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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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NASA NTRS1973

Zonal gravity harmonics from long satellite arcs by a seminumeric method.

A zonal geopotential is presented to degree 21 from evaluation of mean elements for 21 satellites, including two of low (less than 20 deg) inclination. Each satellite is represented by an arc of at least one apsidal rotation. The lengths range from 50 to 660 days. Differential correction of the initial elements in all of the arcs, together with radiation pressure and atmospheric drag coefficients, is accomplished simultaneously with the correction for the zonal harmonics. The satellite orbits and their variations are generated by numerical integration of the Lagrange equations for mean elements. Disturbances due to precession and nutation, atmospheric drag, radiation pressure, and lunisolar gravity are added at 1- to 8-day intervals in the integrated orbits.

Wagner, C. A.↗

NASA NTRS1981

Analysis of Lageos' altitude decrease

The paper treats the inverse problem of celestial mechanics which consists of determining the force field or potential from given or observed orbit(s). From the observational information, according to which Lageos loses approximately 1 mm altitude per day, a linear partial differential equation is formulated. The solution of this equation gives the field responsible for the above-mentioned, as yet unexplained, small but well established secular decrease in the semi-major axis. Note that the altitude-loss is not due to air-drag because of the very high altitude of this satellite.

Szebehely, V.↗

NASA NTRS1991

Nano-G research laboratory for a spacecraft

An acceleration free research laboratory is provided that is confined within a satellite but free of any physical engagement with the walls of the satellite, wherein the laboratory has adequate power, heating, cooling, and communications services to conduct basic research and development. An inner part containing the laboratory is positioned at the center-of-mass of a satellite within the satellite's outer shell. The satellite is then positioned such that its main axes are in a position parallel to its flight velocity vector or in the direction of the residual acceleration vector. When the satellite is in its desired orbit, the inner part is set free so as to follow that orbit without contacting the inside walls of the outer shell. Sensing means detect the position of the inner part with respect to the outer shell, and activate control rockets to move the outer shell; thereby, the inner part is repositioned such that it is correctly positioned at the center-of-mass of the satellite. As a consequence, all disturbing forces, such as drag forces, act on the outer shell, and the inner part containing the laboratory is shielded and is affected only by gravitational forces. Power is supplied to the inner part and to the laboratory by a balanced microwave/laser link which creates the kind of environment necessary for basic research to study critical phenomena such as the Lambda transition in helium and crystal growth, and to perform special metals and alloys research, etc.

Vonbun, Friedrich O.↗

NASA NTRS1992

Analysis of the Cosmic Background Explorer (COBE) helium venting through effects on the orbit

An analysis is described which shows that a helium venting thrust level that is 60 percent higher than the predicted 2.3 millinewtons may be the cause of the unusually high premission-analysis and on-orbit support orbital decay rates and drag correction factors found for the Cosmic Background Explorer satellite. Depletion of the helium allowed a determination of the average mass flow rate and specific impulse. The average mass flow rate of 3.3 mg/sec confirmed the thrust levels indicated by the venting thrust analysis. Liquid helium is used for cooling instruments aboard the satellite.

Cox, C. M.↗

NASA NTRS1998

Global Warming Estimation from MSU

Microwave Sounding Unit (MSU) radiometer observations in Ch 2 (53.74 GHz) from sequential, sun-synchronous, polar-orbiting NOAA satellites contain small systematic errors. Some of these errors are time-dependent and some are time-independent. Small errors in Ch 2 data of successive satellites arise from calibration differences. Also, successive NOAA satellites tend to have different Local Equatorial Crossing Times (LECT), which introduce differences in Ch 2 data due to the diurnal cycle. These two sources of systematic error are largely time independent. However, because of atmospheric drag, there can be a drift in the LECT of a given satellite, which introduces time-dependent systematic errors. One of these errors is due to the progressive chance in the diurnal cycle and the other is due to associated chances in instrument heating by the sun. In order to infer global temperature trend from the these MSU data, we have eliminated explicitly the time-independent systematic errors. Both of the time-dependent errors cannot be assessed from each satellite. For this reason, their cumulative effect on the global temperature trend is evaluated implicitly. Christy et al. (1998) (CSL). based on their method of analysis of the MSU Ch 2 data, infer a global temperature cooling trend (-0.046 K per decade) from 1979 to 1997, although their near nadir measurements yield near zero trend (0.003 K/decade). Utilising an independent method of analysis, we infer global temperature warmed by 0.12 +/- 0.06 C per decade from the observations of the MSU Ch 2 during the period 1980 to 1997.

Prabhakara, C.↗

NASA NTRS1998

The Remote Sensing of Mineral Aerosols and Their Impact on Phytoplankton Productivity using Sea WiFS

The main objective of this proposal was to use SeaWiFs data to study the relationship between aerosols found in aeollan dust and photosynthesis of phytoplankton in open ocean surface waters. This project was a collaborative effort between myself and Dr. Neil Tindale at Texas A&M University and followed on our earlier funded proposal which had been designed as a proof-of-concept study to determine if ocean color sensors such as the Coastal Zone Color Scanner (CZCS) could be used to detect and map large-scale mineral aerosol plumes. Despite the large spatial and temporal gaps inherent in the CZCS data coverage, our results from this initial study indicated that an ocean color sensor could indeed be used to detect aerosols. These encouraging results led us to propose in this proposal the use of SeaWiFS data to study mineral aerosol transport and its impact on phytoplankton production. This proposal orignally intended to make use of SeaWiFS images, but as the launch delay of SeaWiFS dragged on, we had to make do with other satellite data sets. Thus, the focus of this proposal became the CSCS image archive instead. I detail my results and accomplishments with this data set.

Stegmann, Petra M.↗

NASA NTRS2013

Space Weather Impacts to Conjunction Assessment: A NASA Robotic Orbital Safety Perspective

National Aeronautics and Space Administration (NASA) recognizes the risk of on-orbit collisions from other satellites and debris objects and has instituted a process to identify and react to close approaches. The charter of the NASA Robotic Conjunction Assessment Risk Analysis (CARA) task is to protect NASA robotic (unmanned) assets from threats posed by other space objects. Monitoring for potential collisions requires formulating close-approach predictions a week or more in the future to determine analyze, and respond to orbital conjunction events of interest. These predictions require propagation of the latest state vector and covariance assuming a predicted atmospheric density and ballistic coefficient. Any differences between the predicted drag used for propagation and the actual drag experienced by the space objects can potentially affect the conjunction event. Therefore, the space environment itself, in particular how space weather impacts atmospheric drag, is an essential element to understand in order effectively to assess the risk of conjunction events. The focus of this research is to develop a better understanding of the impact of space weather on conjunction assessment activities: both accurately determining the current risk and assessing how that risk may change under dynamic space weather conditions. We are engaged in a data-- ]mining exercise to corroborate whether or not observed changes in a conjunction event's dynamics appear consistent with space weather changes and are interested in developing a framework to respond appropriately to uncertainty in predicted space weather. In particular, we use historical conjunction event data products to search for dynamical effects on satellite orbits from changing atmospheric drag. Increased drag is expected to lower the satellite specific energy and will result in the satellite's being 'later' than expected, which can affect satellite conjunctions in a number of ways depending on the two satellites' orbits and the geometry of the conjunction. These satellite time offsets can form the basis of a new technique under development to determine whether space weather perturbations, such as coronal mass ejections, are likely to increase, decrease, or have a neutral effect on the collision risk due to a particular close approach.

Ghrist, Richard↗

NASA NTRS1983

The high latitude circulation and temperature structure of the thermosphere near solstice

NCAR thermospheric-general-circulation-model (TGCM) computations of solar-maximum thermospheric neutral-gas temperature and circulation around the December solstice are presented and discussed. The TGCM uses a 5 x 5-deg grid and 24 constant-pressure layers, corresponding to altitudes of about 97-500 km. The results are mapped as electron-density contours, polar plots, cylindrical equidistant projections, meridional cross sections, and F-region polar plots comparing the TGCM predictions with DE-2 satellite observations. The significant differences between summer and winter high-latitude F-region winds are attributed to the ion drag momentum associated with magnetospheric convection. The TGCM wind predictions follow the same pattern as the satellite measurements but are too small; possible model corrections are considered.

Roble, R. G.↗

NASA NTRS2017

Differential Drag Demonstration: A Post-Mission Experiment with the EO-1 Spacecraft

Differential drag is a technique for altering the semi-major axis, velocity, and along-track position of a spacecraft in low Earth orbit. It involves varying the spacecrafts cross-sectional area relative to its velocity direction by temporarily changing attitude and solar array angles, thus varying the amount of atmospheric drag on the spacecraft. The technique has recently been proposed and used by at least three satellite systems for initial separation of constellation spacecraft after launch, stationkeeping during the mission, and potentially for conjunction avoidance. Similarly, differential drag has been proposed as a control strategy for rendezvous, removing the need for active propulsion. In theory, some operational missions that lack propulsion capability could use this approach for conjunction avoidance, though options are typically constrained for spacecraft that are already in orbit. Shortly before the spacecraft was decommissioned, an experiment was performed using NASAs EO-1 spacecraft in order to demonstrate differential drag on an operational spacecraft in orbit, and discover some of the effects differential drag might manifest. EO-1 was not designed to maintain off-nominal orientations for long periods, and as a result the team experienced unanticipated challenges during the experiment. This paper will discuss operations limitations identified before the experiment, as well as those discovered during the experiment. The effective displacement that resulted from increasing the drag area for 39 hours will be compared to predictions as well as the expected position if the spacecraft maintained nominal operations. A hypothetical scenario will also be examined, studying the relative risks of maintaining an operational spacecraft bus in order to maintain the near-maximum drag area orientation and hasten reentry.

differential drag↗

NASA NTRS2017

Differential Drag Demonstration: A Post-Mission Experiment with the EO-1 Spacecraft

Differential drag is a technique for altering the semimajor axis, velocity, and along-track position of a spacecraft in low Earth orbit. It involves varying the spacecraft's cross-sectional area relative to its velocity direction by temporarily changing attitude and solar array angles, thus varying the amount of atmospheric drag on the spacecraft. The technique has recently been proposed and used by at least three satellite systems for initial separation of constellation spacecraft after launch, stationkeeping during the mission, and potentially for conjunction avoidance. Similarly, differential drag has been proposed as a control strategy for rendezvous, removing the need for active propulsion. In theory, some operational missions that lack propulsion capability could use this approach for conjunction avoidance, though options are typically constrained for spacecraft that are already in orbit. Shortly before the spacecraft was decommissioned, an experiment was performed using NASA's EO-1 spacecraft in order to demonstrate differential drag on an operational spacecraft in orbit, and discover some of the effects differential drag might manifest. EO-1 was not designed to maintain off-nominal orientations for long periods, and as a result the team experienced unanticipated challenges during the experiment. This paper will discuss operations limitations identified before the experiment, as well as those discovered during the experiment. The effective displacement that resulted from increasing the drag area for 39 hours will be compared to predictions as well as the expected position if the spacecraft maintained nominal operations. A hypothetical scenario will also be examined, studying the relative risks of maintaining an operational spacecraft bus in order to maintain the near-maximum drag area orientation and hasten reentry.

orbital lifetim↗

NASA NTRS1978

Gas densities near 230 km from orbital drag and mass spectrometer measurements - A comparison

Perigee density data near 230 km for the Aeros satellite are analyzed for more than 1000 orbits. A comparison method for such data was developed which is based on the observed rate of change of orbital period as compared with the orbital decay computed from mass-spectrometer data obtained at discrete positions along the orbit. In general, the method confirms the good agreement of the average ratio of in-situ and orbit-drag-inferred perigee densities. In the case of Aeros, absolute densities measured by the NATE mass spectrometer are confirmed.

Roemar, M.↗

NASA NTRS1965

Beam-swinging facilities for the Goonhilly satellite-communication aerial

The mode of satellite tracking adopted at the Goonhilly earth station is to steer the aerial primarily by means of predicted data computed from the satellite orbital parameters and to superimpose, during the passage of the satellite, corrections to remove any prediction errors or aberrations due the transmission path. Predictions have proved to be highly accurate for satellites having a high mass to projected area ratio orbiting at altitudes at which air drag is very small; hence the corrections are small and infrequent.

COMMUNICATIONS SATELLITE↗

NASA NTRS1994

Demonstration of high sensitivity laser ranging system

We report on a high sensitivity semiconductor laser ranging system developed for the Gravity and Magnetic Earth Surveyor (GAMES) for measuring variations in the planet's gravity field. The GAMES laser ranging instrument (LRI) consists of a pair of co-orbiting satellites, one which contains the laser transmitter and receiver and one with a passive retro-reflector mounted in an drag-stabilized housing. The LRI will range up to 200 km in space to the retro-reflector satellite. As the spacecraft pair pass over the spatial variations in the gravity field, they experience along-track accelerations which change their relative velocity. These time displaced velocity changes are sensed by the LRI with a resolution of 20-50 microns/sec. In addition, the pair may at any given time be drifting together or apart at a rate of up to 1 m/sec, introducing a Doppler shift into the ranging signals. An AlGaAs laser transmitter intensity modulated at 2 GHz and 10 MHz is used as fine and medium ranging channels. Range is measured by comparing phase difference between the transmit and received signals at each frequency. A separate laser modulated with a digital code, not reported in this paper, will be used for coarse ranging to unambiguously determine the distance up to 200 km.

Millar, Pamela S.↗

NASA NTRS1991

Aerodynamic calculations related to tethered sub-satellite experiments

The results are presented of four aerodynamic studies that were in support of a broader, preliminary inquiry concerning the potential use of downward-deployed tethered sub-satellites for in-flight aerothermodynamic research. There are a multitude of questions regarding the general tethered satellite concept and the present report addresses only a few of these. A method for estimating drag and local surface pressure and shear on orbiting or re-entereing bodies is described, and examples based on the planned TSS-2 (Tethered Satellite System) are given. The problem of pressure measurement are explored, taking into account thermal transpiration, lag time, and the disturbed flow field created by the satellite body. The performance of an aerodynamic stabilizer, a ring-tail design, is calculated and its influence on satellite motion is illustrated. A method for optimizing future satellite shapes for desired aerodynamic properties is transitional rarefied flow with given geometric constraints is proposed and examples are shown.

Potter, J. Leith↗

NASA NTRS2019

Aeroassist Technologies for Small Satellite Missions

Orbit insertion operations that require large V maneuvers using conventional propulsive technologies are mass inefficient and challenging to package within SmallSat form factors such as the popular CubeSat. Aeroassist technologies offer an alternative approach for V maneuvers and could revolutionize the use of SmallSats for exploration missions and increase the science return while reducing costs for orbital or entry missions to Mars, Venus and return to Earth. Aeroassist refers to the use of an atmosphere to accomplish a transportation system function using techniques such as aerobraking, aerocapture, aeroentry, and aerogravity assist. Aeroassist technologies are power efficient and tolerant to the radiation and thermal environment encountered in deep space, and can be integrated around or within SmallSat geometries. This presentation will discuss various Aeroassist technologies including conventional rigid aeroshells, inflatable decelerators, mechanically deployable decelerators and other drag devices and control methods that should be considered by Small Satellite mission design teams.

Cassell, Alan M.↗

NASA NTRS1994

Computing Satellite Maneuvers For A Repeating Ground Track

TOPEX/POSEIDON Ground Track Maintenance Maneuver Targeting Program (GTARG) assists in designing maneuvers to maintain orbit of TOPEX/POSEIDON satellite. Targeting strategies used either maximize time between maneuvers or force control band exit to occur at specified intervals. Runout mode allows for ground-track propagation without targeting. GTARG incorporates analytic mean-element propagation algorithm accounting for all perturbations known to cause significant variations in ground track. Perturbations include oblateness of Earth, luni-solar gravitation, drag, thrusts associated with impulsive maneuvers, and unspecified fixed forces acting on satellite in direction along trajectory. Written in VAX-FORTRAN.

Shapiro, Bruce↗

NASA NTRS1977

National Geodetic Satellite Program, Part II: University of California, Los Angeles

Satellite orbit analyses are presented which were undertaken for: (1) reasons of insight and economy; (2) obtaining geophysically interesting tesseral harmonics; (3) comparing effects of tracking station location error drag, radiation pressure, and luni-solar attraction to tesseral harmonic effects; and (4) combination of satellite and terrestrial data. The analyses were divided into the following phases: (1) MINITRACK interferometry; early Baker-Nunn camera directions; (2) late Baker-Nunn camera directions; and (3) combined Baker-Nunn camera and TRANET Doppler data.

Kaula, W. M.↗

NASA NTRS2013

An Electric Propulsion "Shepherd" for Active Debris Removal that Utilizes Ambient Gas as Propellant

There is a growing consensus among the space debris technical community that limiting the long ]term growth of debris in Low-Earth Orbit (LEO) requires that space users limit the accumulation of mass in orbit. This is partially accomplished by mitigation measures for current and future LEO systems, but there is now interest in removing mass that has already accumulated in LEO from more than 50 years of space activity (termed "Active Debris Removal", or ADR). Many ADR proposals face complex technical issues of how to grapple with uncooperative targets. Some researchers have suggested the use of conventional ion thrusters to gently "blow" on objects to gradually change their orbits, without ever having to come into physical contact with the target. The chief drawback with these methods is the cost per object removed. Typically, a space "tug" or an ion-drive "shepherd" can only remove a few objects per mission due to limited propellant. Unless a costeffective way that removes tens of objects per mission can be found, it is not clear that any of the ideas so far proposed will be economically viable. In this paper, a modified version of the ion-drive "shepherd" is proposed that uses ambient atmospheric gases in LEO as propellant for the ion drives. This method has the potential to greatly extend the operational lifetime of an ADR mission, as the only mission limit is the lifetime of the components of the satellite itself, not on its fuel supply. An ambient-gas ion-drive "shepherd" would the local atmospheric drag on an object by ionizing and accelerating the ambient gas the target would have encountered anyway, thereby hastening its decay. Also, the "shepherd" satellite itself has a great deal of flexibility to maneuver back to high altitude and rendezvous with its next target using the ion drive not limited by fuel supply. However, the amount of available ambient gas is closely tied to the altitude of the spacecraft. It may be possible to use a "hybrid" approach that supplements high-altitude ion-drive operations with stored gas, and transitions to ambient gas at lower altitudes. This paper will include realistic numbers on the estimated times needed to deorbit objects from different orbit regimes using drives that either partially or completely take advantage of ambient gas. It will conclude with recommendations on whether this is a viable candidate for future ADR efforts.

Matney, Mark J.↗