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Space Forum / Shuttle / December 2007eco sensors.
I have some questions here. Are they all in the same place, or spaced around the tank? How do they differ to the oxygen ones? Following out of that, what are they using to detect the level. I wondered if some hydrogen condensate was forming on the sensors, or if it was a true open circuit measurably different from the wet and dry readings. With one failed, I'd be wanting to bring the level down, then up again and see what occurred. Its amazing that such an apparently simple system can have behaviour which defies the logic and inspection of humans. I'm still suspicious of the connections to the actual sensor elements, as it has to be something to do with the temperature, or rather the different contraction amounts of the interface which can cause this. Assuming of course that its not a wiring problem elsewhere. Brian  SignatureBrian Gaff - briang1@blueyonder.co.uk Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! Musing along here in my usual manner... Did they ever have issues in the Apollo config? How old are these sensors, ie are they part of the batch which had problems before. If they behaved in Apollo, what is different about this application, orientation, siting? As for what they may do, well, I'd imagine its not worth doing anything unless they know why its happening, as even swapping the sensors or the whole tank is not going to make things better without an understanding of the reason is it? I bet they are glad this did not happen on the previous mission though. Brian SignatureBrian Gaff - briang1@blueyonder.co.uk Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! >I have some questions here. > Are they all in the same place, or spaced around the tank? [quoted text clipped - 18 lines] > > Brian > Musing along here in my usual manner... > [quoted text clipped - 47 lines] > > - Show quoted text - well its a scrub today apparently the astronaut office is actually trying to protect the crew. apparently nasa had planned to fill tanks completely launch in a one minute window to save fuel put on their manager hats and fly...... those manager hats tend to kill occasionally.............. On Dec 9, 9:04 am, "hall...@aol.com" <hall...@aol.com> wrote: > > Musing along here in my usual manner... > [quoted text clipped - 58 lines] > > those manager hats tend to kill occasionally.............. Wrong on all accounts. It was the managers that scrubbed. Yes, and as the original all four short window plan came out of the flight crew office, I don't see anyone is in a conspiracy here at all. Some people are more cynical than I am around here! Its ironic though, that if the previous attempt had not occurred, and this was the first try, they would have gone on the old rules anyway. Stick the voltages on, and 'listen' to the actual signature of the signals coming from the sensors. There are distinctive sounds of poor connections. Of course, you cannot have any sparks near hydrogen....! So Holly Ridings is looking at a stage eva. I guess this would be Sarj again, he said changing the subject... Brian SignatureBrian Gaff - briang1@blueyonder.co.uk Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! On Dec 9, 9:04 am, "hall...@aol.com" <hall...@aol.com> wrote: > On Dec 9, 7:44?am, "Brian Gaff" <bria...@blueyonder.co.uk> wrote: > [quoted text clipped - 67 lines] > > those manager hats tend to kill occasionally.............. Wrong on all accounts. It was the managers that scrubbed. > > those manager hats tend to kill occasionally.............. > > Wrong on all accounts. �It was the managers that scrubbed.- Hide quoted text - > > - Show quoted text - manager hats definetely killed the challenger crew..... lets hope they dont try launching around the end of january! Apollo one, challenger and columbia all occured in this time frame Well, Steve Has sent a message to Peggy apologising, but as soon as they get a tank they are happy with, they will be coming, or words to that effect. Sounds like they are thinking of swapping out the tank and taking this one apart to see whats going on once and for all?? Mysteries like this are annoying, but interesting, and its all knowledge to be stored for the future. Brian SignatureBrian Gaff - briang1@blueyonder.co.uk Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! On Dec 9, 7:44?am, "Brian Gaff" <bria...@blueyonder.co.uk> wrote: > Musing along here in my usual manner... > [quoted text clipped - 53 lines] > > - Show quoted text - well its a scrub today apparently the astronaut office is actually trying to protect the crew. apparently nasa had planned to fill tanks completely launch in a one minute window to save fuel put on their manager hats and fly...... those manager hats tend to kill occasionally.............. > Sounds like they are thinking of swapping out the tank and taking this one > apart �to see whats going on once and for all?? > Mysteries like this are annoying, but interesting, and its all knowledge to > be stored for the future. > > Brian well I am a techicia and hate intermittents...... since these sensors fail all the time and the trouble hasnt been solved. how hard would it be to adapt sensors from a current launch vehicle and substitute them in? wonder if all the sensors are old and going bad by aging? >> Sounds like they are thinking of swapping out the tank and taking this one >> apart ?to see whats going on once and for all?? >> Mysteries like this are annoying, but interesting, and its all knowledge to >> be stored for the future. >> >> Brian That might be the best way to go. I think they would want to open the aft of the orbiter and check whatever wiring connections are there. But if everything checks out there, I agree with you, swap out the tank and repair the old one. >well I am a techicia and hate intermittents...... I used to be an electronic bench technician too, and I hated the intermittent problems. I used to component level repair telephone switching equipment, and never understood why a module will work in one rack but not another. >since these sensors fail all the time and the trouble hasnt been >solved. [quoted text clipped - 3 lines] > >wonder if all the sensors are old and going bad by aging? There must be a better way. Seems like they could measure the flow and compute when the fuel level was getting low and shut down the engines based on those computations rather than what amounts to a gas gauge. Too bad float gauges wont work, but there has to be a better way to accomplish this. Since I recently read that there is a proposal to extend the retirement date beyond 2010, they are going to have to think of something more reliable. Regards, Jim in Houston. Contrary to popular opinion RN does not mean Real Nerd! Teddy Roosevelt's mother said: "Fill what is empty, empty what is full, and scratch where it itches" SignaturePosted via a free Usenet account from http://www.teranews.com Jim in Houston stelde de volgende uitleg voor : <SNIPPED> >Since I recently read that there is a proposal to > extend the retirement date beyond 2010, they are going to have to > think of something more reliable. Any source on that? I'd like to read it also, if possible.... André On Dec 9, 4:48�pm, Andr� PE1PQX <pe1pqx_geenvia...@planet.nl> wrote: > Jim in Houston stelde de volgende uitleg voor : > <SNIPPED>>Since I recently read that there is a proposal to [quoted text clipped - 4 lines] > > Andr� nasawatch link "Brian Gaff" > Following out of that, what are they using to detect the level. Piece of platinum wire, dunno if it senses resistance or what. > I wondered if some hydrogen condensate was forming on the sensors Could be. Or moisture in the connector, ground paths. > or if it was a true open circuit measurably different from the wet and dry > readings. They are calling it an "open circuit" but I suspect that it is more subtle. > Its amazing that such an apparently simple system can have behaviour > which defies the logic Which is why I suspect an interface problem, impedance mismatch, bad design. Replace the thing with one that will give a positive reading without this random crap. Interesting that it occurs during fast fill. I would try filling the tank on slow fill and see if it has an effect. Liquid hydrogen is strange stuff. > I'm still suspicious of the connections to the actual sensor elements Bad tack welds are another possibility as seen in the past. SignaturePosted via a free Usenet account from http://www.teranews.com What has changed to cause these multiple ECO sensor failures in recent years ? Or have those been unreliable all the time, but NASA launched anyways without mentioning sensor failure to the public ? Maybe when the cryogenic fuels are loaded, parts around the sensor contract at differing rates, maybe pulling something partially apart and making it go open circuit? These sensors are attached to the ETs and thus NASA must use new ones for every shuttle trip. The connector to the orbitor must take a beating when the ET is jettisoned. Maybe it's time to replace it? http://www.nasa.gov/images/content/122586main_ECO_charts1.JPG The picture shows that there are also similar sensors on top of tanks to detect when the tanks are full (and prevent overfill). We've only heard about the lower sensors which I assume are mission critical during flight whereas the top sensors are used only on the ground. However, has NASA given any indication that the "full tank" sensors have had similar unreliability, or have they been reliable while the "empty tank" sensors been the only ones to exhibit unreliable behaviour ? Are the ECO sensors as unreliable in the O2 and H2 tanks or is it only in the LH2 tank that there is unreliability ? Are temperatures of LH2 and LO2 in the tanks in roughly the same ballpark, or does LH2 have considerably colder temperature ? Do the "tank full" sensors get routed via the shuttle MDMs like the "tank empty" ones, or do they get connected directly to pad systems ? > Are temperatures of LH2 and LO2 in the tanks in roughly the same > ballpark, or does LH2 have considerably colder temperature ? Oh, come on, JD, there's been a *lot* of discussion over the years you've read this group about how the LH temps make materials choices much more difficult (the small molecule doesn't help, either). > Do the "tank full" sensors get routed via the shuttle MDMs like the > "tank empty" ones, or do they get connected directly to pad systems ? The schematics posted by NASA and also shown in Reinhardt's blog show everything going to the MDM. /dps > The schematics posted by NASA and also shown in Reinhardt's blog show > everything going to the MDM. In fact, the one *you* linked to. /dps "robert casey" > Maybe when the cryogenic fuels are loaded, parts around the sensor > contract at differing rates, maybe pulling something partially apart and > making it go open circuit? Right. The platinum wires are welded to connector posts, as well as the sensor leads. There have been instances of "operator training" required to improve the welds. So I wonder if it is a true weld where the metals combine or if it is a cold weld that is causing problems when chilled. > These sensors are attached to the ETs and thus NASA must use new ones for > every shuttle trip. The connector to the orbitor must take a beating when > the ET is jettisoned. Maybe it's time to replace it? Ice accumulation in the external part of the feed-through connector has caused some bad readings in the past. And a worn connector on the shuttle end is entirely possible. But I lean toward a weld problem since the sensors seem to go wacky during the tanking, implying some temperature issue. As well as chip problems on the electronics board that I mention elsewhere. SignaturePosted via a free Usenet account from http://www.teranews.com Does NASA know if the sensors fail "abrubtly" or is it a gradual thing ? I assume that the computers are programmed to generate an alarm when a valus goes below/above prescribed values. But do they record the values that are sampled ? Such a recording might show whether the alarm was the result of a suddently changing voltage or a gradually changing one or ne that is intermittent and finally goes off scale permanently. > Does NASA know if the sensors fail "abrubtly" or is it a gradual thing ? > > I assume that the computers are programmed to generate an alarm when a > valus goes below/above prescribed values. Well functionally if the sensors go dry during boost a command for engine shutdown is given. > But do they record the values > that are sampled ? Such a recording might show whether the alarm was the > result of a suddently changing voltage or a gradually changing one or ne > that is intermittent and finally goes off scale permanently. I think this describes the current method. Previously the interface card would only indicate wet or dry. In the past two flights they have installed an additional "voltage feed through" that allows the sensors to be monitored in an analog mode. And as I understand it there is now some plan to monitor the analog numbers during the climb. I really don't know any more myself. Hall said in the Dec 11 briefing that a tanking test will be run, and that a reflectometer will be spliced in so that it can look for circuit/connector problems once the tank is filled, and he remarked that he thinks this should find the problem. Another test, bench test in the lab, will be run druing thisstand-down, using the hydrogen level sensors and the cable and feed-through connector. The lab test will look for problems in that area. He would not predict whether a roll back would be needed until he sees the results of the tests and presumably identifies the specific cause. He said that it would be pointless to delay this mission and put the next mission on the pad as he has no more or less confidence in any other tank than the one that is already on the pad, and I think that his reasoning is correct on that point. SignaturePosted via a free Usenet account from http://www.teranews.com > I have some questions here. > Are they all in the same place, or spaced around the tank? The ECO ones are on a strut in the bottom of the LH tank. 4 across the width of the reinforcing structure above the opening to the LH feed line. This makes them more or less centered, and well in from the outer wall. Additional sensors are located at various levels of the tank, 1 or 2 to a level. > How do they differ to the oxygen ones? Location, it seems. > Following out of that, what are they using to detect the level. Platinum resistance wire. > Blind user, so no pictures please! NASA has of course put this out in picture form, and Reinhard illustrates his blog with those. Harder to describe with just words, of course. Hope this helps. /dps |
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