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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Orbital Stability Regions for Hypothetical Natural Satellites of 101955 Bennu (1999 RQ36)

The Origins, Spectral Interpretation, Resource Investigation, Security-Regolith Explorer (OSIRIS-Rex) mission will be orbiting and returning a sample from near-Earth asteroid 101955 Bennu. Ground-based observations have determined that no object greater then 15 m in diameter is orbiting Bennu. This investigation explores the possible size and stability of a natural satellite around Bennu. The focus of this research is soley on the existence of stable orbits for a natural satellite and purposefully places how the natural satellite migrated to this orbit outside the bounds of this research. Numerical simulations modeling J2, third-body dynamics and solar radiation pressue is used on a large set of initial conditions that vary in semi-major axis, inclination, longititude of periapsis and natural satellite diameter. Stable orbital initial conditions for a given natural satellite diameter must remain in orbit for more than a thousand years without escape or collision from Bennu. The data found the possible existence of natural satellites in orbit around Bennu as small as 0.75 cm. Certain mechanisms such as the modified Laplace plane, Kozai resonance and the Sun-terminator plane are explored for yielding stable orbits of a given natural satelllite.

asteroids↗
NASA NTRS2018

Enhancements to the Open Access Spectral Band Adjustment Factor Online Calculation Tool for Visible Channels

With close to 40 years of satellite observations, from which, cloud, land-use, and aerosol parameters can be measured, inter-consistent calibrations are needed to normalize retrievals across satellite records. Various visible-sensor inter-calibration techniques have been developed that utilize radiometrically stable Earth targets, e.g., deep convective clouds and desert/polar ice pseudo-invariant calibration sites. Other equally effective, direct techniques for intercalibration between satellite imagers are simultaneous nadir overpass comparisons and ray-matched radiance pairs. Combining independent calibration results from such varied techniques yields robust calibration coefficients, and is a form of self-validation. One potential source of significant error when cross-calibrating satellite sensors, however, are the often small but substantial spectral discrepancies between comparable bands, which must be accounted for. As such, visible calibration methods rely on a Spectral Band Adjustment Factor (SBAF) to account for the spectral-response function- induced radiance differences between analogous imagers. The SBAF is unique to each calibration method as it is a function of the Earth-reflected spectra. In recent years, NASA Langley pioneered the use of SCIAMACHY-, GOME-2-, and Hyperion-retrieved Earth spectra to compute SBAFs. By carefully selecting hyperspectral footprints that best represent the conditions inherent to an inter-calibration technique, the uncertainty in the SBAF is greatly reduced. NASA Langley initially provided the Global Space-based Inter-calibration System processing and research centers with online SBAF tools, with which users select conditions to best match their calibration criteria. This article highlights expanded SBAF tool capabilities for visible wavelengths, with emphasis on the use of the spectral range filtering for the purpose of separating scene conditions for the channel that the SBAF is needed based on the reflectance values of other bands. In other words, spectral filtering will enable better scene-type selection for bands where scene determination is difficult without information from other channels, which should prove valuable to users in the calibration community.

Scarino, Benjamin↗
NASA NTRS2000

Improving Cloud Detection in Satellite Images of Coral Reef Environments Using Space Shuttle Photographs and High-Definition Television

Coral reefs worldwide are suffering from severe and rapid degradation (Bryant et A, 1998; Hoegh-Guldberg, 1999). Quick, consistent, large-scale assessment is required to assess and monitor their status (e.g., USDOC/NOAA NESDIS et al., 1999). On-going systematic collection of high resolution digital satellite data will exhaustively complement the relatively small number of SPOT, Landsat 4-5, and IRS scenes acquired for coral reefs the last 20 years. The workhorse for current image acquisition is the Landsat 7 ETM+ Long Term Acquisition Plan (Gasch et al. 2000). Coral reefs are encountered in tropical areas and cloud contamination in satellite images is frequently a problem (Benner and Curry 1998), despite new automated techniques of cloud cover avoidance (Gasch and Campana 2000). Fusion of multidate acquisitions is a classical solution to solve the cloud problems. Though elegant, this solution is costly since multiple images must be purchased for one location; the cost may be prohibitive for institutions in developing countries. There are other difficulties associated with fusing multidate images as well. For example, water quality or surface state can significantly change through time in coral reef areas making the bathymetric processing of a mosaiced image strenuous. Therefore, another strategy must be selected to detect clouds and improve coral reefs mapping. Other supplemental data could be helpful and cost-effective for distinguishing clouds and generating the best possible reef maps in the shortest amount of time. Photographs taken from the 1960s to the present from the Space Shuttle and other human-occupied spacecraft are one under-used source of alternative multitemporal data (Lulla et al. 1996). Nearly 400,000 photographs have been acquired during this period, an estimated 28,000 of these taken to date are of potential value for reef remote sensing (Robinson et al. 2000a). The photographic images can be digitized into three bands (red, green and blue) and processed for various applications (e.g., Benner and Curry 1998, Nedeltchev 1999, Glasser and Lulla 2000, Robinson et al. 2000c, Webb et al, in press).

Andrefeouet, Serge↗
NASA NTRS1989

Do asteroids have satellites?

A substantial body of indirect evidence suggests that some asteroids have satellites, although none has been detected unambiguously. Collisions between asteroids provide physically plausible mechanisms for the production of binaries, but these operate with low probability; only a small minority of asteroids are likely to have satellites. The abundance of binary asteorids can constrain the collisional history of the entire belt population. The allowed angular momentum of binaries and their rate of tidal evolution limit separations to no more than a few tens of the primary's radii. Their expected properties are consistent with failure to detect them by current imaging techniques.

Weidenschilling, Stuart J.↗
DOE OSTI2020

Changes to the Appearance of Optical Lightning Flashes Observed From Space According to Thunderstorm Organization and Structure

Optical lightning observations from space reveal a wide range of flash structure. Lightning imagers such as the Geostationary Lightning Mapper and Lightning Imaging Sensor measure flash appearance by recording transient changes in cloud top illumination. The spatial and temporal optical energy distributions reported by these instruments depend on the physical structure of the flash and the distribution of hydrometeors within the thundercloud that scatter and absorb the optical emissions. This study reported herein explores how flash appearance changes according to the scale and organization of the parent thunderstorms with a focus on mesoscale convective systems. Clouds near the storm edge are frequently illuminated by large optical flashes that remain stationary between groups. These flashes appear large because their emissions can reflect off the exposed surfaces of nearby clouds to reach the satellite. Large stationary flashes also occur in small isolated thunderstorms. Optical flashes that propagate horizontally, meanwhile, are most frequently observed in electrified stratiform regions where extensive layered charge structures promote lateral development. Highly radiant “superbolts” occur in two scenarios: embedded within raining stratiform regions or in nonraining boundary/anvil clouds where optical emissions can take a relatively clear path to the satellite.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1996

Ultra Small Aperture Terminal: System Design and Test Results

The Ultra Small Aperture Terminal (USAT) has been developed to test and demonstrate remote and broadcast satcom applications via the Advanced Communications Technology Satellite (ACTS). The design of these ground stations emphasize small size, low power consumption, portable and rugged terminals. Each ground station includes several custom design parts such as 35 cm diameter antenna, 1/4 Watt transmitter with built-in upconverter, and 4.0 dB Noise Figure (NF) receiver with built-in downconverter. In addition, state-of-the-art commercial parts such as highly stable ovenized crystal oscillators and dielectric resonator oscillators are used in the ground station design. Presented in this paper are system level design description, performance, and sample applications.

Sohn, Philip Y.↗
NASA NTRS2019

Capsulation Satellite: CapSat

This PowerPoint presentation will discuss a new small spacecraft architecture which takes advantage of ESPA Class rideshare opportunities.

ESPA Class Small Spacecraft↗
NASA NTRS2011

Results from On-Orbit Testing of the Fram Memory Test Experiment on the Fastsat Micro-Satellite

NASA is planning on going beyond Low Earth orbit with manned exploration missions. The radiation environment for most Low Earth orbit missions is harsher than at the Earth's surface but much less harsh than deep space. Development of new electronics is needed to meet the requirements of high performance, radiation tolerance, and reliability. The need for both Volatile and Non-volatile memory has been identified. Emerging Non-volatile memory technologies (FRAM, C-RAM,M-RAM, R-RAM, Radiation Tolerant FLASH, SONOS, etc.) need to be investigated for use in Space missions. An opportunity arose to fly a small memory experiment on a high inclination satellite (FASTSAT). An off-the-shelf 512K Ramtron FRAM was chosen to be tested in the experiment.

MacLeod, Todd C.↗
NASA NTRS2000

Aladdin: Exploration and Sample Return from the Moons of Mars

Aladdin is a remote sensing and sample return mission focused on the two small moons of Mars, Phobos and Deimos. Understanding the moons of Mars will help us to understand the early history of Mars itself. Aladdin's primary objective is to acquire well documented, representative samples from both moons and return them to Earth for detailed analyses. Samples arrive at Earth within three years of launch. Aladdin addresses several of NASA's highest priority science objectives: the origin and evolution of the Martian system (one of two silicate planets with satellites) and the composition and nature of small bodies (the building blocks of the solar system). The Aladdin mission has been selected as a finalist in both the 1997 and 1999 Discovery competitions based on the high quality of science it would accomplish. The equivalent of Aladdin's Phase A development has been successfully completed, yielding a high degree of technical maturity. Aladdin uses an innovative flyby sample acquisition method, which has been validated experimentally and does not require soft landing or anchoring. An initial phasing orbit at Mars reduces mission propulsion requirements, enabling Aladdin to use proven, low-risk chemical propulsion with good mass margin. This phasing orbit is followed by a five month elliptical mission during which there are redundant opportunities for acquisition of samples and characterization of their geologic context using remote sensing. The Aladdin mission is a partnership between Brown University, the Johns Hopkins University Applied Physics Laboratory, Lockheed Martin Astronautics, and NASA Johnson Space Center.

Pieters, C.↗
NASA NTRS1990

LifeSat - A new research vehicle

LifeSat is a reusable recoverable satellite that will support research in the gravitation and radiation biology fields. It can provide sustained lower gravitational levels than manned vehicles and can access orbits where specimens can be exposed to cosmic radiation. The satellite design encompasses environmental support for vertebrate, invertebrate and plant specimens ranging from cells and tissues up to small mammals. The first launch, in a series of 7 satellite flights, is planned for late 1995.

Gilbreath, William P.↗
NASA NTRS1998

Smoke, Clouds, and Radiation-Brazil (SCAR-B) Experiment

The Smoke, Clouds, and Radiation-Brazil (SCAR-B) field project took place in the Brazilian Amazon and cerrado regions in August-September 1995 as a collaboration between Brazilian and American scientists. SCAR-B, a comprehensive experiment to study biomass burning, emphasized measurements of surface biomass, fires, smoke aerosol and trace gases, clouds, and radiation. their climatic effects, and remote sensing from aircraft and satellites. It included aircraft and ground-based in situ measurements of smoke emission factors and the compositions, sizes, and optical properties of the smoke particles; studies of the formation of ozone; the transport and evolution of smoke; and smoke interactions with water vapor and clouds. This overview paper introduces SCAR-B and summarizes some of the main results obtained so far. (1) Fires: measurements of the size distribution of fires, using the 50 m resolution MODIS Airborne Simulator, show that most of the fires are small (e.g. 0.005 square km), but the satellite sensors (e.g., AVHRR and MODIS with I km resolution) can detect fires in Brazil which are responsible for 60-85% of the burned biomass: (2) Aerosol: smoke particles emitted from fires increase their radius by as much as 60%, during their first three days in the atmosphere due to condensation and coagulation, reaching a mass median radius of 0.13-0.17 microns: (3) Radiative forcing: estimates of the globally averaged direct radiative forcing due to smoke worldwide, based on the properties of smoke measured in SCAR-B (-O.l to -0.3 W m(exp -2)), are smaller than previously modeled due to a lower single-scattering albedo (0.8 to 0.9), smaller scattering efficiency (3 square meters g(exp -2) at 550 nm), and low humidification factor; and (4) Effect on clouds: a good relationship was found between cloud condensation nuclei and smoke volume concentrations, thus an increase in the smoke emission is expected to affect cloud properties. In SCAR-B, new techniques were developed for deriving the absorption and refractive index of smoke from ground-based remote sensing. Future spaceborne radiometers (e.g., MODIS on the Earth Observing System), simulated on aircraft, proved to be very useful for monitoring smoke properties, surface properties, and the impacts of smoke on radiation and climate.

Kaufman, Y. J.↗
NASA NTRS1975

A co-accretional model of satellite formation

A model of the accumulation process of a satellite about an accreting planet is proposed in order to explain the difference in relative size between the moon and the outer planets' satellites. The parameter that most strongly affects the final mass ratio of the pair in this model is the time at which the secondary embryo is introduced. Thus the difference between terrestrial and outer planet satellite systems is easily understood in terms of the differences in Q (the specific dissipation function of the particles in the circumplanetary cloud) between these planets. The high Q of the outer planets does not allow a satellite embryo to survive a significant portion of the accretion process; therefore only small bodies formed very late in the accumulation of the planet remain as satellites.

Harris, A. W.↗
NASA NTRS1976

The problem of spiral galaxies and satellite radio sources

Regions 2-deg x 2-deg in area centered on four spiral galaxies were scanned with the Goldstone 64-m antenna in search of satellite radio sources at 2295 MHz. Four control regions of equal area but free of galaxies brighter than 13th magnitude were also scanned. No significant excess in the number density of sources with flux densities greater than 0.10 Jy relative to the control fields was found. A detailed comparison is made between the results of this program and the results of previous investigators. In particular, attention is directed to the potentially important implications of an investigation by Tovmasyan (1968), who searched a large number of spirals and found evidence that a small percentage of them apparently have radio satellites located up to 20 arcmin from the central galaxy. Fifteen sources selected from Tovmasyan's list of 43 satellite sources were measured. The present results confirm his positions and relative flux densities for each of the sources.

Arp, H.↗
NASA NTRS1985

Three-layer Generic Ganymedes: Structure and Evolution

Accurate, three layered structural models were generated for Ganymede and Callisto. Three layered satellites consist of a rock core, a region of mixed rock and ice, and an outer shell of pure ice. This structure would result from either accretional melting of the outermost region of the satellite or differentiation subsequent to localized melting. A completely undifferentiated ice rock satellite possesses only the single, top boundary layer and, in this case, melting is also relatively difficult to initiate; this suggests that, if accretional melting results in a small degree of differentiation initially, subsequent melting may readily occur as the satellite warms due to radiogenic heating. Alternatively, if accretion is not accompanied by a small degree of differentiation, it may prove too difficult to initiate nonaccretional melting and the satellite might remain undifferentiated indefinitely.

Mueller, S. W.↗
NASA NTRS1988

Frequency addressable beams for land mobile communications

Satellites used for mobile communications need to serve large numbers of small, low cost terminals. The most important parameters affecting the capacity of such systems are the satellite equivalent isotropically radiated power (EIRP) and gain to noise temperature ratio (G/T) and available bandwidth. Satellites using frequency addressed beams provide high EIRP and G/T with high-gain antenna beams that also permit frequency reuse over the composite coverage area. Frequency addressing is easy to implement and compatible with low-cost terminals and offers higher capacity than alternative approaches.

Thompson, J. D.↗
NASA NTRS2016

Black Swift Technologies LLC

Colorado-based Black Swift Technologies (BST) created a small unmanned aircraft system(sUAS) to help NASA get a clearer picture of soil moisture through the Small Business Innovation Research (SBIR) program. Soil moisture is defined in terms of volume of water per unit volume of soil. Using BSTs sUAS, NASA scientists can gather ground truth measurements for a clearer observation by getting closer to the source. This can help rule out misleading results generated by satellite imagery.

small unmanned aircraft system↗