ORBCOMM-FM 21, -FM 22, -FM 23, -FM 24, -FM 25, -FM 26, -FM 27, and -FM 28 were the latest to join the ORBCOMM fleet. These American spacecraft were launched at 05:06 UT on 1998 Sep 23 by a Pegasus rocket released from a L-1011 aircraft flying out of Wallops Island in Virginia (USA). The fleet enables voice and data communications from/to remote stations. Initial orbital parameters of all were similar: period 101 min, apogee 830 km, perigee 820 km, and inclination 45 deg.
These satellites were part of a commercial venture to provide global messaging services using a constellation of 26 low-Earth orbiting satellites. The planned system was designed to handle up to 5 million messages from users utilizing small, portable terminals to transmit and receive messages directly to the satellites. The first 2 satellites of the constellation (95-017A + B) experienced communication problems after launch, but were recovered and placed into operational status. The nominal 26 satellite constellation was to be deployed by 1997, with the potential for an additional 8 satellite plane and 2 more polar orbiters depending on demands for increased coverage. The vehicles were controlled from a single control center located in Dulles, VA.
The spacecraft was a circular shaped disk. Circular panels hinged from each side after launch to expose solar cells. These panels articulated in 1-axis to track the sun and provide 160W. Deployed spacecraft measured 3.6 m from end to end with 2.3 m span across the circular disks. VHF telemetry was at 57.6 kbps. The spacecraft contained an on-board GPS navigation and timing system, and 14 volt power system. Gravity gradient stabilization provided 4 degs control with magnetic torques for damping cold gas (nitrogen) propulsion system.
The spacecraft carried 17 data processors and 7 antennas and was designed to handle 50,000 messages per hour. The long boom was 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 to 400.15 MHz. The system used X.400 (CCITT 1988) addressing. Message size was 6 to 250 bytes typical (no maximum).
Facts in Brief
Launch Date: 1998-09-23
Launch Vehicle: Pegasus
Launch Site: Wallops Island, United States
Mass: 41.0 kg