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Post by ka9q on Nov 15, 2011 22:28:19 GMT -4
Because the RCS burnoff and fuel dump was implicated in the failure of Apollo 15's main parachute, those procedures were deleted for the following missions. Apollo 16 landed with approximately 200 lbs of unused NTO/MMH. Oh right, I had forgotten about that parachute failure on Apollo 15. That explains it all; thanks. Speaking of parachute failures, before the cancellation of the Constellation program I saw an analysis by somebody in Air Force range safety saying that an abort during first stage flight of the Aries I would be unsurvivable because of chunks of burning solid rocket propellant raining down on Orion's parachutes. |
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Post by ka9q on Nov 15, 2011 23:03:42 GMT -4
It was Deke Slayton who lost consciousness. Stafford put his oxygen mask on then put an oxygen mask on Slayton. Good thing he listened to those safety briefs the airlines give about loss of cabin pressure. According to the ASTP medical report, the ACDR (Stafford) saw the N 2O 4 come in the vent; the other two crewmembers did not. The capsule initially landed in Stable II position (upside down). Stafford unstrapped himself and fell down into the tunnel. He got out the O 2 masks and handed them out. After the CM uprighted itself 3:30 after landing, he noticed the CMP (Brand) was unconscious and his mask was hanging on the side of his face. Brand was apparently out for about 50 seconds, though having his feet lower than his head may have contributed to this. Brand quickly recovered when his mask was repositioned and the O 2 flow increased. Estimated cabin concentration of N 2O 4 was 700 ppm peak and 250 ppm average, far above the safe limit of 3-5 ppm. 200 ppm can kill humans in an hour. The planned post-landing medical experiments were cancelled and the crew was examined and treated for the exposure. The CMP's blood pressure dropped sharply and he nearly passed out again while standing, but he recovered while lying on his back with legs elevated. The crew continued to feel tightness and burning in the chest with coughing on deep breaths. Lung X-rays were taken and the crew was observed in the sickbay overnight. The next day they actually found it harder to avoid coughing when breathing deeply. The DMP (Slayton) fainted for 1 minute while brushing his teeth but that was probably the effects of returning to gravity. There were continued signs of lung irritation over the next few days so they were treated with steroids. Finally their problems went away 3 days after landing, and exams a month later showed no residual aftereffects. Sounds like it could have been much worse. |
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raven
Jupiter
That ain't Earth, kiddies.
Posts: 509
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Post by raven on Nov 16, 2011 5:24:30 GMT -4
Yes to increased fuel costs putting the Titan out to pasture. Not just the costs of producing, but major handling costs at the launch site. RP-1 can be handled by people with no more certifications than for JP-x fuels, and with the same procedures -- Sheet 128, I believe, same as gasoline and diesel fuel. In fact, due to the removal of most alkenes and aromatics, RP-1 is *less* toxic than gasoline and diesel, at least according to Wikipedia. |
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Post by chew on Nov 16, 2011 13:45:49 GMT -4
(Brand) was unconscious and his mask was hanging on the side of his face. Thanks for the correction. I could have sworn I remember reading it was Slayton who passed out. Now it's going to drive me nuts figuring out where I mistakenly read that. |
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Post by ka9q on Nov 16, 2011 22:47:55 GMT -4
Well, Slayton did pass out later, but it was probably just due to a sudden drop in blood pressure from simply standing while readjusting to gravity.
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Post by PhantomWolf on Nov 17, 2011 3:31:47 GMT -4
Thanks Jay and Bob, you guys rock. You should get a movie together.  |
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Post by ka9q on Nov 17, 2011 9:22:32 GMT -4
Tom Stafford added quite a bit more color to this story in his book. He says that when Brand came to, he started thrashing wildly and punched Stafford in the face. Then his mask came off and he passed out again. So Stafford put it back on Brand and gave him a bear hug to pin his arms as he turned up his O2. This time Brand couldn't hit anybody before his head cleared.
The delayed effects of N2O4 poisoning were very evident in the crew. They felt much worse a day later than after they'd landed as it took time for fluid to build up in the lungs. This is why the stuff is so insidious. You breathe a fatal dose and you think you're fine, and then you die.
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Post by Glom on Nov 20, 2011 17:15:12 GMT -4
I remember asking this question some time ago but didn't get a clear answer back then. Good to have one now.
My frail mind has betrayed me, because I don't remember reading that in Deke! but I just checked again and it is indeed there. There's not a lot of it though. That's probably symptomatic of what made me feel a little bit underwhelmed about that book.
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Post by ka9q on Nov 21, 2011 1:30:02 GMT -4
I've heard of research into less toxic replacements for the classic hypergolic propellants but I haven't followed it closely. Has anyone heard anything?
I also see a fair bit of work with methane. What are its advantages, and why hasn't it been used before? Although it has a low boiling point of 177K and a low density of 0.423, those numbers are still better than for LH2.
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Post by Apollo Gnomon on Nov 21, 2011 3:27:50 GMT -4
There was a story a few months ago regarding people experimenting with LM engines (don't remember which of 'em) using non-hypergolic fuels. NASA, per the story, wasn't interested as they prefer not to add the complexity of an ignition system to an already man-rated motor/fuel combination.
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Post by ka9q on Nov 21, 2011 7:29:07 GMT -4
I've heard it many times: hypergolic engines are more reliable because they don't need an ignition system. But is that really true? Many other rocket components have much worse records.
Especially turbopumps. I remember two failures of the H2-O2-burning Ariane 1 third stage in the 1980s. But I can't think of many (or any) non-hypergolic engines that failed because of their ignition systems. Maybe the S-IVB on Apollo 6? The J-2 required much more than just a spark to reignite; it first had to get the turbines spinning.
Hypergolic rockets do fail. Large ones have often been destroyed by combustion instabilities early in development (e.g., Ariane L02). Smaller hypergolic rockets avoid turbopumps with pressure feeding, but then the whole system has to withstand a pressure above that of the combustion chamber. Check valves leaked propellants on Mars Observer. The high pressure helium bottle seal leaked on AMSAT-Oscar 10. A plug was left in a pneumatic valve vent port on AMSAT-Oscar 40. A propellant line in the Apollo 11 DPS nearly burst after landing due to a fuel freeze. Those are just a few I know off the top of my head.
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Nov 21, 2011 10:38:24 GMT -4
I've heard of research into less toxic replacements for the classic hypergolic propellants but I haven't followed it closely. Has anyone heard anything? No, I’m not familiar with that. I also see a fair bit of work with methane. What are its advantages, and why hasn't it been used before? Although it has a low boiling point of 177K and a low density of 0.423, those numbers are still better than for LH 2. I’ve done some ISP calculations for liquid methane and the conclusion I’ve come to is that it's only marginally better than RP-1. The small ISP advantage seems to be cancelled out by the fact it’s cryogenic and has a poor density. I suspect it has never been used before because it doesn’t offer enough over existing propellants. I think it’s been getting more attention lately because it may be an important fuel of the future, as it can be manufactured in part from in situ resources, particularly on Mars. It also has low toxicity and is clean burning. So in addition to performance, it does have some advantages that might make it a good fuel in the right application. I've heard it many times: hypergolic engines are more reliable because they don't need an ignition system. But is that really true? Surely it is. That’s not to say engines requiring an ignition source are unreliable, but anytime you don’t need something it has got to be simpler than when you do. Hypergolic rockets do fail. Large ones have often been destroyed by combustion instabilities Wouldn’t that be a potential problem with any type of propellant? The J-2 required much more than just a spark to reignite; it first had to get the turbines spinning. Well, the turbopumps need an ignition source to get started. I’m not certain about the J-2, but many engines use a solid fueled cartridge to produce the initial gas to get the turbines spinning. This of course requires a spark to ignite. It also puts a limit on the number of starts-restarts that are possible. It’s also true that many non-hypergolic engines use hypergols as the ignition source. I think the practice is to prime the propellant lines just upstream of the engine with hypergols so they are injected into the engine just ahead of the main propellants. The hypergols ignite spontaneously and start the main propellants burning. Of course this only works once, thus engines using this method can’t be restarted. Smaller hypergolic rockets avoid turbopumps with pressure feeding, but then the whole system has to withstand a pressure above that of the combustion chamber. Pressure-fed systems operate at much lower pressures than pump-fed systems for just the reason you state. This decreases ISP a bit, but it makes the extra weight of a pressurized fuel system more manageable. Note that even a pump-fed system has pressurized tanks, though they may be pressurized to only 2-3 atmospheres, rather than, maybe, 10-15 atmospheres like a pressure-fed system. Pressure-fed systems offer simplicity that make them attractive regardless of the propellant used. It’s true that most pressure-fed systems use hypergols, but the reasons for using a pressure-fed system isn’t necessarily related to the propellant used. A pressure-fed system might be attractive even if the propellant were, say, LOX/RP-1. Of course, when hypergols are used, we not only get the simplicity of a pressure-fed system, but also the elimination of an ignition system and a unlimited start-restart capability. Also note that one of the big advantages of hypergols that you didn’t mention is their good temperature range — they are easily storable. So hypergols do offer many advantages that have to be weighed against their toxicity. edit: spelling |
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Post by gwiz on Nov 21, 2011 11:59:27 GMT -4
No, I’m not familiar with that. a place to start. It was successfully tested on the Swedish PRISMA satellite. |
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Post by Apollo Gnomon on Nov 21, 2011 19:25:21 GMT -4
I've heard/read this described as "subtractive engineering" in contrast to "additive engineering."
At one end of the spectrum you have a 1960's VW Beetle, at the other end you have any product by Microsoft. For example.
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Post by ka9q on Nov 22, 2011 7:19:57 GMT -4
Another way to say it is that you're not done when there's nothing left to add, but nothing left to take out. I repeat that quote often, but I can't take credit for it.
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