From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: A new orbiter? (dont think so--was Re: National Space Plane)
Date: Wed, 26 Aug 1992 19:39:36 GMT
Organization: U of Toronto Zoology

In article <RUCA.92Aug25122029@pinkie.saber-si.pt> ruca@pinkie.saber-si.pt (Rui Sousa) writes:
>   *If* the X-30 is built, and *if* it is highly successful, and *if* funding
>   can be found, then ten or fifteen years after it first flies, derivatives
>   might be hauling useful payloads into space.  Maybe.
>
>   Right now, the way to bet is that it will never be built, because it costs
>   too much and nobody needs it very badly.
>
>what's YOUR personal opinion as to an effective successor to the Shuttle?
>Will the PLS do for launching crews? What aboput cargo?

My personal opinion right now is "don't hold your breath".  All the talk
about PLS, the HL-20, etc. is just that:  talk.  Nobody is bending metal.
Nobody is planning to bend metal on specific dates.  Nobody is applying
for money to bend metal.  NASA has not yet gotten serious about building
a successor to the shuttle; it's just funding the usual nickel-and-dime
studies that will never go anywhere.

As for what I'd do...  It is important to realize that there are about
four different roles involved.  You need to haul substantial loads of
cargo up.  You need to bring rather more modest amounts down.  You need
to take crews up and down (up and down can't really be separated very
well here, because you need the down part to handle emergencies on the
way up).  And you need support for manned missions that want to spend
a while in orbit.

The shuttle tried to fill all these roles, and didn't succeed very well.
There is no fundamental reason why you can't do all of them in one
vehicle -- you don't see very many unmanned cargo aircraft -- but it
does make things harder.  SSTO is basically planning to do the first
three in one vehicle; it's a high-risk project, but the potential payoff
is so huge that it's just got to be tried.  If SSTO works, it's a whole
new ballgame.

Setting aside SSTO...  We need to think about separating those roles.
It's incredibly stupid, for example, to haul Spacelab up into orbit only
to haul the whole thing back down a few days later.

We need a cheap launcher with a payload of 5-10 tons into low orbit.
This is a little beyond Atlas, I think, although I don't have numbers
handy, and Titan is too big and too costly.  This is about the size
range NASA originally planned for the shuttle, by the way.  It needs
to have a surge rate high enough that we can mount a mission using
several of them, eliminating any major need for anything bigger.

We need a reentry vehicle that can carry several men up and return them,
*or* go up empty and return, say, a ton of cargo.  It has to be able
to make a reasonably gentle landing, on land, within, say, 5km of a
chosen point.  (A 10km-wide landing field is no big deal, although more
precision would be nice.  Water landings should be for emergencies only,
they need much more elaborate ground support.)  It does not have to be
a spaceplane or a lifting body; a capsule with a gliding parachute would
probably be adequate.  (The objective is a cheap and effective spacecraft;
if you want to do hypersonics research, please go do it and don't bother
those of us whose interests lie beyond the atmosphere.)  It should *not*
require a runway -- unless we can provide for aborting an approach and
going around for another try, which is probably too messy -- because the
zero-defects piloting required is unsuited to routine operations.

We need a small habitation module, preferably small enough to go up on
the same launch as the reentry vehicle.  The reentry vehicle takes people
*up* and *down*; it is *not* an orbital laboratory.  If you want to stay up
for a while in an orbit where there is no base camp, you take a habitation
module along.  You also plug them together to form base camps in orbits
where repeated missions are planned.  That way, only the things that
actually have to *change* from one mission to another have to go up and
down each time.  If there is enough activity, eventually one or more of
the base camps may end up permanently manned.  That is a side issue, not
a major objective.

We need a small tug, preferably small enough to go up on the same launch
as the reentry vehicle (it is not essential that one launch also be able
to carry a habitation module).  This lets us bring the payloads from
several launches together in orbit and assemble bigger payloads.  We've
been doing this since the 1960s; it's time we started building our
operational concepts around it, because it liberates us from a lot of
stupid limitations.  Again, this is a separate building block; the reentry
vehicle needs a bit of maneuverability but needn't have much -- that's not
its job.  The ability to operate unmanned by remote control would be
useful and is probably not too hard.

There are lots of other bits and pieces needed, but that's the general idea.
Note that it all starts with that cheap medium launcher; without that, it
doesn't work.

I'm not expecting it any time soon.
-- 
There is nothing wrong with making      | Henry Spencer @ U of Toronto Zoology
mistakes, but... make *new* ones. -D.Sim|  henry@zoo.toronto.edu  utzoo!henry
Newsgroups: sci.space.shuttle