Inadvertent Cable Cutter Firing

I just surfed past NASA TV and caught 30 seconds or so of video/narration of
a inadvertently cut umbilical cable on the transporter.
Anybody have any background details?

Thanks

Scott

I did some more digging. Apparently on friday there was a RPC power trip on
the S0 truss. Fault tree analysis led to the TUS-2 umbilical to the mobile
transporter. (TUS = Trailing Umbilical System, provides data and power to
the mobile transporter, is stowed/unstowed on a reel as transporter moves).
Apparently the disconnect actuator on the cable system inadvertently cut the
cable. I haven't figured out if the cut caused the power trip or vice
versa.

The cable is part of a redundant set so the mobile transporter should not be
affected. Interesting though that a cable cutter designed for contingency
use (if the cable gets tangled) should fire without being commanded.

Anybody else with any background on this? Feel free to correct or update my
info.

Scott

"Scott J" wrote in message
...
I just surfed past NASA TV and caught 30 seconds or so of video/narration
of a inadvertently cut umbilical cable on the transporter.
Anybody have any background details?

Thanks

Scott

"Scott J" wrote in message
.. .
The cable is part of a redundant set so the mobile transporter should not
be
affected. Interesting though that a cable cutter designed for contingency
use (if the cable gets tangled) should fire without being commanded.

This is why adding "safety" hardware needs to be done carefully. Adding
something like a cable cutter to handle the contingency of a tangled cable
introduced a new failure mode. Hopefully the root cause can be determined.

Does the redundant cable also have the cable cutter? If so, it's a
possibility that the other cutter could fail in a similar way. :-(

Jeff
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Jeff Findley wrote:
This is why adding "safety" hardware needs to be done carefully. Adding
something like a cable cutter to handle the contingency of a tangled cable
introduced a new failure mode. Hopefully the root cause can be determined.

Does the redundant cable also have the cable cutter? If so, it's a
possibility that the other cutter could fail in a similar way. :-(

And is this cable and cable-cutter assembly designed to be easily
swapped out on an EVA? If so, can we expect that this will be added to
an EVA sometime before the truss construction flights to get the
redundancy back? Do they have a spare on board?

John.

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This is why adding "safety" hardware needs to be done carefully. Adding
something like a cable cutter to handle the contingency of a tangled cable
introduced a new failure mode. Hopefully the root cause can be determined.

Nothing that couldn't be fixed by just than adding another subsystem,
the backup cable splicer, to be activated in case of failure (or
inadvertent use) of the cable cutter :-).

More relevant is why did the actuator fire on it's own and what other,
perhaps more critical, systems have similiar mechanisms.

The orbiter contingency undocking system comes to mind. Is that a orbiter
or station system?

"Jeff Findley" wrote in message
...

Does the redundant cable also have the cable cutter? If so, it's a
possibility that the other cutter could fail in a similar way. :-(

Jeff
--
Remove icky phrase from email address to get a valid address.

"Scott J" wrote in
:

More relevant is why did the actuator fire on it's own and what other,
perhaps more critical, systems have similiar mechanisms.

The orbiter contingency undocking system comes to mind. Is that a
orbiter or station system?

Orbiter. Protected by an arm/fire mechanism as well.

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"Jorge R. Frank" wrote in message
...

Orbiter. Protected by an arm/fire mechanism as well.

--
JRF

Better protected than the ISS cable cutter I hope.

"Scott J" wrote in news:QVVrf.40205$aS5.37445
@bignews4.bellsouth.net:

"Jorge R. Frank" wrote in message
...

Orbiter. Protected by an arm/fire mechanism as well.

Better protected than the ISS cable cutter I hope.

I don't know about the ISS cable cutter, but the orbiter contingency
undocking system (pyros) are also powered off when not in use. It takes
five separate switch throws on two different panels to power up the pyros,
one button press (under a cover secured by a thumbscrew) to arm the pyros,
then another button press (under another cover secured by a thumbscrew) to
fire the pyros.

I think that's sufficient protection.

--
JRF

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"Jorge R. Frank" wrote in message
...
"Scott J" wrote in news:QVVrf.40205$aS5.37445
@bignews4.bellsouth.net:

"Jorge R. Frank" wrote in message
...

Orbiter. Protected by an arm/fire mechanism as well.

Better protected than the ISS cable cutter I hope.

I don't know about the ISS cable cutter, but the orbiter contingency
undocking system (pyros) are also powered off when not in use. It takes
five separate switch throws on two different panels to power up the pyros,
one button press (under a cover secured by a thumbscrew) to arm the pyros,
then another button press (under another cover secured by a thumbscrew) to
fire the pyros.

I think that's sufficient protection.

ISS has similar command protection, believe it or not. One must
command-to-close one RPC downstream of the guillotine, close another
upstream, then remove the close-inhibit for the power RPC, and then close
that power RPC to get the whole thing to fire. All planning has been done
to prevent an inadvertant *command* to sever the TUS cable, we never
expected the guillotine to fire on its own. Now we need to safe the other
one before it goes off, just in case the same failure mechanism is at work
there.

Mike Ross