“It is always difficult to assess the amount of surviving mass and number of fragments without knowing the design of the object, but a reasonable “rule-of-thumb” is about 20-40% of the original dry mass.”
The biggest incident, so far, was in 1979 when NASA’s 76-ton Skylab, had an uncontrolled reentry that scattered debris across the Indian Ocean and Western Australia.
McDowell says he hopes China will make changes in the future to avoid similar events. “I think by current standards it’s unacceptable to let it reenter uncontrolled,” McDowell reports. “Since 1990 nothing over 10 tons has been deliberately left in orbit to reenter uncontrolled.”
It’s not just about what’s coming down this weekend. China’s first space station launch in 2011, the Tiangong-1, or Heavenly Palace is still out there. Its design has no re-entry plan for the school bus-size space station. It is unknown where and when that 10 tons will be heading our way.
