RFIridium Satellite System and Constellation Overview
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This article provides an overview of the Iridium satellite system, including its features and the Iridium satellite constellation. It covers the basics of the constellation, its location, operating frequencies, and how it works with satellite phones.
Introduction
The Iridium system was the first satellite communication system to offer true global coverage with a single worldwide phone number. It’s a great solution for business professionals who travel extensively. It also provides communication to underserved rural and inaccessible areas. Common applications include maritime communications, defense, and disaster relief teams.
System Components
The Iridium satellite system is composed of three key elements:
- 66 Low Earth Orbit (LEO) Satellites: This is the core of the network.
- Iridium Phone: The user’s communication device.
- Earth Stations/Gateways: These connect the satellite network to terrestrial networks.
The system utilizes different frequency bands for communication:
- L-Band: Used for communication between the Iridium phone and the satellite.
- Ka-Band: Used for communication between the satellites and earth stations, as well as between satellites themselves (inter-satellite links).
Features & Description
| Feature | Description |
|---|---|
| Location | Above the Earth’s surface at an altitude of 780 km in 6 polar planes. There are approximately 11 operational satellites in each plane. |
| Number of Satellites | 66 operational satellites and 9 spare satellites. |
| Operating Frequency | L-band for Iridium terminal (1616 to 1626.5 MHz uplink and downlink). Ka-band for inter-satellite links (23.18 to 23.38 GHz). Ka-band for gateway links (uplink from 29.1 to 29.3 GHz and downlink from 19.4 to 19.6 GHz). |
| Coverage Area/Satellite | 4000 km. |
| Signaling | Gateway to International Switching Center: PCM transmission and SS7-ISUP/MFCR2. Iridium telephone: FDMA/TDMA with D-QPSK. |
| Data Rate | 2.4 KBPS. |
| Applications | Voice (2.4 Kbps vocoder), Paging (4 lines with up to 80 characters display), Data (2.4 Kbps two-way), Fax, etc. |
Iridium Satellite Constellation
As shown above, the Iridium constellation consists of 66 satellites arranged in 6 orbital planes. The orbit height is 780 km above the Earth. The orbital planes are inclined at an angle of 86.4 degrees. Each satellite completes one orbit around the Earth in approximately 100 minutes and 28 seconds. This is known as the orbital period.
