Detection of tides on planets and satellites using orbiting spacecraft and landers
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Ground Calibration of an Orbiting Spacecraft Transmitter
The SeaWinds Calibration Ground Station (CGS) is a novel Ku-band receiving station that supports the June 1999-launched JPL/NASA SeaWinds scatterometer radar which measures the near-surface wind speeds over 90% of the ice-free oceans.
QuickSCAT SeaWinds Calibration Ground Station CGS↗
A Simplified, Closed-Form Method for Screening Spacecraft Orbital Heating Variations
A closed-form analytical technique has been developed to screen orbital average heating variations as a function of beta angle, altitude, surface area, and surface optical properties. Using planetary view factor equations for surfaces parallel-to and normal-to the local vertical, a cylindrical umbral shadow approximation, and a simplified albedo flux model, heating rate equations are formulated and then integrated to obtain orbital average heating. The results are compared to detailed analytical predictions using Monte Carlo integration and an assessment of error is presented.
Rickman, S. L.↗
An Alternative Approach to Human Servicing of Crewed Earth Orbiting Spacecraft
No abstract available
Alpert, Brian↗
Control and data systems challenges in design of the Jupiter Icy Moons Orbiter spacecraft.
The objective of this paper is to introduce the readers to some of the challenges facing the Attitude Control and Command and Data Handling subsystems, and give an overview of approaches being considered to deal with these challenges.
Reh, Kim↗
AAS 21-728: Two-Spacecraft Orbiting in Opposition to Enable Bistatic Radar Observations around an Asteroid
No abstract provided
Anderson, Rodney↗
Free-falling Crystals: Biological Macromolecular Crystal Growth Studies in Low Earth Orbit
Spacecraft orbiting the earth experience a reduced acceleration environment due to being in a state of continuous free-fall. This state colloquially termed microgravity, has produced improved X-ray diffraction quality crystals of biological macromolecules. Improvements in X-ray diffraction resolution (detail) or signal to noise, provide greater detail in the three-dimensional molecular structure providing information about the molecule, how it works, how to improve its function or how to impede it. Greater molecular detail obtained by crystallization in microgravity, has important implications for structural biology. In this article we examine the theories behind macromolecule crystal quality improvement in microgravity using results obtained from studies with the model protein, chicken egg white lysozyme.
Judge, Russell A.↗
Simulating Orbital Operations Of Spacecraft
Orbital Operations Simulator, OOS, computer program developed to implement mathematical models of complex outer-space vehicular systems and be "testbed" for new flight software. Has multi-vehicular-simulation capability to model on-orbit proximity and docking operations. Version 1.0, with its Prepare Processor and User Interface Shell designed to be true multivehicle dynamic simulator with capability to change mathematical models of spacecraft subsystems easily. Written in K & R standard C, LEX, and YACC languages and operates under System V shell.
Edwards, Carter↗
Mission Advantages of Constant Power, Variable Isp Electrostatic Thrusters
Electric propulsion has moved from station-keeping capability for spacecraft to primary propulsion with the advent of both the Deep Space One asteroid flyby and geosynchronous spacecraft orbit insertion. In both cases notably more payload was delivered than would have been possible with chemical propulsion. To provide even greater improvements electrostatic thruster performance could be varied in specific impulse, but kept at constant power to provide better payload or trip time performance for different mission phases. Such variable specific impulse mission applications include geosynchronous and low earth orbit spacecraft stationkeeping and orbit insertion, geosynchronous reusable tug missions, and interplanetary probes. The application of variable specific impulse devices is shown to add from 5 to 15% payload for these missions. The challenges to building such devices include variable voltage power supplies and extending fuel throughput capabilities across the specific impulse range.
Oleson, Steven R.↗
Orbital tracking through synchronous spacecraft
Orbit determination accuracy using synchronous satellite system for tracking near earth spacecraft
Cooley, J. L.↗
Measurement error analysis in determination of small-body gravity fields
We consider analytically the use of existing instrumentation in determining asteroid gravity fields from orbiting spacecraft. Asteroids (Eros as an example) are modeled as homogeneous triaxial ellipsoids, with gravitational potential given by a sperical-harmonic expansion. Mass concentrations are modeled as point masses. The character of spacecraft orbits about asteroids is discussed, along with detectibility of gravitational coefficients and of mass concentrations. A Kalman-filtering treatment of the observation process, for Eros as example, shows that using DSN tracking and onboard gravity gradiometry, radar altimetry, and celestial angle measurements, a single orbit yields asteroid mass to 0.03% and coefficients C20 to C44 to 1% accuracies.
Friedlander, A. L.↗
Global and regional/seasonal color mosaics of Mars
Four regional mosaics of Mars acquired during different seasons, along with their composite as a single global mosaic, have been completed in two colors (red and violet) at scales of 1/16 and 1/64 degrees/pixel. These mosaics were put together from a set of 51 separate mosaics, each acquired from a single Viking orbiter spacecraft orbital revolution. Special techniques were developed and applied to suppress large variations between mosaics introcued by highly variable, optically thin, condensate hazes. The techniques utilize a combination of the spatial characteristics of the hazes (generally broad, low-frequency) along with their modulation of the reginal color ratios (strongly enhancing the violet/red ratios). Photometric-function normalization was applied following the haze removal. Most of the single-orbit mosaics consist of red and violet or red, green, and violet filters, but a few mosaics with only red-filter data were included to fill gaps in global coverage at high northern latitudes. Global coverage is approximately 99 percent complete in red-filter mosaics and approximately 95 percent and approximately 60 percent complete in corresponding violet- and green-filter mosaics, respectively. All of the mosaics are geometrically tied to the 1/256 deg per pixel Mars Digital Image Map (MDIM), which is available on Compact Disk (CD), and which will be used as the base map for Mars Observer data sets. Early in 1993, the single-orbit color mosaics will be distributed to the science community in a six-volume set of CDs. Perhaps the most scientifically interesting parts of this dataset are the overlap regions, which show significant temporal variations in surface and atmospheric features. Surface changes can be categorized as (1) changes that probably occurred during the great dust storms of 1977; (2) changes that occurred soon after 1977 storms due to removal of redistribution of recently deposited dust; (3) changes in the northern lowlands that probably occurred during the dusty southern summer of 1979 (when no great dust storm occurred); and (4) changes associated with strong slope winds in the Tharsis and Elysium regions.
Mcewen, Alfred S.↗
Keeping Communication Continuous
General Dynamics Decision Systems employees have played a role in supplying telemetry, tracking, and control (TT&C) and other communications systems to NASA and the U.S. Department of Defense for over 40 years. Providing integrated communication systems and subsystems for nearly all manned and unmanned U.S. space flights, the heritage of this Scottsdale, Arizona-based company includes S-band transceivers that enabled millions of Americans to see Neil Armstrong and hear his prophetic words from the Moon in 1969. More recently, Decision Systems has collaborated with NASA s Goddard Space Flight Center to develop transponders, wireless communications devices that pick up and automatically respond to an incoming signal, for NASA s Tracking and Data Relay Satellite System (TDRSS). Four generations of Decision Systems TDRSS transponders have been developed under Goddard s sponsorship. The company s Fourth Generation TDRSS User Transponder (TDRSS IV) allows low-Earth-orbiting spacecraft to communicate continuously with a single ground station at White Sands, New Mexico, through a constellation of geostationary relay satellites positioned at key locations around the Earth. In addition to the communications of forward link control commands and return link telemetry data, the TDRSS IV also supports spacecraft orbit tracking through coherent turn-around of a pseudo-noise ranging code and two-way Doppler tracking.When the NSBF adopted the use of global positioning system receivers for balloon position tracking, Decision Systems concluded that a simpler, noncoherent transceiver could provide the NSBF with the necessary TDRSS communications without the additional cost and complexity of a coherent transponder. The solution was to take the core design of the TDRSS IV Transponder, but remove the extra functionality that supported coherent turn-around. This would simplify the production effort, reduce the testing required, and result in a lower cost product with smaller size, weight, and power consumption. Once NSBF and Decision Systems agreed on a concept for this new product, known as the Multi-Mode Transceiver (MMT), the NSBF approached Goddard for approval and funding.
Source record↗
Oxygen Concentration Flammability Threshold Tests for the Constellation Program
CEV atmosphere will likely change because craft will be used as LEO spacecraft, lunar spacecraft, orbital spacecraft. Possible O2 % increase and overall pressure decrease pressure vessel certs on spacecraft. Want 34% minimum threshold. Higher, better when atmosphere changes. WSTF suggests testing all materials/components to find flammability threshold, pressure and atmosphere.
Williams, James H.↗
The Ratio of Debris to Meteoroid-Induced Damage in Near-Earth Space
Orbital debris poses a substantial threat to many Earth-orbiting spacecraft, particularly those near Sun-synchronous altitudes. Man-made debris is not equally prevalent at all altitudes, however; geostationary satellites likely experience more damage from meteoroid impacts than from debris. We have conducted a comparison between debris- and meteoroid-induced damage on cubic aluminum spacecraft orbiting the Earth at a variety of altitudes and orbital inclinations using NASA's latest models of these environments: ORDEM 3.1 and MEM 3. We use the results to determine in which regions the risk is debris- or meteoroid-dominated, and find that debris dominates the risk between altitudes of about 600 and 1300 km above the Earth, while meteoroids dominate at altitudes less than 270 km or greater than 4800 km.
Althea Valkyrie Moorhead↗
The Ratio of Debris- to Meteoroid-Induced Damage in Near-Earth Space
Orbital debris poses a substantial threat to many Earth-orbiting spacecraft, particularly those near Sun-synchronous altitudes. Man-made debris is not equally prevalent at all altitudes, however; geostationary satellites likely experience more damage from meteoroid impacts than from debris. We have conducted a comparison between debris- and meteoroid-induced damage on cubic aluminum spacecraft orbiting the Earth at a variety of altitudes and orbital inclinations using NASA's latest models of these environments: ORDEM 3.1 and MEM 3. We use the results to determine in which regions the risk is debris- or meteoroid-dominated, and find that debris dominates the risk between altitudes of about 600 and 1300 km above the Earth, while meteoroids dominate at altitudes less than 270 km or greater than 4800 km.
Althea Moorhead↗
Extreme Spacecraft Charging in Polar Low Earth Orbit
Spacecraft in low altitude, high inclination (including sun -synchronous) orbits are widely used for remote sensing of the Earth fs land surface and oceans, monitoring weather and climate, communications, scientific studies of the upper atmosphere and ionosphere, and a variety of other scientific, commercial, and military applications. These systems episodically charge to frame potentials in the kilovolt range when exposed to space weather environments characterized by a high flux of energetic (approx.10 fs kilovolt) electrons in regions of low background plasma density. Auroral charging conditions are similar in some ways to the space weather conditions in geostationary orbit responsible for spacecraft charging to kilovolt levels. We first review the physics of space environment interactions with spacecraft materials that control auroral charging rates and the anticipated maximum potentials that should be observed on spacecraft surfaces during disturbed space weather conditions. We then describe how the theoretical values compare to the observational history of extreme charging in auroral environments. Finally, a set of extreme DMSP charging events are described varying in maximum negative frame potential from approx.0.6 kV to approx.2 kV, focusing on the characteristics of the charging events that are of importance both to the space system designer and to spacecraft operators. The goal of the presentation is to bridge the gap between scientific studies of auroral charging and the need for engineering teams to understand how space weather impacts both spacecraft design and operations for vehicles on orbital trajectories that traverse auroral charging environments.
Colson, Andrew D.↗