Every now and again, a satellite will fall from orbit back to Earth. But why?
A satellite that has exceeded its useful purpose has several different potential ﬁnal resting places. These depend on the amount of fuel still available on the satellite and whether ground control is still able to manoeuvre it.
One technique is to move the satellite slightly higher in its orbital band, into a ‘graveyard orbit’. This is an area where no other satellites are orbiting, and the dying satellite can be left to degrade over time. However, as it breaks up and potentially shifts in orbit, this could still prove dangerous to other satellites.
Some satellites are merely left in their current orbits, either by choice or through necessity if they are uncontrollable. Other satellites are purposely moved lower into the atmosphere, where they are left to burn up and hopefully disintegrate before reaching the Earth.
Some of the biggest to have done so are:
- A 14.5 ton Russian spacecraft which was intended to retrieve soil samples from the Martian moon Phobos (‘grunt’ means ‘soil’ in Russian)
- Unfortunately, it experienced a failure immediately after launching in early November 2011 and became stuck in Earth orbit.
- It crashed into the Pacific Ocean on 15 January 2012.
Compton Gamma Ray Observatory
- This 17 ton machine was the second of NASA’s “Great Observatories” (it followed the Hubble Space Telescope which launched in 1990).
- It launched on 5 April 1991, but experienced a gyroscope failure nine years later.
- As it wasn’t able to be repaired in orbit like Hubble, NASA carried out a controlled re-entry on 4 June 2000, the first it had ever attempted.
- On 7 February 1991 the Soviet space station Salyut 7 crashed back to Earth in an uncontrolled re-entry after 9 years in space.
- At the time of the re-entry a spaceship called Cosmos 1686 was docked to the station, giving a combined weight of 44 tons.
- The station had been unmanned since 1986 following a series of technical problems, including a power failure that had caused ice to form on the space station’s interior walls.
- It re-entered over Argentina on 7 February 1991, scattering debris over the town of Capitan Bermudez.
- Skylab was NASA’s first space station, weighing 69 tons.
- It launched on 14 May 1973 and completed a variety of Earth observations, but in early 1979 NASA discovered that the station was falling into a lower orbit.
- Amid a huge media storm Skylab re-entered Earth on 11 July 1979.
- The majority of the spacecraft burnt up in the atmosphere but parts of it fell in Western Australia.
- To date, the largest man-made object to fall back to Earth has been Russia’s Mir space station.
- Weighing 135 tons, this giant space station was de-orbited by engineers in 2001.
- Its re-entry was controlled to ensure that the majority of the space station burnt up in the atmosphere and the remainder crashed into the Pacific Ocean.
- The station had remained operational since its launch on 20 February 1986, setting a number of records along the way including the longest stay by a human in space.