Satellites lifespan: the analysis
Of course, a satellite needs a bit of propellant to reach a disposal orbit. This is a fact that limits the lifespan of some satellites. Even if all of the electronics and moving parts on the DirecTV satellite are still functioning after 12 years, it will still need to be decommissioned before it runs out of fuel.For satellites that operate at lower altitudes (including those used for surveillance and GPS), a trip up to disposal orbits may not be necessary. Orbits tend to decay over time, at a rate determined by the initial altitude.
Therefore, anything above 2,000 km will take millennia to return to Earth, while satellites further down might take centuries or decades. A satellite that starts out in a low orbit can be manoeuvred downward to ensure that it falls from space in a reasonable amount of time. In fact, NASA recommends that low-altitude derelicts be brought close enough to the Earth to return within 25 years. The satellite’s operator could also decide that it would be more energy efficient to push it up to a disposal orbit above 2,000 km.
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Satellites lifespan: What happens to Satellites that fall out of Orbit?
When a satellite falls out of orbit, between 10 percent and 40 percent of its mass survives re-entry. Hundreds of objects from orbit do hit the surface of the Earth at random locations every year, but no one has ever been reported injured or killed by falling space debris.
How dangerous is the debris that stays in space? Space agencies around the world keep track of any objects that are more than a few inches in diameter. (There are about 13,000 of these.) Even a small bit of debris could cause significant damage to a working satellite. Although collisions are rare and only a handful have ever been observed. The most recent occurred on Jan. 17, when apart from a U.S. rocket launched in 1974 collided with a piece of a Chinese spacecraft from 2000. Three new chunks of debris were created by the crash.
Graveyard Orbit 300 km above GEO
In order to eliminate collision risk, GEO satellites should be moved out of the geostationary ring at the end of their mission. It is recommended that their orbit should be raised by about 300 km, which is considered a safe distance to avoid future interference with active GEO spacecraft.
The change in velocity that is required to raise the orbit altitude by 300 km is 11 meter/sec, and the required propellant corresponds to that necessary for three months of station keeping. This means spacecraft operators have to stop operations three months before the spacecraft runs out of fuel and give up considerable revenue in order to reorbit their spacecraft. However, today, this is the only possibility for preserving the unique resource of the geostationary ring.