GPS: THE LOGICAL TOOL FOR PRECISION TRACKING IN SPACE

Abstract

As we develop more space vehicles, a pressing requirement emerges to provide precision tracking information. This need for exact time and space-position information (TSPI) persists whether developing and testing space weapons or locating the precise position of intelligence-gathering satellites. Because this is a worldwide tracking requirement, the use of conventional tracking techniques such as radar is precluded. Fortunately the Global Positioning System (GPS) is now in place and can provide the tracking information required. GPS offers two techniques for tracking space vehicles. A GPS receiver can be installed on the vehicle to determine the position that is then relayed to a ground terminal, or a GPS frequency translator can be used to compute the vehicle position at the master groundsite. Since both techniques have been proven satisfactory, the specific tracking requirement determines the method selected. For the flight tests of the Exoatmospheric Reentry-Vehicle Interceptor Subsystem (ERIS), the GPS frequency translator technique is used. A GPS frequency translator is installed on the target (a reentry-vehicle launched on a Minuteman from Vandenberg), and a translator is also installed on the ERIS, which is launched from Meck Island in the Kwajalein Atoll. The GPS frequency translator approach was chosen for these tests for a variety of reasons, the most important of which were the limited instrumentation space on the target and interceptor, the extreme dynamics of the interceptor, the tracking accuracy required, and the range at which the operation must be tracked. For the tracking of orbiting satellites, a GPS receiver can be flown on the satellite with its derived position information continuously stored. This data can then be dumped as the satellite passes over a selected groundsite.