An Innovative GPS Solution for the ORBCOMM Constellation Spacecraft

Bhavesh Patel, Wallace Walter, David Patton

Abstract:	ORBCOMM is a low cost, two-way data messaging system that uses a constellation of 36 spacecraft to provide global coverage. The constellation spacecraft require GPS for navigation and time synchronization. The GPS-provided navigation information is used onboard for magnetometer-based attitude determination and is also transmitted to ORBCOMM subscribers for terrestrial position determination. In addition, the GPS navigation data are used for ground-based orbit determination for the entire constellation. Absolute and relative time outputs from the GPS receiver are utilized by the spacecraft’s time control loops to provide microsecond level time synchronization on the spacecraft. In the presence of very tight cost, mass, power, and volume constraints, the GPS subsystem was designed using commercially available low-cost hardware and management software that was developed in-house. The Rockwell MPE-I five channel GPS receiver was modified for use onboard the ORBCOMM spacecraft. Most of the hardware, including the GPS receiver, had not flown in space prior to the ORBCOMM mission and was successfully up-screened for space flight. The result is a low cost GPS subsystem that is ideal for meeting the requirements of small spacecraft constellations. This paper provides a description of the hardware and software elements of the ORBCOMM GPS subsystem and presents flight performance data that illustrate the successful and innovative utilization of commercially available hardware to meet ORBCOMM’s navigation and time synchronization requirements.
Published in:	Proceedings of the 1999 National Technical Meeting of The Institute of Navigation January 25 - 27, 1999 Catamaran Resort Hotel San Diego, CA
Pages:	551 - 560
Cite this article:	Patel, Bhavesh, Walter, Wallace, Patton, David, "An Innovative GPS Solution for the ORBCOMM Constellation Spacecraft," Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1999, pp. 551-560.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In