Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “EPHEMERIS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Experiments for improved positioning by means of integrated Doppler satellite observations and the NNSS broadcast ephemeris

An effort to improve station position recovery using broadcast ephemeris in Doppler data reduction was studied. A comparison of precise and broadcast ephemerides, treating the former as the standard, yielded information about the state disturbance that can be associated with the broadcast ephemeris. Statistical information about the state disturbance was used with current observational data for improved position recovery. The rank deficiency problem encountered in the short arc geodetic adjustment procedure was analysed and it was deduced that the fundamental rank deficiency is six, scale information being derivable from the wavelength of transmission. Coordinate differences between stations coobserving a pass are estimable. The uncertainty of the broadcast ephemeris, now in the WGS72 system, was assessed. It was conservatively estimated that its positional uncertainty may vary between 19 to 26 m in-track, 15 to 20 m cross-track and 9 to 10 m in radial directions depending on the incidence of the epoch of observations in the interinjection period.

Arur, M. G.↗
NASA NTRS1989

Effect of ephemeris errors on the accuracy of the computation of the tangent point altitude of a solar scanning ray as measured by the SAGE 1 and 2 instruments

An analysis was made of the error in the minimum altitude of a geometric ray from an orbiting spacecraft to the Sun. The sunrise and sunset errors are highly correlated and are opposite in sign. With the ephemeris generated for the SAGE 1 instrument data reduction, these errors can be as large as 200 to 350 meters (1 sigma) after 7 days of orbit propagation. The bulk of this error results from errors in the position of the orbiting spacecraft rather than errors in computing the position of the Sun. These errors, in turn, result from the discontinuities in the ephemeris tapes resulting from the orbital determination process. Data taken from the end of the definitive ephemeris tape are used to generate the predict data for the time interval covered by the next arc of the orbit determination process. The predicted data are then updated by using the tracking data. The growth of these errors is very nearly linear, with a slight nonlinearity caused by the beta angle. An approximate analytic method is given, which predicts the magnitude of the errors and their growth in time with reasonable fidelity.

Buglia, James J.↗
NASA NTRS1990

Compensating user position for GPS ephemeris error

A method for canceling the effect of GPS ephemeris error on user position is proposed. In this method, the baseline vectors from the reference stations to the user are estimated without adjusting the GPS ephemeris. The user position is computed by adjustment using differenced data from the user and each station separately and averaging the results with weights inversely proportional to the lengths of the baselines. Alternatively, the differenced data can be averaged in a similar manner before the user position is estimated. The averaging procedure cancels most of the ephemeris error because the error is proportional to the length of the baseline. A numerical simulation is performed to demonstrate and evaluate the method. Two reference stations with perfectly known locations are assumed to be placed several hundred kilometers apart. A user receiver with a poorly known location is located between the stations. The user positions are first estimated separately using data from the user and each station and then averaged. The averaging reduces the error by about one order of magnitude.

Wu, J. T.↗
NASA NTRS2005

Solar-System Ephemeris Toolbox

NASA s Jet Propulsion Laboratory (JPL) generates planetary and lunar ephemeris data and FORTRAN routines that allow users to obtain state data for the Sun, the moon, and the planets. The JPL Solar System Ephemeris Toolbox, developed at Kennedy Space Center, is a set of functions that provides the same functionality in the MATLAB computing environment along with some additional capabilities. The toolbox can be used interactively via a graphical user interface (GUI), or individual functions can be called from the MATLAB command prompt or other MATLAB scripts and functions. The toolbox also includes utility functions to define and perform coordinate transformation (e.g., mean-of-date, true-of-date, J2000) that are common in the use of these ephemerides. An attached README file guides the user through the process of constructing binary ephemeris files, verifying correct installation, and using functions to extract state data. This process also can be performed using the GUI. Help from each toolbox function is available through MATLAB s "help" function. Many of the functions in the toolbox are MATLAB equivalents of the JPL-written FORTRAN programs and subroutines used for the same purposes. A novice can use the GUI to extract state data, while a more experienced user can use the functions directly, as needed, in his/her applications. The toolbox has been tested using MATLAB Releases 13 an

Walker, Charles F.↗
NASA NTRS2014

The Gravity Field, Orientation, and Ephemeris of Mercury from MESSENGER Observations After Three Years in Orbit

We have analyzed three years of radio tracking data from the MESSENGER spacecraft in orbit around Mercury and determined the gravity field, planetary orientation, and ephemeris of the innermost planet. With improvements in spatial coverage, force modeling, and data weighting, we refined an earlier global gravity field both in quality and resolution, and we present here a spherical harmonic solution to degree and order 50. In this field, termed HgM005, uncertainties in low-degree coefficients are reduced by an order of magnitude relative to the earlier global field, and we obtained a preliminary value of the tidal Love number k(sub 2) of 0.451+/-0.014. We also estimated Mercury's pole position, and we obtained an obliquity value of 2.06 +/- 0.16 arcmin, in good agreement with analysis of Earth-based radar observations. From our updated rotation period (58.646146 +/- 0.000011 days) and Mercury ephemeris, we verified experimentally the planet's 3: 2 spin-orbit resonance to greater accuracy than previously possible. We present a detailed analysis of the HgM005 covariance matrix, and we describe some near-circular frozen orbits around Mercury that could be advantageous for future exploration.

MESSENGER↗
NASA NTRS2019

Ephemeris refinement of 21 hot Jupiter exoplanets with high timing uncertainties

Transit events of extrasolar planets offer a wealth of information for planetary characterization. However, for many known targets, the uncertainty of their predicted transit windows prohibits an accurate scheduling of follow-up observations. In this work, we refine the ephemerides of 21 hot Jupiter exoplanets with the largest timing uncertainties. We collected 120 professional and amateur transit light curves of the targets of interest, observed with a range of telescopes of 0.3 m–2.2 m, and analyzed them along with the timing information of the planets discovery papers. In the case of WASP-117b, we measured a timing deviation compared to the known ephemeris of about 3.5 h, and for HAT-P-29b and HAT-P-31bthe deviation amounted to about 2 h and more. For all targets, the new ephemeris predicts transit timings with uncertainties of less than 6 min in the year 2018 and less than 13 min until 2025. Thus, our results allow for an accurate scheduling of follow-up observations in the next decade.

photometric↗
NASA NTRS1972

Outer planet satellite ephemeris development.

Discussion of the possible effectiveness of an earth-based ephemeris development program for the outer planet natural satellites. Technologies for obtaining and reducing photographic plates are available and new satellite theories needed for data processing are being developed. It is shown that satellite ephemeris accuracies could be reduced to hundreds of km by the end of the 1970s. An earth-based program would have great benefits to future outer planet missions requiring this level of accuracy.

Duxbury, T. C.↗
NASA NTRS1974

Ephemeris data and error analysis in support of a Comet Encke intercept mission

Utilizing an orbit determination based upon 65 observations over the 1961 - 1973 interval, ephemeris data were generated for the 1976-77, 1980-81 and 1983-84 apparitions of short period comet Encke. For the 1980-81 apparition, results from a statistical error analysis are outlined. All ephemeris and error analysis computations include the effects of planetary perturbations as well as the nongravitational accelerations introduced by the outgassing cometary nucleus. In 1980, excellent observing conditions and a close approach of comet Encke to the earth permit relatively small uncertainties in the cometary position errors and provide an excellent opportunity for a close flyby of a physically interesting comet.

Yeomans, D. K.↗
NASA NTRS1977

Development ephemeris number 96

Program tape contains two files: file one contains all software necessary to create binary file and perform ephemeris calculation on that file; file two of distributed tape contains encoded ephemeris data. These data are essentially a blocked listing of complete dump of original binary tape, with double precision data modified to special form.

Keesey, M. S. W.↗
NASA NTRS1980

Phase 1 Navstar/GPS ephemeris and space vehicle clock performance summary

The Navstar/Global Positioning System (GPS) is considered. The issue of control segment accuracy in predicting space vehicle (SV) clock and ephemeris states for broadcast to the user community is addressed. Both the highly precise ephemeris and clock prediction data blocks and the less precise (but longer period of utility) almanac data block are evaluated.

Bierman, A. B.↗
NASA NTRS1979

Experiments for improved positioning by means of integrated Doppler satellite observations and the NNSS broadcast ephemeris

A study to improve position determination using broadcast ephemeris in Doppler data reduction is presented. The uncertainty of the broadcast ephemeris was assessed, and sample autocovariances were computed for acceleration, velocity, and position considering the state disturbance as a signal. An experiment was made in which three stations coobserved 12 passes, and the removal of the radial bias resulted in a chord distance which was in better agreement with the ground survey. In the second experiment, the station positions of the first test simulated the range observations, and the autocovariance function of the acceleration signal in the Cartesian coordinate system was used in an adaptive filtering procedure to improve the state of the satellite in one pass.

Arur, M. G.↗
NASA NTRS1980

Improved Chebyshev series ephemeris generation capability of GTDS

An improved implementation of the Chebyshev ephemeris generation capability in the operational version of the Goddard Trajectory Determination System (GTDS) is described. Preliminary results of an evaluation of this orbit propagation method for three satellites of widely different orbit eccentricities are also discussed in terms of accuracy and computing efficiency with respect to the Cowell integration method. An empirical formula is deduced for determining an optimal fitting span which would give reasonable accuracy in the ephemeris with a reasonable consumption of computing resources.

Liu, S. Y.↗
NASA NTRS1985

On the orientation of ephemeris reference frames

Precession corrections, equinox motions and locations, and obliquities for the FK4 are determined from laser-ranging data only by the ephemeris-fitting method of Standish (1982) and compared with those calculated by Fricke (1971 and 1982) from optical observations. The theoretical basis of the comparison is explained, and the results are presented in a table. No significant differences are found in the equinox offset and equinox motion values, and good agreement is found in the equinox location. The ephemeris-fitting obliquity values are shown to be consistent to within 10 marcsec and to be about 20 marcsec lower than the optical values.

Standish, E. M., Jr.↗
NASA NTRS1987

GUST86 - An analytical ephemeris of the Uranian satellites

The General Uranus Satellite Theory GUST (Laskar, 1986) is used for the construction of an analytical ephemeris for the Uranian satellites. The theory is fitted against earth-based observations from 1911 to 1986, and all radio and optical data obtained during Voyager encounter with Uranus. Earth-based observations alone allow the determination of masses which are within 15 percent of the values determined by the Uranus flyby. The analysis of all the observations confirm the values of the masses obtained during the encounter (Stone and Miner, 1986) and give a complete set of dynamical parameters for the analytical theory. An analytical ephemeris, GUST86, with an estimated precision of about 100 km with respect to Uranus is obtained.

Laskar, J.↗
NASA NTRS1990

An approximation to the outer planet ephemeris errors in JPL's DE 200

The outer planet positions of JPL's recent planetary ephemeris, DE 202, have begun to show significant differences from DE 200, the basic ephemeris of the major national almanacs. The differences DE 202 - DE 200 are plotted and are assumed to approximate the errors of DE 200. For Jupiter, the difference in right ascension varies over the planet's 12 yr period between -0.1 and -0.2 arcsec throughout the century; for Saturn, the right ascension also varies over the 30 yr period, but in addition, shows a drift which reaches -0.25 arcsec at present; for Uranus, the difference is small through the first half of the century, but now has reached -0.4 arcsec; for Neptune, the error was +0.6 arcsec at 1900 and is near -1.0 arcsec by the year 2000; the error for Pluto exceeds +2.0 arcsec by the end of the century and is rapidly increasing. The declination errors are generally periodic and smaller than the right ascensions.

Standish, E. M., Jr.↗
NASA NTRS1992

Compensating For GPS Ephemeris Error

Method of computing position of user station receiving signals from Global Positioning System (GPS) of navigational satellites compensates for most of GPS ephemeris error. Present method enables user station to reduce error in its computed position substantially. User station must have access to two or more reference stations at precisely known positions several hundred kilometers apart and must be in neighborhood of reference stations. Based on fact that when GPS data used to compute baseline between reference station and user station, vector error in computed baseline is proportional ephemeris error and length of baseline.

Wu, Jiun-Tsong↗
NASA NTRS1993

PTTI-aided ephemeris calculation and rapid data link acquisition for manned space flight

Complexity of future manned space flight mission control can be significantly reduced by integrating GPS, the PTTI source, into telemetry, tracking, and command (TT&C). Future telecommunications, space tracking electronic intelligence, metrology, navigation, and data acquisition will thereby be served, including: on-board ephemeris determination, reduced synchronization time for time division multiple access (TDMA) links, and in-flight clock calibration, increasing on-board autonomy and reducing ground support costs. Manned space transportation through the first quarter of the 21st century will probably depend on a mix of vehicles, including the Advanced Manned Launch System (AMLS), the Personnel Launch System (PLS), and continued use of the Shuttle Fleet. Precise Ephemeris is important on-board for mission success, status monitoring, also for rendezvous and docking. Use of GPS can eliminate ground based tracking/processing, enhancing autonomy and reducing communications bandwidth. GPS time can simplify complicated functions used in bandwidth efficient time division multiple access (TDMA) communications, such as: precise and realtime synchronization of receive reference timing, transmit-timing and acquisition control, unique synchronization word (UW) detection, and elastic buffering. High clock accuracy provides increased signal-to-noise (S/N) ratio during acquisition, permitting narrower acquisition frequency and time windows. Spaceborne systems requirements to provide capabilities such as: refinement of the GEM-72 gravity model based on satellite tracking observations from ATS-6 to GEOS-3, relativistic clock experiments, NASA crustal dynamics program for developing space geodetic techniques to study the earth's crust, its gravity field, and earthquake mechanisms, and multi-disciplinary space geodetic tracking for studying global climatic changes are also reviewed.

Anderman, Alfred↗