Conference 7.286::space

You are basically correct.

Unlike other rockets the Shuttle "stack" is asymmetrical.  The best
attitude for it when it is launching is to have the shuttle "underneath"
the external tank.

Other rockets have to pitch towards their orbit inclination as well.  The
shuttle does the same thing, but has to roll as well to keep it in the
proper "heads down" attitude.


The main reason this is done is that is *really hard* to rotate the pad to 
the correct angle.


- dave

    
    This brings up a good point that a lot of (maybe most) people are not
    aware of, that the Space Shuttle enters orbit UPSIDE DOWN, that is,
    with the top of the Shuttle oriented toward the earth.  Which means
    as the shuttle rockets toward orbit, and gradually curves or tilts
    over more'n more parallel to the earth, the shuttle gradually shifts
    to being on the down side,& the external fuel tank gradually shifts
    to being on the up side;  While this is going on, the astronauts see
    the earth begin to come more'n more into view from the TOP  of the
    shuttle's front windshield, not the bottom.  Of course it doesn't
    matter to the crew once the engines cut off, no 'up' or 'down' in
    weightlessness, except by visual reference or G forces.
    
    And to my understanding, this is the reason for the roll, or shifting
    of the shuttle about it's axis (actaully the Tank's axis) just a few
    seconds after liftoff:  So the shuttle will be be in the proper posi-
    tion to end upside down, when the whole rocket/shuttle stack begins
    to tilt over as it heads toward orbit.
    
    But, the natural next question is, why would you want the shuttle to
    become upside down, as it ascends toward orbit?  To my understanding,
    it's for safety reasons, so that the crew always has a good view of
    the earth in case they have to abort the mission, separate from the
    tank & head back toward a landing.  This is a much better situation,
    from a pilot's point of view, then if the shuttle was on the topside
    as the tiltover toward parallel to earth was gradually made.  If on
    top, all they'd see is sky, which would get darker'n darker, with no
    visual cues as to their orientation to earth, the angle to the earth
    they're traveling at any given time.  Visual cues of earth & horizon
    are very important to pilots, whether flying small planes or shuttles.
    
    Also, it's be easier to maneuver the powerless shuttle down & back,
    away from the big tank, then to pull up & back from the tank.
    
    	- Tom

    
    I think another reason for the upside down position is to protect
    the crew and some experiments from long duration exponation of 
    radiation from the sun.
    
    ThPi

    I heard that the shuttle was supposed to ride on top of the stack, and
    it would actually use less fuel in that configuration.  The problem is,
    the dynamic forces are greater, and it is for safety reasons that they
    use the configuration they do.
    
    \Ron

RE: <<< Note 888.4 by SHAKER::BAUER "Ron Bauer" >>>

>    I heard that the shuttle was supposed to ride on top of the stack, and
>    it would actually use less fuel in that configuration.

I can sort of rationalize this by postulating that the orbiter's wing could
help in the middle phases of the ascent. But the angle of attack of the entire
stack is pretty small, so the difference between the AoA with the shuttle up
vs. with it down is doing to be VERY small. Thus the lift generated by the
wing will be almost the same in both cases, it seems to me. 
						-- Tom

    Re.-1:
    I don't know what kind of lift characteristics the shuttle wing has, if
    if it's laminar flow or not, but with the shuttle on the bottom as the
    stack tilts over, the lifting force (which is roughly perpendicular to
    a wing as it cuts thru the air) would be in the same direction as the
    tilt, aiding it.  If the shuttle were on top, this lift would be in the
    opposite direction of the tilt, which might cause undo stresses in the
    connections between the shuttle & the tank.  
    
    - Tom

RE: <<< Note 888.6 by TFH::ANGELOTTI >>>

I bet that the wing is generating very little lift during ascent, such that
there is probably relatively little tension (or compression) force generated on
the orbiter-ET connections. I would imagine that the shear force on the
orbiter-to-ET connections (due to SRB thrust) is much greater than any tension
force on them (due to wing lift). 
						-- Tom