yee@trident.arc.nasa.gov (Peter E. Yee) (04/10/90)
Just watched them scrub the launch. Apparently APU 1 was not performing within acceptable margins. Although there is sufficient time in the window to perform a recycle, the decision was that this problem will require enough time to merit a full scrub. -Peter Yee yee@ames.arc.nasa.gov ames!yee
nraoaoc@nmtsun.nmt.edu (Daniel Briggs) (04/10/90)
In article <47051@ames.arc.nasa.gov> yee@trident.arc.nasa.gov (Peter E. Yee) writes: >Just watched them scrub the launch. Apparently APU 1 was not performing >within acceptable margins. Although there is sufficient time in the window >to perform a recycle, the decision was that this problem will require enough >time to merit a full scrub. > -Peter Yee As I watched them scrub, it seemed to me that there has been an awful lot of trouble in the course of the program with the APUs. Are the APUs just fuel cells ala Apollo, or are they something more sophisticated? (BTW, I am under the impression that this is an acronym for Auxiliary Power Unit. Am I right?) Has any of the NASA watchers (or even NASA itself), compiled a simple list of all the scrubs in the Shuttle program, and the primary cause of each? It would be fascinating to see this list sorted by basic category. My guess is that APUs would come in about third, right after weather and generalized computer troubles. Anyone have the data we need to do this? ----- This is a shared guest account, please send replies to dbriggs@nrao.edu (Internet) Dan Briggs / NRAO / P.O. Box O / Socorro, NM / 87801 (U.S. Snail)
techpubs@PRC.Unisys.COM (Technical Pub. Vince Short) (04/11/90)
Speaking of the launch scrub this morning, on the rebroadcast audio via Amateur Radio from the Goddard Space Flight Center, the numbers meantioned for the APU revs was around 114 to 120. Does anyone know if this is 120 rpm, 12000 rpm, 120,000 rpm or what?
jabishop@uokmax.uucp (Jonathan A Bishop) (04/11/90)
In article <4076@nmtsun.nmt.edu> dbriggs@nrao.edu (Daniel Briggs) writes: >Are the >APUs just fuel cells ala Apollo, or are they something more >sophisticated? (BTW, I am under the impression that this is an >acronym for Auxiliary Power Unit. Am I right?) Has any of the NASA No. This sort of APU's are systems which, I believe, burn hydrazine fuel in order to drive ammonia through a turbine to generate power. They are used only for launch and landing. The Shuttle also carries three fuel cells which generate electricity and drinking water. By the way, not all APU's are the same. Many jet planes (esp. military transports) carry an APU which is essentially a small jet engine. -- jabishop@uokmax.ecn.uoknor.edu "I'm President of the United States and I'm NOT going to eat any more broccoli!" -- George Bush
amichiel@rodan.acs.syr.edu (Allen J Michielsen) (04/12/90)
>In article <4076@nmtsun.nmt.edu> dbriggs@nrao.edu (Daniel Briggs) writes: >>Are the >>APUs just fuel cells ala Apollo, or are they something more >>sophisticated? (BTW, I am under the impression that this is an >>acronym for Auxiliary Power Unit. Am I right?) Has any of the NASA > While avoiding a whole big discussion of these buggers, and since I am not the best qualified to give technical details on this, I will try for a very simple explaination. The APU's for the shuttle which we are currently discussing could & should be thought of as the following: The APU is very much like a chemical turbine similiar to/not unlike a jet engine. Instead of jet fuel (kerosene) & atmos air being brought together & burned, the seperate chemicals (all pretty nasty, toxic, & dangerous stuff) are brought together creating a exothermic reaction (explosion). The explosion drives turbines in both cases & the energy is used to drive pumps. generators, compressors, or whatever is hooked up to it. Where jet engines get rid of the excess heat in the exhaust gas stream, the APU's use a heat exchanger & the excess heat goes into the radiator portion of the cargo bay doors, which basically have to be opened after launch to dissipate this energy. A jet engine is a open system & the APU's are closed for obvious reasons. The waste stream is used a differently for a engine than the APU, but the principle is the same. As I listened to the audio feed, of the aborted launch, one of the APU's was reporting too many RPM's. The problem couldn't be isolated to 1 of the most likely 2 causes & the launch was scrubbed because of the risk involved. The 2 most likely causes were 1. bad rpm pickup 2. bad/faulty/error in the fuel control loop. The APU could have been shut down & if it went down o.k., just done without. This could be bad if another APU developed a in flight problem. Trying to guess what sensor was wrong or control loop was bad would have been dangerous to the entire deal. Too much fuel or too bad a mix & the APU would be a bomb. I really think that NASA did the right thing pulling the plug & fixing the problem, the bad PR would be much worse IF another fatal accident were to occur.