If you put something into space then you have to think about what happens to it in the future so that it doesn’t cause problems for anyone else, either in space or on Earth. A project that puts something in space needs to be thought of from the start until the finish, the finish being the disposal of the spacecraft and all the other bits that get dumped in orbit. Now, we know that our atmosphere is a really great incinerator for space debris so bits of rockets and satellites can successfully burn up if they are deorbited. This is usually a very controlled and planned process to ensure that it all goes well and and nothing solid remains to land on someone’s head. But it isn’t always planed, sometimes things happen and the spacecraft malfunction or simply run out of fuel with no way of refuelling occurring. So at Milky-Way.kiwi, we thought we would have a look at what is happening to the Chinese Tiangong 1 and compare that with previous famous d-orbits such as Skylab and MIR.
The reports of the Tiangong 1 being no longer under control highlights the issue that what goes up (as long as its not too far up) eventually comes down. When it does come down the preference would be for it to be under controlled circumstances. The Tiangong 1 was the initial Chinese space station and in its uncontrolled re-entry, some of it might survive to the surface. The Tiangong 1 is pictured below in an image from CMSE. The spacecraft is about 8 tons and is expected to almost completely burn up. The Chinese are not able to control the re-entry process, hence the concern about where it might end up, the chances of it actually hitting someone are tiny. There’s plenty of effort going in to tracking the spacecraft so at least there’ll be some warning of where it may land. Current estimates put it de-orbiting somewhere between 43S and 43N, which encompasses almost all populated regions in the Southern Hemisphere. On the CMSE website, the last report regarding the Tiangong 1 had it at in an orbit at 286.5km
When it comes to the re-entry of large spacecraft, things don’t always go smoothly, even when they are planned. In 1979 NASA was no longer able to keep the Skylab space station in orbit, but they hadn’t lost control of the craft so planned to burn it up over the Indian Ocean. The spacecraft did mostly burn up, though not entirely as expected as bits of it lasted longer than anticipated and many fragments made to the ground in Western Australia. Fortunately, it was a sparsely populated area and no one was stuck. It certainly highlighted to the world the risk of de-orbiting large spacecraft and the uncertainty over how they breakup. The image below is a piece of Skylab that survived the re-entry from Wikipedia.
MIR was the large Russian space station that operated from 1986 to 2001. This was a huge station, significantly larger than Skylab and Tiangong 1. It was a multi module design and was inhabited for about 12 years of its fifteen year life. The decision to de-orbit was around funding and the new focus on Russian contribution for the International Space Station (ISS). MIR (depicted below from NASA) was also at the end of its life without a significant upgrade programme.
Plans to end the station started with a Progress spacecraft docking with extra fuel to help the de-orbiting process. The Russians aimed to have the space station burn up above a relatively unpopulated area of the South Pacific Ocean. Unlike other de-orbits discussed in this article, the MIR process went to plan and the station caused no problems for anyone on Earth. This image, also from shows the MIR burning up over the South Pacific on 23 Mar 2001.
Upper Atmosphere Research Satellite
On 24 September 2011 the UARS de-orbited out of control. This was a large satellite that weighed over 5 tons. At the time there was some concern that some parts of the satellite would survive re-entry, including one piece that might be around 150kg. Fortunately the satellite re-entered over the Pacific Ocean and caused no problems to any one on the surface.
All of these examples of large spacecraft being de-orbited under varying ranges of control, highlight the need for this to be thought about when the craft are constructed so that the danger from their re-entry to the general public is minimised.