Re: Engine design breakthrough

Henry Spencer wrote:

>On Sat, 17 Apr 2004, Ian Woollard wrote:
>  
>
>>And there's a further point, that the article mentions that this 
>>technology might be needed for orbital taxis, (but then never mentions 
>>why you would want the high chamber pressure that helps cause these 
>>problems in such an engine anyway- you very probably don't...
>>    
>>
>
>There is *some* benefit to be had from high chamber pressure even in
>vacuum.
>
Well, thrust scales with chamber pressure; but I would expect that 
thrust isn't massively important for orbital taxis in a lot of cases.

>  Yes, you could get the same expansion ratio at lower chamber
>pressure just by making the nozzle longer...
>
Yes... if you need the same thrust due to the orbital mechanics.

> but you would take a small
>performance penalty from things like nozzle drag and minimum-gauge issues. 
>  
>
You could avoid these by having multiple chambers. On the plus side, 
your propellent feed is at a lower pressure; so the pumps and feeds 
weigh less.

>And higher pressure suppresses dissociation, so the flame is a bit hotter
>and that helps a little bit too.
>  
>
But these effects are quite small.

>Mind you, most designers would conclude that it's far more trouble than
>it's worth.  But NASA rocketry has a long history of obsession with
>performance regardless of practical issues.
>  
>
Yes, although the Shuttle's OMS runs at 125 psi or so, so it doesn't 
/always /work out like that.

>                                                          Henry Spencer
>                                                       [email protected]
>  
>