emphasize that while “bright time” has been traditionally adequate for RV science, the goal of 10 cm/s precision on the most interesting exoplanetary systems may necessitate access to darker skies for these next generation instruments.

Arpita Roy↗

NASA NTRS2020

The Hubble Space Telescope's Near-UV and Optical Transmission Spectrum of Earth as an Exoplanet

We observed the 2019 January total lunar eclipse with the Hubble Space Telescope’s STIS spectrograph to obtain the first near-UV (1700–3200 Å) observation of Earth as a transiting exoplanet. The observatories and instruments that will be able to perform transmission spectroscopy of exo-Earths are beginning to be planned, and characterizing the transmission spectrum of Earth is vital to ensuring that key spectral features (e.g., ozone, or O3) are appropriately captured in mission concept studies. O3 is photochemically produced from O2, a product of the dominant metabolism on Earth today, and it will be sought in future observations as critical evidence for life on exoplanets. Ground-based observations of lunar eclipses have provided the Earth’s transmission spectrum at optical and near-IR wavelengths, but the strongest O3 signatures are in the near-UV. We describe the observations and methods used to extract a transmission spectrum from Hubble lunar eclipse spectra, and identify spectral features of O3 and Rayleigh scattering in the 3000–5500 Å region in Earth’s transmission spectrum by comparing to Earth models that include refraction effects in the terrestrial atmosphere during a lunar eclipse. Our near-UV spectra are featureless, a consequence of missing the narrow time span during the eclipse when near-UV sunlight is not completely attenuated through Earth’s atmosphere due to extremely strong O3 absorption and when sunlight is transmitted to the lunar surface at altitudes where it passes through the O3 layer rather than above it.

Allison Youngblood↗

NASA NTRSDate not supplied

The Light Bender Concept for Power Distribution on a Lunar Base

Power generation and distribution is a challenge for a future lunar base. A promising concept for lunar power distribution is the light bender—a system that utilizes autonomously deployed mirrors to reflect sunlight to shaded regions on the lunar surface. The light bender system consists of two components: tandem reflector mirrors (TRM) which reflect sunlight to a permanently shaded region and the Cassegrain Fresnel distribution optics (CFDO) which collects the reflected light from the TRM and redirects light to local consumer nodes. This paper describes the light bender system concepts and the associated system analysis and technology development performed as part of a 2021 NASA Innovative Advanced Concepts (NIAC) phase I award.

Bradford Robertson↗

NASA NTRSDate not supplied

The Light Bender Concept for Power Distribution on a Lunar Base

Bradford Robertson↗

NASA NTRS2021

Operational Detection of Sun Glints in DSCOVR EPIC Images

Satellite images often feature sun glints caused by the specular reflection of sunlight from water surfaces or from horizontally oriented ice crystals occurring in clouds. Such glints can prevent accurate retrievals of atmospheric and surface properties using existing algorithms, but the glints can also be used to infer more about the glint-causing objects—for example about the microphysical properties and radiative effects of ice clouds. This paper introduces the recently released operational glint product of the Earth Polychromatic Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) spacecraft. Most importantly, the paper describes the algorithm used for generating the key component of the new product: a glint mask indicating the presence of sun glint caused by the specular reflection of sunlight from ice clouds and smooth water surfaces. After describing the glint detection algorithm and glint product, the paper shows some examples of the detected glints and discusses some basic statistics of the glint population in a yearlong dataset of EPIC images. These statistics provide insights into the performance of glint detection and point toward possibilities for using the glint product to gain scientific insights about ice clouds and water surfaces.

DSCOVR↗

NASA NTRS2022

PACE: How One NASA Mission Aligns With the United Nations Decade of Ocean Science for Sustainable Development (Ocean Shot #2)

The PACE satellite observatory will follow a Sun synchronous, polar orbit at an altitude of 676.5 km with a local 13:00 Equatorial crossing time. Its payload consists of three instruments, a primary hyperspectral imaging radiometer being built at NASA Goddard Space Flight Center and two multispectral, multiangle polarimeters, the combination of which advances far beyond heritage capabilities. The Ocean Color Instrument (OCI) offers one-day global coverage with a ground sample distance of 1 km2 at nadir. As described in this OceanShot, this leap in technology will enable improved understanding of aquatic ecosystems and biogeochemistry, as well as provide new information on phytoplankton community composition and improved detection of algal blooms. OCI will be complemented by two small multi-angle polarimeters with spectral ranges that span the visible to near infrared spectral region. When sunlight interacts with clouds or aerosols, it comes away from that interaction changed. By measuring changes in how reflected light oscillates within a geometric plane (i.e., its viewing angle-specific polarization), we can infer useful properties of the clouds or aerosols. This information is crucial to deciphering the way sunlight is reflected and absorbed by our planet and how aerosols affect cloud formation. The polarimeters include the Spectro-polarimeter for Planetary Exploration (SPEXone) and the Hyper Angular Research Polarimeter (HARP2), both of which will significantly improve aerosol and cloud characterizations and provide opportunities for novel ocean color atmospheric correction. (Figure 3). These instruments offer complementary capabilities: SPEXone is hyperspectral, multiangular, and narrow swath to support advanced atmospheric aerosol characterizations, whereas HARP2 is multispectral, hyper-angular, and wide swath to advance cloud property retrievals. In total, the combined PACE instrument suite will revolutionize studies of global biogeochemistry, carbon cycles, and air–sea exchanges in the ocean–atmosphere system.

Ocean color↗

NASA NTRS2021

Power Operations of the Mars Exploration Rovers

The rovers of the National Aeronautics and Space Administration’s (NASA) Mars Exploration Rovers (MER) project, Spirit (MER-A) and Opportunity (MER-B), safely landed on the surface of Mars three weeks apart during January 2004. Spirit and Opportunity were built and operated by the Jet Propulsion Laboratory (JPL), which is managed by the California Institute of Technology (Caltech) for NASA. Spirit landed at Gusev Crater, 14.8 degrees south of the equator, and operated continuously on the surface of Mars from January 4, 2004 until last contact from Spirit on March 22, 2010. Opportunity landed at Meridiani Planum, a location 2.5 degrees south of the Martian equator. Opportunity operated continuously on the Martian surface from January 25, 2004 until the last received transmission from Opportunity on June 10, 2018. The goal of the MER project was to determine if Mars ever had a habitable environment, in particular, if it ever had water. During their missions, both Spirit and Opportunity found evidence that liquid water once flowed on the surface of Mars. Both Spirit and Opportunity used a 1.33 m2 triple-junction solar array as their power sources. Based on observations of the original Mars rover, the Sojourner rover of the Mars Pathfinder mission that landed on Mars on July 4, 1997, the expectation was that the Martian dust would rapidly accumulate on the solar arrays of Spirit and Opportunity, and that the rovers would not have enough energy to continue operations after 90 Martian days (sols). Instead, due in part to lower dust accumulation rates than expected and numerous dust cleaning events, the Spirit and Opportunity rovers continued to operate on the Martian surface for over 2000 sols (MER-A) and 5000 sols (MER-B), respectively. During this time, the rovers experienced multiple Martian winters and several dust storms. Because the sources of solar array energy loss were known, the solar array energy output offered a method to scientifically estimate the loading and aeolian removal of dust from the solar arrays each sol. The MER Power operations team called this value that they calculated the solar array Dust Factor (DF). Dust Factor was defined as the fraction of sunlight that penetrates the accumulated dust on the surface of the solar array. A Dust Factor of 1.0 would indicate that the solar array was perfectly clean. A Dust Factor of 0.6 would indicate that only 60% of the available sunlight was able to penetrate the accumulated dust on the solar arrays. The MER Power subsystem operations team used the Multi-Mission Power Analysis Tool (MMPAT) to perform these Dust Factor calculations. The MMPAT software tool modeled the behavior of the solar arrays and the batteries as they interacted with the spacecraft power loads over the mission timeline. MMPAT also had knowledge (through telemetry and user inputs) of telemetered Power subsystem voltages and currents, atmospheric opacity (Tau), rover surface location, rover attitude, the planetary tilt and distance of Mars from the sun based on day of year, the instantaneous elevation of the sun based on time of day, temperatures (internal and external), terrain masking, and shadowing (due to the camera mast and antennas). Once all of the known sources of array energy loss are accounted, the remaining difference between the expected array energy and the actual array energy determines the solar array Dust Factor. The assumptions made while determining the Dust Factor are 1) that the single measured atmospheric opacity value (Tau) is constant over the course of the entire sol, 2) there is no measurable solar cell degradation, 3) there are no shorted strings and therefore, 4) all unexpected solar array energy losses are due to accumulated dust on the solar array. Although it cannot provide an absolute measure of dust loading, the determination of solar array Dust Factor provides a useful way of tracking dust accumulation and aeolian dust removal trends on Martian spacecraft. Any spacecraft on the Martian surface is vulnerable to dust, especially solar-powered spacecraft. The Spirit and Opportunity rovers were operational on the Martian surface for much longer than expected due in part to aeolian removal of dust from their solar arrays. The first few dust removal events were a pleasant surprise to the MER operations teams; however, over time a pattern began to arise. In over three Mars Years on the surface, the Power operations team tracked the solar array Dust Factor at Gusev Crater (location of MER-A) and observed that there were several significant dust removal and deposition events in Mars Year (MY) 27, even in the absence of a large dust storm. In MY 28 at Gusev Crater, the large atmospheric opacity (Tau) increase lagged significant dust removal events. Overall at Gusev Crater, there was a pattern of steady dust accumulation on the solar arrays, with a small number of significant dust cleaning events. At Meridiani Planum, where Opportunity rover operated for over seven Mars Years (late MY 26 to mid MY 34), a clear and consistent pattern of dust movement emerged. Meridiani Planum had a predictable, seasonally dependent pattern of gradual and continuous dust accumulation and removal. In summary, this paper explains the reasons for the development of the solar array Dust Factor and how it was used in mission operations. In particular, this paper describes the MMPAT software package, how it models array energy, including the important assumptions, model inputs and sources of error. And finally, this paper will show how the calculated solar array Dust Factor was used at Gusev Crater and Meridiani Planum to predict dust accumulation rates and weather patterns, and the importance of this generated data set for current and future solar- powered missions to Mars, such as the InSight lander and the planned Mars Sample Return rover.

Chin, Keith B.↗

NASA NTRS2025

South Pole Lunar Lighting Studies for Driving Exploration on the Lunar Surface

NASA’s Artemis lunar missions will face new exploration challenges due to inherently low sun angles in the lunar south pole region. Whereas the Apollo missions were afforded sunlight for approximately 8 to 50-degrees above the horizon, sunlight for the next lunar missions will only be 1 to 2-degrees about the horizon. With this low angle, long shadows and high contrasts of light and dark areas will be faced by the crew and remote teleop operators while exploring the lunar surface. With this in mind, NASA developed an integrated virtual Lighting and Navigation Simulation to understand these challenges. Two studies have been conducted in this Lunar South Pole environment to evaluate the effects of natural and artificial lighting on driving and navigating a lunar rover across the surface. Early NASA studies, such as this, are used to aid in developing techniques and explore concepts of operations to promote mission success and crew safety. In the Phase One development evaluation, six astronauts were teleported to ten different lighting conditions. For each location, drivers were to drive to an imaginary target approximately 200-meters straight ahead and provide subjective feedback on their ability to drive under the given lighting conditions. Phase Two, a more operational study, four astronauts and a remote operator tested five different Artemis lunar mission scenarios. Results indicated sun direction at such low angles, especially when driving a high speed, can severely impact the crew’s ability to safely drive the rover. In the up-sun situation, with the sun directly in the driver’s eyes and compounded long shadows, the consistent preference among drivers was to initiate a tacking strategy of approximately +/- 20 to 30-degrees to improve visibility. This maneuver does require more time and rover energetics. Conversely, driving down-sun required the crew to tack as well to avoid the shadow of rover blocking the terrain. Less appreciated is how the surrounding landscape is lit. Traveling into shadowed areas, especially while facing a lit terrain beyond the shadowed area, drivers enter at their own risk due to pupil contraction making artificial lights useless. Additionally, the constant transitioning between dark and light areas are mentally taxing to the crew and natural navigational references such as the stars are invisible and therefore unusable. Slope and depth magnitude are very difficult hazards to judge when approaching a shadowed crater. This naturally leads to slower driving speeds than originally anticipated. As for observing scientifically interesting features, assessing them accurately varies greatly by the lighting condition. In most cases, the task can be completed, but the strategy is to use the sun to one’s advantage. Crew workload distribution in the cockpit for driving operations was split amongst crew. The driver primarily focused attention on visual terrain (80%) but referenced displays approximately 20% of the time, while the co-pilot/navigator generally provided directional cues to the driver. These natural lighting conditions present significant challenges for safe rover operations; however, early studies having given investigators a “first-look” into understanding of how operating on the South Lunar Pole can be accomplished.

LTv↗

NASA NTRS2026

In-Space Demonstration of Spray-on Solar White Paint

Discs coated with spray-on solar white and two similar thermal control coatings were flown in low earth orbit for roughly five hours. While in orbit, the coated discs were exposed to direct sunlight and to deep space for short intervals. Measurements of disc temperatures showed that the spray-on solar white coating had the lowest absorption of sunlight. Numerical modeling was used to infer that spray-on solar white had a solar absorptance between 0.02 and 0.04 and a thermal emittance between 0.93 and 0.99, both of which are consistent with terrestrial laboratory measurements.

Solar White↗