ROSAT (German) : Second big satellite set to resist re-entry burn-up in October or November of 2011

ROSAT (German) : Second big satellite set to resist re-entry burn-up in October or November of 2011

Even if NASA's 6-tonne UARS satellite does not cause any injury or damage when it re-enters the Earth's atmosphere today, there is more space junk headed our way next month. A defunct German space telescope called ROSAT is set to hit the planet at the end of October – and it even is more likely than UARS to cause injury or damage in populated areas.

No one yet knows where UARS (Upper Atmosphere Research Satellite) will fall to earth. Although most of the craft's mass will be reduced to an incandescent plasma, some 532 kilograms of it in 26 pieces are forecast to survive – including a 150-kilogram instrument mounting.

NASA calculates a 1-in-3200 chance of UARS causing injury or damage. But at the end of October or beginning of November, ROSAT – a 2.4-tonne X-ray telescope built by the German aerospace lab DLR and launched by NASA in 1990 – will re-enter the atmosphere, presenting a 1 in 2000 chance of injury.

The higher risk stems from the requirements of imaging X-rays in space, says DLR spokesperson Andreas Schütz. The spacecraft's mirrors had to be heavily shielded from heat that could have wrecked its X-ray sensing operations during its eight-year working life. But this means those mirrors will be far more likely to survive a fiery re-entry. Read More

Since its launch on 1 June 1990, friction due to Earth's upper atmosphere has been causing the X-ray satellite ROSAT to lose altitude continuously. When the spacecraft re-enters the atmosphere, which is expected to occur in November 2011, the satellite will disintegrate and most of the fragments will burn up in the extreme heat caused by atmospheric friction. This FAQ provides answers to the most common questions about the ROSAT mission and its re-entry. Read More

Will ROSAT burn up as it re-enters Earth’s atmosphere?

When spacecraft and space debris leave their orbits and enter Earth’s atmosphere, they are travelling at speeds in excess of 27,500 kilometres per hour. In less than 10 minutes, they are slowed down to subsonic speeds by the friction of re-entry. The air resistance experienced during re-entry generates a massive amount of heat. Without special equipment, such as the heat shields fitted to the American space shuttle, re-entering objects burn up – to a very large extent or even completely. Heat and aerodynamic stresses cause satellites to break apart during this process. DLR has analysed the re-entry and destruction of ROSAT. Based on the latest studies, it is thought possible that up to 30 individual debris items with a total mass of up to 1.6 tons might reach the surface of the Earth.