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Satellite traffic problems

by Redazione FGB [1], 24 February 2009

When I am looking up at the stars on a cold clear winters night I often see what I presume are Satellites passing over, fast moving objects traveling in a straight line from one horizon to the other. The International Space Station is also clearly visible to the naked eye, and any monthly astronomy publication will show you how to locate it.

NASA monitor the 18000 or so objects of medium dimension that currently orbit the Earth, including the more or less 900 working satellites, replacement machines already in orbit and awaiting activation, various other now defunct machines dating back to the late 1950's and other objects that have been lost in space (an example is of a tool bag dropped by an astronaut during a space walk). They can pick up objects about the size of an orange and they produce a statistical analysis of the probability of a collision between two or more of these various objects. They then publish a list of possible flash points and near misses on the basis of their calculations. They do not however calculate the risk for all of the objects in orbit. This analysis is complicated however by the fact that objects may change their orbit due to the effects of solar radiation and moon and Earth gravity. The Universetoday website [2] gives a more in depth explanation of the process and problems involved.

On February 10th there was a traffic accident of a new type. Two satellites were involved, one an American "Iridium" communications satellite and the other an abandoned Russian "Cosmos" military satellite. The American satellite was still in use but the Russian machine had been out of service since 1995 and was no longer actively controlled. It had been launched on 16th June 1993 and was in service for 2 years. The crash took place 491miles above Siberia in one of the most popular orbits for these types of vehicle (military, weather and communications).
A historic event that should not pass by unnoticed. The crash produced at least 600 pieces of debris that need to be monitored as they present a danger to other working satellites. David Wright is a physicist with the Union of Concerned Scientists. [3] He warned of the danger of a runaway chain reaction. He argues that "The number of debris particles is going to continue to increase for at least two centuries as debris runs into other debris and grinds down the large pieces to smaller and smaller pieces. All of those can be deadly at orbital speeds".
In 1996 a French military reconnaissance Cerise satellite was hit by such space debris produced by an Arian rocket. This was the first verified space collision and the impact tore off a 4.2 metre section of the satellite's gravity-gradient stabilization boom, severely damaging the machine's functions.

In January of 2007 the Chinese military brought down one of its own disused satellites using an intercontinental ballistic missile causing another estimated 2500 pieces of debris. More of a military show of strength than a clean up operation I would say. Many countries expressed outrage at the decision to re-open what could turn into a space arms race (the USA and Russia stopped experimenting into satellite destruction in the 1990's due to debris concerns) as the military implications of shooting down spy satellites are obvious.

But what are the options available for the destruction of these objects? A missile capable of reaching space is a large object and the impact with the satellite and resulting explosion creates a lot of debris. This debris then represents a danger to all other satellites including the international Space Station and the Hubble telescope, (which not having any rockets unlike the Space station and most other satellites cannot take any evasive action), traveling at 17 500 miles per hour even a small shard could damage the outer hull of the space station with catastrophic implications. The Space Station is however in orbit only 199 to 215 miles above the Earth in a relatively unpopulated area and NASA claim that the odds of a collision are low.
These pieces and even entire machines sometimes come back down to Earth of their own accord. Panic struck the States in January of last year when a 10 ton satellite lost power and headed back down to land. The American military destroyed the machine using a modified SM3 missile fired from a ship in the Pacific amid fears of the hydrazine inside the fuel tank could be hazardous to the population if it fell to Earth.
An example of the dangers of an unannounced return came in January 1978 when a fireball streaked through the skies of western Canada, heralding the demise of a Russian spy satellite.
The remains of the satellite came down over Great Slave Lake and fell across the North West Territories, Alberta and Saskatchewan spreading mildly toxic radioactive waste over the entire area.
Falling satellites and their trajectories can usually be predicted well in advance and airlines notified, although nothing is fool proof.
Last year 270 passengers on board an airliner above the Pacific had a lucky escape when the wreckage of a blazing Russian satellite narrowly missed their aircraft.
Pilots of the Latin American Airbus A340 saw the fiery debris streaking through the darkness directly ahead of them. The wreckage caused a sonic boom, which temporarily drowned out the noise of the jet's four engines.
The near-disaster happened about four hours southwest of Auckland, New Zealand, and air traffic controllers quickly realized that the flaming wreckage was what remained of a communications satellite that had not been due to enter the Earth's atmosphere for a further 12 hours. The Pacific area is favored for bringing satellites to Earth because of the relatively light population.

The difficulty or predicting reentry was reinforced in 2002 when debris from a science satellite crashed onto the Earth's surface several thousand miles from where it had been expected to impact. Elements of the 7,000lb satellite rained down over the Gulf. Fortunately there was no reported injury to life or property.
These machines can be successfully brought back to Earth as NASA engineers proved in 2000 when they successfully directed a safe return from orbit of the 17-ton Compton Gamma Ray Observatory using rockets on board the satellite, bringing it down in a remote part of the Pacific.
The largest uncontrolled reentry of a NASA spacecraft from space orbit was Skylab, the 78-ton space station that fell back to Earth in 1979. The debris from the station fell across the Indian Ocean and a remote part of Western Australia. There were no reported injuries or damage from Skylab.

As communication, TV, navigation systems and spying are obviously boom industries this congestion can only become worse. Iran launched its own satellite on 4th Feb, a great sense of national pride and tension raiser in its stand off with America and the West. Now 11 countries have satellites in space but more than 110 countries have interests in at least one orbiting satellite. ISRO [4] in India is developing a GSLV mark 3 rocket that may halve launch costs and they already offer a service at 30% less than their competitors so more people will be able to send more things into space.

Reuters report [5]that Simon Brooks of The International Institute for Strategic Studies is calling for "some sort of regulation on low-Earth orbit but people are not sharing because a lot of it is sensitive". The risk that American space debris could damage an Iranian satellite for example could have geopolitical implications as people ask the question "was that crash deliberate?" and radioactive waste pollution from a falling military satellite may also raise tensions between nations.

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Links in this document:

  1. 1] /schedabiografica/Redazione FGB
  2. 2] http://www.universetoday.com/2009/02/14/how-and-why-did-two-satellites-collide-this-week/
  3. 3] http://www.ucsusa.org/
  4. 4] http://www.isro.org/index.htm
  5. 5] http://www.reuters.com/article/newsone/idUSTRE51B5AF20090212
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