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Shuttle Aerodynamics
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 |
#13
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Shuttle Aerodynamics
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 |
#14
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Shuttle Aerodynamics
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. |
#15
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Shuttle Aerodynamics
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 |
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Shuttle Aerodynamics
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 |
#17
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Shuttle Aerodynamics
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 |
#18
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Shuttle Aerodynamics
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? |
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