Shuttle Aerodynamics

Ignorance confession time.
I wonder, as I watch the shuttle lift off, which aero surfaces or
engine gimbals are responsible for what movements?
Roll immediately after clearing the tower: I have tried to discern
movement of the elevons but for the life of me I cannot see them move.
It can't be the rudder, so is it the gimbaling of the SSME or SRM
nozzles?
While I'm at it I might as well really do myself in. I have no
understanding of what force causes the ballistic arc path of the
vehicle. I would suppose that gravity and the rotation of the earth
have something to do with it. Is the arcing a natural occurrence?
If some one can give me a link to a site that explains these and
associated subjects I would appreciate it. Or if someone just wants to
give me an explanation that would be great.
I really hope that everyone here subscribes to the "no stupid
question" rule.
Thanks in advance.
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

Jim in Houston wrote:
Ignorance confession time.
I wonder, as I watch the shuttle lift off, which aero surfaces or
engine gimbals are responsible for what movements?

The SRB and SSME gimbals do all the flying.

The aerosurfaces are moved during ascent, but only for load relief, not
flight control.

On Thu, 20 Sep 2007 08:24:10 -0500, "Jorge R. Frank"
wrote:

Jim in Houston wrote:
Ignorance confession time.
I wonder, as I watch the shuttle lift off, which aero surfaces or
engine gimbals are responsible for what movements?

The SRB and SSME gimbals do all the flying.

The aerosurfaces are moved during ascent, but only for load relief, not
flight control.
Thanks Jorge for the prompt reply. One more question, when the SSME's
move do they move independently or together? Thanks again.

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

One more question, when the SSME's
move do they move independently or together? Thanks again.


Life is a lot better if they move together.

Jim in Houston wrote:
On Thu, 20 Sep 2007 08:24:10 -0500, "Jorge R. Frank"
wrote:

Jim in Houston wrote:
Ignorance confession time.
I wonder, as I watch the shuttle lift off, which aero surfaces or
engine gimbals are responsible for what movements?
The SRB and SSME gimbals do all the flying.

The aerosurfaces are moved during ascent, but only for load relief, not
flight control.
Thanks Jorge for the prompt reply. One more question, when the SSME's
move do they move independently or together? Thanks again.

More of a Danny question. I believe they move together during first
stage and for pitch/yaw control during second stage, and independently
for roll control during second stage. But I could be wrong.

On Thu, 20 Sep 2007 22:34:20 -0500, "Jorge R. Frank"
wrote:


More of a Danny question. I believe they move together during first
stage and for pitch/yaw control during second stage, and independently
for roll control during second stage. But I could be wrong.
Thanks again for the prompt reply. Can you direct me to a site which
discusses such subjects?
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

Jim in Houston wrote:

On Thu, 20 Sep 2007 22:34:20 -0500, "Jorge R. Frank"
wrote:


More of a Danny question. I believe they move together during first
stage and for pitch/yaw control during second stage, and independently
for roll control during second stage. But I could be wrong.
Thanks again for the prompt reply. Can you direct me to a site which
discusses such subjects?

Andy Foster has a very good set of web pages on the subject of Shuttle
ascent.
http://www.theandyzone.com/index.html
I think you'll have to ask him to put them back up if you really want to
read them.

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.
--
Craig Fink
Courtesy E-Mail Welcome @

On Fri, 21 Sep 2007 07:51:47 -0500, Craig Fink
wrote:


Andy Foster has a very good set of web pages on the subject of Shuttle
ascent.
http://www.theandyzone.com/index.html
I think you'll have to ask him to put them back up if you really want to
read them.

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.
Thanks Craig, for that very useful post, I really appreciate it.
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

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.


~ CT

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