SAT CRASH - Satellitenzusammenstoß - Weltraumschrott
At 16:56 UTC on February 10, 2009; a collision occurred between Iridium 33 and Kosmos 2251, a defunct Russian military communications satellite. Iridium plans to move one of its in-orbit spares into the network to replace the destroyed satellite within 30 days of the collision. This is the first time two intact satellites have collided. Iridium 33 was in active service when the accident took place but was one of the oldest satellites in the constellation, having been launched in 1997.
KOSMOS 2251
Conspiracy? Deliberate smash?
HIGHLY Unlikely.- Russians had no control over their satellite for many years
- If they had, they would have used a more valuable target. Iridium Satellites provide slow-modem speed (28k8 kbit/sec), mostly to support civilian telephony (artic stations) and NGO and disaster relief. The US military doesn't depend on the obsolete technology.
- There are many dozens of iridium satellites. Killing one of them makes not even a dent in the communication service that (the bankrupt) IRIDIUM system provides.
On 10 February 2009 at 16:56:00 UTC, Iridium 33 (97-051C) collided in orbit with the defunct Russian Kosmos 2251 satellite (93-036A). The collision occurred at 789 km altitude over the Siberian arctic, near 97.9 E, 72.5 N, with an orbital interception angle of 83.5 degrees. A cloud of rapidly spreading debris is now all that remains.
The collision occured at roughly the same altitude as the Chinese ASAT test on Fengyun 1C, and the resulting scenario for the debris cloud will be roughly similar to the latter event. An analysis of the Fengyun 1C debris field formation by Kelso can be read here.
http://sattrackcam.blogspot.com/
The collision occured at roughly the same altitude as the Chinese ASAT test on Fengyun 1C, and the resulting scenario for the debris cloud will be roughly similar to the latter event. An analysis of the Fengyun 1C debris field formation by Kelso can be read here.
http://sattrackcam.blogspot.com/
Screen shot from AGI Viewer file of Chinese ASAT scenario (five minutes post-attack)
View of ISS Orbit (green) and Debris Ring (red) from Chinese ASAT Test
Download ISS-ASAT Debris Scenario
View of LEO Satellites (green) and Debris Ring (red) from Chinese ASAT Test
Download LEO-ASAT Debris Scenario
This debris event is so large that the debris can still be fairly easily seen without doing anything to emphasize the debris cloud, although the debris ring has widened considerably over the past eleven months.
View of All Satellites including Debris Ring from Chinese ASAT Test Readily Visible
German:
(ENGLISH ARTICLE FURTHER BELOW!)
COSMOS 2251 kollidierte am 10.02.2009 gegen 18:00H CET mit IRIDIUM 33. Dabei haben sich ca. 600 Trümmerteile entwickelt. Genaue Zahlen und Vektordaten stehen noch nicht fest. Sobald diese verfügbar sind, werden die Trümmer im obigen Bild in Pink dargestellt. Iridium 33 kann im MISSION CONTROl CENTER ausgewählt und verfolgt werden. COSMOS 2421, ein russischer Marineaufklärungssatellite erzeugt Trümmerteile. COSMOS 2421 bringt es auf ca. 508 katalogisierte Teile, davon sind ca. 48 im Orbit und 444 verglüht.
Hier eine Statistik zu Cosmos2421 (30. Januar 2009):
Katalogisierte Teile: 508
On Orbit: 48
Verglüht: 444
Inklination Exentrizität Apogäum Perigäum Umlaufzeit
MIN 63,63 0,0001 232,1 227,0 89,09
MAX 66,02 0,0411 926,0 412,0 97,91
Über 600 Teile
Zerstörter Iridium-Satellit soll binnen 30 Tagen ersetzt werden.
Bei der Kollision zweier Satelliten hat sich ein riesiges Trümmerfeld gebildet, das möglicherweise für weitere Erdtrabanten gefährlich werden könnte.
Iridium World Phones
In an unprecedented space collision, a commercial Iridium communications satellite and a defunct Russian satellite ran into each other Tuesday above northern Siberia, creating a cloud of wreckage, officials said today. The international space station does not appear to be threatened by the debris, they said, but it's not yet clear whether it poses a risk to any other military or civilian satellites.
"They collided at an altitude of 790 kilometers (491 miles) over northern Siberia Tuesday about noon Washington time," said Nicholas Johnson, NASA's chief scientist for orbital debris at the Johnson Space Center in Houston. "The U.S. space surveillance network detected a large number of debris from both objects."
Air Force Brig. Gen. Michael Carey, deputy director of global operations with U.S. Strategic Command, the agency responsible for space surveillance, said initial radar tracking detected some 600 pieces of debris. He identified the Russian spacecraft as Cosmos 2251, a communications relay station launched in June 1993, and said the satellite is believed to have been non-operational for the past 10 years or so.
"As of about 12 hours ago, I think the head count was up (to around) 600 pieces," Carey told CBS News late today. "It's going to take about two days before we get a solid picture of what the debris fields look like. But you, I think, can imply that the majority of that should be probably along the same line as the original orbits."
He said U.S. STRATCOM routinely tracks about 18,000 objects in space, including satellites and debris, that are 3.9 inches across or larger. Tracking priority and "conjunction analysis" - identifying which objects may pose a threat to manned spacecraft - is the first priority.
"It's going to take a while" to get an accurate count of the debris fragments, Johnson said. "It's very, very difficult to discriminate all those objects when they're really close together. And so, over the next couple of days, we'll have a much better understanding."
Asked which satellite was at fault, Johnson said "they ran into each other. Nothing has the right of way up there. We don't have an air traffic controller in space. There is no universal way of knowing what's coming in your direction."
Iridium Satellite LLC operates a constellation of some 66 satellites, along with orbital spares, to support satellite telephone operations around the world. The spacecraft, which weigh about 1,485 pounds when fully fueled, are in orbits tilted 86.4 degrees to the equator at an altitude of about 485 miles. Ninety-five Iridium satellites were launched between 1997 and 2002 and several have failed over the years.
"Yesterday, Iridium Satellite LLC lost an operational satellite," the company said in a statement. "According to information shared with the company by various U.S. government organizations that monitor satellites and other space objects (such as debris), it appears that the satellite loss is the result of a collision with a non-operational Russian satellite.
"Although this event has minimal impact on Iridium’s service, the company is taking immediate action to address the loss. The Iridium constellation is healthy, and this event is not the result of a failure on the part of Iridium or its technology. While this is an extremely unusual, very low-probability event, the Iridium constellation is uniquely designed to withstand such an event, and the company is taking the necessary steps to replace the lost satellite with one of its in-orbit spare satellites."
Johnson said the collision was unprecedented.
"Nothing to this extent (has happened before)," he said. "We've had three other accidental collisions between what we call catalog objects, but they were all much smaller than this and always a moderate sized objects and a very small object. And these are two relatively big objects. So this is a first, unfortunately."
As for the threat posed by the debris, Johnson said NASA carried out an immediate analysis to determine whether the space station faced any increased risk. The station, carrying three crew members, circles the globe at an altitude of about 220 miles in an orbit tilted 51.6 degrees to the equator.
"There are two issues: the immediate threat and a longer-term threat," he said. "It turns out, when you have a collision like this the debris is thrown very energetically both to higher orbits and to lower orbits. So there are actually debris from this event which we believe are going through the space station's altitude already. Most of it is not, most of it is still clustered up where the event took place. But a small number are going through station's altitude.
"Yesterday, we did an assessment of what the risk might be to station and we found it's going to be very, very small. As time goes on, those debris will (come down) some over months, most over years and decades and as the big ones come down they'll be tracked, we'll see them and the worst-case scenario, we'll just dodge them if we have to. It's the small things you can't see are the ones that can do you harm."
Asked if other satellites might be at risk, Johnson said "technically, yes. What we're doing now is trying to quantify that risk. That's a work in progress. It's only been 24 hours. We put first things first, which is station and preparing for the next shuttle mission."
Most, if not all, of the debris is expected to eventually burn up in Earth's atmosphere.
THIS WAS THE WASHINGTON POST ARTICLE... NOT A GOOD INFORMATION SOURCE.
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, United States, 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.
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 were 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 hand held 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 Web site, 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.
On February 10, 2009, Iridium 33 collided with a defunct Russian satellite, Cosmos-2251, 500 miles over Siberia. A pair of massive debris clouds was created
Present status
Iridium Satellite LLC has 280,000 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 DoD pays $36 million a year for unlimited access for up to 20,000 users. An investigation was begun into the DoD contract after a protest by Globalstar, to the U.S. General Accounting Office that no tender was provided. The investigation was suspended at the request of the Pentagon, who cited national security reasons.
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 continuous data services to the station for the first time. Total bandwidth is 28.8 kbit/s.
Phone numbers
Iridium controls the virtual country codes +8816 and +8817, part of the 881 range designated by the ITU for the Global Mobile Satellite System. Each subscriber is given an 8-digit number prefixed by one of these country codes
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°. Orbital velocity of the satellites is approximately 17,000 mph (27,000 km/h). Satellites communicate with neighboring 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.
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 cellular look down antenna has 48 spot beams arranged as 16 beams in three sectors. The four inter-satellite 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 cross links. Although optical links could have supported a much greater bandwidth and a more aggressive growth path, microwave cross links were favored because the bandwidth was more than sufficient for the desired system. Nevertheless, a parallel optical cross link option was carried through a critical design review, and ended when the microwave cross links 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, inter-satellite communications links. Such cross-links are unique in the satellite telephone industry, as other providers do not relay data between satellites.
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 phone calls and weighs about 1,500 pounds (700 kg). The vast majority of patents filed by Motorola during the Iridium project concern ways to manufacture and launch satellites affordably. The satellites were designed to mount sideways on a gimbal for easy access during manufacture (most satellites up until that time had been assembled vertically.) Motorola hired the chief manufacturing engineer from Apple Computer, who had set up the first Macintosh manufacturing line, to help design and automate satellite production.
In-orbit spares
Spare satellites are usually held in a 667 kilometres (410 mi) storage orbit. These will be boosted to the correct altitude and put into service in case of a satellite failure. Many satellites have failed over the years, the most recent being Iridium 28 which failed in July 2008, and Iridium 33 which collided with the defunct Russian satellite, Cosmos-2251, on February 10, 2009. Currently, there appear to be seven spares in orbit, along with several partially failed satellites that are not in active service. Five non-functional satellites have also reentered the Earth's atmosphere.
Erste Radaruntersuchungen des US-Militärs haben ergeben, dass nach dem Zusammenstoß eines russischen Militärsatelliten mit einem US-Kommunikationssatelliten über 600 Trümmerteile zurückgeblieben seien.
Dabei handelt es sich laut NASA-Sprecher Michael Carey allerdings nur um eine erste grobe Schätzung. Genauere Daten seien erst in einigen Tagen zu erwarten, so Carey laut dem US-Sender CBS.
Radioaktive Strahlung
Während auch der russische Militärsprecher Alexander Jakuschin betonte, dass die Beschaffenheit der Trümmerwolke noch untersucht werden müsse, gab ein Weltraumexperte gegenüber der russischen Agentur Interfax zu bedenken, dass die Trümmer durchaus mit weiteren Satelliten zusammenstoßen könnten.
Eine Gefahr könnte etwa bei alten sowjetischen Spionagesatelliten entstehen, die Atombatterien an Bord haben. Bei einer Kollision mit Trümmerteilen könnten diese beschädigt werden und radioaktive Strahlung im All austreten, so der Experte weiter.
ISS-Ausweichmanöver notwendig?
Nach Ansicht des Sprechers der russischen Weltraumbehörde Roskosmos, Alexander Worobjow, bestehe allerdings für die Internationale Raumstation (ISS) "keinerlei Gefahr".
Die "Washington Post" zitierte indes ein NASA-Dokument, dem zufolge ein leicht erhöhtes Risiko für die ISS bestehe, von Satellitenschrott getroffen zu werden. Dieses Risiko halte sich aber "in akzeptablen Grenzen".
Die ISS befindet sich in nur 354 Kilometer Höhe, also deutlich unter dem Kollisionsorbit der beiden Unglückssatelliten. NASA-Sprecher John Yembrick sagte, der Schrott werde sich ausbreiten, weshalb die ISS möglicherweise ein Ausweichmanöver starten müsse. Dazu sei die Raumstation aber in der Lage, das sei ihr bereits in acht Fällen gelungen.
Spionagesatellit seit Jahren außer Betrieb
Der rund 900 Kilogramm schwere russische Satellit Kosmos-2251 der mit dem 560 Kilogramm schweren US-Satelliten Iridium-33 kollidiert war, war nach Angaben von Jakuschin seit 1993 im All und seit Jahren nicht mehr in Betrieb.
Der Aufprall ereignete sich bereits am Dienstag gegen 18.00 Uhr MEZ rund 800 Kilometer über Sibirien. Experten sprachen von einer einmaligen Kollision so großer Satelliten.
Nach Angaben des Deutschen Raumfahrt-Kontrollzentrums (DLR) in Oberpaffenhofen war es sogar der erste derartige Zwischenfall in der Geschichte der Raumfahrt. Die Wahrscheinlichkeit für einen Zusammenstoß zweier Satelliten sei "extrem gering", sagte DLR-Direktor Felix Huber der Nachrichtenagentur AFP.
3.000 Satelliten in Betrieb
Seit die Sowjetunion im Jahr 1957 mit Sputnik 1 den ersten künstlichen Flugkörper in eine Erdumlaufbahn gebracht hatte, wurden weltweit rund 6.000 Satelliten gestartet. Derzeit sind laut NASA-Angaben noch etwa 3.000 in Betrieb.
Ersatz binnen 30 Tagen
Die US-Betreiberfirma Iridium Satellite teilte indes mit, das der verloren gegangene Kommunikationssatellit binnen 30 Tagen durch einen bereits im All befindlichen Satelliten ersetzt werden soll. Zwischenzeitlich könne es zu kurzen Kommunikationsstörungen und -ausfällen kommen.
Nach eigenen Angaben betreibt Iridium Satellite ein Netzwerk von 66 Kommunikationssatelliten sowie mehreren Ersatzsatelliten im All. Die Firma betonte, die Kollision sei nicht auf technisches Versagen bei dem Iridium-Satelliten zurückzuführen.
U.S. And Russian Satellites Collide
Communications Satellite Hits Russian Satellite; International Space Station Deemed Safe
Iridium World Phones
In an unprecedented space collision, a commercial Iridium communications satellite and a defunct Russian satellite ran into each other Tuesday above northern Siberia, creating a cloud of wreckage, officials said today. The international space station does not appear to be threatened by the debris, they said, but it's not yet clear whether it poses a risk to any other military or civilian satellites.
"They collided at an altitude of 790 kilometers (491 miles) over northern Siberia Tuesday about noon Washington time," said Nicholas Johnson, NASA's chief scientist for orbital debris at the Johnson Space Center in Houston. "The U.S. space surveillance network detected a large number of debris from both objects."
Air Force Brig. Gen. Michael Carey, deputy director of global operations with U.S. Strategic Command, the agency responsible for space surveillance, said initial radar tracking detected some 600 pieces of debris. He identified the Russian spacecraft as Cosmos 2251, a communications relay station launched in June 1993, and said the satellite is believed to have been non-operational for the past 10 years or so.
"As of about 12 hours ago, I think the head count was up (to around) 600 pieces," Carey told CBS News late today. "It's going to take about two days before we get a solid picture of what the debris fields look like. But you, I think, can imply that the majority of that should be probably along the same line as the original orbits."
He said U.S. STRATCOM routinely tracks about 18,000 objects in space, including satellites and debris, that are 3.9 inches across or larger. Tracking priority and "conjunction analysis" - identifying which objects may pose a threat to manned spacecraft - is the first priority.
"It's going to take a while" to get an accurate count of the debris fragments, Johnson said. "It's very, very difficult to discriminate all those objects when they're really close together. And so, over the next couple of days, we'll have a much better understanding."
Asked which satellite was at fault, Johnson said "they ran into each other. Nothing has the right of way up there. We don't have an air traffic controller in space. There is no universal way of knowing what's coming in your direction."
Iridium Satellite LLC operates a constellation of some 66 satellites, along with orbital spares, to support satellite telephone operations around the world. The spacecraft, which weigh about 1,485 pounds when fully fueled, are in orbits tilted 86.4 degrees to the equator at an altitude of about 485 miles. Ninety-five Iridium satellites were launched between 1997 and 2002 and several have failed over the years.
"Yesterday, Iridium Satellite LLC lost an operational satellite," the company said in a statement. "According to information shared with the company by various U.S. government organizations that monitor satellites and other space objects (such as debris), it appears that the satellite loss is the result of a collision with a non-operational Russian satellite.
"Although this event has minimal impact on Iridium’s service, the company is taking immediate action to address the loss. The Iridium constellation is healthy, and this event is not the result of a failure on the part of Iridium or its technology. While this is an extremely unusual, very low-probability event, the Iridium constellation is uniquely designed to withstand such an event, and the company is taking the necessary steps to replace the lost satellite with one of its in-orbit spare satellites."
Johnson said the collision was unprecedented.
"Nothing to this extent (has happened before)," he said. "We've had three other accidental collisions between what we call catalog objects, but they were all much smaller than this and always a moderate sized objects and a very small object. And these are two relatively big objects. So this is a first, unfortunately."
As for the threat posed by the debris, Johnson said NASA carried out an immediate analysis to determine whether the space station faced any increased risk. The station, carrying three crew members, circles the globe at an altitude of about 220 miles in an orbit tilted 51.6 degrees to the equator.
"There are two issues: the immediate threat and a longer-term threat," he said. "It turns out, when you have a collision like this the debris is thrown very energetically both to higher orbits and to lower orbits. So there are actually debris from this event which we believe are going through the space station's altitude already. Most of it is not, most of it is still clustered up where the event took place. But a small number are going through station's altitude.
"Yesterday, we did an assessment of what the risk might be to station and we found it's going to be very, very small. As time goes on, those debris will (come down) some over months, most over years and decades and as the big ones come down they'll be tracked, we'll see them and the worst-case scenario, we'll just dodge them if we have to. It's the small things you can't see are the ones that can do you harm."
Asked if other satellites might be at risk, Johnson said "technically, yes. What we're doing now is trying to quantify that risk. That's a work in progress. It's only been 24 hours. We put first things first, which is station and preparing for the next shuttle mission."
Most, if not all, of the debris is expected to eventually burn up in Earth's atmosphere.
THIS WAS THE WASHINGTON POST ARTICLE... NOT A GOOD INFORMATION SOURCE.
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, United States, 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.
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 were 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 hand held 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 Web site, 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.
On February 10, 2009, Iridium 33 collided with a defunct Russian satellite, Cosmos-2251, 500 miles over Siberia. A pair of massive debris clouds was created
Present status
Iridium Satellite LLC has 280,000 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 DoD pays $36 million a year for unlimited access for up to 20,000 users. An investigation was begun into the DoD contract after a protest by Globalstar, to the U.S. General Accounting Office that no tender was provided. The investigation was suspended at the request of the Pentagon, who cited national security reasons.
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 continuous data services to the station for the first time. Total bandwidth is 28.8 kbit/s.
Phone numbers
Iridium controls the virtual country codes +8816 and +8817, part of the 881 range designated by the ITU for the Global Mobile Satellite System. Each subscriber is given an 8-digit number prefixed by one of these country codes
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°. Orbital velocity of the satellites is approximately 17,000 mph (27,000 km/h). Satellites communicate with neighboring 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.
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 cellular look down antenna has 48 spot beams arranged as 16 beams in three sectors. The four inter-satellite 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 cross links. Although optical links could have supported a much greater bandwidth and a more aggressive growth path, microwave cross links were favored because the bandwidth was more than sufficient for the desired system. Nevertheless, a parallel optical cross link option was carried through a critical design review, and ended when the microwave cross links 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, inter-satellite communications links. Such cross-links are unique in the satellite telephone industry, as other providers do not relay data between satellites.
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 phone calls and weighs about 1,500 pounds (700 kg). The vast majority of patents filed by Motorola during the Iridium project concern ways to manufacture and launch satellites affordably. The satellites were designed to mount sideways on a gimbal for easy access during manufacture (most satellites up until that time had been assembled vertically.) Motorola hired the chief manufacturing engineer from Apple Computer, who had set up the first Macintosh manufacturing line, to help design and automate satellite production.
In-orbit spares
Spare satellites are usually held in a 667 kilometres (410 mi) storage orbit. These will be boosted to the correct altitude and put into service in case of a satellite failure. Many satellites have failed over the years, the most recent being Iridium 28 which failed in July 2008, and Iridium 33 which collided with the defunct Russian satellite, Cosmos-2251, on February 10, 2009. Currently, there appear to be seven spares in orbit, along with several partially failed satellites that are not in active service. Five non-functional satellites have also reentered the Earth's atmosphere.
Stumble It!
posted at 2/15/2009 12:29:00 AM
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