Shuttle Aerodynamics

On Fri, 21 Sep 2007 15:20:27 -0700,
wrote:

Oh yeah, another good search term for shuttle ascent control is
"squatcheloid".

No foolin. It sounds like a joke, but it isn't. Well, I mean, I'm
sure the designers had a lot of fun throwing that term around, but it
is has very serious life/death-type ramifications.


~ CT
Thank you very much for the info. Have a good one.
Best Regards
Jim in Houston.

Contrary to popular opinion RN does not mean Real Nerd!
Teddy Roosevelt's mother said: "Fill what is empty,
empty what is full, and scratch where it itches"

--
Posted via a free Usenet account from http://www.teranews.com

wrote in message
oups.com...
On Fri, 21 Sep 2007 07:51:47 -0500, Craig Fink
wrote:

The SSME are moved independently, it's the flight control portion of the
On-Board flight software and the mixing logic that transforms the error
signals into gimbal movements. This mixing logic is changed during
flight
for various reasons. So, with respect to pitch rate errors, they all
move
together because the flight control mixing logic commands them to do it
that way.

Or, google groups sci.space.shuttle, there are plenty of good
discussions in
the past about this subject.

Or just google the web at large for terms like [space shuttle tvc] or
[shuttle atvc] and you'll find great pages like this:

http://spaceflight.nasa.gov/shuttle/.../thvector.html

...that will tell you more stuff than you ever cared to know, like
that there are three different sizes for SSME actuators. Strange that
they don't go ahead and tell you *why* there are three different sized
actuators, but it is easy to deduce that the reason is because the
engine bells experience different aero loads in each axis and that the
center engine has the biggest fight against pitch of all of them.

Here's another good reference that Google coughed up:

http://science.ksc.nasa.gov/shuttle/...f/sts-mps.html

Again, they still leave room for going into greater detail, such as
the history of the design decisions. I've been told by the designers
that they tried to get away with fixed nozzles on the SRBs, but that
there was not enough control authority in the SSMEs to do this. And I
expect that the loads on the stack get improved once you sink the
extra cost and complexity for vectoring the SRBs.

And after deciding to control the SRBs, they found there was so much
flexing in the stack that each SRB needed their own set of RGA
sensors. They couldn't just control off the orbiters RGAs.

One thing that I have not understood is why the SRB actuators were
designed 45degrees off-axis from the SSME actuators. While SSME
nozzles move in Pitch and Yaw, the SRB nozzles move in "Rock" and
"Tilt". My best guess is that this improves robustness in case an
actuator fails.

Kind of a related question to Jim's; all the thrust from the SSME is
transmitted through a gimbal bearing to the shuttle frame - I'm interested
in the engineering of that and was trying to find a diagram of this
arrangement but had no luck, do you or anyone else know of one?

TIA

From MichaelJP:
Kind of a related question to Jim's; all the thrust from the SSME is
transmitted through a gimbal bearing to the shuttle frame - I'm interested
in the engineering of that and was trying to find a diagram of this
arrangement but had no luck, do you or anyone else know of one?

Not quite what you're asking for, but...

Here's a photo of the SSMEs being mounted to the orbiter that removes
some of the mystery:
http://www-pao.ksc.nasa.gov/kscpao/i...06pd2167-s.jpg

And here's a webpage with a "contact us" link you might want to try:
http://www.pw.utc.com/vgn-ext-templa...c4 5a529fRCRD


~ CT

wrote in message
ups.com...
From MichaelJP:
Kind of a related question to Jim's; all the thrust from the SSME is
transmitted through a gimbal bearing to the shuttle frame - I'm
interested
in the engineering of that and was trying to find a diagram of this
arrangement but had no luck, do you or anyone else know of one?

Not quite what you're asking for, but...

Here's a photo of the SSMEs being mounted to the orbiter that removes
some of the mystery:
http://www-pao.ksc.nasa.gov/kscpao/i...06pd2167-s.jpg

That's the area but I suppose I was really looking for an insight into how
you can transmit the massive thrust of a rocket engine but still allow it to
be gimballed freely in two axes for control purposes.

And here's a webpage with a "contact us" link you might want to try:
http://www.pw.utc.com/vgn-ext-templa...c4 5a529fRCRD

Thanks.

From MichaelJP:
Kind of a related question to Jim's; all the thrust from the SSME is
transmitted through a gimbal bearing to the shuttle frame - I'm
interested
in the engineering of that and was trying to find a diagram of this
arrangement but had no luck, do you or anyone else know of one?

Not quite what you're asking for, but...

Here's a photo of the SSMEs being mounted to the orbiter that removes
some of the mystery:
http://www-pao.ksc.nasa.gov/kscpao/i...06pd2167-s.jpg

That's the area but I suppose I was really looking for an insight into how
you can transmit the massive thrust of a rocket engine but still allow it to
be gimballed freely in two axes for control purposes.

That photo didn't satisfy a big part of your curiosity? Take that #2
engine in the lower left. That socket in the center is the pivot
point that also transmits all the thrust forces into the orbiter
fuselage. Then at the 12 o'clock position you have the bracket for
the pitch actuator. At the 3 o'clock position you have the bracket
for the yaw actuator. And around toward 6 o'clock and 9 o'clock you
have the big pipes for fuel & ox.

Since the pivot point for the engine lies directly along the axis of
thrust, the hydraulic actuators don't need to fight against the thrust
in order to move the bell around. That's the basics as I see it.


~ CT

On Oct 3, 6:42 pm, wrote:
[...]
That photo didn't satisfy a big part of your curiosity? Take that #2
engine in the lower left.


Easier to do with the large format copy:
http://www-pao.ksc.nasa.gov/kscpao/images//large/06pd2167.jpg

/dps

From Snidely:
On Oct 3, 6:42 pm, wrote:
[...]

That photo didn't satisfy a big part of your curiosity? Take that #2
engine in the lower left.

Easier to do with the large format copy:
http://www-pao.ksc.nasa.gov/kscpao/images//large/06pd2167.jpg

Yeah, that's much nicer. Thanks. Over on SSME#3 on the right, you
can see the load bearing pivot point just to the left of that guy's
head. Yaw actuator over at 3 o'clock and the pitch actuator down at 6
o'clock. Fuel/ox plumbing has been opened for the mating. To be more
accurate about their locations in relation to the center pivot, it is
more like 2:30 & 7:30 (or 4:30 & 10:30 back on SSME#2 to the left).

If the .jpg file wasn't dated as '06, you could still narrow down the
year +/-1 by that Pratt&Whitney sticker slapped by the Rocketdyne
label on the yellow workstand.

And note the "DO NOT ENTER" warning on the OMS nozzle cover!


~ CT

wrote in message
ups.com...
From Snidely:
On Oct 3, 6:42 pm, wrote:
[...]

That photo didn't satisfy a big part of your curiosity? Take that #2
engine in the lower left.

Easier to do with the large format copy:
http://www-pao.ksc.nasa.gov/kscpao/images//large/06pd2167.jpg

Yeah, that's much nicer. Thanks. Over on SSME#3 on the right, you
can see the load bearing pivot point just to the left of that guy's
head. Yaw actuator over at 3 o'clock and the pitch actuator down at 6
o'clock. Fuel/ox plumbing has been opened for the mating. To be more
accurate about their locations in relation to the center pivot, it is
more like 2:30 & 7:30 (or 4:30 & 10:30 back on SSME#2 to the left).

If the .jpg file wasn't dated as '06, you could still narrow down the
year +/-1 by that Pratt&Whitney sticker slapped by the Rocketdyne
label on the yellow workstand.

And note the "DO NOT ENTER" warning on the OMS nozzle cover!


~ CT

Thanks, guys, that larger photo is excellent and so much clearer

I guess the fuel/ox piping must be flexible at some point also, though I
can't see that in the photo?