John Doe wrote in :

"Jorge R. Frank" wrote:
In the current ISS configuration, there is no place the SSRMS could
hold the stranded shuttle to get it completely out of the way of the
rescue shuttle without causing major control difficulties for ISS.

Isn't the whole architecture designed to make it easy to add
additional grapple points on the station ?

In *no* configuration of ISS is there a place where the SSRMS could
hold the stranded shuttle and still withstand plume impingement and
docking loads from the rescue shuttle.

I can understand plume impingement for the thin solar arrays. But
franckly, is this really a valid argument for a tile equipped shuttle
being held by the arm ?

Yes. The arm is the weak point; the moments on the arm from the plumes will
damage it.

There is no ground commanding capability for the docking mechanism,
nor is there commanding capability for the post-contact thrusting
required to trip the capture latches.

If there is a data connection via the SSRMS, then couldn't the station
send the commands tyo trigger the locking motors ?

That is not as trivial as it sounds. You need a command interface at the
ISS end *and* a path on the shuttle side to send the commands to the
docking mechanism. The docking mechanism is Russian - currently *all*
commanding is done by switches on the Russian-supplied control panel. Data
goes *out* from the docking mechanism to the computers and the ground but
there's no *path* for commands to go the other way.

And if the shuttle is held by the SSRMS, can't the SSRMS provide the
equivalent of post contact thrusting to trip the latches ?

No. It's not strong enough.

The SSRMS is capable of transmitting small amounts of
power, but the level of power required to allow an automated shuttle
re- docking is beyond the design limits.

All that is needed is keepalive power, as well as driving the docking
motors. The SSMR is the one who would perform the docking, no need to
use shuttle's thrusters.

Incorrect. The SSRMS is not strong enough. You need the thrusters, plus the
RJDs, flight-critical MDMs, and at least two GPCs (one GNC to command the
thrusters, one SM to command the docking mechanism). Then you need to
activate at least enough of the ECLSS to keep all that equipment cool.

There are, at least in theory, 23 days to salvage parts from the
damaged shuttle before its consumables are depleted.

But wouldn't the point be to have the rescue shuttle bring the spare
parts to fix the broken shuttle ?

What about just letting shuttle go a day or two before the rescue one
arrives, and then the rescue shuttle could still approach the damaged
one to EVA to it and fix whatever is needed ?

Once the damaged shuttle has given up all its consumables to keep the crew
alive to wait for the rescue shuttle, there won't be enough consumables for
it to keep itself alive until the rescue shuttle can get to it. The plan is
to leave just enough capability (~2 hours) after undocking for the damaged
shuttle to destructively deorbit itself after undocking.


--
JRF

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