Iridium (satellite)


The Iridium satellite constellation is a system of 66 active communication satellites with spares in orbit and on the ground. It allows worldwide voice and data communications using handheld satellite phones. The Iridium network is unique in that it covers the whole earth, including poles, oceans and airways.
The company, based in Bethesda, Maryland, US, derives its name from the chemical element iridium; the number of satellites projected in the early stages of planning was 77, the atomic number of iridium, evoking the metaphor of 77 electrons orbiting the nucleus.
The satellites are frequently visible in the night sky as satellite flares – a phenomenon typically observed as short-lived bright flashes of light.

History

Iridium communications service was launched on November 1, 1998. The first Iridium call was made by then-Vice President of the United States Al Gore. Motorola provided the technology and major financial backing.
The founding company went into Chapter 11 bankruptcy nine months later on August 13, 1999. The handsets could not operate as promoted until the entire constellation of satellites was in place, causing a massive initial capital cost running into the billions of dollars. The increased coverage of terrestrial cellular networks (e.g. GSM) and the rise of roaming agreements between cellular providers proved to be fierce competition. The cost of service was prohibitive for many users, and the bulkiness and expense of the handheld devices when compared to terrestrial cellular mobile phones discouraged adoption among potential users.
Mismanagement has also been cited as a major factor in the original program's failure. In 1999, CNN writer David Rohde detailed how he applied for Iridium service and was sent information kits, but was never contacted by a sales representative. He encountered programming problems on Iridium's website, and a "run-around" from the company's representatives. After Iridium filed bankruptcy, it cited "difficulty gaining subscribers".

The initial commercial failure of Iridium had a dampening effect on other proposed commercial satellite constellation projects, including Teledesic. Other schemes (Orbcomm, ICO Global Communications, and Globalstar) followed Iridium into bankruptcy protection, while a number of other proposed schemes were never constructed.
At one stage there was a threat that the Iridium satellites would have to be de-orbited;however, they remained in orbit and operational. Their service was restarted in 2001 by the newly founded Iridium Satellite LLC, which was owned by a group of private investors. Although the satellites and other assets and technology behind Iridium were estimated to have cost on the order of US$6 billion, the investors bought the firm for about US$25 million.

Present status
Iridium Satellite LLC claims to have 285,000 subscribers as of early August 2008 (compared to 203,000 in July 2007). Revenue for the second quarter of 2008 was US$81.7 million with EBITDA of US$25.8 million.
The system is being used extensively by the U.S. Department of Defense through the DoD gateway in Hawaii.The commercial gateway in Tempe, Arizona, provides voice, data, and paging services for commercial customers on a global basis. Typical customers include maritime, aviation, government, the petroleum industry, scientists, and frequent world travelers.
Iridium satellites are now an essential component of communications with remote science camps, especially the Amundsen-Scott South Pole Station. As of December 2006, an array of twelve Iridium modems was put online, providing 24/7 data services to the station for the first time. Total bandwidth is 28.8 kbit/s, making real time e-mail conversations finally possible.

Subscriber equipment
Handsets
The former Iridium provided phones from two vendors, Kyocera and Motorola. Neither still manufacture these handsets. The Motorola phone 9500 is a design from the first commercial phase of Iridium, whereas the current 9555 model is the most current version of the handset and was released in October 2008. Until the release of the 9555 the 9505A was the sole handset sold by the company - a phone functionally identical clone of the Motorola 9505 with some slightly different components.
Kyocera phone models SS-66K and SD-66K are no longer in production but still available in the second-hand and surplus market. The SD-66K phone was a small 900 MHz GSM phone that fitted in a cradle (KI-G100) that included a large antenna and facilitated connection to the Iridium network.The SS-66K was a self contained phone, but featured a rather unusual ball antenna.
All handsets can receive SMS, but only the 9505, 9505A, 9555 and those based on the 9522 can send them.

Pagers
Two pagers were made for the Iridium network - the Motorola 9501 and Kyocera SP-66K these are one-way devices that could receive messages delivered in the form of SMS.
Other satellite phones
Several other Iridium based telephones exist such as payphones, bag phones and car phones and equipment intended for installation on ships and aircraft. A handset made by NAL research combined with a 9522 transceiver is used for some of these products. The DPL handset provides a user interface nearly identical to that of the 9505 series phones.

Standalone transceiver units
These can be used for data-logging applications in remote areas, now a common practical use for Iridium's services. Some types of buoys such as those used for the tsunami warning system use Iridium satellites to communicate with their base. The remote device is programmed to call or send SBD messages to the base at specified intervals, or it can be set to accept calls in order for it to offload its collected data.
The 9522A is the most current version of the OEM L-Band Transceiver module designed for integration into specific applications. It is based upon the original 9522 transceiver made by Motorola. Several variants of this modem exist, some with built in GPS receivers and autonomous position reporting capabilities. The 9522 provides audio, RS-232 and power supply connectors through a DB-25 connector and supports voice calls, SMS and low-speed data calls. Recent versions of the 9522 are able to send and receive SBD messages.
The 9601 modem supports only SBD and several tracking devices and other products have been built around this modem. It is the only mass produced Iridium transceiver that does not use a SIM card, instead it only uses its IMEI number for identification.

Services
Calls to Iridium phones are notoriously expensive, ranging from US$3 to US$14 per minute. It is possible to call with charges reversed by first dialing a number in Arizona; the call is charged to the receiver at the standard rate for satellite to landline calls, but the caller only pays for the call to Arizona.
Since Iridium will not sell prepaid cards or even its subscription call service directly, it is hard to obtain the exact price of making a call. There are numerous distributors that will activate Iridium phones and sell pre-paid vouchers and SIM cards.

Voice and data calls
The Iridium system deals with 'minutes' which are subdivided into several much smaller 'units'. These minutes are the "basic rate" to landlines and ordinary mobile phones around the world. For a 500 minute annual plan the cost of the "basic rates" fluctuates around US$1.50/min depending on a distributor. There are also regional plans that offer slightly cheaper rates than the normal, but these minutes can only be used in a specified geographic location (such as Africa, North America, Canada or Alaska).

* Calls to landlines worldwide: 1.00× basic rate
* Calls to other Iridium phones or voice mail: 0.50×
* Sending SMS messages: 0.33×
* Calls to other satellite phones: 5–13.50×
* Data calls: 1.00×

Iridium and other satellite phones may be identifiable to the listener by the "clipping" effect of the data compression and the latency (time delay) due to the electronic equipment used and the distances the signal must travel. The voice codec used is called Advanced Multi-Band Excitation.
Iridium operates at only 2.2 to 3.8 kbps, which requires very aggressive voice compression and decompression algorithms. Latency for data connections is around 1800 ms round-trip using small packets.
Despite the bandwidth limitations, transparent TCP/IP is supported. Iridium claims data rates up to 10 kilobits per second for their "direct internet" service. Phones can be connected to computers using a RS-232 connection, as can the 9522A transceiver module.

Technical details

The Iridium system requires 66 active satellites in orbit to complete its constellation, with spare satellites in orbit to serve in case of failure. Satellites are in low Earth orbit at a height of approximately 485 miles (780 km) and inclination of 86.4°. Satellites communicate with neighbouring satellites via Ka band intersatellite links. Each satellite can have four intersatellite 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 at the North and South poles, where there are few customers. The over-the-pole orbital design produces a "seam" where satellites in counter-rotating planes next to one another are travelling in opposite directions. Cross-seam intersatellite-link handoffs would have to happen very rapidly and cope with large Doppler shifts; therefore, Iridium supports intersatellite links only between satellites orbiting in the same direction.

The cellular lookdown antenna has 48 spot beams arranged as 16 beams in three sectors. The four intersatellite cross links on each satellite operate at 10 Mbit/s. The inventors of the system had previously worked on a government study in the late 1980s that showed that microwave cross links were simpler and had fewer risks than optical crosslinks. Although optical links could have supported a much greater bandwidth and a more aggressive growth path, microwave crosslinks were favored because the bandwidth was more than sufficient for the desired system. Nevertheless, a parallel optical crosslink option was carried through a critical design review, and ended when the microwave crosslinks were shown to support the size, weight and power requirements allocated within the individual satellite's budget. In recent press releases, Iridium Satellite LLC has stated that their second generation satellites would also use microwave, not optical, intersatellite communications links. Such cross-links are unique in the satellite telephone industry, as other providers do not relay data between satellites.

The existing constellation of 66 satellites is expected to remain operational until at least 2014, with many satellites expected to remain in service until the 2020s. Iridium is planning a new generation of satellites with improved bandwidth to be operational by 2016. This system will be backward compatible with the current system. In August 2008, Iridium selected two companies - Lockheed Martin and Thales Alenia Space - to participate in the final phase of the procurement of the next generation satellite constellation, with the winner to be announced in mid-2009.

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