Re: STS-75 TSS Tether Break

Philip Chien (kc4yer@amsat.org)
Mon, 26 Feb 1996 23:13:05 -0400

"Rob Matson" <Rob_Matson@cpqm.saic.com> said:
>
>What amazes me about this whole experiment is the apparent lack of a recovery
>mode for the single-point failure of the tether breaking.  How expensive was
>the satellite?

According to ASI the satellite was worth about $200-400M (depending on
whether or not you count the cost for the original satellite, modifications
after the first flight, etc.)  But in any case the satellite was designed
for only two flights.  So from one point of view nothing of value was lost
- since it wasn't designed to be used again.

>I trust the only reason they can't attempt recapture of the
>satellite is the danger posed by the trailing tether.

well, that and that the laws of conservation of angular momentum caused the
tether satellite and tether to go in to a higher orbit than the shuttle,
and that Columbia doesn't have enough propellant on board for a rendezvous.

The astronauts actually practiced a procedure where they could cut the
tether, and then run after the satellite, and use two spacewalking
astronauts to manually grab the satellite and put it back in to its cradle
- just to prove that they could do it.  But of course that scenario would
only be possible while the satellite was relatively close to the shuttle.

>I can't believe they
>wouldn't have included a pyro-device in the design to cut the cable at the
>satellite-end!  Differential drag would soon separate the satellite from the
>tether, allowing a safe Shuttle retrieval.

Again - you're assuming that it's much more important to bring back the
satellite.  Admitedly the satellite does have *some* value - it will look
good in a museum, it's always good to recover stuff from space for
materials analysis, and there is a *possibility* that the other end of the
tether might have the clue needed to solve the problem of what happened.
(not likely that the end of the tether attached to the satellite would be
the only smoking gun - but still admitedly possible).

The possibility of the tether getting cut, or other scenarios where the
satellite would have to be cut loose were examined before the mission
fairly carefully.


latest TLEs I've got for the shuttle and TSS:

STS-75
1 23801U 96012A   96057.59567041  .00049324  00000-0  13693-3 0  9050
2 23801  28.4668 258.9663 0005946 323.4450  36.5922 15.92287714   614
tss
1 23805U 96012B   96057.92247828  .00297831  00000-0  21701-2 0  9066
2 23805  28.4912 256.6623 0066809 181.7526 178.3015 15.68022562   669



Philip Chien, Earth News - space writer and consultant  PCHIEN@IDS.NET
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