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SSTO propulsion overview
Catching up on some unread journals, I note that the March/April 2003
issue of JBIS has a very interesting paper: "A comparison of propulsion concepts for SSTO reusable launchers", by Richard Varvill and Alan Bond. While the authors have a mild case of hydrogen religion -- non-hydrogen rockets are never mentioned -- and they obviously have their own axe to grind, they generally give a good overview of the alternatives, including why scramjets are such a lousy idea for space launch. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
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SSTO propulsion overview
Henry Spencer wrote:
Catching up on some unread journals, I note that the March/April 2003 issue of JBIS has a very interesting paper: "A comparison of propulsion concepts for SSTO reusable launchers", by Richard Varvill and Alan Bond. While the authors have a mild case of hydrogen religion -- non-hydrogen rockets are never mentioned -- and they obviously have their own axe to grind, they generally give a good overview of the alternatives, including why scramjets are such a lousy idea for space launch. This is all my opinion, of course... After reading this newsgroup for a while, I have come to the conclusion that any type of air-breathing for orbital launch is a waste of time and money. Turbojets, scramjets, whatever. It just makes getting into orbit harder, not easier. The only exception to this is an aircraft carrier 1st stage. There are some advantages to high altitude launch (less altitude compensation needed for your rocket nozzle, for example), and it can give you a lot of flexibility with launch site location. But that's the only exception in my view. I just can't understand why so much time and research dollars are being spent on hypersonic research. If you want to get into orbit, you want to get _out_ of the atmosphere as soon as possible. It is completely counter-intuitive to try and gain lots of velocity while still inside the atmosphere, where you are subject to drag (inefficiency) and heating (exotic materials and/or cooling systems needed). While this is drifting off-topic for this newsgroup, can someone explain to me why so many in the aero/astro field still think hypersonics for orbital launch are a good idea? And are hypersonics a good idea for anything at all? James Graves |
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SSTO propulsion overview
In article ,
James Graves wrote: ...any type of air-breathing for orbital launch is a waste of time and money. Turbojets, scramjets, whatever. It just makes getting into orbit harder, not easier. The only exception to this is an aircraft carrier 1st stage... I'm inclined to say that the jury is still out on LACE and its relatives (such as Alan Bond's concepts) and on things like the original Roton, which airbreathe a little bit at the start of a largely rocket-powered ascent. The idea is plausible; what remains unproven is that it's any better than a pure rocket. I wouldn't build one myself, but wouldn't exclude the possibility of success that way. While this is drifting off-topic for this newsgroup, can someone explain to me why so many in the aero/astro field still think hypersonics for orbital launch are a good idea? To some extent this is a lingering echo of the idea that spaceships are, or *should be*, just especially high-performance aircraft. There has never been any very strong justification for this belief, but it remains an article of faith for many from the "aero" side of aerospace. And to some extent, it's pure public-relations hype, the result of the hypersonics people -- who have been largely rejected by the aero side of the house -- trying to find funding from the space side (which has long been the rich side of the family). And are hypersonics a good idea for anything at all? For high-speed cruise within the atmosphere -- assuming you have some urgent reason to want to do that -- they look promising. But they have nothing much to do with spaceflight. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
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SSTO propulsion overview
James Graves wrote:
Henry Spencer wrote: Catching up on some unread journals, I note that the March/April 2003 issue of JBIS has a very interesting paper: "A comparison of propulsion concepts for SSTO reusable launchers", by Richard Varvill and Alan Bond. While the authors have a mild case of hydrogen religion -- non-hydrogen rockets are never mentioned -- and they obviously have their own axe to grind, they generally give a good overview of the alternatives, including why scramjets are such a lousy idea for space launch. This is all my opinion, of course... After reading this newsgroup for a while, I have come to the conclusion that any type of air-breathing for orbital launch is a waste of time and money. Turbojets, scramjets, whatever. It just makes getting into orbit harder, not easier. The only exception to this is an aircraft carrier 1st stage. There are some advantages to high altitude launch (less altitude compensation needed for your rocket nozzle, for example), and it can give you a lot of flexibility with launch site location. But that's the only exception in my view. I just can't understand why so much time and research dollars are being spent on hypersonic research. If you want to get into orbit, you want to get _out_ of the atmosphere as soon as possible. It is completely counter-intuitive to try and gain lots of velocity while still inside the atmosphere, where you are subject to drag (inefficiency) and heating (exotic materials and/or cooling systems needed). While this is drifting off-topic for this newsgroup, can someone explain to me why so many in the aero/astro field still think hypersonics for orbital launch are a good idea? "If the only tool you have is a hammer, every problem looks like a nail." And to the less technically inclined, there's the carrot of not carrying your oxidizer along. The price, of course, is taking it in at increasing Mach numbers, and the drag imposed thereby, likely a heavier engine for the same thrust, major thermal issues, etc. Everything you said, and then some. And LOX is cheap. And are hypersonics a good idea for anything at all? If all you *want* is high-altitude, hypersonic cruise (as opposed to accelerationg to orbital velocity), sure. Recon, *perhaps* commercial flights depending on the economics, etc. And perhaps expendable hypersonic weapons. But airbreathing to orbit, while it might yet be acheived, will be only a niche application. Most access to LEO will be with rockets, until/unless 'beanstalks' can be done, and even those will not completely replace independent spacecraft. James Graves -- You know what to remove, to reply.... |
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And are hypersonics a good idea for anything at all? For high-speed cruise within the atmosphere -- assuming you have some urgent reason to want to do that -- they look promising. But they have nothing much to do with spaceflight. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | I think the sonic boom forbids any hypersonics aircraft service. If you want such a possibility, the only practical solution is going out of the atmosphere for most of the trip, so you get back to the rocket solution even if there is no space travel or orbital capabilitiy. So I don't see any use for "hyper" whatever the intended use. Yvan Bozzonetti. |
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