Space-watchers are looking skywards again as another large piece of space junk approaches re-entry. The 2,400 kg German ROSAT is due to re-enter sometime between October 21 and October 24, according to DLR, the German space agency.
It is also predicted to be a “dangerous” re-entry, with the DLR saying that 30 individual pieces weighing a total of 1.7 tonnes could reach the surface of the Earth. The agency highlights the satellite’s mirror as likely to be the source of the largest fragments, because of its heat resistance.
ROSAT – the Roentgen satellite – is an X-ray observatory that was launched in 1990 to perform an all-sky survey of X-ray sources. It detected 80,000 such sources, along with 6,000 ultra-violet sources with its wide-field camera. The project was abandoned and shut down in 1999.
The DLR expects its velocity at re-entry to be around 28,000 kilometers per hour.
The current plus-or-minus two days’ uncertainty in re-entry should be reduced as re-entry approaches. The agency attributes the uncertainty to solar activity, since at a current altitude of less than 300 km, the satellite is affected by changes in drag as the atmosphere heats and cools (and consequently expands and contracts).
This latest fall is given a 1:2,000 chance that some fragment may hit someone on Earth (which puts it at somewhat more dangerous than the 1:3,200 chance estimated for UARS on its re-entry).
ROSAT is approaching long an extensive path that extends from 53 degrees North to 53 degrees South, with a ground track that could be as much as 80 kilometers wide.
While hefty, ROSAT is nothing like the largest satellite to make an uncontrolled re-entry: UARS was more than 6.5 imperial tons, and, as this slideshow on space.com details, other large re-entries include MIR, Cosmos, Salyut 7, Pegasus 2, Skylab, and the shuttle Columbia. ®