Engineering Papers⌕ Search

Engineering topics

Davis, R. P.

Publications and source records attributed to Davis, R. P..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Navigation for Rendezvous and Orbit Missions to Small Solar-System Bodies

All previous spacecraft encounters with small solar-system bodies, such as asteroids and comets, have been flybys (e.g. Galileo's flybys of the asteroids Gaspra and Ida). Several future projects plan to build on the flyby experience and progress to the next level with rendezvous and orbit missions to small bodies. This presents several new issues and challenges for navigation which have never been considered before. This paper addresses these challenges by characterizing the different phases of a small body rendezvous and by describing the navigation requirements and goals of each phase. Prior to the encounter with the small body, improvements to its ephemeris and initial estimates of its physical parameters, e.g. size, shape, mass, rotation rate, rotation pole, and possibly outgassing, are made as accurately as ground-based measurements allow. This characterization can take place over years...

Helfrich, C. E.↗
NASA NTRS1994

Navigation for Low-Cost Missions to Small Solar-System Bodies

A variety of low-cost space missions planned by NASA for flight in the late 1990's and early 2000's will involve rendevous with, and orbits about, small solar-system bodies such as asteroids and comets.

low-cost missions solar system bodies asteroid exp↗
NASA NTRS1993

Galileo Satellite Tour: Orbit Determination Performance

The Galileo mission is an ambitious attempt to explore the Jovian system by spacecraft. This voyage of exploration is a logical successor to the reconnaissance voyages of Pioneers 10 and 11, Voyagers 1 and 2, and Ulysses. These spacecraft merely flew past Jupiter, spending relatively little time in its system. Galileo differs from these earlier spacecraft in that it will remain within the Jovian system, studying the planet and its four major satellites for a period of two years. Insertion into orbit around Jupiter will occur on December 7, 1995. The portion of the mission encompassing observations of Jupiter and the major and minor satellites, and magnetospheric mapping, has become known as the Jovian tour. During this period Galileo will encounter each of Europa, Ganymede, and Callisto at least three times on trajectories that will bring it to altitudes from 200 to 3100 kilometers.

Haw, R. J.↗
NASA NTRS1993

Galileo Satellite Tour: Orbit Determination

This paper discusses orbit determination results for the Galileo satellite tour. Lacking a high gain antenna, the mission will use a low gain antenna for communication and tracking. This change implies far less navigation data will be available than previously expected. A baseline orbit analysis was completed assuming this decreased data schedule. Variations on this baseline were studied to determine sensitivity to data loss. Results indicate that the probability of completing the tour is less than 90 percent, although future improvements in orbit determination promise to raise the probability of completion above 90 percent.

Haw, R. J.↗
NASA NTRS1992

Optical navigation for the Galileo Gaspra encounter

The optical navigation process as practiced during the Gaspra encounter is presented. The characteristics of image formation for a single-frame mosaic picture required the development of a new image processing algorithm to extract the optical measurements. A detailed formulation of this algorithm is presented along with the results of applying it to the pictures returned from the spacecraft.

Vaughan, R. M.↗
NASA NTRS1987

Galilean satellite tour orbit determination assessment

Results are given which demonstrate the ability of the orbit determination system to satisfy accuracy requirements in support of the Galileo Project's planned tour of Jupiter's satellites. The results are derived through the application of mission operation strategies and assumptions. It is shown that the achievement of the requisite orbit determination accuracies is predicated on the availability of optical navigation data. It is further demonstrated that the unavailability of tour optical navigation data yields not only degraded orbit determination accuracies which fail to meet propellant budget and science instrument pointing requirements, but also produces, for the planned 200 km flyby of Europa, an approximate 0.02 risk of having the spacecraft collide with the satellite.

Moultrie, B.↗
NASA NTRS1986

Voyager 2 navigation to Uranus

Navigating the upcoming Voyager 2 encounter with Uranus presents unique challenges and opportunities. Uranus will be the most distant planetary encounter carried out to date, with a 2.75 hour delay each way for communication. Furthermore, Voyager 2 is the most sophisticated spacecraft ever used for first encounter with a planetary system. In this paper the special features of the encounter are analyzed from a navigation point of view. First, the most relevant science opportunities are introduced. Then the challenges posed by the Uranian distance and geometry are outlined. The result of a detailed navigation accuracy study is presented. Finally, the unique features of optical navigation at Uranus are shown.

Gray, D. L.↗
NASA NTRS1980

Interplanetary optical navigation using Charge Coupled Devices

Charge Coupled Devices (CCD) will be used as optical navigation image detectors in space missions planned for the 1980's. This paper presents analyses directed at assessing the performance of an imaging system employing a CCD (i.e., a solid state imager (SSI)), for a Jovian satellite tour environment. CCD operating principles are summarized and methods of calculating theoretical dynamic range presented. Methods of analyzing the SSI's ability to perform the fundamental optical navigation function of imaging a target body and one or more stars, are presented. This capability is expressed as a function of SSI optical and electronic parameters and of astrophysical parameters. The influence of these factors and pointing control errors on navigation picture budgets is analyzed. The effect of the sun's glare is analyzed from the standpoint of its reduction of SSI dynamic range and increase of navigation picture budget. Radiation effects on SSI navigation imaging performance are discussed and a method of analyzing probabilities of distinguishing real from false stars presented.

Davis, R. P.↗