Conference 7.286::space

With regard to using Vandenberg for polar launches:

I can understand why we want to avoid flying over populated areas on
take-off, but why can't we put the Shuttle into a polar orbit once we are
in LEO?  Is it simply because of fuel limitations, or is something else
responsible?

	Mike

I suspect the problem is lack of fuel.  A large change of
velocity would be required to swing the orbit.
    John Sauter 

You might even call it a lack of engines...

I doubt very much that the OMS engines have enough thrust to pull off
such a feat - even if they had enough fuel.

The main engines fuel tank gets dropped off long before such a manuver
could be executed.

Trivia: Do they HAVE to jettison the external fuel tank to achieve orbit?

- dave

	Re:-1 Do they have to jettison the external tank?

	I venture a guess of yes.  While the OMS engines are gimbaled, I 
	don't think they can move enough to offset the change to the center
	mass of the vehicle that would occur with the tank attached.  Also,
	isn't there just enough atmosphere left at jettison that there still
	a good deal of drag being exerted?  That's more effort added to
	getting to orbital velocity.

	Now the for the obvious reasons.  Why drag 78,000 lbs of dead weight
	into orbit?  The ET carries the LOX and LH for the main engines, but
	the OMS burns monomethly hydrazine and nitrogen tetroxide which is 
	stored in the OMS pods.  Lastly, at 6,000 lbs. of thrust each, that's 
	a lot of extra fuel the OMS engines would need to reach orbit.

	Maybe I'm all wrong, so somebody let me know.

	Klaes

    The reason I asked was that I recall some plans (maybe invalid
    ones) that proposed using the external tanks as building
    components for a space station.  [The ET is an amazing piece of
    engineering - while remaining very lightweight it holds volatile,
    pressurized, cryogenic fluids and withstands enormous sheer
    pressures where it connects to the shuttle.] While the ET makes a
    very good fuel tank, I doubt it would make a good space station
    module. 
    
    I doubted it could be carried into orbit either, but I thought I'd
    ask if people had heard otherwise. 

>	                 Lastly, at 6,000 lbs. of thrust each, that's 
>	a lot of extra fuel the OMS engines would need to reach orbit.

    Hmmm.  I didn't know OMS engines were used to attain orbital
    velocity! I thought they are used only to round out the orbit,
    make attitude/direction changes, and initiate re-entry.  Live and
    learn. 

- dave

I don't believe they are normally used to reach orbit, but
I think they were used recently when one of the main engines
shut down prematurely.
    John Sauter

There are 2 OMS burns necessary to acheve orbit. About 2 minutes after the ET is
dropped, the shuttle is oriented for OMS-1 burn, which lasts about 2 minutes.
This puts the shuttle into an elliptical orbit. OMS-2 comes half way around the
world, about 45 minutes into the flight. It is about 1/2 minute long. This burn
circularizes the shuttles orbit. The OMS engines are used for any major orbital
manuvering (chasing satellites, etc.) and finally for the de-orbit (retro) burn.
[Source: Space Shuttle Operator's Manual]

John, what they did on the Abort To Orbit was to burn the other two main engines
for an extra 90 seconds or so, using up the fuel in the ET not burned by the
engine that shut down. Since this changes the thrust profile, they ended up in a
somewhat lower than normal orbit, only some of which could be compensated for
via the OMS engines. They had to save enough OMS propellant for the many orbital
manuvers required by the experiments, de-orbit manuvers, and a safety margin
that NASA always requires. 

As to the trivia question, I believe they go out of their way to dump the tank
in such a manner as to cause it to fall from orbit and burn up in re-entry.
There is an awful lot of useless junk in space already; an ET per flight would
mess things up even more. With some extra fuel here or there, it should be
relatively easy to carry the ET to low orbit.   Someone mentioned that it could
not be directly used as a space station component, but I am sure thare are some
things that could be salvaged, or remanufacturered. I saw this discussed
somewhere. The Saturn-V third stage that was used for Skylab was outfitted as a
lab on the ground, and NEVER HAD ANY PROPELLANT IN IT. I guess there is a lot of
nasty residue left in the ET, so that you really couldn't live in it without a
major rehab. Refitting it in space would be a complex task. They would do better
to take up small pieces of a lab designed to be assembled in orbit; using the
shuttle as the launch vehicle. maybe if they wanted to build an interplanetary
probe of some sort, it could be built around an old ET, but it would still have
to be refueled in space. 

Oops, I should have checked my copy of the Space Shuttle
Operator's Manual before exposing my ignorance. 

The Saturn series all used kerosene and liquid oxygen.  Liquid
oxygen isn't so bad, but leftover kerosene can be pretty icky.
The space shuttle, on the other hand, carries liquid hydrogen and
liquid oxygen in its external tank.  The ET should be lots easier
to clean out than a Saturn stage would have been. 

I agree, though, that the best method would be to carry material
up in the cargo bay.  Someday we'll be able to launch rocks from
the moon, thus eliminating the energy cost of lifting raw
material from the Earth's surface. 
    John Sauter 

re .8

Only the S-1C (first stage) of the Saturn V used Rp1/LOX. All the upper stages
used LH2/LOX so purging the S-IVB probably would not have been to tricky,
it just wasn't necessary with the lifting capabilities of the first two stages.

I don't know the delta-V capability of the OMS but original shuttle plans
called for the ability to carry propellant packs (up to 3) in the cargo bay
to complement the OMS propellant supply so it should be possible to carry
enough to reach true polar orbit (and de-orbit).

gary

Re: .8

Thanks for the confirmation on the Saturn V.  I was *sure* only the engines
in the 2nd/3rd stages burned liquid hydrogen/oxygen (I just didn't have
a reference handy to check).

- dave (glad that his memory is intact)

Associated Press Fri 15-NOV-1985 20:05                       Military Shuttle

   First West Coast Shuttle Launch Will Be Delayed, Aldridge Says

   VANDENBERG AIR FORCE BASE, Calif. (AP) - Although March 20
remains the scheduled date for the first West Coast launch of the
space shuttle, a top Air Force official says it almost certainly
will be delayed.
   ``It will be tough to make the March date,'' Air Force
Undersecretary Edward C. ``Pete'' Aldridge Jr., who will be an
astronaut on the flight, told about 300 military and aerospace
officials attending a Thursday symposium.
   Aldridge, who goes to Houston next week to start conditioning,
was not specific about when Discovery would blast off from
Vandenberg, but said: ``We won't make it (the March 20 date)
exactly; there will probably be some slippage.''
   Lt. Thom Connell, an Air Force spokesman, said Friday that there
has been no official change in plans for Discovery to blast off
March 20 from the new, $2.8 billion shuttle launch complex at the
coastal military base.
   But ``if the undersecretary of the Air Force is saying it's
going to slip a little bit, that's probably our new official
position,'' Connell said.
   The schedule depends on how well testing proceeds on fuels
systems at the launch complex.
   During his speech, Aldridge repeated a suggestion he made in
October that the launch complex be renamed the ``Ronald Reagan
Space Flight Facilities'' as a tribute to President Reagan.
   Aldridge indicated he doesn't like the existing name, Space
Launch Complex-Six, which base officials and workers call
``Slick-6.''
   The undersecretary also repeated that he has confidence in the
construction of the launch complex, saying he only has ``about four
microseconds' worth'' of anxiety about being shot into space.
   Last year, NBC News quoted unidentified inspectors as saying bad
welds and wiring at the launch complex could lead to a disaster at
blastoff. At the time, the Air Force and Aldridge denied any
possibility of a launch mishap and said welding and other problems
were being corrected.