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#41
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"Ed Kyle" wrote in news:1110339171.176808.196650
@g14g2000cwa.googlegroups.com: Will McLean wrote: I would argue that segmented solids with thrust vector control have a higher failure rate than the liquid engines used in the core stages of Titan, Delta II, Atlas II and STS during the same period. I count a premature SSME shutdown and a Titan first stage propulsion problem, vs. three SRB catastrophic failures on STS and Titan. Am I missing anything? Two liquid failures in a combined 234 core liquid stage cycles (113 STS + 121 Titan) is a 0.0085 failure rate. Three solid failures in a combined 468 booster cycles (234*2) is a 0.0064 failure rate, so solids had a lower realized failure rate in this comparison. Wasn't one of those liquid failures an in-flight shutdown of a SSME with a resulting abort-to-orbit? That might tip the statistics in favor of liquids. --Damon |
#42
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"Jon S. Berndt" wrote in message oups.com... (somewhat tongue-in-cheek): The STS SRBs are flown on a manned vehicle. Therefore, they are man-rated. Not really. Just because people ride them doesn't make them man-rated, at least if one applies NASA's man-rating standards to the vehicle. Fact is, Shuttle doesn't meet NASA's own standards for man-rating. -Kim- |
#43
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"Jon S. Berndt" wrote in message oups.com... FWIW: "Human-Rating Requirements, JSC - 28354" http://www.hq.nasa.gov/office/codea/...documentd.html That's been replaced by NPR 8705.2A. Look it up he https://ice.exploration.nasa.gov/Windchill/gov/nasa/esmd/web/jsp/bidders/BiddersFolderContents.jsp?folder=/Default/Bidder's%20Library/Reference%20Documents -Kim- |
#44
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"Jon S. Berndt" jsb.at.hal-pc-dot.org wrote in message ... Yes, I thought about that, too. Seems to me that roll control could be done with RCS quads on the CEV "service module" itself, or mounted on the upper stage? Current ELV practice is to use RCS for second-stage attitude control. I doubt RCS sized for vacuum operations would have much effect deep in the atmosphere. -Kim- |
#45
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Ed Kyle wrote: Will McLean wrote: I would argue that segmented solids with thrust vector control have a higher failure rate than the liquid engines used in the core stages of Titan, Delta II, Atlas II and STS during the same period. I count a premature SSME shutdown and a Titan first stage propulsion problem, vs. three SRB catastrophic failures on STS and Titan. Am I missing anything? Two liquid failures in a combined 234 core liquid stage cycles (113 STS + 121 Titan) is a 0.0085 failure rate. But if you count the Delta II and Atlas II cores, that changes. Will McLean Three solid failures in a combined 468 booster cycles (234*2) is a 0.0064 failure rate, so solids had a lower realized failure rate in this comparison. - Ed Kyle |
#46
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"Kim Keller" wrote in message
"Jon S. Berndt" jsb.at.hal-pc-dot.org wrote in message Yes, I thought about that, too. Seems to me that roll control could be done with RCS quads on the CEV "service module" itself, or mounted on the upper stage? Current ELV practice is to use RCS for second-stage attitude control. I doubt RCS sized for vacuum operations would have much effect deep in the atmosphere. -Kim- Whups. Overlooked that. I guess that's where some kind of fins might help. Just curious: is a little bit of roll rate OK? Some solid rocket-propelled ICBMs operate the same way, don't they - that is, no roll control? Jon |
#47
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Will McLean wrote:
Ed Kyle wrote: Will McLean wrote: I would argue that segmented solids with thrust vector control have Two liquid failures in a combined 234 core liquid stage cycles (113 STS + 121 Titan) is a 0.0085 failure rate. But if you count the Delta II and Atlas II cores, that changes. We were looking at segmented solids, but nonsegmented solids can provide an interesting comparison too. Delta II has suffered two failures in 118 missions. One was due to an SRB case burn through. One was caused by a failed SRB separation. I'm not sure how you classify the latter failure, but it was not an SRB propulsion problem. If we assume an average of six solids per launch (a guess), the realized solid failure rate is 1/708 = 0.0014. No first stage propulsion problems have occurred, but there have only been 118 "samples". I suspect that the sampling error is greater than 0.0014. There were only 30 Atlas IIAS flights, with four solids each. And no failures. So while we can't very accurately predict the failure probability for a hypothetical 31st launch, we can say that we have four times as many successful solid booster samples as first stage samples for Atlas IIAS. Looking back futher into the Delta flight history to get more samples, consider the 238 Delta flights since the introduction of the Long Tank Thor first stage in 1968. There have been 10 or so failures, including two outright SRB failures and two failures during first stage flight. One of the failures, in 1968, involved a control system failure at 108 seconds. The other, in 1986, involved a premature shutdown of the RS-27A engine due to an electrical glitch. Even if we only assume that the 1986 failure was the only first stage problem, we get a realized first stage failure rate of 0.0042. If we again assume an average of 6 SRBs per flight, we get an SRB failure rate of 2/1428 = 0.0014. - Ed Kyle |
#48
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Ed Kyle wrote: Will McLean wrote: Ed Kyle wrote: Will McLean wrote: I would argue that segmented solids with thrust vector control have Two liquid failures in a combined 234 core liquid stage cycles (113 STS + 121 Titan) is a 0.0085 failure rate. But if you count the Delta II and Atlas II cores, that changes. We were looking at segmented solids, but nonsegmented solids can provide an interesting comparison too. Delta II has suffered two failures in 118 missions. One was due to an SRB case burn through. One was caused by a failed SRB separation. I'm not sure how you classify the latter failure, but it was not an SRB propulsion problem. If we assume an average of six solids per launch (a guess), the realized solid failure rate is 1/708 = 0.0014. No first stage propulsion problems have occurred, but there have only been 118 "samples". I suspect that the sampling error is greater than 0.0014. There were only 30 Atlas IIAS flights, with four solids each. And no failures. So while we can't very accurately predict the failure probability for a hypothetical 31st launch, we can say that we have four times as many successful solid booster samples as first stage samples for Atlas IIAS. Looking back futher into the Delta flight history to get more samples, consider the 238 Delta flights since the introduction of the Long Tank Thor first stage in 1968. There have been 10 or so failures, including two outright SRB failures and two failures during first stage flight. One of the failures, in 1968, involved a control system failure at 108 seconds. The other, in 1986, involved a premature shutdown of the RS-27A engine due to an electrical glitch. Even if we only assume that the 1986 failure was the only first stage problem, we get a realized first stage failure rate of 0.0042. If we again assume an average of 6 SRBs per flight, we get an SRB failure rate of 2/1428 = 0.0014. - Ed Kyle So counting the other Atlas II models, the liquid first stage failure rate is either 2/415, or if you include the earlier Delta, 3/535, or ..0048-.0056. I think you need to include the separation failure for the smalller strap-ons, since it's a failure mode that isn't present without the booster, and it killed the mission. It then becomes .0021, which is still pretty good relative to the liquid stage. The interesting question is whether a failure of one of a pair of segmented solids should be considered one failure and one success out of two trials. The segment that failed had a twin poured from the same batch on the other booster, and range safety destroys it before you find out if it would also have failed later in the burn. Will McLean |
#49
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"Murray Anderson" wrote:
:A shuttle SRB would require modification to be used as an ordinary first :stage. At minimum it would need roll control and new guidance software. The :configuration would put a very dense first stage (specific gravity about :1.25) under a large hydrogen-burning upper stage and large payload and :fairing, so the current gimballing system might need hardware modifications :for faster response. You'd need more hydraulic fluid. :The current SRB reliability wouldn't carry over to the new configuration. If :the steering ever failed, you'd need to get the payload away very fast. It would also need a new thrust termination system, since I believe the current one is to blow the nose off. Not what you want to do if there's something sitting up there. -- "Millions for defense, but not one cent for tribute." -- Charles Pinckney |
#50
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On Thu, 10 Mar 2005 15:25:41 GMT, in a place far, far away, Fred J.
McCall made the phosphor on my monitor glow in such a way as to indicate that: :The current SRB reliability wouldn't carry over to the new configuration. If :the steering ever failed, you'd need to get the payload away very fast. It would also need a new thrust termination system, since I believe the current one is to blow the nose off. Not what you want to do if there's something sitting up there. The current SRB has no thrust-termination system. |
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