From: gary@ke4zv.uucp (Gary Coffman)
Subject: Re: Terminal Velocity of DCX? (was Re: Shuttle ...)
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Organization: Gannett Technologies Group
Date: Sun, 13 Dec 1992 18:04:22 GMT

In article <ewright.724094906@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>In <1992Dec9.151157.7256@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes:
>
>>In article <ewright.723846898@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>
>>>The engines used by every commercial airliner were "radically new"
>>>and "never flight tested" at one time also.  Despite your claims
>>>of "radicalism," the rocket engines are little different from those
>>>we have been building for more than 40 years.  They are a new design,
>>>not a new technology.
>
>>Yes, they are basically a *new* design despite being based on the
>>proven RL-10. Adding throttleability to a rocket engine isn't simply
>>a matter of adding a valve. 
>
>By that logic, every jet-engine design is a "radically new technology."
>This "isn't trivial engineering that can be brushed aside by saying
>it's been done before with other engine designs... It *should* work, 
>but they won't know until they try it what problems may develop."  For
>some reason, I don't see airliners falling out of sky because of the
>"radically new" engines that are introduced, quite regularly, every
>few years.

That's because you rarely see the prototype engines that blow up in
testing and are discarded for a different design. Nor do you see the
engines that worked, but didn't meet the required performance goals.
A large rocket engine that has to work from sea level to vacuum can't
be completely debugged on a static stand. You've got to actually flight
test them on an orbital vehicle, if they have to restart in orbit, 
before you can know if they will meet your design goals. That's 
inherently higher risk and higher cost than jet engine development.

>>The aerospike is the alternative design if the variable expander
>>doesn't work out.
>
>Oh?  Well, then, it doesn't sound to me like they "intend to use [it]."
>However, aerospike engines were built and tested as long ago as the
>1960's.  Suffice it to say that your conception of what is and is
>not "radically new technology" is 30 years out of date.  

What flight articles were they used on? How many went into orbit and
what was their throttle characteristic? You can't answer because none
have ever flown.

>>>Saying that doesn't make it so.  The engine is about as "radically
>>>new" as a new microprocessor.  The control problem is the same one
>>>that was solved, for ICBMs, in the 1960's.
>
>>That's funny, I didn't know ICBMs did controlled powered landings. I
>>thought they used ballistic re-entry vehicles atop a multistage suborbital
>>rocket.
>
>Oh.  I thought you were talking about the reentry.  No, the controlled
>powered landing was demonstrated, again in the 1960's, by a vehicle
>called the LEM.  Which had the additional requirement of landing solely
>in unprepared fields.

In 1/6th G in vacuum, single engine, with a vehicle that massed less than 
1/10th of DC. A totally different environment, totally different control
problem, and totally different scale.

>It's amazing that things we did routinely in the 1960's are considered
>challenging today.  I guess we've lost a lot of technology since then,
>right?

We had cars in 1910 that could go 130 MPH too, on unprepared roads, isn't 
it amazing that that's still considered challenging today?

Gary