Chinese space station set for uncontrolled Easter reentry

Artist's impression of Tiangong-1 burning up on reentry
Artist’s impression of Tiangong-1 burning up on reentry(Credit: Aerospace Corporation)

China’s Tiangong-1 space station is set to make an uncontrolled  reentry into the Earth’s atmosphere on or around April 1. The update from the Aerospace Corporation, which is tracking the abandoned orbital laboratory, predicts that it will make its final plunge at 00:00 GMT on April 1 with a margin of error of ±36 hours, when it will burn up somewhere between 43° North and 43° South latitudes.

Launched on September 30, 2011 from the Jiuquan Satellite Launch Center, China, atop a Long March 2F/G rocket, the Tiangong-1 was China’s first space station and was designed to accommodate two astronauts. In 2012, it was visited by the three-astronaut Shenzhou 9 mission that included China’s first female astronaut, and in 2013 by Shenzhou 10.

Unfortunately, there was some undisclosed malfunction aboard the spacecraft after the last visit and two years ago the Chinese National Space Administration said that it had lost telemetry contact with the 8,500-kg (18,740-lb) Tiangong-1. The agency is notoriously secretive, but it is highly probable that the spacecraft is inactive and amateur astronomers claim that it has definitely been dormant since June 2016.

Running status graphic of Tiangong-1
Running status graphic of Tiangong-1(Credit: Aerospace Corporation)

Since then, government and private agencies have been tracking the derelict. Normally, large satellites and other spacecraft in low-Earth orbit are sent on a controlled trajectory into either a graveyard orbit out of the way of other satellites or plunged into the atmosphere to burn up over the land-free expanses of the South Pacific.

Without ground control, this isn’t possible with Tiangong-1, so its orbit has been decaying naturally as it is slowed down by faint traces of the upper atmosphere. Because the thickness of these traces varies with solar activity, how much drag it is encountering isn’t known for certain. In addition, the orientation of the station is unknown, as is its exact location at any given moment.

The result is that calculating the time of reentry has a 20 percent margin of error and, aside from which area of the Earth is involved, exactly where it will enter is completely unknown. In this case, that’s two-thirds of the Earth surface. However, as the time of reentry approaches, the absolute margin of error narrows because the 20 percent is measured against the remaining days or hours until the event.

Graph showing Tiangong-1's altitude
Graph showing Tiangong-1’s altitude(Credit: Aerospace Corporation)

According the Aerospace Corporation, the chances of fragments reaching the Earth’s surface are small and that of anyone being injured are extremely remote. However, the public is warned that if they find what they think is a fragment of Tiangong-1, they should avoid touching it because it could be contaminated with the highly corrosive hydrazine fuel used by the attitude control thrusters.

As of today, Tiangong-1 is orbiting at an average altitude of about 200 km (125 mi) and is expected to lower to 190 km (118 mi) within 72 hours.

The video below gives a preview of the last moments of Tiangong-1.
Source: Aerospace Corporation.