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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
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Use of known landmarks for satellite navigation

The use of known landmark measurements along with an onboard attitude reference system for estimation of both the ephemeris and attitude of an earth orbiting satellite is discussed. Simulation results are presented which show that, although known landmarks alone do not provide sufficient information to bound the uncertainty in attitude and ephemeris, they are useful in combination with other navigation aids, such as star tracking, ground tracking, or satellite tracking. An extended Kalman filter is used for optimal estimation. The result of using a smoothing algorithm is also shown.

White, R. L.↗
NASA NTRS1975

On the comparison of numerical theories of orbital motion

The requirements for the independent numerical replication of an ephemeris generated by numerical integration are examined and an investigation concerned with the duplication of the ephemeris of the numerical theory reported by Oesterwinter and Cohen (1972) is discussed. Discrepancies between the results of the investigation and the data reported by Oesterwinter and Cohen are considered. It was found very difficult to determine the cause for the discrepancies. Proposals are, therefore, made to provide together with the results of a numerical calculation sufficient information concerning the theoretical and computational basis on which the data were obtained.

Mulholland, J. D.↗
NASA NTRS1976

LS-44: An improved deep space network station location set for Viking navigation

Improved estimates for the spin axis and longitude components of the Deep Space Network station locations were obtained from post-flight processing of radio metric data received from various Mariner planetary missions. The use of an upgraded set of ionospheric calibrations and the incorporation of near-Venus and near-Mercury radio metric data from the Mariner 10 spacecraft are the principal contributing effects to the improvement. These new estimates, designated Location Set (LS) 44, have supported Viking navigation activities in the vicinity of Mars. As such, the station locations were determined relative to the planetary positions inherent in JPL Development Ephemeris (DE) 84, which was used throughout the Viking mission. The article also presents and discusses a version of LS 44 based upon the latest planetary ephemeris, DE 96.

Koble, H. M.↗
NASA NTRS1976

LANDSAT D position determination and correction study

An assessment of accuracy of the knowledge of LANDSAT D spacecraft ephemeris data, an evaluation of the impact of expected attitude and alignment accuracies and analysis of the various options for the combining of precision ephemeris and attitude data with scene image data are provided. The potential geometric correction system in order to determine overall system costs and impact on other system elements is characterized.

Source record↗
NASA NTRS1978

A demonstration of dual spacecraft tracking conducted with the Viking spacecraft during the approach phase

The potential improvements in navigation capability of dual spacecraft tracking were demonstrated using Viking approach data. Under unfavorable conditions of large plasma noise, low spacecraft declination and large earth-spacecraft distance, the dual spacecraft tracking technique improved the Viking B approach accuracy based on short-arc radio metric data, by a factor of 7, to less than 200 km at Mars orbit insertion minus 3 days. From the results of an analytical expansion and the Viking demonstration with a large intentional error in Mars ephemeris, that dual spacecraft data types are shown to be insensitive to ephemeris error. Results also reveal the potential reduction of tracking time requirements during planet approach.

Chao, C. C.↗
NASA NTRS1978

Nimbus 6 Doppler processing using the Fairbanks calibration platform

A weighted least squares processor is examined. Research conducted in support of the NASA satellite aided Search and Rescue program is presented. An estimated NIMBUS 6 ephemeris, accurate to 1.5-2.5 km and 0.5-2.5 m/s relative to a reference orbit, is obtained during the three day signal transmission period. This suggests updating the knowledge of the relay satellite ephemeris by one reference beacon is needed during the Search and Rescue demonstration.

Koch, D. W.↗
NASA NTRS1980

The Seasat Precision Orbit Determination Experiment

The objectives and conclusions reached during the Seasat Precision Orbit Determination Experiment are discussed. It is noted that the activities of the experiment team included extensive software calibration and validation and an intense effort to validate and improve the dynamic models which describe the satellite's motion. Significant improvement in the gravitational model was obtained during the experiment, and it is pointed out that the current accuracy of the Seasat altitude ephemeris is 1.5 m rms. An altitude ephemeris for the Seasat spacecraft with an accuracy of 0.5 m rms is seen as possible with further improvements in the geopotential, atmospheric drag, and solar radiation pressure models. It is concluded that since altimetry missions with a 2-cm precision altimeter are contemplated, the precision orbit determination effort initiated under the Seasat Project must be continued and expanded.

Tapley, B. D.↗
NASA NTRS1980

Precision orbit analyses in support of the Seasat altimeter experiment

It is noted that major improvements have been made in the Goddard Space Flight Center (GSFC) geodynamic models for Seasat. It is pointed out that the dominant error source in Seasat ephemeris computation is currently the uncertainty in modeling the earth's gravity field. Attention is also given to significant errors arising from atmospheric drag and solar radiation pressure modeling. It is noted that a comparison of GSFC and Naval Surface Weapons Center (NSWC) Seasat ephemerides indicate the presence of an unexplained difference of about 4 m in the location of the center of mass along the Z axis. This difference is consistent with that obtained with earlier geoid and station coordinated comparisons performed by other investigators. It is expected that future combinations of Seasat and GEOS-3 altimeter data, together with laser and Unified S-Band tracking data, will ultimately produce a gravity field which allows computations of a global Seasat ephemeris with an rms radial accuracy of about 50 cm.

Marsh, J. G.↗
NASA NTRS1981

MAGSAT data processing: A report for investigators

The in-flight attitude and vector magnetometer data bias recovery techniques and results are described. The attitude bias recoveries are based on comparisons with a magnetic field model and are thought to be accurate to 20 arcsec. The vector magnetometer bias recoveries are based on comparisons with the scalar magnetometer data and are thought to be accurate to 3 nT or better. The MAGSAT position accuracy goals of 60 m radially and 300 m horizontally were achieved for all but the last 3 weeks of Magsat lifetime. This claim is supported by ephemeris overlap statistics and by comparisons with ephemerides computed with an independent orbit program using data from an independent tracking network. MAGSAT time determination accuracy is estimated at 1 ms. Several errors in prelaunch assumptions regarding data time tags, which escaped detection in prelaunch data tests, and were discovered and corrected postlaunch are described. Data formats and products, especially the Investigator-B tapes, which contain auxiliary parameters in addition to the basic magnetometer and ephemeris data, are described.

Langel, R. A.↗
NASA NTRS1982

Spaceborne scanner imaging system errors

The individual sensor system design elements which are the priori components in the registration and rectification process, and the potential impact of error budgets on multitemporal registration and side-lap registration are analyzed. The properties of scanner, MLA, and SAR imaging systems are reviewed. Each sensor displays internal distortion properties which to varying degrees make it difficult to generate on orthophoto projection of the data acceptable for multiple pass registration or meeting national map accuracy standards and is also affected to varying degrees by relief displacements in moderate to hilly terrain. Nonsensor related distortions, associated with the accuracy of ephemeris determination and platform stability, have a major impact on local geometric distortions. Platform stability improvements expected from the new multi mission spacecraft series and improved ephemeris and ground control point determination from the NAVSTAR/global positioning satellite systems are reviewed.

Prakash, A.↗
NASA NTRS1982

Evaluation of LANDSAT-D Orbit Determination Using a Filter/Smoother (PREFER)

Simulated range and range rate data for five tracking stations were first generated using batch least squares orbit determination (GTDS). Then GTDS was used (in the differential correction mode) to produce a nominal trajectory which was input to PREFER. The GTDS differential correction (DC) run was made using models which differed from those used to produce the simulated data. These model differences were chosen to be fairly realistic approximations to the errors in the models actually used for operational orbit determination. Several different simulation runs were made with different types of model errors in order to determine the sensitivity to these errors. The nominal trajectory and the simulated measurement data were input to PREFER to produce a smoothed ephemeris file. Numerous runs of PREFER were made in which parameters describing the statistics of the model errors were varied. The likelihood function computed by the Kalman filter determined the ""best'' choice of input parameters. There was strong negative correlation between the likelihood function and the errors in the smoothed ephemeris.

Gibbs, B. P.↗
NASA NTRS1984

An integrated software system for geometric correction of LANDSAT MSS imagery

A system for geometrically correcting LANDSAT MSS imagery includes all phases of processing, from receiving a raw computer compatible tape (CCT) to the generation of a corrected CCT (or UTM mosaic). The system comprises modules for: (1) control of the processing flow; (2) calculation of satellite ephemeris and attitude parameters, (3) generation of uncorrected files from raw CCT data; (4) creation, management and maintenance of a ground control point library; (5) determination of the image correction equations, using attitude and ephemeris parameters and existing ground control points; (6) generation of corrected LANDSAT file, using the equations determined beforehand; (7) union of LANDSAT scenes to produce and UTM mosaic; and (8) generation of output tape, in super-structure format.

Parada, N. D. J.↗
NASA NTRS1986

Reference frame studies at JPL/CALTECH

Studies being undertaken in order to interconnect the three principal celestial coordinate systens are reviewed. These systems are the optical frame (FK4/FK5) based on positions of Galactic stars, the planetary/lunar ephemeris frame based on the major celestial bodies of the solar system, and the radio frame constructed from observations of quasars. The optical frame is being connected to the radio frame by VLBI observations of radio-emitting stars, and the radio frame is being tied to the ephemeris frame in several ways; for example, differential VLBI measurements between quasars and planet-orbiting spacecraft. Prospects for future interconnection studies are briefly discussed.

Dickey, J. O.↗
NASA NTRS1987

Using a horizon sensor for Mars observer spacecraft attitude control

A modified earth horizon sensor design is proposed for the Mars Observer mission. The horizon sensor modification are based on Mars horizon radiance profiles. Attention is given to the Mars Observer's attitude control system, whose primary mode is horizon sensor-based and therefore obviates the use of an onboard spacecraft ephemeris; control accuracy of the order of 10 mrad 3sigma/axis is achieved. The attitude control system's second, celestial-backup mode, wich requires greater operational effort, employs an onboard celestial sensor as the spacecraft ephemeris; its control accuracy is of the order of 8 mrad 3sigma/axis.

Langmaier, J. K.↗
NASA NTRS1987

Potential GPS user architecture for the NASA Space Station based on Landsat 4/5 experience

A Landsat 4/5 GPS system is described which uses an inertial reference attitude control system and precision real-time ephemeris generation to achieve precision earth pointing. The system has application to the validation of the use of GPS for the low earth orbit navigation of the Space Station. The present system consists of a receiver/processor assembly (R/PA), an L-band GPS antenna, a precision oscillator, and the Landsat computer. The R/PA is integrated with a GPS receiver which selects, acquires, tracks, times, and decodes navigation signals from GPS satellites in order to derive ephemerides. Ephemeris estimates were found to be accurate to better than 50 meters.

Korenstein, David A.↗
NASA NTRS1989

Bounds on dark matter in solar orbit

The possibility is considered that a spherical distribution of dark matter (DM), matter not visible with current instruments, is trapped in the sun's gravitational field. Bounds are placed from the motion of Uranus and Neptune, on the amount of DM that could be so trapped within the radius of those planets' orbits, as follows: from the Voyager 2, Uranus-flyby data new, more accurate ephemeris values are generated. Trapped DM mass is bounded by noting that such a distribution would increase the effective mass of the sun as seen by the outer planets and by using the new ephemeris values to bound such an increase.

Anderson, John D.↗
NASA NTRS1990

Navigational utility of high-precision radio interferometer for Galileo's approach to Jupiter

The effect of very long baseline interferometry (VLBI) measurements of 2-nanoradian (nrad) accuracy has been studied for use in Galileo's approach to Jupiter's moon Io. Of particular interest is reducing the error in the minimum altitude above Io's surface. The nominal tracking strategy includes Doppler, range, and onboard optical data, in addition to VLBI data with 25-nrad accuracy. For nominal data, the altitude error is approximately 250 km with a data cutoff of 19 days before closest approach to Io. A limited number (two to four) of 2-nrad VLBI measurements, simulating a demonstration of improved VLBI data, were found to reduce the altitude error by 10 to 40 percent. Improving the accuracy of the VLBI measurements of the nominal tracking strategy to 2 nrads, to simulate the results from an operational few-nrad VLBI capability, was found to reduce the altitude error by an approximate factor of four. This reduction in altitude error is attributed to the ability that VLBI data give to help determine the along-track component of Jupiter's ephemeris. This capability complements the ability of the onboard optical data to determine the radial and cross-track components of Jupiter's ephemeris.

Folkner, W. M.↗
NASA NTRS1991

A search for stellar occultations by Uranus, Neptune, Pluto, and their satellites: 1990-1999

A search for occultations of stars by Uranus, Neptune, and Pluto between 1990 and 1999 was carried out by combining ephemeris information and star positions using very accurate occultation modeling software. Stars from both the Space Telescope Guide Catalog and photographic plates taken by Arnold Klemola at Lick Observatory were compared with planet positions from the JPL DE-130 ephemeris, with local modifications for Pluto and Charon. Some 666 possible occultations by the Uranian ring, 143 possible occultations by Neptune, and 40 possible occultations by Pluto and/or Charon were found among stars with visual magnitudes as faint as 16. Before the star positions could be obtained, the occultation prediction software was used to aid many observers in observing the occultation of 28 Sagitarii by Saturn in July 1989. As a test on other outer solar system objects, 17 possible occultations were found in a search of the Guide Star Catalog for occultations by 2060 Chiron, and interesting object between Saturn and Uranus which shows both cometary and asteroidal properties.

Mink, Douglas J.↗