alan@comp.lancs.ac.uk (Alan Phillips) (09/06/90)
I'm a casual visitor to this group, so apologies if this question is fequently asked and answered, and more so if it's fundamentally stupid :-) Why does the stack roll after lift off to bring the orbiter upside down? Is it to make an RTLS abort easier, allowing the stack to do a loop and come out with the orbiter the right way up without needing a 180 degree roll, or is there a fundamental aerodynamic reason? I have a recollection that one of the problems with launches from Vandenberg was that the stack needed to be the other way up (orbiter the right way up). What was the reasoning there? Thanks, Alan Phillips.
henry@zoo.toronto.edu (Henry Spencer) (09/07/90)
In article <1013@dcl-vitus.comp.lancs.ac.uk> alan@comp.lancs.ac.uk (Alan Phillips) writes: >Why does the stack roll after lift off to bring the orbiter upside down? The major reason is simply that flying "right side up" would put the external tank between the orbiter's radio antennas and the ground stations. -- TCP/IP: handling tomorrow's loads today| Henry Spencer at U of Toronto Zoology OSI: handling yesterday's loads someday| henry@zoo.toronto.edu utzoo!henry
cs63bld@unccvax.uncc.edu (b. daniels) (09/08/90)
As I remember, it was to provide a visual reference horizon to the
commander in case of an emergency seperation. I vaguely remember it
being easier on the Orbiter in terms of dynamic pressure loads...
Later,
Brian
--
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I access the net, therefore I am...
Brian Daniels (cs63bld@unccvax.uucp)
----------------------------------------------------------------------rick@ofa123.fidonet.org (Rick Ellis) (09/11/90)
On <Sep 06 09:39> Alan Phillips writes:
AP> Why does the stack roll after lift off to bring the orbiter upside
AP> down?
It lowers the dynamic stress on the vehical assembly.
--
Rick Ellis
Internet: rick@ofa123.fidonet.org
--------------------------------------------------------------------------v055mvw3@ubvmsb.cc.buffalo.edu (Gregory J Schaffer) (09/14/90)
In article <1103.26EC49AE@ofa123.fidonet.org>, rick@ofa123.fidonet.org (Rick Ellis) writes... >On <Sep 06 09:39> Alan Phillips writes: > > AP> Why does the stack roll after lift off to bring the orbiter upside > AP> down? > >It lowers the dynamic stress on the vehical assembly. > > > >-- >Rick Ellis >Internet: rick@ofa123.fidonet.org >-------------------------------------------------------------------------- Just curious...where on the vehicle is this stress lowered, and why? The orbiter's wings produce lift while en route to orbit...being upside down *ADDS* this force to the direction of gravity, creating what I would think would be *MORE* stress on the orbiter. Am I missing something? Maybe it is, if you'll pardon the expression, the "natural tendency" of the orbiter to "hang" on the rest of the assembly. If I'm missing something obvious, forgive me...I just woke up :). --------------------------------------------------------------------------- Gregory J. Schaffer schaffer@acsu.buffalo.cc University at Buffalo V055MVW3@UBVMS "Seven years of college, down the OPNSGREG@UBVM drain!" "sleeping on Lockwood 5!" ---------------------------------------------------------------------------
rick@ofa123.fidonet.org (Rick Ellis) (09/19/90)
On <Sep 14 11:45> Gregory J Schaffer writes:
GJS> Just curious...where on the vehicle is this stress lowered, and why?
GJS> The orbiter's wings produce lift while en route to orbit...being
GJS> upside down *ADDS* this force to the direction of gravity, creating what
GJS> I would think would be *MORE* stress on the orbiter. Am I missing
GJS> something? Maybe it is, if you'll pardon the expression, the "natural
GJS> tendency" of the orbiter to "hang" on the rest of the assembly.
From NSTS-7:
The vehicle lifts off the pad 0.3 second after SRB ignition, rising vertically
in attitude hold until the SRBs' nozzles clear the lightning rod tower by
approximately 41 feet. The vehicle begins a combined roll, pitch and yaw
maneuver that positions the orbiter head down, with wings level and aligned with
the launch pad. The orbiter flies upside down during the ascent phase. This
orientation, together with trajectory shaping, establishes a trim angle of
attack that is favorable for aerodynamic loads during the region of high dynamic
pressure, resulting in a net positive load factor, as well as providing the
flight crew with use of the ground as a visual reference. By about 20 seconds
after lift-off, the vehicle is at 180 degrees roll and 78 degrees pitch.
During the first 90 seconds of flight, the flight control system provides load
relief by making adjustments to reduce vehicle loads at the expense of
maintaining a precise trajectory profile. A special schedule of elevon position
with respect to velocity is followed to protect the wings from excessive loads
and to hold the body flap and rudder/speed brake in place. The surface position
indicator displays the position of the aerosurfaces. To keep the dynamic
pressure on the vehicle below a specified level, on the order of 580 pounds per
square foot (max q), the main engines are throttled down at approximately 26
seconds and throttled back up at approximately 60 seconds. This also reduces
heating on the vehicle. Because of the throttling at this time, the term
"thrust bucket" evolved. Maximum dynamic pressure occurs shortly after throttle
up.
--
Rick Ellis
Internet: rick@ofa123.fidonet.org
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