Engineering topics

Williamson, R. G.

Publications and source records attributed to Williamson, R. G..

44 records · Page 3

NASA NTRS1974

Lunar gravity analysis results from Explorer-49

An analysis of the lunar gravity field utilizing 234 days of Explorer-49 mean Keplerian elements is presented. A third-degree and third-order gravity model developed at the Goddard Space Flight Center (GSFC) for mission operations is compared with published models derived from Lunar Orbiter data. Improved predictions of e and Omega using the GSFC model are observed. The results suggest that use of Explorer-49 orbital data in a multisatellite solution would lead to improved global estimates of low-order spherical harmonic coefficients of the lunar gravitational potential.

Bryant, W. C., Jr.↗

NASA NTRS1974

The ROAD program

The philosophy, history, operation, calibration of and some analyses with the ROAD (Rapid Orbit Analysis and Determination) program are described. This semi-numeric trajectory program integrates and analyses mean element variations for earth orbits with great efficiency. Through it's use, extensive zonal, resonant harmonic and earth tidal determinations have been made at Goddard Space Flight Center since 1969.

Wagner, C. A.↗

NASA NTRS1974

Techniques for evaluating long periodic orbit variations

A method of analyzing long periodic variations of orbits from osculating elements is presented. A precision of 0.03 arc sec in inclination has been achieved with this technique for the GEOS 1 and 2 orbits. A combined numerical-analytical technique for computing mean elements is also described. This method has given mean elements with a precision of 0.1 arc sec in inclination and 10 cm in semimajor axis for the GEOS satellites. Application of these techniques to the determination of earth tidal parameters is also discussed.

Douglas, B. C.↗

NASA NTRS1972

Tidal perturbations on the orbits of GEOS-1 and GEOS-2

Analysis of the luni-solar tidal perturbations of the inclination of GEOS-1 (1965-89A) and GEOS-2 (1968-002A) yielded the values k2 = 0.22 (sigma = 0.02) and 0.31 (sigma = 0.01) respectively for the second degree Love number. For GEOS-1 a new, purely numerical method involving osculating elements was employed. For GEOS-2 it was necessary to analyze the variations of the mean elements because of the very long period (450d) of the dominant solar tidal perturbation. An additional analysis of the variation of the mean elements of GEOS-1 confirmed the value of k2 obtained from the osculating elements.

Douglas, B. C.↗

NASA NTRS1971