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| ORBCOMM System | |
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below excerpts from various specified documents are copyright ORBCOMM LLC and
are reproduced wi
ORBCOMM System Overview
A80T
SYSTEM DESCRIPTION
The ORBCOMM System is a wide area, packet switched, two-way data
communication system. Communications to and from Subscriber Communicators (SC)
to ORBCOMM Gateways are accomplished through a constellation of low-Earth orbit
(LEO) Microstar satellites (Satellites). ORBCOMM Gateways are connected to
dial-up circuits, private dedicated lines or networks such as the Internet.
The ORBCOMM System consists of a Network Control Center (NCC) that manages
the overall system worldwide and three operational segments:
- a space segment consisting
of 30 LEO Satellites;
-
a ground segment consisting
of Gateway Earth Stations (GES) and control centers located throughout the
world; and
-
a subscriber segment
consisting of communicators used by ORBCOMM System subscribers to transmit and
receive information to and from the LEO Satellites.
RF communication within the ORBCOMM System operates in the very high
frequency (VHF) portion of the frequency spectrum between 137 and 150 (MHz). The
ORBCOMM Satellites have a subscriber transmitter that provides a continuous 4800
baud stream of packet data. Each Satellite also has multiple subscriber
receivers that receive short bursts from the SCs at 2400 baud. The
ORBCOMM System is capable of providing near real-time wireless data
communications service around the world.
All communications within the ORBCOMM System must pass through an ORBCOMM
Gateway. An ORBCOMM Gateway consists of one Gateway Control Center (GCC)—the
facility that houses the computer hardware and software that manages and
monitors message traffic—and a GES. The GES provides the link between the
Satellite constellation and an ORBCOMM GCC.
EXAMPLE: Using the ORBCOMM System, a typical messaging scenario proceeds as
shown in the following sequence:
1.
An ORBCOMM System subscriber
creates a message, which is intended for receipt by another subscriber’s home
computer. Using an e-mail program on a laptop PC, the subscriber downloads the
message to a SC.
2.
The SC transmits the message
to the Satellite that receives, reformats and relays the message to a GES.
3.
The GES transmits the message
over a dedicated line to the GCC that places the message on the public switched
network for delivery to the receiver subscriber’s PC Internet provider.
4.
The receiver subscriber
downloads the message via modem from a POP3 mailbox at his Internet service provider.
5.
A message from the home base
to the subscriber follows the reverse route: PC to the Internet over a public
switched network to the GCC, GCC to GES, GES to Satellite, and finally Satellite
to SC and SC to the user display. Even “direct” subscriber-to-subscriber
transmissions must pass through an ORBCOMM Gateway.
The interrelationship of these elements is shown in the following
illustration:
SPACE SEGMENT
Constellation Coverage and Availability
The ORBCOMM System consists of 30 Satellites launched into 6 orbital
planes. ORBCOMM has received a license to launch up to 48 Satellites. The main
constellation consists of four orbital planes (planes A, B, C and D) of
eight Satellites each. The first three planes are inclined at 45° to the
equator, launched to an altitude of approximately 825 km (451 nautical or 513
statute miles) and separated 45° apart in each of the four main planes. Two
supplemental orbital planes (planes F and G), containing two Satellites each,
provide coverage from approximately 780 km altitude and are spaced 180° apart.
Plane F is inclined at 70° and plane G is inclined at 108°. The fourth plane
of eight Satellites (plane D), is to be inclined at 0° (equatorial orbit) at an
825 km altitude and spaced 45° apart. The functional design of all
Satellites—other than the first two placed in orbit—is to be substantially
identical.
Figure 4.1 illustrates the configuration of the ORBCOMM System Satellite constellation. |
Satellite Description
Twelve ORBCOMM Satellites have been launched from one Orbital Pegasus® XL
launch vehicle. Each of the Satellites comprising the ORBCOMM System Satellite
constellation is an Orbital Microstar™ Satellite. Undeployed, the Microstar
Satellite resembles a disk weighing approximately 90 lbs. (43 kg.), measuring
approximately 41 inches (1 meter) in diameter and 6.5 inches (16-cm.) in depth.
The Satellite solar panels and antennas fold up into the disk (also called the
“payload shelf”) with the remainder of the payload during launch and
deployment. Once fully deployed, its length is approximately 170 inches (4
meters) and the width of its solar panels is approximately 88 inches (2.2
meters). Figure 4.2 shows the main parts of a fully deployed Microstar
Satellite.
The Microstar Satellite electrical power system is designed to deliver
approximately 70 Watts on an orbit-average basis while in a worst case orbit.