Europe's ROSAT Telescope Weighs 2.4 Tons, Can't Be Steered
It looks as falling satellite debris will become a regular part
of life in the 21st Century. Sometime between this Friday, and
Monday, October 24, just a month after NASA's six-ton UARS fell
into the Pacific, a defunct German satellite (pictured) called
ROSAT will take the plunge. As was the case last month, scientists
will not know until just before impact where the space junk is
likely to hit the surface of the Earth.
ROSAT is an acronym for "Roentgen Satellite," named after
physicist Wilhelm Roentgen, who won the first Nobel Prize for his
1895 discovery of X-rays. The satellite is an x-ray telescope which
was launched on an 18-month mission in 1990, ended up providing
useful functionality for more than eight years, and is credited
with helping researchers map over 100,000 sources of x-ray
radiation in space.
In an official statement, Heiner Klinkrad of the European Space
Agency (ESA) explained, "In the final phase, ROSAT will be 'caught'
by the atmosphere at which point it will not even complete an orbit
around the Earth: Instead, it will go into 'free fall.'" The exact
point at which that happens is a matter of chance because the
satellite has no rocket propulsion capability, and its steering
gyroscopes have all failed, ruling out the ability to command an
attitude change for more drag to force a quicker re-entry over an
ocean.
While ROSAT weighs about 2.4 tons, smaller than UARS, the German
Aerospace Center predicts one-in-2,000 odds of debris hitting a
human, making it a little more dangerous than UARS at one-in 3,500.
There are 30 pieces of the satellite thought likely to survive the
heat of re-entry.
USA Today's Dan Vergano notes that under an international
treaty, unless the risk to humans is less than one-in-10,000,
nations launching satellites are expected to provide some means to
steer them to safe landing sites during re-entry. Both ROSAT and
UARS were launched before the treaty took effect.
While it may be natural to feel anxiety over the threat of
getting hit by a piece of a falling satellite, NASA Space Debris
Expert Nicholas Johnson of NASA's Johnson Space Center tells the
paper uncontrolled re-entry of space junk the size of ROSAT happens
many times a year, while something the size of UARS drops from the
sky about once a year.
By comparison, an estimated 500 meteorites reach the surface of
Earth each year.