(J. Porter Clark) writes:

"Jorge R. Frank" writes:

Porter Clark used to post here... maybe he will de-lurk.


Thanks Jorge.

Huh? Whazza?

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.


Hi Porter,

Thanks for getting back to us!

I linked to your website on Angelfire after an intensive Google
search in response to a question by Jordan Hazen about the
ATU having water lines running to it.

Since the ATU in the cupola shares an equipment bay with several
other electronics modules (such as the one that controls the station's
robotic arm, etc.) I was wondering if you could tell us if the cold
plates are shared between the modules in the cupola or if there are
separate water lines running to each, such as one for the ATU, another
for the robotic arm controller [I have no handy acronym for that :-)]
etc, or if they share a common cold plate which water cools for
everything in the cupola?

What is that connector at the top of the ATU, designed for immortals
;-), actually for?

As regards the rear cabling, I'm guessing:

1. Left-most multipin connector looks like it loops pins to
possibly +V or GND. I'm assuming this is the addressing connector
and the connections are unique per ATU? In practice does this
allow an ATU to be swapped with any other ATU in case you have
a failure and can afford to sacrific one less used? Has that
ever happened on the ISS?

2. The middle connector has the 3 fiber optic communications links.
So what is up with that 3rd fiber? From your caption it sounds like
it is dark? Does it not exist in the flight configuration?

3. The bottom right connector is power? Are you running a standard
voltage on the ISS? Curious to know if it's 48VDC?

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.


Does the cold plate attach on the finned side of the ATU?

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

Yeah not much outside the telecom space and high end computers
used fiber optic in that time-frame. Any insight into what
caused those failures?


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.

That makes good sense. Your photo site seems to be depicting
interoperability testing between the Russian comm gear and
NASA's, among other things. Was that the case?

If Jordan has any further questions, I'll defer them to him.

It was great to get to actually write you here, many, many
thanks for getting back to us.

Dave