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I am really amazed by all these optimistic people trying to do rlvs
and i belive in these peoples cause! however it strikes me that these people all seem a bit to optimistic for ex almoast all the groups i have investigated are into liquid propellant engines, and they seem to think they can make these engines totaly reuseble, let me remind you about the physical laws of thermodynamics (heat) that makes it impossible to turn the engines on and off forever or atleast alot of times! for me it seems almoast impossible to make a liquid rocket engine reuseble. Or am i wrong ? will these people beat the heat laws of rocket engines somehow ? |
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#3
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In article ,
Paul Spielmann wrote: ...liquid propellant engines, and they seem to think they can make these engines totaly reuseble, let me remind you about the physical laws of thermodynamics (heat) that makes it impossible to turn the engines on and off forever or atleast alot of times! How, exactly, do the laws of thermodynamics make it impossible to turn a rocket engine on and off a lot? Be specific. The small engines used as attitude-control thrusters in spacecraft are sometimes rated (by testing, not theoretical calculation) for 300,000 or more firings. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
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James Logajan wrote in message 5...
(Paul Spielmann) wrote: [...] let me remind you about the physical laws of thermodynamics (heat) that makes it impossible to turn the engines on and off forever or at least alot of times! I turn my car engine on and off a lot. Jet engines get turned on and off a lot. Not sure what physical law you are talking about. Or am i wrong ? I don't want to be the one to break the bad news to you.... here is the thing i am really not so sure by my own nolage, its just that i have asked peoeple that i think are credible people that work in the field of physics (not space engineering though) and accoarding to what they have said: the energy and heat stress of going to orbit and back are much more higher than for example what a car experience and therefore it cuts back what is possible to do with space crafts. Either the person i asked is right or wrong because he is no expert in space crafts and is too "theoretical". I still wonder though how long life spans sub/orbital rlv vehicles will have though.. |
#5
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Paul Spielmann wrote:
I am really amazed by all these optimistic people trying to do rlvs and i belive in these peoples cause! however it strikes me that these people all seem a bit to optimistic for ex almoast all the groups i have investigated are into liquid propellant engines, and they seem to think they can make these engines totaly reuseble, let me remind you about the physical laws of thermodynamics (heat) that makes it impossible to turn the engines on and off forever or atleast alot of times! for me it seems almoast impossible to make a liquid rocket engine reuseble. Or am i wrong ? will these people beat the heat laws of rocket engines somehow ? Have you heard of jet engines? The Space Shuttle Main Engine? Are you aware that most reusable rocket engine designs (apart from thrusters) employ active cooling? You design them to not operate close to the physical margins (not even as close as the SSME does). This is why the engine in your car needs less repair and maintenance than engines used in various forms of racing, where they're typically pushed to the limit and kept there, sometimes for hours. And in all the above examples, materials science doesn't stand still. What's not to understand? -- You know what to remove, to reply.... |
#6
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Henry Spencer wrote:
In article , Paul Spielmann wrote: ...liquid propellant engines, and they seem to think they can make these engines totaly reuseble, let me remind you about the physical laws of thermodynamics (heat) that makes it impossible to turn the engines on and off forever or atleast alot of times! How, exactly, do the laws of thermodynamics make it impossible to turn a rocket engine on and off a lot? Be specific. The small engines used as attitude-control thrusters in spacecraft are sometimes rated (by testing, not theoretical calculation) for 300,000 or more firings. I have an engine sitting on my desk at work that went for 632000 pulses - and still performed the last pulse within 5% of what it did on the first! Laws of thermodynamics (??) be damned! Brett |
#7
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In article ,
Paul Spielmann wrote: that i have asked peoeple that i think are credible people that work in the field of physics (not space engineering though) and accoarding to what they have said: the energy and heat stress of going to orbit and back are much more higher than for example what a car experience and therefore it cuts back what is possible to do with space crafts. The extent of these problems is much exaggerated, especially by people who don't have direct knowledge of space engineering. In some cases, there are real problems but they are artifacts of current design practices, which can and should be changed. For example, rocket engines often experience a great deal of thermal stress during startup, due to very rapid temperature rises. But there is no fundamental reason why their startup sequences need to be so fast. Limiting warmup to rates normally found in jet engines is not a big problem, once designers start caring about reliability and long life rather than absolute maximum performance. In other cases, these beliefs are simply misunderstandings, partly based on authoritative statements from people with vested interests in keeping spaceflight expensive and difficult. (Of *course* NASA will tell you that space is terribly hard; it would be immensely embarrassing for them to admit that they've been wasting your money all these years...) ...I still wonder though how long life spans sub/orbital rlv vehicles will have though.. It's an open question. The first-generation ones may indeed have somewhat limited lives. There is much speculation about this, most of which boils down to religious arguments about basic assumptions. The only way to know for sure is to try it and see. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#8
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Please perform a web search on something called the "X-15". You may be
surprised to learn that this RLV flew 40 years ago. (Paul Spielmann) wrote in message om... I am really amazed by all these optimistic people trying to do rlvs and i belive in these peoples cause! however it strikes me that these people all seem a bit to optimistic for ex almoast all the groups i have investigated are into liquid propellant engines, and they seem to think they can make these engines totaly reuseble, let me remind you about the physical laws of thermodynamics (heat) that makes it impossible to turn the engines on and off forever or atleast alot of times! for me it seems almoast impossible to make a liquid rocket engine reuseble. Or am i wrong ? will these people beat the heat laws of rocket engines somehow ? |
#9
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Please perform a web search on something called the "X-15". You may be
surprised to learn that this RLV flew 40 years ago. (Paul Spielmann) wrote in message om... I am really amazed by all these optimistic people trying to do rlvs and i belive in these peoples cause! however it strikes me that these people all seem a bit to optimistic for ex almoast all the groups i have investigated are into liquid propellant engines, and they seem to think they can make these engines totaly reuseble, let me remind you about the physical laws of thermodynamics (heat) that makes it impossible to turn the engines on and off forever or atleast alot of times! for me it seems almoast impossible to make a liquid rocket engine reuseble. Or am i wrong ? will these people beat the heat laws of rocket engines somehow ? |
#10
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Virtually all managers and most all engineers that have grown up in the
current space hardware design bureaus have been steeped in the "rockets as artillery" school. Design constraints are fire the engine once for testing, put it on the stand for its first flight, then through it away after four or five minutes operation. Any effort or materials to give it a longer life are considered a waste. This does not mean that large rocket engines can't be built for longer service, only that the engineers don't need it for "artillery" use. A good example of a flight weight engine with long life is the RL-10. This engine used on several upper stages was used (in the short bell version) for the DC-X, and has had dozens of starts and hours of total time. Another area that is not considered by most engineers developing RLVs is that propellents used by most designs are about three orders of magnitude lower in cost than flight hardware, and that adding propellent to reduce the quantity of flight hardware will eliminate any failure modes that were possible in the eliminated hardware. An example would be if the Shuttle had no wings there would have been no wing leading edge failure. RLVs require companies and engineers willing to try new paradigm, not just incremental improvements. The Space Shuttle was a try, however many of its design requirements were made for political reasons not economic or technical. Mike In article , (Henry Spencer) wrote: In article , Paul Spielmann wrote: that i have asked peoeple that i think are credible people that work in the field of physics (not space engineering though) and accoarding to what they have said: the energy and heat stress of going to orbit and back are much more higher than for example what a car experience and therefore it cuts back what is possible to do with space crafts. ...I still wonder though how long life spans sub/orbital rlv vehicles will have though.. |
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