Use of Low Earth Orbit Satellite Technology in the Development of a Unique Communications and Marine Positioning System

Robert W. Kelly

Abstract:	Commencing in the frost quarter of 1994 Orbital Communications Corporation of Dulles, VA, a wholly owned subsidiary of Orbital Sciences Corporation (OSC), will launch a constellation of satellites into low earth orbit (LEO) for the purpose of establishing a worldwide, low cost, messaging and data communications system with inherent position determination capability. One of the many applications for this system will be to take advantage of its dual capabilities of both communications and position determination. ORBCOMM plans to introduce it to the marine marketplace where it can be used as both a navigational tool and means of sending and receiving record traffic from anywhere on earth at low cost and using low power. The three main components of the ORBCOMM System are the space segment, ground segment, and STs (subscriber terminals). For coverage of the U.S., there will be four unmanned Gateway Earth Stations (GES) in the four corners of the U.S., one Network Control Center @ICC), and a constellation of 26 small satellites. Other countries around the world will have their own NCC and GES (the number of GES being dependent on the size of the country). To date, companies in twenty countries have signed candidate licensee agreements with ORRCOMM to procure ground segments and provide service. The space segment is comprised of 26 small communication satellites in orbit 425 miles (785 km) above the earth. The satellites relay messages between ORBCOMM Sts and the ground segment. LEO satellite systems advantages are: Lower launch costs. Less power required. Integrated position determination. Inexpensive VHF electronics, and omnidirectional VHF antennas. Excellent overall link availability. The ground segment is comprised of the unmanned GES and the NCC. Each GES has two steerable VHF antennas that track the satellites as they cross the sky. The GES and the satellites provide transparent access from the ST to the NCC. The NCC routes messages to the addressee of the message. The conventional STs are full function compact, lightweight devices with long life batteries, 5-watt transmitters, antenna, keypad and LCD screens. Many will have RS-232 data ports and some will be integrated (black box version) with GPS receivers, lap-tops and palm-top computers and other systems. With the system’s inherent position &termination capability via doppler shift and enhanced position determination capability with the integration of GPS technology into the ST, the use of the ORBCOMM system as a new generation integrated navigation/communications system is apparent.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	199 - 204
Cite this article:	Kelly, Robert W., "Use of Low Earth Orbit Satellite Technology in the Development of a Unique Communications and Marine Positioning System," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 199-204.
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