Iridium (satellite)
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The Iridium satellite constellation is a system of 66 active communication satellites and spares around the Earth. The system was originally to have 77 active satellites, and as such was named for the element iridium, which has atomic number 77. The original name was retained even though the number of active satellites is less than planned (the element with atomic number 66 is called dysprosium, which in Greek means "hard to get at/hard to get in contact with" and thus was unacceptable). Iridium allows worldwide voice and data communications using handheld devices. The service is interdicted due to American embargoes in North Korea, Iran, Libya and Sudan.
The satellites used are frequently visible in the night sky as short-lived bright flashes, known as Iridium flares.
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[edit] History
Iridium communications service was launched on November 1, 1998 and went into Chapter 11 bankruptcy on August 13, 1999. The first Iridium call was made by then-Vice President of the United States Al Gore.
Its financial failure was largely due to insufficient demand for the service. 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 also prohibitive for many users, despite the continuous worldwide coverage of the Iridium service. In addition, the bulkiness and expense of the handheld devices when compared to terrestrial cellular mobile phones discouraged adoption among users.
Mismanagement has also been cited as a major factor in the 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 its "difficulty [in] gaining subscribers".
The initial commercial failure of Iridium has 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 proposed schemes were never constructed.
The Iridium satellites, however, remained in orbit, and their services were re-established in 2001 by the newly founded Iridium Satellite LLC, owned by a group of private investors who bought the company for $25 million.
[edit] Present status
The system is being used extensively by the U.S. Department of Defense for its communication purposes 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 Satellite LLC claims to have approximately 169,000 subscribers as of November 8th, 2006, a 19% increase from the total as of December 31, 2005. Revenue for the calendar year 2005 was up 55% over 2004. As the outlook is good, new satellites are planned to be launched after 2010. The new satellites have already been manufactured and the company does not plan to manufacture additional satellites until 2020.
Phone rates from land lines to Iridium phones are $3 to $14 per minute, from Iridium to land lines about $1.50 per minute and between Iridium phones less than $1 per minute. Iridium and other satellite phones may be identifiable to the listener because of the particular "clipping" effect of the data compression and the latency (experienced as a noticeable lag or time delay) due to the electronic equipment used and the distances the signal must travel. Iridium operates at a data rate of 2400 baud, which requires very aggressive voice compression and decompression algorithms. The voice codec used is called Advanced Multi-Band Excitation. Iridium claims data rates up to 10 kilobits per seconds for their 'direct internet' service. Phones can be connected to computers using a RS-232 connection, as can the 9522A which is just a tranceiver module. These can be used for data-logging applications in remote areas. This is a common practical use for Iridium's services and the new Tsunami warning system uses Iridium satellites to communicate with their base. The remote device must be programmed to call base on specified intervals, or can be set to accept calls in order for it to offload its collected data.
The former Iridium provided phones from two vendors, Kyocera and Motorola. Neither still manufacture handsets. Kyocera phone models SS-66K and SD-66K are no longer in production, but still available in the second hand and surplus market. The Motorola phone 9500 is a design from the first commercial phase of Iridium, whereas the current 9505A model is the most current version of the handset and the 9522A is the most current version of the OEM L-Band Transceiver module designed for integration into specific applications.
Iridium phone numbers all start with +8816 or +8817 (which is like the country code for a virtual country) and the 8-digit phone number.
[edit] Technical details
[edit] The constellation
The Iridium system requires 66 active satellites in orbit to complete its constellation, with spare satellites in orbit to fill in case of failure. Satellites are in low Earth orbit at a height of approximately 485 miles. Satellites communicate with neighbouring satellites via 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. Because satellites use an over-the-pole orbital constellation design there is 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; Iridium only supports intersatellite links 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 cross links were originally envisioned to be optical, however future satellites may be equipped with optical links. Such cross-links are unique in the satellite telephone industry as other providers such as Globalstar depend on local base stations and do not relay data between satellites. This in turn means that calls between satellite phones are cheaper, as many such calls never get passed through a ground-based repeater station.
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 2020's. Iridium currently has about a dozen of the original satellites on the ground waiting to be launched but doesn't plan to launch them until at least 2010 and doesn't plan to produce any new satellites until at least 2020
[edit] The satellites
The satellites each contain seven Motorola/FreeScale PowerPC 603E processors running at roughly 200 MHz. Processors are connected by a custom backplane network. One processor is dedicated to each cross-link antenna ("HVARC"), and two processors ("SVARC"s) are dedicated to satellite control — one being a spare. Late in the project an extra processor ("SAC") was added to perform resource management and phone call processing.
The original design envisioned a completely static 1960s "dumb satellite" with a set of control messages and time-triggers for an entire orbit that would be uploaded as the satellite passed over the poles. It was found that this design did not have enough bandwidth in the space-based backhaul to upload each satellite quickly and reliably over the poles. Therefore, the design was scrapped in favor of a design that performed dynamic control of routing and channel selection late in the project, resulting in a one year delay in system delivery.
Each satellite can support up to 1100 concurrent phonecalls.
[edit] Earth base-stations
Iridium routes phone calls through space. There are four earth stations and the space-based backhaul routes phone call packets through space to one of the downlinks ("feeder links"). Station-to-station calls can be routed directly through space with no downlink. As satellites leave the area of an Earth base station the routing tables change and frames are forwarded to the next satellite just coming into view of the Earth base station.
[edit] Patents
The main patents on the Iridium system are in the area of mass production of satellites. Iridium made a key hire of the engineer who set up the automated factory for Apple's Macintosh, and he created the technology necessary to mass-produce satellites in weeks (instead of months or years) on a gimbal, at a record low cost of only $5 million per satellite ($40M including launch costs, 1998 dollars.)
[edit] Quotes
- "Iridium will succeed because every time we estimated the growth of cellular phones, we were LOW by a factor of four" - Bary Bertiger of Motorola, system inventor.
[edit] See also
[edit] External links
- So how do you order Iridium satellite service? (CNN)
- Iridium 9500 Phone Documentation and Manuals (PDF)
- Iridium 9505 Phone Documentation and Manuals (PDF)
- Details of the Iridium system'
- Technical success and economic failure (MIT)de:Iridium (Kommunikationssystem)
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