INTER - SATELLITE TIME TRANSFER: TECHNIQUES AND APPLICATIONS

E. Detoma, S.C. Wardrip

Abstract:	The role of the NASA Tracking and Data Rekay Satellite System (TDRSS) is to increase the volume and frequency of communication between an orbiting spacecraft and the Earth, while at the same time providing command and tracking functions with extended coverage via a network of orbiting satellites and one or more ground stations. The same concept is currently being studied and is planned by the European Space Agency (ESA) under the name of Data Relay Satellite System (DRSS). TDRSS is an answer to the increasing complexity of new satellites and space missions that, especially in the field of scientific and application satellites, are placing increasing requirements in terms of mission support. New satellites, designed for scientific missions, such as astronomical observatories, or earth applications, for remote sensing, geodesy and precise navigation, are relying on precise onboard clocks to accomplish their missions. All these spaceborne clocks require precise synchronization to some external ground reference, synchronization that must be provided as a part of the standard mission support. Since mission support is the primary role for the TDRS systems, synchronization must be provided through the same links used for telemetry, command and data acquisition. There have been many time transfer experiments, and the techniques are well known and established throughout the years. A number of experiments have evolved into operational services now available worldwide and, in the case of the GPS, even to satellites in low earth orbit. However, the requirement to provide timing support as a part of the standard support to the space missions, has resulted in NASA providing timing services to user spacecraft directly via the TDRSS. The same service is being considered for the new Advanced TDRSS (ATDRSS) and the ESA Data Relay Satellites (DRS). We will start with a brief review of the well known time transfer techniques that have been studied and tested throughout the years. We will then discuss the applicability of time transfer techniques to a timing service as provided through a TDRS/DRS System, the problems related to the choice of the timing signal within the constraints imposed by the existing systems, and the possible practical implementations, including a description of the time synchronization support via TDRSS to the Gamma Ray Observatory (GRO).
Published in:	Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting December 4 - 6, 1990 Sheraton Premiere Hotel Vienna, Virginia
Pages:	61 - 86
Cite this article:	Detoma, E., Wardrip, S.C., "INTER - SATELLITE TIME TRANSFER: TECHNIQUES AND APPLICATIONS," Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting, Vienna, Virginia, December 1990, pp. 61-86.
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