The world was gripped by the Nasa UARS satellite that fell back to Earth last Saturday and now there’s another that’s plummeting back from orbit. In late October or early November a Germany astronomy satellite called ROSAT- will plunge uncontrolled back to Earth. Experts believe that two dozen metal pieces from the bus-sized Nasa satellite fell over a 500-mile span in the Pacific Ocean. It began hitting the water southwest of Christmas Island.
The German ROSAT satellite was launched in 1990, 'died' in 1998 and weighs two and a half tonnes. The German space agency estimates that 30 pieces weighing less than two tons will survive re-entry. Debris may include sharp mirror shards. The German space agency puts the odds of somebody somewhere on Earth being hurt by its satellite at 1-in-2,000 — a slightly higher level of risk than was calculated for the Nasa satellite.Again, it seems certain that information on when or where the satellite might land will be scant.
Equipped with an 84cm mirror, it completed an X-ray survey of the sky, finding more than 150,000 objects. It followed up with targeted observations of interesting objects from galaxies, to neutron stars and even comets. It was switched off in 1999 and I calculate that it is now perhaps three weeks away from re-entry as its orbit decays, though it could survive into November.
At 2,400kg, Rosat is less than half as massive as UARS, but more than half of it is thought likely to survive re-entry, including much of its heavy mirror which was built from a glass-ceramic material with a high melting point. The expectation is that this will drop harmlessly into an ocean. The US tracking authorities took more than two days to confirm the details of UARS's plunge into the Pacific, so let us hope that they do better with Rosat.
