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Riedel, J. E.

Publications and source records attributed to Riedel, J. E..

28 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Voyager 2 orbit determination at Neptune

In August 1989 the Voyager 2 spacecraft encountered Neptune and Triton. Precise knowledge of the trajectory of the spacecraft relative to the Neptunian system was essential to ensure successful observations during the flyby, and to perform trajectory control. Determination of the orbit of Voyager 2 with respect to the Neptunian system was accomplished by the use of radiometric Doppler, range, and VLBI observations of the spacecraft in combination with spacecraft-based optical observations of Neptune, Triton, Nereid, and the Voyager-discovered satellite 1989N1. These data types were used in a new version of the JPL Orbit Determination Program to determine the orbit of the spacecraft as well as Neptunian system ephemerides and dynamical parameters, resulting in accurate delivery of the spacecraft to targeted conditions at Neptune and Triton.

Lewis, G. D.↗
NASA NTRS1990

Ephemerides of the major Neptunian satellites determined from earth-based astrometric and Voyager imaging observations

The Voyager project used Neptunian satellite ephemerides to support both navigation and acquisition of scientific data. The development of postencounter ephemerides for the satellites Triton, Nereid, and 1989N1 is discussed. Primary results are the final set of model parameters which generate orbits that best fit both the earth-based satellite observations and data acquired by Voyager. The ephemerides are compared with those generated preencounter, and the accuracy of the final ephemerides is assessed. Mean orbital elements are also provided as a geometrical representation for the satellite orbits.

Jacobson, R. A.↗
NASA NTRS1986

Orbit determination using synthetic aperture radar

The use of synthetic aperture radar (SAR) images to estimate orbital parameters is studied. The SAR image formation process which requires the ability to repeatedly transmit identical signals and accurately sense the return echoes from a region of terrain is described. The orbit determination capabilities of the SAR system's observables are investigated. Five SAR observations were collected from a simulated shuttle orbit, which was circular with a latitude of 220 km and along-track velocity of 7.7 km/sec, to obtain along-track and line-of-sight direction position measurements; the simulation reveals that only three SAR observations were required to determine the position of the spacecraft to within 100 m. A prototype SAR orbit determination system was developed. The system consists of a VAX 11/780 time-shared computer, a frame buffer, topographic maps, and software for line-pixel location of an object within a SAR image and for orbit determination. The prototype is applied to the processing of a single short arc of Shuttle Imaging-Radar-B (SIR-B) data. It is observed that the SAR data is useful as orbit determination or tracking data; however, the low SNRs in the SIR-B data made feature identification difficult.

Taber, W. L.↗
NASA NTRS1986

Ephemerides of the Uranian satellites determined from earth-based astrometric and Voyager imaging observations

Uranian satellite ephemerides were needed by the Voyager project to support both navigation and acquisition of scientific data. This paper outlines the mathematical modeling approach taken to generate those ephemerides and discusses their pre-encounter development, real time updating, and post-encounter refinement. The results presented include the final set of model parameters which generate the ephemerides that best fit the Voyager optical data as well as the earth based observations of the satellites.

Jacobson, R. A.↗
NASA NTRS1986

Orbit determination for the Voyager II Uranus encounter

The Voyager II flyby of Uranus in January 1986 was the most distant planetary encounter ever attempted, and presented unique challenges to the process of orbit determination. Long light-times and spacecraft receiver difficulties hampered the collection of two-way radiometric data and helped bring about the maturation of a Very Long Baseline Interferometry navigational data type during the long cruise from Saturn. Planet and satellite ephemeris uncertainties necessitated the use of the onboard spacecraft optical system for Uranus-relative navigation. During the close approach phase, these optical data were combined with radiometric data to drive the Uranus system-relative uncertainties down to the level of a few tens of kilometers. This paper contains qualitative and quantitative results and conclusions based on orbit determination experience during Uranus cruise and encounter. Topics include an overview of the navigation-related mission events and requirements, and a review of the salient orbit determination results.

Taylor, T. H.↗
NASA NTRS1986

Interplanetary optical navigation - Voyager Uranus encounter

Optical observations were necessary during the Voyager II Uranus approach and encounter in order to meet mission navigational requirements. In this paper, the overall optical navigation system and operation at Uranus are outlined. The formulation of the optical observables are presented, as well as their subsequent integration into the overall orbit determination products. Optical data analysis and some resulting orbit determination results from Uranus are shown. Certain scientifically important results were natural outcomes of the optical data analysis, and these are also reviewed. Finally, certain optical navigation related problems are anticipated at the forthcoming Neptune encounter in 1989; these are briefly discussed as are plans to deal with them.

Synnott, S. P.↗
NASA NTRS1982

Performance of differenced range data types in Voyager navigation

Voyager radio navigation made use of a differenced rage data type for both Saturn encounters because of the low declination singularity of Doppler data. Nearly simultaneous two-way range from two-station baselines was explicitly differenced to produce this data type. Concurrently, a differential VLBI data type (DDOR), utilizing doubly differenced quasar-spacecraft delays, with potentially higher precision was demonstrated. Performance of these data types is investigated on the Jupiter-to-Saturn leg of Voyager 2. The statistics of performance are presented in terms of actual data noise comparisons and sample orbit estimates. Use of DDOR as a primary data type for navigation to Uranus is discussed.

Taylor, T. H.↗
NASA NTRS1982

Performance of differenced range data types in Voyager navigation

Voyager radio navigation made use of differenced range data type for both Saturn encounters because of the low declination singularity of Doppler data. Nearly simultaneous two-way range from two-station baselines was explicitly differenced to produce this data type. Concurrently, a differential VLBI data type (DDOR), utilizing doubly differenced quasar-spacecraft delays, with potentially higher precision was demonstrated. Performance of these data types is investigated on the Jupiter to Saturn leg of Voyager 2. The statistics of performance are presented in terms of actual data noise comparisons and sample orbit estimates. Use of DDOR as a primary data type for navigation to Uranus is discussed.

Taylor, T. H.↗
NASA NTRS1982

Voyager 1 and Voyager 2 Saturn encounter orbit determination

This paper contains quantitative results and conclusions from the Saturn approach orbit determination for Voyagers 1 and 2. The major topics covered include an overview of the navigation-related requirements and a review of the salient orbit determination results obtained. Special attention is paid to the use of combined spacecraft-based optical observations and earth-based radiometric observations to achieve accurate orbit determination during the Saturn encounter approach phase.

Campbell, J. K.↗