In article ,
J. Porter Clark wrote:
ATU power consumption when in full power mode is about 28 W.
This is just enough so that we can't count on ambient air to
keep it cool in zero G. All of the flight ATUs are on cold
plates. The mount in the Cupola is unusual in many ways.
There's a flight rule that allows the ATUs to run for some
period of time (IIRC, 30 minutes) without cooling water running.

The ATU was originally designed to allow for either cold plate
cooling or for ambient airflow at some rate and temperature.
That's why it has pin-fin heatsinks on the outside. However,
Boeing never found a good way to make the airflow method work in
any of their elements, and so it was abandoned.

ATUs sitting open in a rack in one G don't get hot enough to
need any help cooling, although the rack we usually put them in
for testing has fans in it.

The ATU features were the result of requirements from many
groups of people, and so it has a lot of buttons for features
that most people don't use--probably about like your office
phone or cell phone. Usually, the crew just leaves them
configured in the Big Loop (with S/G 1) and they go to other
loops as they need. There is a way to call from one ATU to
another, but the crew isn't even trained to use it nowadays.

The ATUs were designed in the late 1980s. They were fairly
advanced in those days, but they are big and bulky by today's
standards.

Thanks for all the interesting details.

I found a NASA photo showing the Cupola ATU in question just before
installation (taken around the same time as the video shown earlier?),
with its cold-plate and mounting bracket attached:

http://spaceflight.nasa.gov/gallery/...130e009537.jpg

This provides good frame of reference for the size and bulk. At least
they're not quite so *deep* as those non-flight units pictured in the
test rack on your web site.

They do work, however. We have had two ATU failures
on orbit; they were both in the same location in the Airlock.

The Airlock is the only element with 3 ATUs. The reason
the Airlock needs 3 is that 2 of them are used for hardline
connections to two EVA-suited crewmen. This was a cheaper
solution than the creation of a unique interface box just for
the suits.

Ah. I'd guessed as much from following the attached cables in
downlinked imagery...

--
Jordan.