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 17:47:59 GMT

In article <ewright.724092627@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>In <1992Dec9.140455.6628@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes:
>
>>Titan IV is turning into a bigger hanger queen than Shuttle ever
>>was, DC-1 is a paper airplane, etc. A more intelligently designed
>>spacecraft is badly needed to replace Shuttle, but the DC program
>>isn't it. 
>
>Interesting.  DC-1 isn't a viable replacement for the Shuttle
>because it's a "paper airplane."  Of course, any new design
>will be a "paper airplane."  If we reject every design before
>it's even built, we'll never have a replacement. 

No, the fact that it's still a paper airplane means it may not
work, just like many prototype aircraft do not work and are
scrapped. If it works, then see below.

>>It may be *part* of a fleet of specialized vehicles that
>>replace Shuttle, but it can't do many of the things that Shuttle
>>is capable of doing, 
>
>No space vehicle is capable of doing all the things the Shuttle
>is capable of doing (in theory).  Trying to design a single launch
>vehicle capable of satisfying every possible user and every possible
>mission is as ridiculous as designing a single "national airplane" 
>capable of carrying out every military and civilian air mission.

Yep.

>>lifting large payloads, 
>
>Most large payloads are not solid chunks of metal.  They are assemblages
>of smaller parts.  If the cost of space transportation drops far enough,
>it will become feasible to assembly some of those pieces in space. That
>reduces the need to carry large payloads.

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. 

>>carrying large crews,
>
>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.

>>support Canadarm, 
>
>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. 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. The CIS has offered suited Cosmonaut time at $5 million
an hour and their guys are already in orbit. With a new suit design ($$)
and *two* DCs, one with a shirtsleeve bay and airlock and the other with
the cargo hold and arm, you could do a refurbishment of Hubble or a satellite
recovery, if you worked fast and didn't hit any snags that required a
new plan of attack requiring an on orbit stay in excess of two days.
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.

>>Compare SSTO to Proton, the payload capacities are similar. SSTO has
>>to beat Proton costs and reliability to be a success. $300 a pound
>>is a difficult target. Of course CIS prices are likely to increase
>>once the fire sale is over.
>
>Why?  I can buy a ticket to Australia for $1100.  With my luggage,
>I weigh well over 200 pounds.  That's less than $5.50 a pound.
>
>It takes less energy to put a pound of payload into orbit than
>it does to fly it through the atmosphere to Australia. Why should
>it be difficult at 60 times the price?

It requires even less energy to just winch payloads into space, but
that doesn't mean that there aren't other constraints than energy
on operating the system. Fuel costs are a minor component of launch
costs.

>There is a common view, nothing more than a technological superstition,
>that space transportation must be hideously expensive because rockets
>are so complex.  But a rocket engine is conceptually much *simpler* than 
>a turbojet.  There is no reason it should cost an order of magnitude
>more to build and operate.

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. Jets have massive amounts of "free"
air to feed them oxygen and to cool them. 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. 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) Rockets have to work in a more hostile and varied environment
than jets. Man has been building rockets for 2,000 years while he has
only been building jets for 50, but all that experience hasn't translated
into cheap spacecraft yet while cheap jet aircraft are routine. There
must be *some* reason other than government bureaucracy for that.

Gary
Newsgroups: sci.space