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"Ed Kyle" wrote in message oups.com... Jon S. Berndt wrote: ... Considering that (according to the original article in TSR about SRBs used for a CEV launcher) the concept has the support of some in the astronaut office, and that strap-on SRBs would be used anyway to supplement an Atlas or Delta Medium launcher for CEV (according to AvWeek, above), I feel that Dinerman shouldn't have blown off the concept so casually. The overall reliability record is good for solid boosters, but when they've gone, they've gone nasty in a hurry. I'm thinking of the Titan 34D in 1986, of a Titan 4 in the early 90s, and of the Delta II during the late 90s and a Delta during the late 70s. These all ended in big detonations. That is why incorporating them into manned launchers is so difficult. Again: which one is safer, a single STS SRB as a first stage, or a Delta IV or Atlas Medium with several strap-on SRBs? Single SRB is statistically more reliable. But is it safer? Probably. On the other hand, an argument can be made that neither SRB or EELV with solids would be safer than an all-liquid system. The problem with this editorial is that it starts out arguing for a new heavy-lifter, but ends up talking about whether solid boosters should be used for manned launches. It would have been better to keep the two topics separate. Few will argue that solids shouldn't be used for unmanned, heavy-lift launchers. That discussion is about how big heavy-lifters should be - or whether they're needed at all. The solids-for-humans question is an entirely different problem. The astronaut office is going to have a say in this one. Right now, if sounds like the majority is saying "no". It could be that we already have the heavy launcher (EELV Heavy - just augmenting a little can get it up to 30 tons to LEO) but that a new or derived all-liquid Medium is needed to boost the 20 ton-ish CEV. It could be a matter of adding a second RS-68 or RD-180 to the EELV boosters. - Ed Kyle 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. Murray Anderson |
#12
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Ed Kyle wrote:
The overall reliability record is good for solid boosters, but when they've gone, they've gone nasty in a hurry. I'm thinking of the Titan 34D in 1986, of a Titan 4 in the early 90s, and of the Delta II during the late 90s and a Delta during the late 70s. These all ended in big detonations. [nerd] NONE of these detonated. [/nerd] |
#13
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"Ed Kyle" wrote in message
Single SRB is statistically more reliable. But is it safer? Probably. On the other hand, an argument can be made that neither SRB or EELV with solids would be safer than an all-liquid system. I'm not so sure this one is cut-and-dried, either. Liquid boosters have many more moving parts. Are they more likely to fail, or to be prematurely shut down (think of shuttle history)? How does solid propellant act in the most likely failure scenarios? Liquid propellant? I remember the Titan SRB failure shortly after 51-L. That one was spectacular. But the Shuttle SRB seems more robust. Also, in the case of an axial configuration for launching a CEV, there would presumably be less odd flexing loads placed on the SRB. The problem with this editorial is that it starts out arguing for a new heavy-lifter, but ends up talking about whether solid boosters should be used for manned launches. It would have been better to keep the two topics separate. Yes, I noticed that, too. Few will argue that solids shouldn't be used for unmanned, heavy-lift launchers. That discussion is about how big heavy-lifters should be - or whether they're needed at all. Yep. The solids-for-humans question is an entirely different problem. The astronaut office is going to have a say in this one. Right now, if sounds like the majority is saying "no". Why do you say that? Jon |
#14
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"Ed Kyle" wrote in message
In addition to the flight safety issues that make solids a bigger challenge for human launches, there is a perhaps more important ground safety issue. Accidents on the ground have killed far more people than have died in space missions. The presence of "live" SRBs in the VAB has added cost to the shuttle program due to safety limitations, for example. A worst-case fear has long been the unlikely-but-not- impossible case of an SRB lighting up within the VAB during processing. From what I've read, it takes a whole lot to ignite the SRB propellant. Is this really a concern? Jon |
#15
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"Murray Anderson" wrote in message
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 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? 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's a problem with any single-engine configuration. With all that weight out front I'm thinking the stack would be stable enough, CG ahead of CP, to get away in time. You could also maybe add fins to the SRB. The SRBs work for the first two minutes, and qbar is high enough to make fins useful throughout most of the envelope, I'd think. Jon |
#16
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"Jon S. Berndt" jsb.at.hal-pc-dot.org wrote in message ... Taylor Dinerman's article in "The Space Review" this morning raised some questions for me. 1) It did not appear that the question of infrastructure support was addressed in the article - only the need for heavy lift. A shuttle derived heavy lift vehicle keeps getting mentioned, but the part that seems to be ignored is the cost of the supporting workforce, maintaining productions lines, etc. I haven't yet seen any plausible situation requiring an HLV to be launched at regular and frequent intervals that might justify the need for an HLV. Am I missing something? NASA seems to want something capable of 55 tons to launch the fuel to get to the Moon in just one launch. At least one industry study has indicated that 55 tons is the ideal size. Personally I disagree and think 30-35 would work just fine. 2) The idea of using an SRB for a CEV launcher was gently dismissed in the article with the argument that the SRBs are inherently less safe than liquid boosters. Having fired successfully 225 out of 226 times, and with the single failure (SRB burnthrough) being an abortable failure in the CEV (possibly even an ATO?), I'd suggest that the SRB has earned some respect. Regardless, the heavy lift forms of the Delta and Atlas that were mentioned also use SRBs, no? Multiple ones? Now, which launcher might be more reliable? The concept of using a SRB for a manned rocket just scares me. No engine out, no health monitoring, no shut down capability. It violates every rule NASA has set for manned flight. The Delta and Atlas Heavies use no solids but have no engine out capability. Based on NASA's proposals I would suggest a 2 engine version of the Atlas and Delta. A 2 engine first stage and 2 MB/RL 60 engine second stage. This would meet almost every requirment NASA is proposing. It would also allow for future expansion and Heavy Lift in the long term. |
#17
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"Jon S. Berndt" jsb.at.hal-pc-dot.org wrote in message ... "Murray Anderson" wrote in message 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 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? 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's a problem with any single-engine configuration. With all that weight out front I'm thinking the stack would be stable enough, CG ahead of CP, to get away in time. You could also maybe add fins to the SRB. The SRBs work for the first two minutes, and qbar is high enough to make fins useful throughout most of the envelope, I'd think. Jon The CG is way behind the CP at least until the SRB is close to burnout. There isn't all that much weight up front. The specific gravity of a Centaur upper stage is something like .25 and the payload, including the payload fairing, is even less dense. Even when the SRB is half burned the CG is 2 or 3 diameters behind the CP. I'm sure the problems can be worked out, on a cost-plus contract. Fins would be highly desirable. Murray Anderson |
#18
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"Murray Anderson" wrote in message
The CG is way behind the CP at least until the SRB is close to burnout. There isn't all that much weight up front. The specific gravity of a Centaur upper stage is something like .25 and the payload, including the payload fairing, is even less dense. Even when the SRB is half burned the CG is 2 or 3 diameters behind the CP. Is the CG really so far behind the CP - and for that long? Where do you get that data from? Remember 51-L? They _appeared_ neutrally stable, to me, as they flew from 73 seconds to destruct - for some of that time flying nose forward into Vinf. Add on an upper stage and a "20 metric ton" CEV and I'd guess that the CG is ahead of the CP. Might be an interesting "extra credit" problem for someone ... Jon |
#19
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Jon S. Berndt wrote:
"Ed Kyle" wrote in message ... an argument can be made that neither SRB or EELV with solids would be safer than an all-liquid system. I'm not so sure this one is cut-and-dried, either. Liquid boosters have many more moving parts. Are they more likely to fail, or to be prematurely shut down (think of shuttle history)? How does solid propellant act in the most likely failure scenarios? Liquid propellant? Liquid boosters have a slightly higher failure rate, but they may still be safer for crewed flight because their failure modes are more benign. This would make escape systems more likely to succeed. The solids-for-humans question is an entirely different problem. The astronaut office is going to have a say in this one. Right now, if sounds like the majority is saying "no". Why do you say that? The AWST article included these paragraphs. "The Astronaut Office at the Johnson Space Center is not keen on any of these options (AW&ST June 14, 2004, p. 15). The astronauts have taken a position that "human rating should be designed in, not appended on." The Office is calling for an order of magnitude reduction in the risk of fatalities on ascent, and has expressed concern that an EELV--be it Delta or Atlas--may not be safe enough even with upgrades." " ...The concern in part is due to the potential for rare, but instantaneously catastrophic, failure modes inherent with solid rocket boosters on the medium options for both Atlas and Delta EELVs. Such failure modes would be difficult for an advanced health-monitoring system to catch before loss of control to separate the CEV safely." - Ed Kyle |
#20
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Scott Lowther wrote:
Ed Kyle wrote: The overall reliability record is good for solid boosters, but when they've gone, they've gone nasty in a hurry. I'm thinking of the Titan 34D in 1986, of a Titan 4 in the early 90s, and of the Delta II during the late 90s and a Delta during the late 70s. These all ended in big detonations. [nerd] NONE of these detonated. [/nerd] Sure they did, when the range safety systems initiated. The dictonary says that a detonation is "the act of detonating an explosive". Irregardless, solids have, as AW&ST put it, "rare, but instantaneously catastrophic, failure modes" that liquids do not have. These flights demonstrated some of "instantaneously catastrophic" modes. - Ed Kyle |
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