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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 |
#2
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Shuttle Aerodynamics
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. |
#3
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Shuttle Aerodynamics
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 |
#4
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Shuttle Aerodynamics
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. |
#5
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Shuttle Aerodynamics
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. |
#6
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Shuttle Aerodynamics
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 |
#7
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Shuttle Aerodynamics
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 @ |
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Shuttle Aerodynamics
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 |
#9
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Shuttle Aerodynamics
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 |
#10
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Shuttle Aerodynamics
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 |
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