From: hollis@titan.ksc.nasa.gov
Newsgroups: sci.space.shuttle
Subject: Re : Shuttle as an space tug...
Date: 21 Jan 93 16:34:20 EST
Organization: NASA, Kennedy Space Center

Greetings and Salutations:

From: BrianT@cup.portal.com (Brian Stuart Thorn), The Portal System (TM)
>There is very definitely something wrong here. Apollo got to the
>Moon and back from an Earth parking orbit not much different than
>Shuttles. It did this on the power of a partially spent S-IVB
>Third Stage and the Service Propulsion System of the Apollo
>spacecraft. No matter how you calculate this, that does not add
>up to three times the energy of the SSMEs and SRBs.

Two different spacecraft.  Two different objectives.  The Saturn-V had almost
all fuel as weight.  Shuttle is a payload delivery system to low earth orbit. 
The Saturn-V was dropping off pieces / parts of the system all of the way to
the moon and back until all it was moving was a small capsule to return men to
the ocean.  A capsule, I might add, that could VERY easily fit in the shuttle
bay with room for a real payload...

>Work in the aft compartment is mostly (entirely?) for the SSMEs,
>which wouldn't be necessary for LEO tug work. APUs and Fuel Cells
>are below the payload bay, not that difficult to reach. APUs

Where DO you get your info from... APU's are in the aft compartment, along with
all of the electronics for the APUs, electronics for the SSMEs, electronics for
the aft OMS / RCS pods, the SSMEs, water spray boilers, APU fuel tanks, misc.
hydraulic lines, misc. freon cooling lines, lots of wiring.

>wouldn't be required, either. If we seriously wanted to use old
>Shuttles as OTV, strip the SSMEs off and pull out the APUs. They

How would we strip out these items?  Once again, these are man intensive items
to pull during ground servicing, much less in space.  You need the SSMEs to get
to orbit, so the only place to pull them is in space.  Same with the APU's.

>are already designing a Solar Powered Extended Duration Orbiter
>(SPEDO) kit, so use that to replace the maintenance-intensive
>fuel cells. What's left isn't that complicated. OMS and RCS are
>already designed for multiple flights before heavy maintenance.

How do we fuel these?  They would have to be redesigned for astronaut
servicing.

>Remember that Apollo was *much* lighter than the shuttle. Besides, in
>Apollo, parts of the vehicle were jettisoned when they were not needed
>any more. For example the S-IVB was jettisoned after TLI; something that
>can't be done to an ET, if it contains the fuel for subsequent burns.
>The SPS was only used to get on and off lunar orbit and course corrections,
>both of which requires much less velocity change than TLI.

>No disputing that, but the previous poster claimed that Trans
>Lunar Injection (TLI) required x (3 times?) the energy of the
>boost from Earth to LEO. I was simply saying that is not true,

The original post did not specify from LEO, and I said it took 2 times the
energy.  See the previous post as I was wrong.  From surface to the moon, it is
about 11 times more energy.

>load for TEI. Then again, even a single SSME has an order of
>magnitude more thrust than the Apollo SPS engine.

The Apollo (Saturn V) J2 engine was 230,000 Lbs thrust, the SSME is 512,300 Lbs
thrust (Aerospace America, November 1991).  Not even close to an order of
magnitude.

>The Main Engines and the ET are an option, not a requirement for
>a LEO OTV. No Main Engines, you need no APUs either. Leave one
>ex-Shuttle at Freedom to service HST, GRO, and things yet to come
>without having to launch a special DC mission for the job.

You might wish to thoroughly read previous posts before wading in so daringly
8-}.  As en explained previously, there are MANY black boxes throughout the
shuttle, including 3 avionics bays in the aft with dozens of electronics boxes
in each.  Changing these out is a pain even on the ground, and we change one
out every other mission or so.  You would have to do this in orbit, and without
special redesign, I doubt that the astronauts could even get through the doors
or into thru the aft thrust structure in a pressure suit to even GET to these
boxes much less change them out.  You would also have to redesign the OMS pods
for on orbit refueling.

>If they wanted to use the SSMEs and the ET, perhaps some sort
>of interconnecting unit could be built to make connecting the 
>Shuttle to the ET less difficult. It wouldn't need to withstand
>the rigors of a launch (and the SRBs) just the propulsion from
>a single SSME.

Once again, you might wish to review the previous posts.  SSMEs are not just
fill em up & light em.  The Saturn - V J-2 was restarted only after the
thrusters on the sides were run and some of the boiling off LO2 & LH2 was used
for thrust.  This settled the LOX & LH2 in the tank.  The thrust chamber of the
J-2 also recirculated LH2 before it was lit.  The SSME requires a few hours of
chilldown with the LOX being dumped on the ground, and then during final count
an hour of chilldown minimum.  The LH2 is also required to recirculate, but
that goes back into the LH2 tank.  Translation, the SSMEs are not easy to get
set up correctly for launch.


-- 
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Ken Hollis  INTERNET: HOLLIS@TITAN.KSC.NASA.GOV
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