IRIDIUM 97 and IRIDIUM 98 are two American IRIDIUM communications satellites that were launched by a Rockot rocket from Plesetsk at 09:34 UT on 2002 Jun 20. (Rockot is a modified SS-19 ICBM.) These two 690-kg satellites augment the fleet of in-orbit spares to 14 satellites that are intended as backup to the operational fleet of 66 IRIDIUMs. The fleet provides L-band links between mainly mobile telephones, many of which have been recently DOD/Pentagon-owned. The initial orbital parameters of both were close: period 98.0 min, apogee 670 km, perigee 658 km, and inclination 86.6 deg.
Iridium 97 and 98 are part of a commercial communications network comprised of a constellation of 66 LEO spacecraft. The system uses L-Band to provide global communications services through portable handsets. A total of 125 spacecraft were built by Lockheed for more than $700M. Commercial service began in 1998. The system employs 15-20 ground stations with a master control complex in Landsdowne, VA, a backup in Italy, and a third engineering center in Chandler, AZ. The spacecraft are 3-axis stabilized, with a hydrazine propulsion system. They have 2 solar panels with 1-axis articulation. The system employed L-Band using FDMA/TDMA to provide voice at 4.8 kbps and data at 2400 bps with a 16 dB margin. Each satellite had 48 spot beams for Earth coverage and used Ka-Band for crosslinks and ground commanding.
The constellation of 66 active satellites has 6 orbital planes spaced 30 degrees apart, with 11 satellites in each plane (not counting spares). Each satellite can have four inter-satellite links: two to neighbors fore and aft in the same orbital plane, and two to satellites in neighboring planes to either side. The satellites orbit from pole to pole with an orbit of roughly 100 minutes. This design means that there is excellent satellite visibility and service coverage, even at the North and South poles, where there are few customers.
The original concept was to have 77 satellites. This is where the name Iridium came from; Iridium is the element with atomic number 77. Because of the unique shape of the Iridium satellites' reflective antennae, the satellites focus sunlight on a small area of the Earth's surface. This results in an effect called "Iridium flares", where the satellite momentarily appears as one of the brightest objects in the night sky.
On 10 February 2009, at 16:56 GMT, the Iridium-33 satellite, which was operational at the time, collided with the defunct Russian Cosmos 2251 satellite. This was the first, and so far the only, collision, between two intact satellites. The collision created thousands of pieces of space debris.
Facts in Brief
Launch Date: 2002-06-20
Launch Vehicle: Rokot
Launch Site: Plesetsk, Russia