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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
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NASA NTRS1981

Venus gravity fields

Results of Pioneer Venus Orbiter observations concerning the gravity field of Venus are presented. The gravitational data was obtained from reductions of Doppler radio tracking data for the Orbiter, which is in a highly eccentric orbit with periapsis altitude varying from 145 to 180 km and nearly fixed periapsis latitude of 15 deg N. The global gravity field was obtained through the simultaneous estimation of the orbit state parameters and gravity coefficients from long-period variations in orbital element rates. The global field has been described with sixth degree and order spherical harmonic coefficients, which are capable of resolving the three major topographical features on Venus. Local anomalies have been mapped using line-of-sight accelerations derived from the Doppler residuals between 40 deg N and 10 deg S latitude at approximately 300 km spatial resolution. Gravitational data is observed to correspond to topographical data obtained by radar altimeter, with most of the gravitational anomalies about 20-30 milligals. Simulations evaluating the isostatic states of two topographic features indicate that at least partial isostasy prevails, with the possibility of complete compensation.

Sjogren, W. L.↗
NASA NTRS2013

Improvements of VIIRS and MODIS Solar Diffuser and Lunar Calibration

Both VIIRS and MODIS instruments use solar diffuser (SD) and lunar observations to calibrate their reflective solar bands (RSB). A solar diffuser stability monitor (SDSM) is used to track the SD on-orbit degradation. On-orbit observations have shown similar wavelength-dependent SD degradation (larger at shorter VIS wavelengths) and SDSM detector response degradation (larger at longer NIR wavelengths) for both VIIRS and MODIS instruments. In general, the MODIS scan mirror has experienced more degradation in the VIS spectral region whereas the VIIRS rotating telescope assembly (RTA) mirrors have seen more degradation in the NIR and SWIR spectral region. Because of this wavelength dependent mirror degradation, the sensor's relative spectral response (RSR) needs to be modulated. Due to differences between the solar and lunar spectral irradiance, the modulated RSR could have different effects on the SD and lunar calibration. In this paper, we identify various factors that should be considered for the improvements of VIIRS and MODIS solar and lunar calibration and examine their potential impact. Specifically, we will characterize and assess the calibration impact due to SD and SDSM attenuation screen transmission (uncertainty), SD BRF uncertainty and onorbit degradation, SDSM detector response degradation, and modulated RSR resulting from the sensor's optics degradation. Also illustrated and discussed in this paper are the calibration strategies implemented in the VIIRS and MODIS SD and lunar calibrations and efforts that could be made for future improvements.

VIIRS↗
NASA NTRS2010

Global Trends in Space Access and Utilization

In the not-so-distant past, space access and air/space technology superiority were within the purview of the U.S. and former Soviet Union's respective space agencies, both vying for global leadership in space exploitation. In more recent years, with the emergence of the European Space Agency (ESA) member countries and Asian countries joining the family of space-faring nations, it is truer now more than ever that space access and utilization has become a truly global enterprise. In fact, according to the Space Report 2007, this enterprise is a $251-billion economy. It is possible to gauge the vitality of worldwide efforts from open sources in today's transparent, media-based society. In particular, print and web broadcasters regularly report and catalog global space activities for defense and civil purposes. For the purposes of this paper, a representative catalog of missions is used to illustrate the nature of the emerging "globalization." This paper highlights global trends in terms of not only the providers of space access, but also the end-users for the various recently accomplished missions. With well over 50 launches per year, in recent years, the launch-log reveals a surprising percentage of "cooperative or co-dependent missions" where different agencies, countries, and/or commercial entities are so engaged presumably to the benefit of all who participate. Statistics are cited and used to show that recently over d0% of the 50-plus missions involved multiple nations working collectively to deliver payloads to orbit. Observers, space policy professionals, and space agency leaders have eloquently proposed that it might require the combined resources and talents of multiple nations to advance human exploration goals beyond low earth orbit. This paper does not intend to offer new information with respect to whether international collaboration is necessary but to observe that, in continuing to monitor global trends, the results seem to support the thesis that a global interdependent effort with all its likely complexities is an increasingly viable and pragmatic option. The discussion includes a breakdown of space missions into those of civil (scientific), military, and strictly commercial nature. It concludes that all three are robust components of a globally diversified portfolio of activities relying, essentially, on a common space industrial base and space infrastructure. As in other industries, the distribution of space industry assets and knowledge across countries and continents enables a diverse suite of options and arrangements, particularly in the areas of civil and commercial space utilization. A survey of several ongoing bilateral and multilateral space collaboration examples are provided to augment the observations regarding multinational work in space.

Rahman, Shamim A.↗
NASA NTRS1992

Periodic magnetopause oscillations observed with the GOES satellites on March 24, 1991

The GOES 6 and 7 satellites were in the dayside magnetosphere late on March 24, 1991, when the magnetopause moved in to geosynchronous orbit. Observations on GOES 6 near 1030 local time (LT) indicated six inward and outward periodic movements of the magnetopause past the satellite over a 30-min interval. Later the magnetopause moved farther in, placing GOES 6 (1100 LT) in the magnetosheath and then moving in past GOES 7, near 1245 LT. The periodic oscillations of the magnetopause at GOES 6 suggest surface waves propagating toward the dawn flank of the magnetopause.

Cahill, L. J., Jr.↗
NASA NTRS1999

Implementation of Autonomous GPS Guidance and Control for Spacecraft Formation Flying

This paper presents the general relative orbit dynamics equations and GPS (Global Positioning System) orbit observational equations that have been developed for on-board control of spacecraft flying in formation. The approach to the implementation of the autonomous control for orbit acquisition and maintenance of spacecraft formation using GPS code pseudoranges are presented. As a practical application of the models and method provided in this paper, the orbit control of the Earth-Orbiter 1(EO-1) / Landsat 7 system has been designed, using the discrete-time linear optimal output feedback control. For the actuator of the on/off type reaction jets, the implementation problem of the pulse-amplitude modulation is also studied. Simulation results of autonomous orbit control and maintenance, for 3-dimensional initial orbit error, using optimal output feedback control are shown. These simulation results certified the feasibility of the implementation of the autonomous maintenance control for EO-1/Landsat 7 formation flying by means of the discrete-time linear optimal output feedback control.

Xing, Guang Q.↗
NASA NTRS2024

The Diurnal Variation of Dust and Water Ice Aerosol Optical Depth at Jezero Crater Observed By MEDA/TIRS Over A Full Martian Year

The Thermal InfraRed Sensor (TIRS) on the Perseverance rover has provided nearly two full Mars years of systematic monitoring of the total aerosol optical depth above Jezero Crater. These observations span a wide range of timescales, capturing seasonal patterns, diurnal variations, and minute-to-minute fluctuations in aerosol loading. By combining TIRS retrievals with orbital observations, the relative contributions of dust and water ice aerosols can be estimated, revealing their different seasonal and diurnal behaviors. The TIRS record shows distinct periods of dust storm activity, including strong regional storms during the perihelion season as well as short lived but intense dust events outside the typical dust storm season. Water ice clouds exhibit pronounced seasonal and diurnal variability, with peak activity occurring during the aphelion season but with a presence throughout the year. The diurnal variation of clouds differs significantly between the aphelion and perihelion seasons, with clouds persisting throughout the night during the aphelion season, while largely absent outside of specific periods after sunrise and sunset during the perihelion season. These results provide new insights into the complex behavior of aerosols at Jezero Crater and their connections to atmospheric dynamics and the Martian dust and water cycles.

Michael D Smith↗
NASA NTRS1985

Propagation mechanism of daytime Pc 3-4 pulsations observed at synchronous orbit and multiple ground-based stations

Observational data obtained during the last two decades show that the amplitude of daytime Pc 3-4 magnetic pulsations is controlled by the solar wind conditions. The high degree of correlation between the solar wind parameters and Pc 3-4 pulsations in the dayside magnetosphere suggests that the ultimate cause of the daytime Pc 3-4 pulsations must be the interaction of the solar wind with the earth's magnetosphere. The present paper is concerned with details regarding the control of the properties of the Pc 3-4 pulsations by the solar wind parameters, taking into account observations made at multiple ground-based stations. It is attempted to establish the relation between the daytime Pc 3-4 pulsations at the ground stations and the compressional Pc 3-4 waves in the magnetosphere. Attention is given to the most probable propagation mechanism of the daytime Pc 3-4 pulsations in the magnetosphere.

Yumoto, K.↗
NASA NTRS1972

Crew observations

Crew observations of the Apollo 15 flight are presented. The observations are concerned with the following phases of the flight: (1) translunar and transearth coasts, (2) lunar landing and ascent, (3) standup extravehicular activity, (4) surface experiment deployment, (5) lunar traverse geology, and (6) orbital observations.

Scott, D. R.↗
NASA NTRS1971

Astrodynamics. Volume 1 - Orbit determination, space navigation, celestial mechanics.

Essential navigational, physical, and mathematical problems of space exploration are covered. The introductory chapters dealing with conic sections, orientation, and the integration of the two-body problem are followed by an introduction to orbit determination and design. Systems of units and constants, as well as ephemerides, representations, reference systems, and data are then dealt with. A detailed attention is given to rendezvous problems and to differential processes in observational orbit correction, and in rendezvous or guidance correction. Finally, the Laplacian methods for determining preliminary orbits, and the orbit methods of Lagrange, Gauss, and Gibbs are reviewed.

Herrick, S.↗
NASA NTRS1987

Planetary science - 1983-1986

Results obtained in the U.S. planetary science programs during 1983-1986 are discussed in a brief review. Topics examined include Halley observations and probes, the flyby of comet Giacobini-Zinner by ISEE-3 (ICE), the Voyager 2 encounter with Uranus, analysis of Voyager 1 and 2 data from the Jupiter and Saturn systems, Pioneer Venus Orbiter observations, theoretical models of lunar evolution, and antarctic meteorites of lunar and perhaps Martian origin.

Clifford, Stephen M.↗
NASA NTRS2020

Cross-Calibration of Terra and Aqua MODIS Using RadCalNet

The twin MODIS instruments onboard the Terra and Aqua spacecraft have been successfully operating for nearly two decades and providing complementary observations of the Earth’s land, ocean, and atmosphere. Although the two MODIS instruments view the entire Earth’s surface once every 2-3 days, simultaneous views between them are limited due to their varying orbits. Therefore, the intercomparison between these two instruments has been previously performed using a transfer instrument (such as AVHRR) or using lunar measurements normalized using a common model such as the USGS ROLO. In recent years RadCalNet, a CEOS initiative, has provided SI-traceable Top-of-Atmosphere (TOA) reflectances from a coordinated network of instrumented land-based sites. RadCalNet facilitates a unique mechanism to perform cross-calibration of instruments by minimizing the uncertainties associated with overpass time differences. In this work, the near-simultaneous TOA reflectance measurements from the Railroad Valley, US (RVUS) are used as a transfer to compare the on-orbit observations for the Terra and Aqua MODIS RSB. Near-nadir overpasses from January 2013 to January 2019 are processed and matched up with near-simultaneous RadCalNet measurements. Results show that the VIS/NIR bands agree to within 2% and the SWIR bands agree to within 5%. Also, discussed in this work are the future efforts that will be undertaken to expand this comparison to include other instruments, other sites, and both nadir- and off-nadir views after compensation for BRDF effects.

Amit Angal↗
NASA NTRS1978

Lunar occultation of Saturn. III - How big is Iapetus

The orbital light curve of Iapetus is analyzed, and the bright material on the trailing face of the satellite is found to have an effective limb-darkening parameter of 0.62 (+0.10, -0.12). This result is combined with observations of a lunar occultation of Iapetus to derive a radius of 718 (+87, -78) km for the satellite. The specific patchy albedo model of Morrison et al. (1975) is shown to fit the observed orbital light curve precisely and to yield an occultation radius of 724 + or - 60 km. It is noted that the values determined for the limb-darkening parameter and for the normal reflectance (in V) of the material at the center of the bright face are consistent with a partial water-frost cover on the bright side of Iapetus. It is concluded that if the albedo model of Morrison et al. reliably represents the surface of Iapetus, the radius of that satellite is 724 + or - 60 km, which is consistent with the radiometric radius of 835 (+50, -75) km derived by Morrison et al. (1975).

Veverka, J.↗
NASA NTRS2017

Do Bare Rocks Exist on the Moon?

Astronaut surface observations and close-up images at the Apollo and Chang'e 1 landing sites confirm that at least some lunar rocks have no discernable dust cover. However, ALSEP (Apollo Lunar Surface Experiments Package) measurements as well as astronaut and LADEE (Lunar Atmosphere and Dust Environment Explorer) orbital observations and laboratory experiments possibly suggest that a fine fraction of dust is levitated and moves across and above the lunar surface. Over millions of years such dust might be expected to coat all exposed rock surfaces. This study uses thermal modeling, combined with Diviner (a Lunar Reconnaissance Orbiter experiment) orbital lunar eclipse temperature data, to further document the existence of bare rocks on the lunar surface.

Allen, Carlton↗
NASA NTRSDate not supplied

Characterization of the Eugene Stansbery-Meterclass Autonomous Telescope on Ascension Island

In a focused effort to meet full operational capability for NASA’s Eugene Stansbery Meter Class Autonomous Telescope (ES-MCAT), a thorough system characterization analysis was completed. NASA’s Orbital Debris Program Office (ODPO)utilizes ES-MCAT as the primary sensor for characterizing the geosynchronous orbit (GEO)environment to acquire photometric data of small, faint debris objects in or near GEO. ES-MCAT is located on Ascension Island in the middle of the Atlantic Ocean at nearly 8° South latitude and 15° West longitude. This location provides dark skies suited for faint object observations but is also continuously subject to a harsh environment exposed to volcanic ash and salt spray. To better assess the overall system performance of the optical instrument, a historical assessment of the system’s performance was conducted. This analysis investigated all systematic and optical operational data to determine the overall performance parameters for ES-MCAT.A complete optical system throughput calculation was performed to determine the optimal filter for observing orbital debris in GEO orbits. The responses of each optical component to the solar spectrum, with atmospheric absorption, were multiplied and integrated to give ES-MCAT’s total system response for various filters. With the highest flux values, the Sloan Digital Sky Survey (SDSS) r’ and g’ were determined to be the optimal filters for ES-MCAT observations. Further analysis with known GEO debris objects enabled the selection of the r’ filter for characterization of the GEO debris population. A detailed overview of the optical system throughput, data reduction, photometric and astrometric data, and other system characteristics that define ES-MCAT will be discussed in the subsequent paper.

C. Cruz↗
NASA NTRSDate not supplied

Characterization of the Eugene Stansbery-Meter Class Autonomous Telescope on Ascension Island

In a focused effort to meet full operational capability for NASA’s Eugene Stansbery-Meter Class Autonomous Telescope (ES-MCAT), a thorough system characterization analysis was completed. NASA’s Orbital Debris Program Office (ODPO) utilizes ES-MCAT as the primary sensor for characterizing the geosynchronous Earth orbit (GEO) environment to acquire photometric data of small, faint debris objects in or near GEO. ES-MCAT is located on Ascension Island in the middle of the Atlantic Ocean at nearly 8° South latitude and 14° West longitude. This location provides dark skies suited for faint object observations but is also continuously subject to a harsh environment exposed to volcanic ash and salt spray. To better assess the overall system performance of the optical instrument, a historical assessment of the system’s performance was conducted. This analysis investigated all systematic and optical operational data to determine the overall performance parameters for ES-MCAT. A complete optical system throughput calculation was performed to determine the optimal filter for observing orbital debris in GEO orbits. The responses of each optical component to the solar spectrum, with atmospheric absorption, were multiplied and integrated to give ES-MCAT’s total system response for various filters. With the highest flux values, the Sloan Digital Sky Survey (SDSS) r′ and g′ were determined to be the optimal filters for ES-MCAT observations. Further analysis with known GEO debris objects enabled the selection of the r′ filter for characterization of the GEO debris population. A detailed overview of the optical system throughput, data reduction, photometric and astrometric data, and other system characteristics that define ES-MCAT are discussed.

Corbin L Cruz↗
NASA NTRS1998

Martian Polar Region Impact Craters: Topographical Perspectives from the Mars Orbiter Laser Altimeter

The Mars Orbiter Laser Altimeter (MOLA) has acquired over 100 topographic cross-sections of impact landforms in the polar regions of Mars as part of Mars Global Surveyor (MGS) Science Phasing Orbit observations during the period from April to July, 1998. These MOLA topographic profiles offer the first three-dimensional perspectives of high latitude craters on Mars yet available, and provide evidence of landform geometries not previously recognized. Indeed, the relatively poor quality of Viking Orbiter images of many high northern latitude regions has allowed the MOLA data to provide insights into the cavities and ejecta topologies of non-degraded impact landforms that have clearly experienced interactions with condensates, either as part of their formation, or as a post-modification stage effect. Here we report a preliminary summary of the results associated with topographic measurements for a statistically significant population of impact features all of which lie north of 60N latitude. MOLA sampled four impact features with frost-related interior deposits, including the 81 km (diameter) Korolev feature. In several cases, there is evidence from near-centerline MOLA cross-sections of crater interior features (i.e., central peak or ice-dust deposits) that are anomalously large relative to the crater cavity. Central structures that make up more than 50% of the volume of a crater cavity are observed, suggesting that either substantial accumulation of mantling materials has occurred, or that crater excavation triggered production of volume-enhancing materials (ice?). Pedestal craters sampled by MOLA also attest to enhanced production of ejecta materials in high latitude terrains. For example, many of the pedestal craters suggest a volume of ejecta (Ve) to volume of cavity (Vc) ratio far in excess of 1.0 (i.e., over 3.0), even in cases where the floor of the cavity appears unfilled. Finally, the well-defined transitions between simple and complex craters observed in MOLA data for non-polar latitude impact features is not preserved at high northern latitudes (for non-degraded craters). This further suggests the role of target materials (i.e., frozen volatiles?) in the cratering process on Mars in such regions.

Garvin, J. B.↗
NASA NTRS1975

The light curve of CV Serpentis, the sometimes-eclipsing Wolf-Rayet star

New photoelectric observations of the B-magnitude of CV Ser made in 1973 and 1974 show no clear evidence of an eclipse, but they establish night-to-night variability of several percent, a systematic brightness change of 0.035 mag during a portion of the single orbit observed in 1973, and irregular flaring in 1974. We made iris photometer measurements of Harvard patrol plates taken between 1905 June and 1953 July, and find no evidence of a very deep eclipse such as observed by Hjellming and Hiltner. We present several new light curves and discuss then in the light of the recent results of Cowley et al.

Schild, R.↗