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: Wed, 16 Dec 1992 11:56:04 GMT

In article <ewright.724444108@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>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.

I believe that astronauts, who do train underwater for EVA, would
tell you that it is different. As I said above, when we get further
down the learning curve some of these tasks may become easier, or
be done in a different way because they aren't easy at all.

>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?

The CIS quotes $5 million an hour suited time, and their guys are
already in space. Now that may be simple profiteering on their part,
but it should be obvious that it's more expensive to ship materials,
crews, their life support, tools, etc, to orbit than to simply ship
a finished product assembled in shirtsleeves on the ground if per 
pound launch costs become relatively low. Only if you can only launch
little bits cheaply, and need a big bit in orbit is assembly justified.
Such an example is SSF. Of course most assembly is still done on the
ground and the modules simply plugged together in space with the robot
arm. Reducing EVA time has been a priority for the SSF program. I
don't see welders, pipefitters, and electricians plying their trades
in space any time in the next few decades simply because their support
on orbit costs too much. Never mind launch costs, suits are expensive,
pre-breathe time is expensive, crew quarters are expensive, special
zero G tools are expensive, skilled manhours are expensive, etc. It's
simple fact that a skilled worker on the ground can do more work in
an hour than a skilled worker in space and labor costs are not 
inconsequential. In fact, labor costs dominate every other cost of
space activity. Reducing the standing army is the major cost savings
projected for the DC program. Standing armies *in space* will remain
more expensive than standing armies on the ground. This leads to the
conclusion that cheap heavy lift is more cost effective than cheap
light lift for large space structures. For small structures, cheap
lift of any kind negates the need for in space assembly. 

>>>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.

Indeed. And since there are no factories or hotels in space, and
the one being designed is neither large enough for more than
4 occupants, nor cost effective enough for redneck assembly workers,
DC is moot for those tasks requiring in space assembly.

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

But that reduces reach which reduces capability. Telescoping arm sections
should be rather easy to design, and a new arm to fit DC is a very real
possiblity. It reduces the need for EVA. If DC works, an arm is almost
certainly in it's future.

>>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.

If you have a suggestion on how spending two days in a spacesuit can be
made tolerable, please speak up. You can't do that with current suits,
and there are no funds to develop a suit to allow it.

>>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.

Well first we don't *have* a garage. And second DC isn't a tow
truck, nor is there any assurance that a repair mission would
be in the same orbital plane as any orbital garage. You fix
them where you find them because it's too expensive to move
them somewhere else to fix them and then bring them back where
they were. An example is heavy farm equipment. Nearly every
service shop for farm equipment goes to the job rather than
trying to trailer the equipment to the shop. It's cheaper and
easier to fix it on the spot than to transport it. Thus you
have service trucks complete with welders, compressed air,
and tools. Most of the things we might want to fix are in
GEO anyway and DC can't get there, so the point is moot.


>>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.

Yes, propellants are relatively cheap, but having to *carry* them
is not. Every pound of oxidizer you carry is a pound of payload you
can't carry.

>>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.

Are you seriously contending that wing drag consumes more fuel than
the lift they provide saves?

>>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.

Now look in the Yellow Pages and find out how expensive it is to 
store liquid hydrogen and liquid oxygen in tankage that is very
light weight and capable of surviving G loads.

>>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.

Oh? I'd like to hear about this Greek jet. All I know about is
an external combustion steam *reaction* engine, (IE a form of
rocket). 

Gary

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