Introduction
Orbcomm Generation 2
Orbcomm Updates
Additional satellites in orbit
Tracking
Uplink frequencies
Downlink frequencies
Magellan GSC 100
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 is in the process of deploying 18 second generation (OG2) satellites,
built by Sierra Nevada Corporation.
The first satellite was lost on October 10, 2012, three days after launch.
The remaining 17 satellites will be launched via two SpaceX Falcon 9 rocket missions,
inserting the satellites into four orbital planes of
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AIS-equipped Orbcomm satellites are capable of receiving signals between
161 and 163 MHz. Initially they will receive maritime AIS transmissions
on 161.975 MHz (Channel 87B) and 162.025 MHz (Channel 88B).
Under a demonstration contract with the U.S. Coast Guard, AIS data will be received by the satellite and sent back down in the feederlink. |
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Orbcomm launched six satellites
into orbit on June 19, 2008, from Kapustin Yar, Russia. These satellites
are equipped with Automatic Identification System (AIS) payloads.
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 network data page. 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 and 150.025 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.) The phase shifts
are filtered via a 0.4 root-raised cosine (RRC) filter.
Information bits are differentially encoded (each bit is exclusive-ORed with the previous bit) in a Non-Return to Zero Mark (NRZ-M). The spacecraft can vary the downlink power from 10 to 40 Watts. EIRP is about 12 dBW. 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 (unmodulated carrier) at 400.1 MHz via a one watt transmitter and a small RHCP antenna. 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. Data on the downlink is packetized and contains user data as well as satellite position and velocity information derived every four seconds from the on-board Rockwell MPE-II GPS receiver. Data words are 8 bits, with the LSB transmitted first. A minor frame is one second long, containing 4800 bits (600 words). A major frame is 16 minor frames.
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The GSC-100 provides handheld, two-way, electronic mail text messaging
capability via Orbcomm. It also contains an integrated Magellan Global
Positioning System (GPS) receiver.
The GSC-100 measures 8" (h) x 3.5" (w) x 1.75" (d) and weighs 37 ounces. The waterproof transceiver can be used as a hand-held terminal, operating on its rechargeable NiCad battery pack, or it can be bracket-mounted and operated by a 10-35 VDC external power source. Discontinued in December 2001. |
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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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