From: ewright@convex.com (Edward V. Wright)
Subject: Re: Terminal Velocity of DCX? (was Re: Shuttle ...)
Date: Tue, 15 Dec 1992 18:28:28 GMT
Organization: Engineering, CONVEX Computer Corp., Richardson, Tx., USA
X-Disclaimer: This message was written by a user at CONVEX Computer
              Corp. The opinions expressed are those of the user and
              not necessarily those of CONVEX.

In <1992Dec13.174759.9626@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes:

>If the cost per pound of space transportation drops enough, we won't want to 
>do *any* space assembly since that's very expensive, difficult, and time
>consuming. Only if space transport remains high cost will space assembly
>be worthwhile, at least until we are much further down the learning curve
>of doing assembly work in space. 


Difficult?  Nah.  No more so than working under water.  How many
man-hours of SCUBA experience and experimentation were required
before divers started to get much work done?  How does that compare
with the number of man hours that have been spent in EVA?  How often
do astronauts have their work interrupted by a passing shark.

Expensive?  If it becomes inexpensive to get workers into space,
to get materials into space, and to get equipment into space, 
why should assembly and construction work be expensive?

This is a technological superstition.  "It will always that way,
because that's the way it's always been."

"Aluminum has always been more expensive than platinum and gold,
and always will be."

Time consuming?  Again, if transportation costs drop, so do life-
support costs.  People can afford to stay in space for longer periods
of time, so they have time to do the job.  Where's the problem?


>>True, a passenger version of the DC-1 couldn't carry more than
>>about 20 people.  Of course, the Shuttle can only carry 7-10.
>>What's your point?

>The Shuttle can carry large *working* crews while the proposed DC would
>carry sardine packed *passengers* because there's no room for them to work. 
>That point should be obvious.

Well, you got me there.  Yeah, the DC will be just like the old
DC-3, or the modern B-747.  Passengers are crammed in like sardines.
No room for them to work.  But I'll think you find that most people
who fly on business don't do their business on the plane anyway. An
airliner makes a poor factory and a lousy hotel.



>>I don't really see why not, as long as the arm can be folded to
>>fit the DC's cargo bay.  Of course, a man in a space suit is more
>>versatile than Canadarm and, if the transportation costs are low
>>enough, cheaper too.

>The current arm cannot be made to fit the proposed DC payload bay,
>a new one would have to be designed with either considerably less
>capability, or some very intricate folding geometry. That's probably
>only a billion dollar project so it would likely be done if DC works
>out. 

The complicated part of the arm is the joints.  Shortening the
length of the pipes between the joints shouldn't be a major undertaking.



>Spending two days in a spacesuit isn't likely to be either practical
>or cost efficient. As we've found out from Shuttle, work in a suit is
>slow and cumbersome. 

Yeah.  We've got tens of hours of experience, so that settles that....
Obviously there are no new ideas left to try.


>Some things are just easier with a bigger vehicle that has both a crew
>space *and* a cargo bay at the *same* time and that can stay in orbit
>for 10 to 30 days.

A service station needs a repair bay, a work crew, and enough
time to do the job.  I don't understand why it needs to be a 
transportation system also.  Most garages own a tow truck.  I've
never seen a garage that was a tow truck.


>Rockets aren't more complex, an SRB has fewer moving parts than a 747 
>engine for example. But that doesn't automatically mean that an SRB 
>is cheaper per mile to operate. 

If you scrapped the 747 after one flight, or crash-landed it in
the ocean, then towed it back to land for refurbishment up to
ten times, it would be much more expensive than the SRB.


>Jets have massive amounts of "free" air to feed them oxygen and to 
>cool them. 

But LOX is cheap, and you've just said that propellents are a small
part of the cost.

>They have the benefit of wings to bear most of the loads so that 
>they don't have to support the vehicle by brute force as well as 
>move it horizontally to it's destination. 

Wings also produce drag.


>They operate at lower temperatures and pressures than
>rocket engines. And their fuel is non-corrosive and storable at
>room temperature (though some lower performance rockets share this
>feature) 

Liquid hydrogen, methane, propane -- none of those are corrosive.
LOX is corrosive, but so is the gaseous O2 used by turbojets.  Look
in the Yellow Pages under "bottled gas" and find out how hard it is
to store liquid propane at room temperature.


>Rockets have to work in a more hostile and varied environment
>than jets. 

So, when was the last time LEO was hit by a blizzard, typhoon,
thunderstorm, monsoon, tornado, or hurricane?


>Man has been building rockets for 2,000 years while he has
>only been building jets for 50, 

I think the ancient Greeks, who built a working jet engine, 
lived a little more than 50 years ago.




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