ORBCOMM: A Low-Earth Orbit Data Communication and Position Determination Satellite System

David C. Schoen

Abstract:	Orbital Communications Corporation has filed a petition for rulemaking and an application[l] to construct a network of low-Earth orbit satellites operating in the low VHF frequency band. The objective of the system is to provide communication of very short data messages and position determination services to very low cost user terminals. Low cost is achieved through the use of the low-Earth orbit, which minimizes power requirements and the use of VHF which minimizes the cost of the RF components. A constellation of 20 satellites in 970 km circular orbits transmit at 137-138 MHz and 400.1 MHz. Transmissions from the user terminals are received at the satellites in the 148 to 149.9 MHz band. As a satellite travels above the local horizon of a user tetminal, it creates a Doppler signature which can be used to determine the user terminal’s position. This paper describes the information transmitted by the satellites to the user terminal for position determination calculations and how it is organized to reduce the computational load on the user terminal.
Published in:	Proceedings of the 46th Annual Meeting of The Institute of Navigation (1990) June 26 - 28, 1990 Atlantic City, NJ
Pages:	147 - 150
Cite this article:	Schoen, David C., "ORBCOMM: A Low-Earth Orbit Data Communication and Position Determination Satellite System," Proceedings of the 46th Annual Meeting of The Institute of Navigation (1990), Atlantic City, NJ, June 1990, pp. 147-150.
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