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"The most stupid thing they've done is stay with an experimental rubber/nitrous hybrid engine this whole time, instead of switching to liquid/liquid engine, a w

by termain 12y ago

"The most stupid thing they've done is stay with an experimental rubber/nitrous hybrid engine this whole time, instead of switching to liquid/liquid engine, a well proven technology." 1. They didn't stay with rubber/nitrous. 2. Like the sort used on Antares? "Seeing only the first paragraph, I already know that some rubber in the hybrid engine detached blocking the nozzle and causing the whole engine to explode." But what you know is wrong, they weren't using rubber. I think a good case can be made that they didn't do enough ground testing, but your post mixing disdain and falsity doesn't advance that case.

dandelany 12y ago
Point 1 is a good one, point 2 is not. Yes, liquid engines like the sort used on Antares, Soyuz (most reliable rocket ever built), Falcon, Proton, Atlas, Shuttle, Delta, Ariane, Saturn, and nearly every other orbital launch platform ever. Liquid/liquid engines, by any measure, are orders of magnitude more stable and well proven than hybrid rocket engines.
- deleted 12y ago
  [deleted]
- termain 12y ago
  My point is that they still fail. Both liquid and solid boosters are a lot more mature than hybrids, no doubt. But I'm not so sure that either is fundamentally more reliable. And for hybrids to mature, somebody has to use them. "Liquid/liquid engines, by any measure, are orders of magnitude more stable." What do you mean by stable? A reason to go with hybrids, at least on paper, is that they are mechanically simple but throttlable, hopefully combining the simplicity of a solid booster with the ability to throttle and shutdown of a liquid. Of course, much of that also applies to blowdown liquid systems, and I personally find a blowdown methane/lox system particularly compelling. I figure Virgin wanted to avoid cryogens, though.
marze 12y ago
"1. They didn't stay with rubber/nitrous." This you believe so strongly because a news story stated it? Wait for the accident report. It will say "rubber".
- termain 12y ago
  Aviation Week reported it back in May. So, yes. I'll keep an eye out for the accident report. http://m.aviationweek.com/space/new-fuel-boost-spaceshiptwo http://m.aviationweek.com/space/new-fuel-boost-spaceshiptwo
  - marze 12y ago
    Well you could be right, but it is very hard to imagine that being true since the plastic hybrid has only been tested once on the ground. Doing a flight test so soon would be totally insane. In any case, the disaster was undoubtably a result of inadequate ground testing. Problems like these are almost always the result of management pushing things faster than the engineering progress warrants.
    - termain 12y ago
      I think it's also possible that a bad fuel grain slipped through whatever QA process they had. You might count that as insufficient ground testing, though. "Problems like these are almost always the result of management pushing things faster than the engineering progress warrants." Coincidentally, we were talking about such an instance today at work, the Conestoga 1620. As relayed to me, the "low frequency noise" mentioned in the wikipedia post was a low frequency structural mode that was missed because management didn't want to pay for a high enough fidelity finite element analysis. https://en.wikipedia.org/wiki/Conestoga_%28rocket%29 https://en.wikipedia.org/wiki/Conestoga_%28rocket%29
    - Steko 12y ago
      Virgin has to get Brandon to space this year or their funding is subject to considerable clawback.
marze 12y ago
"2. Like the sort used on Antares?" I think Paul McCartney was about 23 years old when the engines powering that Antares launch vehicle were fabricated in Russia in their race against the Americans to the moon. An antique liquid/liquid vs an inadequately qualified hybrid: no winners.
- termain 12y ago
  I think they're a little newer than that, but that's a good point. Still, I'm not sure either engine was inadequately qualified. I'm not sure what constitutes adequate qualification, though. Both engines were ground tested at least some. And in Virgin's case, this flight was one of tests.
  - ceejayoz 12y ago
    > I think they're a little newer than that, but that's a good point. http://en.wikipedia.org/wiki/NK-33 http://en.wikipedia.org/wiki/NK-33 says the AJ-26 engines are from the 1960s and 1970s.

by termain 12y ago

dandelany 12y ago

Point 1 is a good one, point 2 is not. Yes, liquid engines like the sort used on Antares, Soyuz (most reliable rocket ever built), Falcon, Proton, Atlas, Shuttle, Delta, Ariane, Saturn, and nearly every other orbital launch platform ever. Liquid/liquid engines, by any measure, are orders of magnitude more stable and well proven than hybrid rocket engines.

deleted 12y ago
[deleted]
termain 12y ago
My point is that they still fail. Both liquid and solid boosters are a lot more mature than hybrids, no doubt. But I'm not so sure that either is fundamentally more reliable. And for hybrids to mature, somebody has to use them. "Liquid/liquid engines, by any measure, are orders of magnitude more stable." What do you mean by stable? A reason to go with hybrids, at least on paper, is that they are mechanically simple but throttlable, hopefully combining the simplicity of a solid booster with the ability to throttle and shutdown of a liquid. Of course, much of that also applies to blowdown liquid systems, and I personally find a blowdown methane/lox system particularly compelling. I figure Virgin wanted to avoid cryogens, though.

marze 12y ago

"1. They didn't stay with rubber/nitrous." This you believe so strongly because a news story stated it? Wait for the accident report. It will say "rubber".

termain 12y ago
Aviation Week reported it back in May. So, yes. I'll keep an eye out for the accident report. http://m.aviationweek.com/space/new-fuel-boost-spaceshiptwo http://m.aviationweek.com/space/new-fuel-boost-spaceshiptwo
- marze 12y ago
  Well you could be right, but it is very hard to imagine that being true since the plastic hybrid has only been tested once on the ground. Doing a flight test so soon would be totally insane. In any case, the disaster was undoubtably a result of inadequate ground testing. Problems like these are almost always the result of management pushing things faster than the engineering progress warrants.
  - termain 12y ago
    I think it's also possible that a bad fuel grain slipped through whatever QA process they had. You might count that as insufficient ground testing, though. "Problems like these are almost always the result of management pushing things faster than the engineering progress warrants." Coincidentally, we were talking about such an instance today at work, the Conestoga 1620. As relayed to me, the "low frequency noise" mentioned in the wikipedia post was a low frequency structural mode that was missed because management didn't want to pay for a high enough fidelity finite element analysis. https://en.wikipedia.org/wiki/Conestoga_%28rocket%29 https://en.wikipedia.org/wiki/Conestoga_%28rocket%29
  - Steko 12y ago
    Virgin has to get Brandon to space this year or their funding is subject to considerable clawback.

marze 12y ago

"2. Like the sort used on Antares?" I think Paul McCartney was about 23 years old when the engines powering that Antares launch vehicle were fabricated in Russia in their race against the Americans to the moon. An antique liquid/liquid vs an inadequately qualified hybrid: no winners.

termain 12y ago
I think they're a little newer than that, but that's a good point. Still, I'm not sure either engine was inadequately qualified. I'm not sure what constitutes adequate qualification, though. Both engines were ground tested at least some. And in Virgin's case, this flight was one of tests.
- ceejayoz 12y ago
  > I think they're a little newer than that, but that's a good point. http://en.wikipedia.org/wiki/NK-33 http://en.wikipedia.org/wiki/NK-33 says the AJ-26 engines are from the 1960s and 1970s.