Last week, the US shot down a defunct, out-of-control spy satellite. This satellite, the size of a bus, is just one of many that man has sent into orbit in half a century of satellite launches. Most usually stay the course but some, like the USA 193, take the plunge down to Earth

It’s crowded out there
In the last four decades, there have been more than 4,000 successful satellite launches. Currently, there are over 9,000 objects—including satellites and debris—that are monitored and catalogued by the US Space Surveillance Network. Roughly two-thirds of them have re-entered the Earth’s atmosphere and most of them burned up during the re-entry process. India contribution to the space mass is 142 objects—31 payloads and 111 rocket bodies and debris.

BUSY ORBIT
The most cluttered is the geo-stationary orbit, located at about 36,000 km above the earth’s equator. There has to be a minimum 2-degree separation between two orbital slots here, which means theoretically, geo-stationary orbit can accommodate 180 satellites at any given time. However, by having different orientations, it is possible to have more than one satellite in the same slot. As on January 2007, there were 238 fully controlled operational satellites in GSO, out of which India had 11 in five orbital slots.

When out of service, satellites in the GSO are generally pushed 200 km up to make way for newer satellites. Together with such satellites and their parts, there were about 1,120 space objects in the GSO and its neighbourhood.

BREAK-UP OF TOTAL MASS
Operational satellites:

6 per cent
Pieces of hardware released during payload deployment: 12 per cent
Non-operational payloads: 20 per cent
Satellite and rocket fragments: 40 per cent

Traffic ControlBr>USA and Russia have the technical prowess to track these objects in space using optical and electronic systems. Their ground systems can track objects bigger than 10 cm in size in the lower orbits (200 km to 2,000 km) and bigger than 1 metre in size in the geo-stationary orbit (36,000 km). There is also an Inter-Agency Space Debris Coordination Committee, an expert group for global coordination of activities related to issues of debris in space. ISRO is a member.
CLASH IN COSMOS
There have been three incidents of space accidents involving debris and operational satellites in the last one decade. Last year, the remains of a Russian defunct satellite hit a functional communication satellite of the same country. The functional satellite failed within 12 hours.

THE PLUNGE
Satellites or their parts routinely come out of orbit and harmlessly fall back to Earth every year. But there has never been any report of a human being struck by space debris
In 1979, a 77.5-tonne US space laboratory, Skylab I, plunged to Earth, scattering debris across the southern Indian Ocean and sparsely populated Western Australia. An Australian municipality, the Shire of Esperance, fined the United States $400 for littering.Skylab was the first space station the United States launched into orbit, and the second space station ever visited by a human crew. The 75 metric tonne station was in the Earth’s orbit from 1973 to 1979. Following the last mission, Skylab was left in a parking orbit expected to last at least eight years. An unmanned satellite called the Teleoperator was to be launched to save Skylab, but funding never materialized.
Mir, a Soviet orbital station, was humanity’s first consistently inhabited research station in space. The station existed until 23 March 2001, at which point it was deliberately de-orbited, breaking apart during atmospheric re-entry over the South Pacific Ocean. In anticipation of the reentry of Mir, the owners of Taco Bell towed a large target out into the Pacific Ocean. If the target was hit by a falling piece of Mir, every person in the United States would be entitled to a free Taco Bell taco. The company bought a sizable insurance policy for this “gamble.” No piece of the station struck the target.
The Chinese military used a ground-based missile to hit and destroy one of its aging satellites orbiting more than 500 miles in space last year. The US had then criticised China’s action, saying it would trigger a possible arms race in space.

editor@expressindia.com

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