Orbcomm is a commercial venture to provide global messaging services using a constellation of 26 low-Earth orbiting satellites. The planned system is designed to handle up to 5 million messages from users utilising small, portable terminals to transmit and receive messages directly to the satellites. The first two satellites of the constellation experienced communications problems after launch, but were recovered and placed into operational status. The nominal 26 satellite constellation will be deployed by 1997, with the potential for an additional 8 satellite plane and two more polar orbiters depending on demands for increased coverage. The vehicles will be controlled from a single control centre located in Dulles, Virginia. The cost per satellite has been estimated at $1.2 million. A small forerunner vehicle, Orbcomm-X, was launched in 1991 as a feasibility demonstration. This vehicle had a different design than the operational vehicles and will not be included in the operational system.
Spacecraft: Circular disk shaped spacecraft. Circular panels hinge from each side after launch to expose solar cells. These panels articulate in 1-axis to track the sun and provide 160W. Deployed spacecraft measures 3.6 m from end to end with 2.3 m span across the circular disks. VHF telemetry at 57.6 kbps. On-board GPS navigation and timing system.14 volt power system. Gravity gradient stabilisation provides 5 degrees control with magnetic torquers for damping. Cold gas (nitrogen) propulsion system. Payload: Each spacecraft carries 17 data processors and seven antennas. Designed to handle 50,000 messages per hour. Long boom is a 2.6 meter VHF/UHF gateway antenna. Receive: 2400 bps at 148 - 149.9 MHz. Transmit: 4800 bps at 137 - 138 MHz and 400.05 - 400.15 MHz. The system uses X.400 (CCITT 1988) addressing. Message size is 6 to 250 bytes typical (no maximum).
$ 330 million program. 3 planes x 8 satellites. First satellite lost but put back into operation May 22 1995. Satellite costs $ 135 million for 26 units.
Design Life: 4 years. Total Length: 0.2 m. Maximum Diameter: 1.1 m. Total Mass: 22 kg.
Store and forward communication.
Plane B. Ascending node 61.1 degrees.
Plane C. Ascending node 178 degrees.