TINY particles of dust pose a more serious risk to satellites than huge lumps
of space junk, according to a team of British scientists who have analysed
damage to solar panels from the Hubble Space Telescope.
Most bits of space junk, even pieces as small as a few centimetres across,
are tracked by the US Air Force. This allows any spacecraft that is on a
collision course to be moved out of the way. But some particles are too small to
be tracked by radar.
This week scientists from the Open University and Oxford Brookes University
will tell the Hypervelocity Impact Symposium in Galveston, Texas, that these
particles, just a few micrometres across, pose a serious threat. They believe
that dust grains vaporise on impact, creating a hot, conducting plasma that can
induce currents that seriously perturb electronic systems on spacecraft,
potentially rendering them helpless.
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One way to assess the risks posed by space dust is to examine the tiny
craters which pepper the surface of space shuttles after orbital missions. But
this is often impossible, as telltale residues in the craters are usually burnt
away as the shuttle re-enters the Earth鈥檚 atmosphere. So the British team
examined solar cells removed from Hubble at the same time as its famously
defective mirror was replaced. The panels were brought down in the shuttle鈥檚
hold, so the residues remained intact.
The researchers found that the craters on the solar
cells contain enough residue from impacting dust particles to identify the
culprits, say Giles Graham at the OU and Anton Kearsley at Oxford Brookes. They
found traces of iron, nickel and magnesium in the craters. This suggests the
damaging particles were asteroids or comet debris. 鈥淲e also found residues of
aluminium and titanium from space debris in the smallest craters,鈥� says
Graham.
Neil McBride of the OU says the findings highlight the risk posed to
satellites by the numerous particles of space dust orbiting Earth: 鈥淣atural
particles can be travelling up to seven times faster than space debris
particles, which means they produce over a thousand times more plasma on
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The warning is timely, because on 17 November the Earth will pass through the
tail of Comet Tempel-Tuttle, and the debris from it will rain down on
Earth鈥攑roducing the display better knows as the Leonid meteors. Next
year鈥檚 Leonid shower is expected to be the strongest since 1966. The stream of
debris will be rich in micro-particles. 鈥淭here鈥檚 a very serious risk to
satellites,鈥� says David Asher of the Armagh Observatory in Northern Ireland.
McBride points out that a satellite called Olympus suffered an electrical
malfunction at the peak of the 1993 Perseid meteor shower, which eventually led
to its loss. 鈥淲e can鈥檛 say that it was definitely hit by a particle, but it
seems likely,鈥� he says.