From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: A new orbiter? (dont think so--was Re: National Space Plane)
Date: Thu, 27 Aug 1992 17:28:28 GMT
Organization: U of Toronto Zoology

In article <BtML5q.7Ln@news.cso.uiuc.edu> jbh55289@uxa.cso.uiuc.edu (Josh 'K' Hopkins) writes:
>>For one thing, I don't
>>consider anything with large solid boosters "man-rateable" :-). 
>
>I'm skeptical myself, but NASA and ESA seem to disagree.

NASA has changed its mind; they've said recently that they don't want
to see solid boosters on future man-rated launch systems.

>What you want is an Atlas II series at a lower price...

It may be a little small, but it probably matches the requirements as well
as anything we've actually got right now.  Slightly greater lift might be
had by small liquid-fuel strap-ons a la Ariane 4.

>a little extra (well, okay, a factor of 2) because I didn't think you could 
>get a crew vehicle and a tug on the same rocket with only 10 tons...

I haven't done detailed estimates on weight, but I don't think it should
be that hard.  Remember, my reentry vehicle is not an all-singing-all-dancing
craft that supports a crew for a week and doubles as a laboratory; taking
them up and down is its only job.  Occupied lifetime of perhaps 24 hours.
The cargo load is a toothbrush apiece. :-)  It needs a heatshield, attitude
control, retrorockets, a gliding parachute, crushable foam as a shock
absorber, an air supply, and not much more.  It's hardly worth trying to
make it reusable; re-use the subsystems and throw away the structure.
If I were really being minimalist, I'd put the crew in spacesuits and
wouldn't even bother to pressurize it.  (Remember, if they're staying
up for any length of time, they've got a habitation module or they're
heading for an already-existing base camp.)  Think "airport shuttle bus",
not "motor home".

We can certainly do the reentry vehicle for 1500kg/man, because at that
weight we can simply give each one his own Mercury capsule!  I would
hope we could do it for a few men at 500kg apiece, just off the top of
my head.

And my tug isn't a big husky thing meant to move comsats into Clarke
orbit.  Its job is rendezvous and docking for payloads that have already
been fairly carefully inserted into essentially identical orbits.  Its
job is assembly, not major orbit changes.  At an exhaust velocity of
3000m/s (good fuels but not liquid hydrogen), assuming a 1000kg tug
carrying 5000kg of fuel, we can impart about 280m/s to each of five
10000kg payloads.  I don't know offhand what rendezvous+docking needs,
and five payloads is somewhat arbitrary, but my gut reaction is that
this ought to be adequate.

That's a fully-fuelled tug plus an eight-man reentry vehicle in 10 tons.
The reentry vehicle probably doesn't need to be that big, and we can
get by with a minimally-fuelled tug if we must (the first payload
includes a tank module for the tug), so there's margin.  If worst comes
to worst, we launch the tug separately and remote-control it long enough
to r+d with the first payload, which is the reentry vehicle plus some cargo.
Cut the fuel load in the tug a bit, and we can do that with a 5-ton launcher.

>Maybe we can both agree that Ariane 5 is the closest real-world hardware to 
>what you want but is still sadly lacking.

Actually, I think a (possibly somewhat souped-up) Atlas is the closest
match in current hardware, and a bulk buy might get the costs down to
something approaching practicality.
-- 
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