orbiter assent attitude
Spinks Albert H.
I remember reading somewhere that it was necessary for the crew to
see the earth's horizon during assent and that it is difficult to do
that with a normal attitude because the tank and boosters would be
in the way. With todays guidance control systems, it has been hard
for me to buy that argument completely. Does anyone know the true
poop on this subject?
--
Albert H. Spinks
Henry Spencer
As I understand it, it's simply so that the tank and SRB's don't block
line-of-sight for radio communications between the orbiter and the ground.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry
Bruce T. Lowerre
A rocket's thrust line must go through its center of mass, otherwise
it will tumble. The center of mass for the shuttle structure at
launch is located within the ET. The three main engines on the
shuttle are offset and are pointing upwards toward the rear when
viewed setting on its wheels. Thus, during ascent, the shuttle must
be on its back so as to allow the engines to lift the center of
mass of the entire launch vehicle.
Ed Weiss
But, why the role? Why doesn't it just fly straight onto its back?
--
Ed Weiss
ihnp4!iham1!spock
--> Live Long and Prosper <--
Greg Titus
>
> Albert H. Spinks
I believe I recall something about the antennas on top of the shuttle
needing to be able to "see" the ground, without the shuttle body and
ET in the way. This is not for sure, though.
greg
--
Greg Titus ..!ucbvax!unmvax!nmtvax!greg (uucp)
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======================================================================
David Messer
The shuttle does indeed fly upside down so the pilot can see the
horizon. I think you are probably right about todays guidance
systems (if a system failure was so complete as to create a need
to 'eyeball it', I don't think it would matter), but American
manned spacecraft have always flown upside down for that reason.
I think the bottom line is that there is now reason to pick any
other attitude, so they might as well choose one that provides
some marginal safety advantage.
--
David Messer UUCP: ...ihnp4!quest!dave
...ihnp4!encore!vaxine!spark!14!415!sysop
FIDO: 14/415 (SYSOP)
Lyle McElhaney
> >
> > As I understand it, it's simply so that the tank and SRB's don't block
> > line-of-sight for radio communications between the orbiter and the ground.
>
The initial orientation of the shuttle (roll, or vertical axis) is defined
by the high radius turns in the lane from the VAB to the launch pad.
The crawlers cannot turn easily, and so straight-on approaches to the pad
are made, and the pads were designed with this in mind. Also, Kennedy
supports launch azimuths of from 35 degrees (northeast) to 120 degrees
(southeast), so some kind of roll manuever would be required in most
flights anyway before pitch over.
Lyle McElhaney
...hao!cisden!lmc
Brent P. Callaghan
>> > Can anyone explain why during assent the orbiter flies upside-down?
>>
>> As I understand it, it's simply so that the tank and SRB's don't block
>> line-of-sight for radio communications between the orbiter and the ground.
>> --
>> Henry Spencer @ U of Toronto Zoology
>> {allegra,ihnp4,linus,decvax}!utzoo!henry
>
>But, why the role? Why doesn't it just fly straight onto its back?
>--
The roll is initiated once the tower is clear to put the
launch vehicle on the correct azimuth for the desired orbital plane.
It is much easier to do it this way than to have some kind of
turntable launch pad.
--
Made in New Zealand --> Brent Callaghan
AT&T Information Systems, Lincroft, NJ
{ihnp4|mtuxo|pegasus}!poseidon!brent
(201) 576-3475
Henry Spencer
> > line-of-sight for radio communications between the orbiter and the ground.
>
The attitude at launch is constrained by the structure of the launch site.
Things like the flame trenches were originally set up for the Saturn V,
and rebuilding the pads totally for the shuttle wasn't thought reasonable.
So the shuttle lifts off in an attitude that's different from what's wanted
in flight. Hence the roll.
Incidentally, it has nothing to do with getting the thrust line to pass
through the center of gravity, since that depends on which way the nozzles
point *with respect to the vehicle* and has nothing to do with attitude.
David Messer
> > > line-of-sight for radio communications between the orbiter and the ground.
> >
> > But, why the role? Why doesn't it just fly straight onto its back?
>
> The attitude at launch is constrained by the structure of the launch site.
> Things like the flame trenches were originally set up for the Saturn V,
> and rebuilding the pads totally for the shuttle wasn't thought reasonable.
> So the shuttle lifts off in an attitude that's different from what's wanted
> in flight. Hence the roll.
Also, if you think back to the Apollo days, you will notice that
the Saturn launches also had a roll program. Apollo also flew
upside-down.
--
+-----------------------------------+----------------------------------+
| Disclaimer: | David Messer |
| I'm always right and I never lie. | |
| My company knows this and agrees | UUCP: ...ihnp4!quest!dave |
| with everything I say. | FIDO: 14/415 (Sysop) |
+-----------------------------------+----------------------------------+
David desJardins
>
>Also, if you think back to the Apollo days, you will notice that
>the Saturn launches also had a roll program. Apollo also flew
>upside-down.
>
rocket fly upside-down??
-- David desJardins
Bruce T. Lowerre
Easy, put the hot end at the top. :-)
Burch
Really, they did not so much roll as spin.... Gyroscope-wise for stability.
--
-David B. (Ben) Burch
Analyst's International Corp.
Chicago Branch (ihnp4!aicchi!dbb)
"Argue for your limitations, and they are yours"