This is interesting. The ROSAT X-ray observatory is expected to burn up in about a week and it has quite a checkered and colorful history. According to Wikipedia, ROSAT was originally planned to be launched on the Space shuttle but the Challenger disaster caused it to be moved to the Delta rocket platform. Then on April 25th 1998, failure of the primary star tracker on the X-ray Telescope led to pointing errors that in turn had caused solar overheating. It was severely damaged on September 20th 1998 when a reaction wheel in the spacecraft’s Attitude Measuring and Control System (AMCS) reached its maximum rotational speed, losing control of a slew, damaging the High Resolution Imager by exposure to the sun.
In 2008, NASA investigators were reported to have found that the ROSAT failure was linked to a cyber-intrusion at Goddard Space Flight Center.
The root of this allegation is a 1999 advisory report by Thomas Talleur, senior investigator for cyber-security at NASA. This advisory is reported to describe a series of attacks from Russia that reached computers in the X-ray Astrophysics Section (i.e. ROSAT’s) at Goddard, and took control of computers used for the control of satellites, not just a passive “snooping” attack. The advisory stated:
“Hostile activities compromised [NASA] computer systems that directly and indirectly deal with the design, testing, and transferring of satellite package command-and-control codes.”
Other reports said the attack may have been only coincidental with the failure, but we’ll never know for certain. Since the failure of the satellite in 1998, due to atmospheric drag, the satellite has slowly lost height.
The ROSAT X-ray observatory, launched in 1990 by NASA and managed for years by the German Aerospace Center (DLR), will return to Earth within the next two weeks. Current best estimates place the re-entry between Oct. 22nd and 24th over an unknown part of Earth. Although ROSAT is smaller and less massive than UARS, which grabbed headlines when it re-entered on Sept. 24th, more of ROSAT could reach the planet’s surface. This is because the observatory is made of heat-tolerant materials. According to a DLR study, as many as 30 individual pieces could survive the fires of re-entry. The largest single fragment would likely be the telescope’s mirror, which is very heat resistant and may weigh as much as 1.7 tons.
ROSAT is coming, but it’s not here yet. On Oct. 13th, Marco Langbroek photographed the observatory still in orbit over Leiden, the Netherlands:
“I observed ROSAT this evening in deep twilight,” says Langbroek. “It was bright, magnitude +1, and an easy naked-eye object zipping across the sky where the first stars just had become visible.”
Update: Scott Tilley of Roberts Creek, British Columbia, made a video of ROSAT on Oct. 15th: “It did get pretty bright, at least 1st magnitude, as it passed overhead after sunset.”
Also, check the German ROSAT re-entry page for updates.
The role of space weather: Solar activity has strongly affected ROSAT’s decay. Only a few months ago, experts expected the satellite to re-enter in December. However, they did not anticipate the recent increase in sunspot count. Extreme ultraviolet radiation from sunspots has heated and “puffed up” Earth’s atmosphere, accelerating the rate of orbital decay. The massive observatory now has a date with its home planet in October.