Why You Shouldn’t Worry About the Uncontrolled Reentry of Tiangong-1 – China’s Falling Space Station

Tiangong-1, China’s falling space station will make an uncontrolled re-entry on late Sunday, April 1, or early Monday, April 2. But, there’s no need to panic: the risk is quite low that people on Earth will be in danger. Since two-thirds of Earth’s surface is covered by water, any remaining debris that doesn’t burn up in the atmosphere has a high chance of falling into an ocean. In fact, in every few years, uncontrolled spacecraft of this size enter the Earth’s atmosphere. For example, the 5,900-kilogram (13,000 lb) NASA-operated orbital observatory Upper Atmosphere Research Satellite (UARS) decommissioned and re-entered Earth’s atmosphere on 24 September 2011. It ultimately impacted in a remote area of the Pacific Ocean, which is called Point Nemo. Some decommissioned spacecraft has returned so remotely that there was no visual evidence of their fall. So, the headlines of tabloid papers about Tiangong-1 crash are just sensational and click-bait.

There were uncontrolled reentries of even much larger spacecrafts in space exploration history. The biggest uncontrolled entry of a spacecraft was on February 1, 2003: the Space Shuttle Columbia disintegrated upon reentering Earth’s atmosphere, killing all seven crew members.

Tiangong-1

Tiangong-1 artist illustration
Artist’s illustration of China’s Tiangong-1 space station. Means literally “Heavenly Palace 1” in English, the 8.5-tonne spacecraft was China’s first prototype space station.
Launched on 29 September 2011, and its operational life cycle was predicted at two years. On 21 March 2016, after its lifespan extended by two years, the Space Engineering Office of China announced that they had disabled data service since the space station had operated two and half years longer than its intended two-year service plan. The officials went on to state that the telemetry link with Tiangong-1 had been lost. But, a couple of months later, amateur satellite trackers watching Tiangong-1 began to speculate that China’s space agency had lost control of the station.
Update: Tiangong-1 started reentry over the southern Pacific Ocean, northwest of Tahiti, on 2 April 2018 at 00:15 UTC and burned up in the atmosphere.

Tiangong-1 (literally: “Celestial Palace 1”) was China’s first prototype space station, serving as both a manned laboratory and an experimental testbed to demonstrate orbital rendezvous and docking capabilities. Launched unmanned aboard a Long March 2F/G rocket on 29 September 2011, it was the first operational component of the Tiangong program, which aims to place a larger, modular station into orbit by 2023. Tiangong-1 was initially projected to be deorbited in 2013, to be replaced over the following decade by the larger Tiangong-2 and Tiangong-3 modules, but China’s space agency had lost control of the station and as of March 31, 2018, it was still aloft, though in a decaying orbit. It is expected to make an uncontrolled reentry to Earth’s atmosphere between March 31 and April 2.

The time for uncontrolled descent of Tiangong-1’s still remains highly uncertain, according to SPACE.com. It is strongly related to how quiet or active the sun has been. If the sun is active, its energy pushes more strongly against Earth’s atmosphere. The atmosphere then balloons and becomes denser at higher altitudes. The density of the atmosphere affects the drag (the denser the atmosphere, the stronger the drag) against Tiangong-1’s orbital speed. As Tiangong-1 loses energy due to drag, it falls towards Earth.

Update: Tiangong-1 burned up in Earth’s atmosphere

Tiangong-1 broke apart and burned up in Earth’s atmosphere over the southern Pacific Ocean at about 8:16 p.m. EDT on April 1 (00:16 a.m. April 2 GMT).

Top 10 Biggest Uncontrolled Reentries

Large Spacecraft Reentries
There were uncontrolled reentries of even much larger spacecraft than Tiangong-1 in space exploration history. The biggest uncontrolled entry of a spacecraft was on February 1, 2003: the Space Shuttle Columbia disintegrated upon re-entering Earth’s atmosphere, killing all seven crew members.

Spacecraft :: Reentry mass – tonnes :: Date :: Location

  1. Apollo BP-13/Saturn SA-6 :: 16.2 :: June 1, 1964 :: Pacific Ocean
  2. Almaz-1 space station (Salyut-2) :: 16.3 :: May 28, 1973 :: Pacific Ocean, near Fiji
  3. Apollo BP-15/Saturn SA-7 :: 16.4 :: September 22, 1964
  4. N-6 No. 1 satellite (Proton-4) :: 17.0 :: July 24, 1964 :: Unknown
  5. Saturn SA-5 rocket/Jupiter nosecone :: 17.2 :: April 30, 1966 :: Brazil
  6. DOS 3 space station (Kosmos-557) :: 18.5 :: May 22, 1973 :: Indian Ocean
  7. DOS 6 space station/TKS-M module (Salyut-7/Kosmos-1686) :: 39.0? :: February 7, 1991 :: Argentina
  8. Saturn S-II-13 (Skylab rocket) :: 45.1 :: January 11, 1975 :: Atlantic Ocean (west of Madeira)
  9. Skylab space station :: 75.7 :: July 11, 1979 :: Australia
  10. OV-102 Columbia (STS-107) :: 106.4 :: February 1, 2003 :: Texas/Louisiana

Sources

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