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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
In recent discussions about lowering the Q on the 121 ascent profile, to the 'Lo-Q' trajectory (and accepting the performance penalty), I saw some remarks that the current ascent trajectory is actually an innovation introduced for Mir and ISS orbital inclinations, to regain some performance lost by the higher inclination. Is that true -- and what were the performance consequences? Does this make the higher-Q (and higher aero stress on TPS) another 'benefit' of the Russian partnership? Or am I more confused than usual? Thanks! Jim O |
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- ClarificationNeeded
In recent discussions about lowering the Q on the
121 ascent profile, to the 'Lo-Q' trajectory (and accepting the performance penalty), I saw some remarks that the current ascent trajectory is actually an innovation introduced for Mir and ISS orbital inclinations, to regain some performance lost by the higher inclination. Is that true -- and what were the performance consequences? I seem to remember changing the angle of attack so that there was actually some lift from the wings during ascent. That certainly was to increase performance for the high- inclination and weight-limited launches. How much of a difference that makes I dunno. Jan |
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
Jan Vorbrüggen wrote:
: In recent discussions about lowering the Q on the : 121 ascent profile, to the 'Lo-Q' trajectory (and : accepting the performance penalty), I saw some : remarks that the current ascent trajectory is : actually an innovation introduced for Mir and ISS : orbital inclinations, to regain some performance : lost by the higher inclination. Is that true -- and : what were the performance consequences? : :I seem to remember changing the angle of attack so that :there was actually some lift from the wings during ascent. :That certainly was to increase performance for the high- :inclination and weight-limited launches. How much of a :difference that makes I dunno. I would think this would actually DECREASE performance, since you would then be deliberately putting the vehicle into a 'draggier' attitude (lift creates drag) and losing energy to that drag. Orbit isn't about HEIGHT. It's about SPEED. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
On Tue, 09 May 2006 14:27:06 GMT, Fred J. McCall
wrote: Jan Vorbrüggen wrote: : In recent discussions about lowering the Q on the : 121 ascent profile, to the 'Lo-Q' trajectory (and : accepting the performance penalty), I saw some : remarks that the current ascent trajectory is : actually an innovation introduced for Mir and ISS : orbital inclinations, to regain some performance : lost by the higher inclination. Is that true -- and : what were the performance consequences? : :I seem to remember changing the angle of attack so that :there was actually some lift from the wings during ascent. :That certainly was to increase performance for the high- :inclination and weight-limited launches. How much of a :difference that makes I dunno. I would think this would actually DECREASE performance, since you would then be deliberately putting the vehicle into a 'draggier' attitude (lift creates drag) and losing energy to that drag. The delta increase in drag from an epsilon increase in lift isn't that big if you can use the lift to get higher quicker. There's less drag at higher altitudes. There's also less lift, but the reduction in drag is bigger because parasite drag is reduced, too, not just induced. Orbit isn't about HEIGHT. It's about SPEED. But speed can be about height. Drag is, so speed is. Mary -- Mary Shafer Retired aerospace research engineer We didn't just do weird stuff at Dryden, we wrote reports about it. or |
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
On Mon, 08 May 2006 14:06:24 +0000, Jim Oberg wrote:
Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed In recent discussions about lowering the Q on the 121 ascent profile, to the 'Lo-Q' trajectory (and accepting the performance penalty), I saw some remarks that the current ascent trajectory is actually an innovation introduced for Mir and ISS orbital inclinations, to regain some performance lost by the higher inclination. Is that true -- and what were the performance consequences? Does this make the higher-Q (and higher aero stress on TPS) another 'benefit' of the Russian partnership? Or am I more confused than usual? No, I wouldn't blame the Russian for how NASA decides to the increase performance of the Space Shuttle. Yes, higher Q increases loads on the vehicle including TPS. As for the performance gain, they should have been quoting a performance loss in their presentations. HighQ to LowQ with the NominalQ in between. I'd imagine it would be around a 1000 lbs, maybe more, but you need to look at their recent presentations for a better number. -- Craig Fink Courtesy E-Mail Welcome @ |
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
On Tue, 09 May 2006 08:17:56 -0700, Reunite Gondwanaland (Mary Shafer)
wrote: On Tue, 09 May 2006 14:27:06 GMT, Fred J. McCall wrote: Jan Vorbrüggen wrote: : In recent discussions about lowering the Q on the : 121 ascent profile, to the 'Lo-Q' trajectory (and : accepting the performance penalty), I saw some : remarks that the current ascent trajectory is : actually an innovation introduced for Mir and ISS : orbital inclinations, to regain some performance : lost by the higher inclination. Is that true -- and : what were the performance consequences? : :I seem to remember changing the angle of attack so that :there was actually some lift from the wings during ascent. :That certainly was to increase performance for the high- :inclination and weight-limited launches. How much of a :difference that makes I dunno. I would think this would actually DECREASE performance, since you would then be deliberately putting the vehicle into a 'draggier' attitude (lift creates drag) and losing energy to that drag. The delta increase in drag from an epsilon increase in lift isn't that big if you can use the lift to get higher quicker. There's less drag at higher altitudes. There's also less lift, but the reduction in drag is bigger because parasite drag is reduced, too, not just induced. Orbit isn't about HEIGHT. It's about SPEED. But speed can be about height. Drag is, so speed is. The object during first stage is to not break the wings/tail off during ascent. It's really a constraints problem with a little optimization within those constraints. The Orbiter in first stage is flying above it's manuvering speed. During high Q, it's flying a negative angle of attack to reduce loads on the wings. It must fly within an angle-of-attack/dynamic pressure (QAlpha) and QBeta tunnel, so to speek. Any optimization within this tunnel would put the Orbiter at the edge of the "acceptable" tunnel, as opposed to fly down the center of the tunnel. And, some small amount of performance would be gained. In the case of the Shuttle, it's flying upside down with a negative angle of attack. A more positive angle of attack increase performance, while more negative angle of attack decrease performance. A more negative angle would actually produce more lift in the up direction. So, it really about gaining speed downrange, letting the flight path angle fall off with time, not fighting gravity with lift. -- Craig Fink Courtesy E-Mail Welcome @ |
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
Craig Fink wrote in
news On Mon, 08 May 2006 14:06:24 +0000, Jim Oberg wrote: Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed In recent discussions about lowering the Q on the 121 ascent profile, to the 'Lo-Q' trajectory (and accepting the performance penalty), I saw some remarks that the current ascent trajectory is actually an innovation introduced for Mir and ISS orbital inclinations, to regain some performance lost by the higher inclination. Is that true -- and what were the performance consequences? As for the performance gain, they should have been quoting a performance loss in their presentations. I think Jim knew that - the "regain some performance" was in reference to the switch *to* high-Q. HighQ to LowQ with the NominalQ in between. I'd imagine it would be around a 1000 lbs, maybe more, but you need to look at their recent presentations for a better number. 1000 lbs is about right for the loss from high-Q to low-Q. 121 could spare it because they had around 1900 lbs margin. 115 and other performance- critical flights will need some other solution. -- JRF Reply-to address spam-proofed - to reply by E-mail, check "Organization" (I am not assimilated) and think one step ahead of IBM. |
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
Jim Oberg wrote:
Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed In recent discussions about lowering the Q on the 121 ascent profile, to the 'Lo-Q' trajectory (and accepting the performance penalty), I saw some remarks that the current ascent trajectory is actually an innovation introduced for Mir and ISS orbital inclinations, to regain some performance lost by the higher inclination. Is that true -- and what were the performance consequences? try http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=2248&start=1 |
#9
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- ClarificationNeeded
1000 lbs is about right for the loss from high-Q to low-Q. 121 could spare
it because they had around 1900 lbs margin. 115 and other performance- critical flights will need some other solution. The other quesions is: What problem does this solve? OK, so there is less aero stress on the orbiter including its TPS. How does that influence the chance that any foam from the tank actually impacts the TPS? It seems to me the mechanism could actually work in the other direction: higher Q could mean less chance of hitting the orbiter with debris. So what's actually the case and the rationale? Jan |
#10
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Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed
On Tue, 09 May 2006 17:47:40 -0500, Jorge R. Frank wrote:
Craig Fink wrote in news On Mon, 08 May 2006 14:06:24 +0000, Jim Oberg wrote: Low-Q, High-Q, and 'Normal-Q' Ascent Profiles -- Clarification Needed In recent discussions about lowering the Q on the 121 ascent profile, to the 'Lo-Q' trajectory (and accepting the performance penalty), I saw some remarks that the current ascent trajectory is actually an innovation introduced for Mir and ISS orbital inclinations, to regain some performance lost by the higher inclination. Is that true -- and what were the performance consequences? As for the performance gain, they should have been quoting a performance loss in their presentations. I think Jim knew that - the "regain some performance" was in reference to the switch *to* high-Q. Well, the performance gain from a "Nominal" Q to High Q probably would have been something like 300-400 lbs. At the performance Optimal Q the derivative dWT/dQ is zero, by definition. Like being at the top of a hill, varying Q and loads doesn't change performance. As Q is increased from "Nominal" Q the gain dWT/dQ becomes less and less, so High Q doesn't gain that much. Essentially, gaining less and less performance while steadily increasing Q/loads. HighQ to LowQ with the NominalQ in between. I'd imagine it would be around a 1000 lbs, maybe more, but you need to look at their recent presentations for a better number. 1000 lbs is about right for the loss from high-Q to low-Q. 121 could spare it because they had around 1900 lbs margin. 115 and other performance- critical flights will need some other solution. Included in DOLILU I software was an input variable Delta Meco WT, which would have allowed the Shuttle to use excess margin to decrease dynamic pressure and loads on the Day of Launch. Trading excess performance for decreased loads in first stage. So in the case of the next flight, on the Day of Launch, -1900 lbs delta Meco WT could have been entered and vehicle would fly a much lower Q. But, you say, all the ISS mission have zero margin. Well, that's not quite true. To be able to launch on any given day, in the flight performance reserve, some amount of performance must be included to cover the worst performance case. In this case, a large head wind. But on the actual day of launch, a large head wind is rarely the case. It could be a large tail wind and we really wouldn't know it until the day of launch. So, on the day of launch, we have additional information about the winds and in almost every cases some amount of excess performance. This excess performance improves abort boundaries a little, but is essentially thrown away with the tank at MECO. If you look at performance vs loads tradeoff dWT/dQ becomes smaller and smaller as dynamic pressure in increased from "Nominal" Q to High-Q to Optimal-Q. Essentially zero at Optimal-Q. The inverse of this derivative, dQ/dWT, is what would have been important on the day of launch. At Optimal-Q, dQ/dWT is infinity, at High-Q it's less but still large and at "Nominal"-Q even less... At Optimal-Q a little tiny decrease in performance is a hugh decrease in Q/loads and it's still somewhat true for High-Q. It doesn't cost much performance to get large reductions in Q and loads. Flying High-Q is a very poor way to gain a little bit of performance. -- Craig Fink Courtesy E-Mail Welcome @ |
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