Re: What Happened to the MMU?

In article <1170445715.802853.64790@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
<Dr.Colon.Oscopy@xxxxxxxxx> wrote:
...In particular, it turned out that the best way to take the spin
off a spinning satellite is to just have spacewalkers in the cargo bay
reach up and grab it. (Moreover, the more complicated plans involving
the MMUs did not actually work terribly well on the Solar Max repair
and the Palapa/Westar salvage.)...

The plans for Solar Max were in fact overly complicated, but I don't
think a failure of the MMU per-se contributed to mission problems.

No, it was the *plans* which failed, not the MMU. And the same thing
happened on the P/W salvage. Fancy hardware which had to be exactly
matched to the satellites turned out not to be, and the missions were
saved only by backing off to more general-purpose equipment like the arm
and human hands. (Years later, the lesson had to be relearned on the
Intelsat salvage flight...) As future plans -- like those for the Syncom
repair -- accordingly ditched the fancy hardware, they also lost their
requirement for the MMU.

The MMU docking pin on Solar Max had a screw placed in the a wrong
place (at build) that prohibited the docking, with the MMU interface.

Nelson actually *had* the grabber over the trunnion pin that it was
to grab, and had it tried to grab, it probably would have succeeded.
But he couldn't get it quite far enough onto the pin to trigger it, and
*there was no manual trigger*! The mission was salvaged only by some
spectacular good luck -- Solar Max was tumbling and its batteries were
nearly drained, and mission control had pretty much written it off, but
it managed to restabilize itself pointed *exactly* at the Sun -- and
some careful arm work.

I don't remember the P/W details, but it was the same general story:
the fancy grappling hardware didn't fit, but *this* time there was a
hands-and-arm backup plan, and it worked.

For the Syncom repair, they didn't bother with the fancies at all. Slide
the orbiter up beside the satellite; a spacewalker reaches out and quickly
clamps a handle on it, and proceeds to take the spin off the massive
spinning satellite by *grabbing the handle and pulling* each time it comes
past. Grapple with arm, fix defective hardware, release satellite again.
And finally, put spin back on by shoving on the handle, waiting until it
comes around again, shoving again, repeat as necessary until desired spin
rate is built up. Worked the first time. No need or use for MMU.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@xxxxxxxxxxxxx
.

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