New and Improved GPS Satellite Constellation Availability Model

摘要

This paper describes a new and improved GlobalrnPositioning System (GPS) satellite constellationrnavailability model. As used here, improved means arnmodel that corresponds more closely to the actual GPSrnsatellite constellation availability seen in the real worldrnthan currently existing models. Realistic models are veryrnimportant in this area, since the satellite constellationrnavailability is a key factor in determining whether GPSrncan ever become a sole/primary means of navigation. Thernimprovements in this new model are primarily gained byrnaccounting for the realities of GPS satellite constellationrnmanagement. The model accomplishes this by emulatingrnthe processes for scheduling satellite downtimes, dealingrnwith the presence of on-orbit surplus satellites, andrnplanning replenishment satellite launches. Secondaryrnimprovements come from using better estimates of thernMean Time Between Failure (MTBF) and Mean Time tornRepair (MTTR) for the various classes of satellite outagernevents. The results of the new and improved model arernpresented and compared with the observed on-orbitrnhistory to serve as a qualitative validation of the model.rnThe results give an interesting prediction of what thern“steady-state” GPS satellite constellation will eventuallyrnlook like, barring any unforeseen changes in thernconstellation management processes.