Introduction
Orbcomm Updates
Additional satellites in orbit
Tracking
Uplink frequencies
Downlink frequencies
Launch information
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NEWS
Introduction
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LINKS
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Orbcomm is a constellation of
low earth orbiting satellites providing two-way data and positioning
service to small, portable user terminals in the VHF and UHF
frequency bands.
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| Orbcomm launched seven satellites into orbit on December 4, 1999, bringing the constellation total to 35. |
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Orbcomm is now publishing TLE's (two-line elements) on their
webpage. A very enlightened and friendly attitude that should be
duplicated by other satellite companies.
Click here to jump to their list. A great tracking program to use with those elements is "Orbcomm View" from Northern Lights Software.
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Subscriber terminals transmit data at 2400 baud up to Orbcomm spacecraft.
FCC frequency allocations are as follows:
Uplink power of 5W, frequencies between 148 and 150.05 (189 channels), at 2400 bps. Ground stations transmit feederlink information to the satellites on 149.610 MHz at 57.6 kbps. The signal is approximately 50 kHz wide. |
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Orbcomm satellites transmit to subscriber terminals at 4800 baud
using symmetric differential phase shift keying (SDPSK) modulation.
(SDPSK indicates a zero bit with a negative 90° phase shift
and a one bit with a positive 90° phase shift.)
Transmissions are right-hand circularly polarized (RHCP). Downlink sensitivity of -118 dBm with a bit error rate of 10-5, frequencies between 137 and 138 MHz (399 channels), at 4800 bps. Here are the frequencies allocated by the FCC for Orbcomm satellite downlinks:
Feederlink data is transmitted by the satellite on 137.560 MHz at 57.6 kbps. Orbcomm spacecraft also transmit a UHF beacon at 400.1 MHz via a one watt transmitter. Active subscriber downlink frequencies are:
Individual satellite frequency assignments are as follows:
The frequencies noted as "Hearsat" are derived from two-line element (TLE) data available at the Hearsat website operated by John David Corby.
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As of December 4, 1999, Orbcomm had launched 35 satellites.
Not all of them work.
The FCC has authorized Orbcomm to launch a total of 48 satellites, but plans for the remaining 13 are not finalized.
These low earth orbit (LEO) satellites are designed to communicate with low-data rate subscriber communicators (SCs) and fixed site stations.
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