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#2280
by
Jim
on 07 Sep, 2011 13:15
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but exactly how are the elevons moved? My guess is that they are moved in order to reduce the lift created on the wings but I'm not sure.
The angle of attack vs altitude is known, so the elevons are moved to reduce the loads. The AOA is negative so it is actually a down force on the wings that they are trying to reduce.
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#2281
by
Specifically-Impulsive
on 07 Sep, 2011 13:18
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Pre-loaded and purely for load relief (no steering) and prior to max-q.
Andy
It's closed loop at least in the sense that it only happens if needed. I'm looking at an MMT pitch from STS-130 (the ascent performance quick-look) and it states "no elevon load relief". From what I remember the 2 big things that could change in real time were presence/absence of load relief and the throttle bucket settings. I remember the throttle bucket changing a few times but I never remember load relief happening.
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#2282
by
Specifically-Impulsive
on 07 Sep, 2011 13:26
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but exactly how are the elevons moved? My guess is that they are moved in order to reduce the lift created on the wings but I'm not sure.
The angle of attack vs altitude is known, so the elevons are moved to reduce the loads. The AOA is negative so it is actually a down force on the wings that they are trying to reduce.
If I recall correctly, the wing zero lift angle of attack for the Orbiter is about -7, and during high q the alpha target is -4, transitioning to +2 after Mach 2 ish.
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#2283
by
sivodave
on 07 Sep, 2011 13:37
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It's closed loop at least in the sense that it only happens if needed. I'm looking at an MMT pitch from STS-130 (the ascent performance quick-look) and it states "no elevon load relief". From what I remember the 2 big things that could change in real time were presence/absence of load relief and the throttle bucket settings. I remember the throttle bucket changing a few times but I never remember load relief happening.
very interesting...what do you mean for throttle buckt changing? The throttling was always done isn't?
where can I find these performance quick-looks?
Davide
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#2284
by
Specifically-Impulsive
on 07 Sep, 2011 13:41
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It's closed loop at least in the sense that it only happens if needed. I'm looking at an MMT pitch from STS-130 (the ascent performance quick-look) and it states "no elevon load relief". From what I remember the 2 big things that could change in real time were presence/absence of load relief and the throttle bucket settings. I remember the throttle bucket changing a few times but I never remember load relief happening.
very interesting...what do you mean for throttle buckt changing? The throttling was always done isn't?
where can I find these performance quick-looks?
Davide
The throttling was always done and the min throttle and duration of the bucket was planned out preflight. But, if the SRBs were more powerful than planned, the SSMEs would throttle down more, or vice versa if the SRBs were less powerful than planned.
I don't know where the MMT pitches are publicly available. Maybe on L2? Chris seems to have a pipeline to the MMT.
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#2285
by
alk3997
on 07 Sep, 2011 14:23
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Remember so-called adaptive guidance was purely an attempt to match the vehicles actual velocity at a given time versus what it was expected to be. The engines (SSMEs) could then be throttled an additional amount if the vehicle was going faster than expected (hotter SRBs). It was not closed-loop guidance in a 2nd stage sort of way by any means. First stage remained opened loop - it has to given our present abilities to measure winds in real-time.
For accuracy, the Adaptive Guidance and Throttling (AGT) test was at a pre-loaded velocity and then time was computed and compared. A very simple method. You can see a short discussion of this in one paragraph of the following article from this actual website,
http://www.nasaspaceflight.com/2011/07/sts-135-ascent-reviews-point-superb-launch-performance-atlantis/Andy
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#2286
by
sivodave
on 08 Sep, 2011 00:20
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Hi all.
Again another question about the ascent. Before STA-87, the orbiter didn't perform the roll head up towards the end of the ascent. So I was the maneuver for ET sep? being in an head-down attitude, how could the orbiter avoid colliding with the ET that was just "over" it?
thanks
Davide
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#2287
by
Jorge
on 08 Sep, 2011 00:31
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Hi all.
Again another question about the ascent. Before STA-87, the orbiter didn't perform the roll head up towards the end of the ascent. So I was the maneuver for ET sep?
Same maneuver, 4 fps -Z RCS with an optional +X RCS for ET photography.
being in an head-down attitude, how could the orbiter avoid colliding with the ET that was just "over" it?
The orbiter is no more likely to collide with the ET in a heads-down vs a heads-up orientation.
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#2288
by
sdsds
on 08 Sep, 2011 01:46
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Ah, so that was "Go for the plus x" -- positioning for ET photos. And "Go for the pitch?"
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#2289
by
Jorge
on 08 Sep, 2011 02:10
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Ah, so that was "Go for the plus x" -- positioning for ET photos.
Right, from the ET umbilical well cameras. Doing a +X allows more of the tank to pass below the cameras while they're still close enough to get good resolution.
And "Go for the pitch?"
That's for ET photography from the overhead windows.
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#2290
by
DaveS
on 08 Sep, 2011 03:36
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Including the ribs and radiator panels, how thick are the PLBDs(average thickness if the thickness is not uniform)?
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#2291
by
wolfpack
on 08 Sep, 2011 13:26
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Hi all.
Again another question about the ascent. Before STA-87, the orbiter didn't perform the roll head up towards the end of the ascent. So I was the maneuver for ET sep?
Same maneuver, 4 fps -Z RCS with an optional +X RCS for ET photography.
being in an head-down attitude, how could the orbiter avoid colliding with the ET that was just "over" it?
The orbiter is no more likely to collide with the ET in a heads-down vs a heads-up orientation.
Is there any impulse provided for ET sep, or is the RCS required to perform the separation? In other words, does residual tank pressure or something similar serve to "pop" it loose once the disconnect is made?
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#2292
by
Specifically-Impulsive
on 08 Sep, 2011 13:40
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Is there any impulse provided for ET sep, or is the RCS required to perform the separation? In other words, does residual tank pressure or something similar serve to "pop" it loose once the disconnect is made?
The jets were used. Residual pressure in the feedlines would have been bad, leading to a pitching moment on the tank while it was in close proximity to the orbiter. In fact, if the valves isolating the orbiter from the tank did not all indicate closed, the separation was inhibited until enough time had passed for the tank to vent down.
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#2293
by
Jim
on 08 Sep, 2011 14:04
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Is there any impulse provided for ET sep, or is the RCS required to perform the separation? In other words, does residual tank pressure or something similar serve to "pop" it loose once the disconnect is made?
The tension in the bolts also provides a small impulse
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#2294
by
alk3997
on 08 Sep, 2011 17:13
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Is there any impulse provided for ET sep, or is the RCS required to perform the separation? In other words, does residual tank pressure or something similar serve to "pop" it loose once the disconnect is made?
The jets were used. Residual pressure in the feedlines would have been bad, leading to a pitching moment on the tank while it was in close proximity to the orbiter. In fact, if the valves isolating the orbiter from the tank did not all indicate closed, the separation was inhibited until enough time had passed for the tank to vent down.
The jets would have been even more critical during ET Sep in an RTLS scenario. Luckily we never got to try one of those out...
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#2295
by
Fequalsma
on 09 Sep, 2011 11:23
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The PLBD skins are 4-ply graphite/epoxy face sheets over a honeycomb core. I'll have to look for my Rockwell/Tulsa PLBD briefing to find the thicknesses, and the rib dimensions. Can't remember if it talked about the radiators too.
F=ma
Including the ribs and radiator panels, how thick are the PLBDs(average thickness if the thickness is not uniform)?
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#2296
by
Fequalsma
on 11 Sep, 2011 04:41
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Interesting paper on the ascent loads relief discussed earlier...
http://www.aiaa.org/pdf/industry/Why_the_Wings_Stay_On.pdfSo here's what I found on the PLBD structures:
Each PLBD has 4@~15ft,1@~2ft sections connected at expansion joints by shear pins.
Skins - Al wire mesh screen on OML for lightning protection. Mostly 3 ply, tape/fabric/tape gr-ep FS (16-22 mil thick) over 0.6 in.-thick Nomex HC cores.
Hingelines has [90/0/±45/0/90]t laminate w/ 0.3-in core.
Frames – 4.41 in. deep x 1.125 in. wide, spaced at 22.5 inches. 0/±45 tape/fabric caps and flats, ±45 fabric webs.
Radiator panels - 11-mil Al FS over 0.5-0.9 in. thk Al HC cores.
Refs: NASA TM 107793 (avail NTRS); Rockwell/Tulsa govt/industry briefing on PLBDs
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#2297
by
sivodave
on 14 Sep, 2011 11:46
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Interesting paper on the ascent loads relief discussed earlier...
http://www.aiaa.org/pdf/industry/Why_the_Wings_Stay_On.pdf
very interesting paper indeed...thanks very much...but just out of curiosity: how did you find it? if I just use the following addresss
www.aiaa.org/pdf I can't get any access. Are there papers from AIAA freely available?
now the question of the day: for the ascent the pilots can see the information regarding the progress of the ascent on three different displays, which are ASCENT TRJ 1 (used up to SRB sep), ASCENT TRJ 2 (used up to ET sep) and ASCENT TRJ (it displays the whole ascent). This is at least what I've understood from what I've been reading lately. My question is: when the ASCENT TRJ is used? Also are the ASCENT TRJ 1 and 2 generated by the PASS or by the BFS?
thanks
Davide
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#2298
by
AnalogMan
on 14 Sep, 2011 13:14
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very interesting paper indeed...thanks very much...but just out of curiosity: how did you find it? if I just use the following addresss www.aiaa.org/pdf I can't get any access. Are there papers from AIAA freely available?
A bit off-topic, but try pasting the following into google:
site:aiaa.org/pdf filetype:pdf
You should get a list of ~1200 pdf files, some of which are academic papers and briefings. Bit of a blunderbuss method though!
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#2299
by
sivodave
on 15 Sep, 2011 10:19
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During the roll for placing the orbiter in the head up attitute halfway the ascent, is there any kind of sideslip deviation from the nominal trajectory path? I mean, does the orbiter stay centered on the nominal trajectory or it jsut goes a bit sideaways for then recenter itself on the ascen path?
I hope the question is clear enough.
Best regards
Davide