SIMPLIFIED PREDICTION EQUATIONS FOR THE NRL SATELLITE POSITION DISPLAY.
NAVAL RESEARCH LAB WASHINGTON D C
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A satellite position prediction and display equipment SPAD has been conceived and developed at NRL. Details regarding the operation and performance of the equipment have been described previously AD-622 198. The present report concerns itself primarily with the equations utilized in a digital computer for performing the position prediction computations. With periodically updated orbital elements for each satellite stored in the computer memory, these equations provide position coordinates and height above the earths surface for any satellite, at any desired time. Restricted by the limited computer speed and memory space available, the equations arrived at, in order to both satisfy the display system requirements and to meet the desired accuracy, are of a degree of complexity which places them between the basic planetary equations of celestial bodies and the much more sophisticated equations of todays space computer centers. Although modifications of the basic equations have previously been developed and reported in AD-266 596 and AD-264 949, they were successful in computing positions of only those satellites whose orbits are relatively stable. The equations of the report, which are extensions of these modified equations, are able to provide geocentric coordinate positions for those unstable satellites whose orbits are decaying rapidly. This extension is accomplished by including the time rate of change of the semimajor axis as an input orbital element and by the manner in which the period is computed.
- Spacecraft Trajectories and Reentry