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#121
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Why not use jets as 1st stage? (was Multiple Engines???)
wlhaught wrote:
Alright, back to powered flybacks for first stages. Are jet engines worth the trouble of extra systems? As I recall, I read somewhere that the shuttle uses half its fuel to reach 1,000 mph. You sure? I have a copy of a speed/height/time diagram of the shuttles ascend. 1000 mph would be 1600 km/h. The diagram says that this speed is reached within the first minute of launch at a height of about 8-10 km. Launch takes 8.5 minutes, boosters burn 2 minutes. If you would say half of the boosters fuel is used up at 1000 mph that would fit. But total fuel including the fuel of the big external tank? Ok, solid booster rocket fuel is quite heavy, and the booster burns faster in the beginning than at the end. So maybe overall this could be true. But what does it mean? Solid rocket boosters are not economic? A somewhat related fact: the shuttle has to throttle its main engines during ascent within atmoshpere, because the fragile orbiter wings can't stand the wind pressure. Does anone know how much of a performance penalty this means? (And at what height/speed this happens) |
#122
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Why not use jets as 1st stage? (was Multiple Engines???)
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#123
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Why not use jets as 1st stage? (was Multiple Engines???)
Carsten Nielsen wrote: There have been lots of plans of that sort. The most important thing about it would be to lift the vehicle above the lower dense athmosphere, not so much to get it moving at supersonic speed. Then how about a propeller plane as 1st stage? Recall that the Helios holds the altitude record for a non-rocket plane, c. 100,000 feet. As ridiculous as the Helios concept is, that record is impressive. Although the Helios was a solar-powered electric plane, I see no reason why that altitude couldn't be reached with a piston engine. It would use a turbocharger with a multi-stage compressor. Should this be the goal for TSTO? A slow booster plane with a huge wing? Mike Ackerman |
#124
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Why not use jets as 1st stage? (was Multiple Engines???)
In sci.space.policy Axel Walthelm wrote:
wlhaught wrote: Alright, back to powered flybacks for first stages. Are jet engines worth the trouble of extra systems? As I recall, I read somewhere that the shuttle uses half its fuel to reach 1,000 mph. You sure? I have a copy of a speed/height/time diagram of the shuttles ascend. 1000 mph would be 1600 km/h. The diagram says that this speed is reached within the first minute of launch at a height of about 8-10 km. Launch takes 8.5 minutes, boosters burn 2 minutes. If you would say half of the boosters fuel is used up at 1000 mph that would fit. But total fuel including the fuel of the big external tank? Ok, solid booster rocket fuel is quite heavy, and the booster burns faster in the beginning than at the end. So maybe overall this could be true. But what does it mean? Solid rocket boosters are not economic? "You should use a different flight profile that didn't try to get to high speed while in teh densest parts of teh atmosphere"? -- Sander +++ Out of cheese error +++ |
#125
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Why not use jets as 1st stage? (was Multiple Engines???)
Hi,
The answer to the origional question is quite simple. The thrust to weight ratio of jet engines is BAD, really bad. The best jet engines are around 10 or 12:1 and most are 5:1 or less. Bottom line: they are just too friggin heavy... lol As Always, Jay Troetschel "Sander Vesik" wrote in message ... In sci.space.policy Axel Walthelm wrote: wlhaught wrote: Alright, back to powered flybacks for first stages. Are jet engines worth the trouble of extra systems? As I recall, I read somewhere that the shuttle uses half its fuel to reach 1,000 mph. You sure? I have a copy of a speed/height/time diagram of the shuttles ascend. 1000 mph would be 1600 km/h. The diagram says that this speed is reached within the first minute of launch at a height of about 8-10 km. Launch takes 8.5 minutes, boosters burn 2 minutes. If you would say half of the boosters fuel is used up at 1000 mph that would fit. But total fuel including the fuel of the big external tank? Ok, solid booster rocket fuel is quite heavy, and the booster burns faster in the beginning than at the end. So maybe overall this could be true. But what does it mean? Solid rocket boosters are not economic? "You should use a different flight profile that didn't try to get to high speed while in teh densest parts of teh atmosphere"? -- Sander +++ Out of cheese error +++ |
#126
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Multiple Engines???
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