From: bondage@frontiernet.net   
      
   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   
      
      
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