杏吧原创

A MICROSCOPIC shard of metal was probably to blame for the loss of a
$443-million tethered satellite earlier this year, according to
NASA.

The satellite was deployed from the space shuttle Columbia on 25 February to
test the idea of generating electricity in orbit from the motion of a conducting
tether through the Earth鈥檚 magnetic field.

Six hours into the experiment, with all but 300 metres of the 20-kilometre
cable played out, the tether snapped. The satellite, built by the ASI, Italy鈥檚
space agency, burnt up in the Earth鈥檚 atmosphere three weeks later.

NASA鈥檚 inquiry team believes that the tether melted after a microscopic piece
of metal punctured a thin insulating layer made from Kevlar, causing an arc in
the current running through a copper wire at its core. Investigators found
aluminium and silver fragments embedded in parts of the tether, apparently left
over from the manufacturing process. These shards could have punctured the
insulating layer while the tether was still stored on its reel. Metal fragments
were also found in the winding mechanism.

Announcing the findings last week, Kenneth Szalai, director of NASA鈥檚 Dryden
Flight Research Center in Edwards, California, said that not enough attention
was paid to the effects of a puncture in the tether鈥檚 insulation. But the basic
design is sound, he said.

鈥淲e just need to pay more attention to some of the engineering aspects,鈥�
agreed Carlo Bonifazi of the ASI. Despite the loss of the satellite, Bonifazi
rated the experiment a partial success. The tether generated a current of 1
amp鈥攖hree times more than had been predicted.