Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Misc Shuttle questions
Message-ID: <1989Dec6.164948.632@utzoo.uucp>
Organization: U of Toronto Zoology
References: <32253@cci632.UUCP>
Date: Wed, 6 Dec 89 16:49:48 GMT

In article <32253@cci632.UUCP> lmm@cci632.UUCP (Lance Michel) writes:
>       1.   Couldn't a (removable) additional fuel tank be mounted
>            in one of the shuttles.  And say (for sake of discussion) 
>            that this tank took up most or all of the payload area.  Then
>            could the shuttle reach high orbits, maybe even geosync. orbit?
>            Would there be any advantage to such a mod?

Well, it could probably be done.  Of course, if it's fuel for the main
engines, as opposed to the OMS engines (I'm not sure which would be preferred.
The main engines have a significantly higher exhaust velocity, but hydrogen
is very bulky.  It would depend on whether the cargo-bay tanks turned out
to be weight-limited or volume-limited, I guess.), that brings back the
hysteria about cryogenic fuels in the payload bay.  It would get you to a
somewhat higher orbit.  I don't think it would get you to Clarke orbit,
though:  the orbiter is much heavier than its payload, and the added
performance would be relatively modest.  Just getting up to somewhat higher
orbits than usual is not spectacularly useful; in particular, you do *not*
want to take a manned mission higher than about 1000km for any length of
time unless you're going straight out at high speed, because the inner
Van Allen belt is not a good place for humans.  It's also not clear what
use such a mission would be without any payload, unless it was something
like a repair mission for a high-value satellite.

>       2.   If a sat. is in geosnyc, is it very stable there?  Or does it
>            require hydozine adjustments like other lower sats?  Will a 
>            geosync ever come down if left unattended?

The orbital lifetime that high up is very long, infinite for all practical
purposes.  However, if you want a satellite to stay in *one spot* in
Clarke orbit, then you do need stationkeeping thrusters.  Various small
perturbations -- for example, lumpinesses in the Earth's gravitational
field -- make satellites in Clarke orbit drift slowly, and periodic
corrections are needed.  Some of the newer comsats actually use small
ion rockets for this (!), since stationkeeping fuel is often the limiting
factor in comsat lifetime.

>       3.   What about the LDEF.  When Columbia brings it down it will be
>            a record landing weight correct?  ...

Actually, I think one of the Spacelab missions may hold that distinction,
but I'm not sure and I don't have numbers handy.

>		...Could any of
>            the shuttles perform this task, or does it require the "Mack
>            Truck" of the fleet? ...

No, or they wouldn't send Columbia!  Compared to the later orbiters,
Columbia is somewhat overweight to begin with.

>       4.   This question I just have to ask:  Henry S. (In Toronto), how
>            do you know all this stuff? Where do you get these resources?

A lot of it is just persistent interest and a lot of reading and following
of cross-references.  For the shuttle, there is actually a lot of technical
detail in NASA's Shuttle News Reference, which is intended to answer most
technical questions that the media might have.  The National Space Society
and several other groups sell reprints of it.  For more detail, World
Spaceflight News (Box 98, Sewell NJ 08080) publishes a long list of special
reports based on NASA material which go into nitty-gritty detail about
shuttle systems and equipment.  (WSN itself publishes things like the
complete flight plan and cargo manifest for each shuttle flight, the
postflight reports, and complete texts of things that are hard to find
elsewhere [e.g. the Kerwin medical/forensic report on Challenger,
the entire Ride Report, Feynman's appendix to the Rogers Commission
report, etc.].  Highly recommended.)

>            ... Do you make any public appearances regarding
>            space technology,  if so when and where, (I'll be there!)

Not unless you count an occasional talk at the Canadian Space Society
meetings here, and regular attendance at the BIS parties at the World
Science Fiction Conventions.
-- 
1233 EST, Dec 7, 1972:         |     Henry Spencer at U of Toronto Zoology
last ship sails for the Moon.  | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
