From: gary@ke4zv.uucp (Gary Coffman)
Newsgroups: sci.space
Subject: Re: Terminal Velocity of DCX? (was Re: Shuttle ...)
Date: 16 Dec 92 14:26:33 GMT
Article-I.D.: ke4zv.1992Dec16.142633.450
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Organization: Gannett Technologies Group

In article <1glf0hINN5v9@mirror.digex.com> prb@access.digex.com (Pat) writes:
>
>Certainly, a staged rocket designed with clean sheet approach can carry
>more weight to orbit at a better mass ratio then an SSTO.   That does not
>mean that you want to take that approach,  if an SSTO CAN!!!  important point
>deliver cargo to LEO  for significantly less cost then any staged rocket
>then why go with staged rockets for routine access to space?

Why no reason at all. The problem as I see it is that those low costs
have yet to be demonstrated with the reusability, lack of ground support,
and quick turnaround required of the DC proposal to meet those cost goals.
Suppose flight experience shows that rebuilds are needed every 10 flights,
or that the ground manpower has been underestimated because of tighter
than expected government flight rules requiring more inspection between
flights. Shuttle looked cheap too at a similar stage of development because 
it's components were expected to be reused again and again with minimal 
ground manpower for inspection and repair. That didn't pan out, DC may not 
either.

>Gary,  use your brain.    Just because a staged rocket can be built with
>greater margins then a SSTO, does not mean that is the way to go.  
>
>Right now,  all staged rockets are vintage 60's/50's designs.  they have
>absolutely no margin for safety.  neither does the shuttle.  All the
>models for rocket costing indicate a major cost item is in the building/
>stacking operation related to launch.   The russians turn these guys out
>like sausages and still expand thousands of hours on stacking ops.  

Yes again, I agree that stacking is currently expensive with 50's era
designs. That doesn't say that a fresh design *with low launch preparation
cost* as a design goal couldn't cut that expense by a large fraction.
A big dumb booster that just goes up can be cheap to build and cheap to 
launch. The keys are cheap mass produced engines, simple modular stacking,
and easy fueling, the rest is just bent aluminum and some cheap silicon.
Since it's payload fraction can be higher than the reusable SSTO, the
costs it does have are spread over more pounds of payload.

>If a 747 had to change engines every time it flew,  a ticket would
>cost 10 times as much.  asirlines are cheap to fly, cuz most items only
>need routine maintenance.   literally, you can gas up a 747, clean the
>cabin and turn right around.  i've seen it done.  

And as someone pointed out, running the Shuttle at 80% throttle could
reduce engine rebuilds on it too. Shuttle and flyback SSTO have the
advantage of reusing components from one flight to another. DC intends
to run at part throttle to extend that reuse even further, but because
it *is* SSTO, the payload fraction becomes proportionately smaller.

Now reusing components can be good. For example Shuttle would cost only
$20 million per flight if it lasted 100 flights based on component
reuse. Of course fixed ground costs, fuel, and rebuilds of some
components push that back up to around $170-$270 million per flight
at current flight rates. But component rebuilds don't dominate 
costs. It's that damned standing army needed to launch it with man 
rated safety checkers checking the work of checkers checking the work 
of workers and many levels of supervision on top of that. Shuttle is 
expensive because it's labor intensive, not because it's two stage. 
It was designed to a performance spec instead of a cost spec. Now DC 
is supposed to be designed to a cost spec, and that's good, but it's 
also exploring new territory by being SSTO which thins payload margins 
and that's tricky.

>Sure,  a NASP, could probably be built with  170% margin of load,  but why?
>and if it costs 4 times what DC-1 could deliver, then you are wasting money.

Agreed, *if* it costs 4 times DC-1 to operate, which it may well do, I'm 
no fan of current NASP approaches either.

>My belief is that the DC-1, will deliver loads to orbit cheaper then anything
>else flying.  if it can,  then we are in great shape.

And my belief is that big dumb boosters designed to cut costs can cut the 
cost to orbit to under $300 a pound, and I don't think DC can touch that in 
the real world. The best numbers I've seen for DC work out to $666 per pound. 
Shuttle was quoted as cheaper than that at a similar stage of development.
I think expendibles offer a better path to cheap access to space. DC may turn 
out to be cheaper than Shuttle for ferrying crew up *and* down, but I don't 
think it can compete with big dumb boosters on a cost basis for pounds of 
payload to orbit. And neither are replacements for Shuttle's unique 
capabilities. DC may be the answer, but to what question?

Gary
Newsgroups: sci.space