Broken tether lost in space
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Tethered satellite investigation report
News story originally written on June 4, 1996
NASA and the Italian Space Agency (ASI) have released the
report of the investigative board appointed to determine
factors which resulted in the Feburary 25 tether break and loss of
the Tethered Satellite during the STS-75 Space Shuttle mission.
"The tether failed as a result of arcing and burning of
the tether, leading to a tensile failure after a significant
portion of the tether had burned away," the report concludes.
The arcing occurred because either external foreign object
penetration (but not orbital debris or micrometeoroids) or a
defect in the tether caused a breach in the layer of
insulation surrounding the tether conductor. The insulation
breach provided a path for the current to jump, or arc, from
the copper wire in the tether to a nearby electrical ground.
The board found that the arcing burned away most of the
tether material at that location, leading to separation of the
tether from tensile or pulling force. The break occurred when
approximately 12.2 miles (19.7 km) of tether was unreeled, in
a period when the tether was experiencing normal stresses of
approximately 15 pounds (65 newtons).
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