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ISS ATU's (communication panels) need water cooling? Why?
"Jorge R. Frank" writes:
Porter Clark used to post here... maybe he will de-lurk. 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. 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. 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. |
#12
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ISS ATU's (communication panels) need water cooling? Why?
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#13
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ISS ATU's (communication panels) need water cooling? Why?
David Spain writes:
(J. Porter Clark) writes: 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? The ATUs use the smallest ("-5") coldplates in the inventory. As far as I know, nothing else uses them or even has the same bolt pattern. The three ATUs in the airlock share one big coldplate. None of the other ATUs share coldplates with anything else. I don't know much about the ATCS plumbing, except that Node 2 is unusual in that it has two completely separate water loops. I was under the impression that the coldplates are generally connected in series in any given area. If I get a chance, I'll actually look at some diagrams. What is the reason for asking? The acronym you're searching for is RWS, Robotic Work Station. What is that connector at the top of the ATU, designed for immortals ;-), actually for? It's a test connector for factory use. The Harris documentation gives names to the pins, but that's about it. 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? That is the address connector. The addresses correspond to locations. You can swap ATUs from one place to another. As far as I can remember, we've never swapped any audio boxes on orbit, but we did swap that one ATU in the Airlock with a "new" unit twice. None of the other audio boxes have failed, although there have been some unexplained hiccups that have been cleared by power cycling. 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? The ATU has 4 fiber optic connections: 2 in, 2 out. Redundant buses. A common connector for both buses violates separation of redundant paths, but not too much. 8-) We couldn't figure any good reason for an ATU cable to have exactly 3 fibers. Admittedly, it was a test cable of uncertain origin. 3. The bottom right connector is power? Are you running a standard voltage on the ISS? Curious to know if it's 48VDC? Like most Freedom-era boxes, and a good many later ones, it runs on 120 VDC. ISS using 120 VDC instead of 28 VDC or something else is of long and tedious history. Does the cold plate attach on the finned side of the ATU? No, it goes on the bottom, which is smooth and unpainted. The fins (really pins) are on the sides. 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? I'd have to do some digging; it's been long enough for my aging memory to forget. IIRC, they were from parts failures inside the units. Because the first two units we put into that one location both failed, albeit in somewhat different ways, we spent some time proving that the location wasn't the problem and that we wouldn't be wasting time and money installing a third ATU there. 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? Yes. The "Joint" Airlock was designed to be used with the Russian and U.S. EVA suits. We were testing the hardline and RF communication with both types of suits. All of the voice comm with these suits ultimately goes through the ISS (U.S.) audio system, so we were doing a dev test to make sure that everything worked together. We ran many tests like that from 1994 to 2001. The disappointing thing about the Airlock Mockup testing was that the program decided not to fly some hoses or cables that are necessary to use the Orlan in the Airlock. Therefore, much of that compatibility testing was ultimately wasted. I do not know if this situation was ever corrected. 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. My pleasure. |
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ISS ATU's (communication panels) need water cooling? Why?
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#15
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ISS ATU's (communication panels) need water cooling? Why?
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. |
#16
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ISS ATU's (communication panels) need water cooling? Why?
In article ,
Jordan Hazen wrote: 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. And after being mounted, in the lower-right corner of this image: http://spaceflight.nasa.gov/gallery/...130e009694.jpg It looks deeper from that angle. I wonder if those water loops will be tucked more out of the way later, or if other equipment-- maybe the robotic workstation when it's finally moved?-- will end up in front of them). -- Jordan. |
#17
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ISS ATU's (communication panels) need water cooling? Why?
"David Spain" wrote in message ... (J. Porter Clark) writes: Like most Freedom-era boxes, and a good many later ones, it runs on 120 VDC. ISS using 120 VDC instead of 28 VDC or something else is of long and tedious history. OK, I *won't* ask, I'll wait for Jorge to write about it someday! ;-) It's been discussed in the sci.space groups in the past. Here's a hint: I remember seeing posters in the EE building at Purdue talking about the 20kHz power system for Freedom... Here's a hit at NRTS: http://ntrs.nasa.gov/search.jsp?N=13...ll&Ntt=2 0khz Computer modeling and simulation of a 20kHz ac distribution system for Space Station Author(s): Tsai, Fu-Sheng; Lee, Fred C. Abstract: A computer model of a 20 kHz, ac distribution testbed for Space Station is presented. The system consists of six resonant inverters, a one-hundred-meter transmission line, and three load receivers: a dc receiver, a ... NASA Center: NASA (non Center Specific) Publication Year: 1987 Added to NTRS: 2004-11-03 Accession Number: 88A11827; Document ID: 19880024600 Granted the above isn't a history, but it does show how extreme the "research" part of R&D was for portions of the Freedom program. Freedom provided for lots of research "sandboxes" for people to play in. Not surprisingly, when costs soared, schedules slipped, and NASA was forced to redesign the station, many of these "sandboxes" quickly disappeared. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon |
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