Orbcomm

ORBCOMM is a mobile satellite service provider offering high value, two-way data and message communications globally through international service licensees and in the U.S. through value-added resellers, as well as through direct sales.17 Since ORBCOMM has offered commercial service on two satellites since 1996, they could have been included in the previous section for systems available now. However, since with only two satellites the service has been limited to about 90 minutes per day, and with the full constellation going into service in mid-1998, they have been included in this section. ORBCOMM is a data-only LEO satellite system. They will offer worldwide coverage in both “real-time” and store-and-forward modes. When the user terminal or Subscriber Communicator (SC) is not within range of a a gateway Earth Station (GES), the satellite will store messages and forward them when it passes over a GES. When both the SC and the GES are within the satellite footprint, the system operates in “real-time” mode, with an end-to-end transmission time of about 5 seconds. The ORBCOMM system will provide the following services: tracking, monitoring, commercial messaging, and personal messaging. The system transmits and receives small packets of data. The Subscriber Communicators also automatically report their position using either the inherent Doppler position calculation, or GPS position if the user terminal is equipped with an embedded GPS receiver.

Space Segment

The ORBCOMM constellation will consist of up to 36 small low earth orbit (LEO) satellites orbiting at 825 km. The first two satellites were launched into near-polar orbit on 3 April 1995. These two satellites were used for testing and initial commercial service; they will probably be retired. Twenty-four satellites will be launched into circular orbit, in three planes of eight satellites each. The first eight of these were launched in December 1997. The other two planes will be launched in 1998. An additional two satellites were launched into near-polar orbit in February 1998. The full constellation of 28 is scheduled to be online by July 1998. ORBCOMM also has the option of launching an additional eight satellites, if there is sufficient demand. These are planned to be launched into a circular orbit about the Equator. ORBCOMM has plans to use two different launch vehicles. Their own Pegasus launcher can carry eight satellites into orbit. Orbital Science’s Taurus rocket can lift two satellites to orbit.

User Segment

ORBCOMM has commissioned several terminal manufacturers. They will be making models for different markets with various capabilities. Some will have embedded GPS receivers for enhanced positioning, others will have keypads and displays, and some are “black boxes” for SCADA applications. The terminals will range in cost from $250 to $1,500. All operate in the VHF band using a small whip antenna. They transmit data to the satellite at 2400 bps and receive at 4800 bps. Usage rates are not known at this time.