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#2340
by
alk3997
on 01 Oct, 2011 01:12
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Hi all.
a question about re-entry. I was wondering if for re-entry there was something similar to DOLILU. I mean, before giving the go no go for deorbit burn, is there anybody designing (or optimizing) the re-entry trajectory based on the wind profile at the landing location? Something similar to what the DOLILU group did but done for re-entry rather then for the ascent.
Thanks
Davide
All computed onboard. The deorbit burn was the only thing uplinked. Winds were radioed to the CDR and PLT on the way down, but if autoland had been used, the autoland system would sense what the winds were doing to the vehicle and correct the winds out. I phrased that the way I did so as to not give the impression that there was a "look ahead" capability. Guidance that was displayed to the crew used the same algorithms.
The PGSC had a deorbit burn target program included so that *if* no communications were available with the ground, the crew could compute their own burn targets. That was never used to compute the real targets.
From a terminology standpoint, we would in general break-up entry into deorbit (up to entry interface), entry, TAEM, HAC and then autoland guidance and then touchdown and rollout.
Now, to give the ground credit, the guidance algorithms were also simulated on the ground, so only a runway that had acceptable guidance solutions would be chosen. So while very little was uplinked, the ground always made sure we would reach the runway with the actual conditions.
Andy
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#2341
by
alk3997
on 01 Oct, 2011 01:18
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Anyone have any information on the velocities when the plasma begins to show and fade during entry?
Depened upon the entry, but somewhere around the first roll reversal.
Andy
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#2342
by
DaveS
on 02 Oct, 2011 23:38
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How is the maneuver to entry attitude accomplished? Through ITEM 27 on MM303?
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#2343
by
Jorge
on 03 Oct, 2011 02:57
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How is the maneuver to entry attitude accomplished? Through ITEM 27 on MM303?
Yes.
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#2344
by
NavySpaceFan
on 03 Oct, 2011 19:27
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Quick question re: orbiter attitude, was the gravity gradient attitude SOP for all Spacelab/Spacehab research flights?
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#2345
by
alk3997
on 03 Oct, 2011 21:56
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Quick question re: orbiter attitude, was the gravity gradient attitude SOP for all Spacelab/Spacehab research flights?
No, Spacelabs like Spacelab 2 were astronomy releated and had strict pointing requirements. Usually microgravity experiments were gravity gradient. Thermal requirements could have also been a reason for not using gravity gradient.
Andy
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#2346
by
DaveS
on 04 Oct, 2011 01:53
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On page 3-14 of the Entry FDF it mentions the De-orbit burn cue card. Where can one find this cue card?
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#2347
by
Jorge
on 04 Oct, 2011 02:35
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On page 3-14 of the Entry FDF it mentions the De-orbit burn cue card. Where can one find this cue card?
Page CC 8-8.
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#2348
by
DaveS
on 04 Oct, 2011 03:31
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On page 3-14 of the Entry FDF it mentions the De-orbit burn cue card. Where can one find this cue card?
Page CC 8-8.
Thanks. Another that has had me looking for ages now: The FDF/page that lists the camera pan/tilt angles used for elevon viewing during FCS C/O.
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#2349
by
NavySpaceFan
on 04 Oct, 2011 10:37
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Quick question re: orbiter attitude, was the gravity gradient attitude SOP for all Spacelab/Spacehab research flights?
No, Spacelabs like Spacelab 2 were astronomy releated and had strict pointing requirements. Usually microgravity experiments were gravity gradient. Thermal requirements could have also been a reason for not using gravity gradient.
Andy
Rgr, thanks Andy!!!
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#2350
by
Malderi
on 05 Oct, 2011 01:17
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Quick question re: orbiter attitude, was the gravity gradient attitude SOP for all Spacelab/Spacehab research flights?
No, Spacelabs like Spacelab 2 were astronomy releated and had strict pointing requirements. Usually microgravity experiments were gravity gradient. Thermal requirements could have also been a reason for not using gravity gradient.
Andy
How accurate was the pointing capability of the Shuttle, and how frequent were the thruster firings to accomplish it?
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#2351
by
Jorge
on 05 Oct, 2011 01:44
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Quick question re: orbiter attitude, was the gravity gradient attitude SOP for all Spacelab/Spacehab research flights?
No, Spacelabs like Spacelab 2 were astronomy releated and had strict pointing requirements. Usually microgravity experiments were gravity gradient. Thermal requirements could have also been a reason for not using gravity gradient.
Andy
How accurate was the pointing capability of the Shuttle, and how frequent were the thruster firings to accomplish it?
There's really multiple parts to the first question. First, how accurate was the shuttle's attitude determination? The shuttle used IMUs to maintain its attitude reference, and the IMU platforms slowly drifted over time. Flight Rules required the IMU misalignment be maintained <0.5 deg for safe entry, so to protect for extended loss of comm, an IMU alignment would be performed if the misalignment exceeded 0.25 deg. This was done using the star trackers. The star trackers were accurate within 1-2 hundredths of a degree. The original KT-70 IMUs required alignment about every 12 hours. The HAINS IMUs used at the end of the program could go 48 hours between alignments, and sometimes as much as 96.
Second, how precisely could the shuttle hold attitude? This was a function of the attitude deadband setting in the digital autopilot (DAP). Minimum attitude deadband was 0.033 deg using the vernier RCS thrusters. 0.5 deg for primary RCS, I think.
Obviously there is no simple answer to your second question; thruster firing frequency depended on the deadband width, which thrusters were used, and the environmental torques acting on the vehicle (which in turn were a function of attitude, mass properties, and altitude).
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#2352
by
alk3997
on 05 Oct, 2011 13:29
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Quick question re: orbiter attitude, was the gravity gradient attitude SOP for all Spacelab/Spacehab research flights?
No, Spacelabs like Spacelab 2 were astronomy releated and had strict pointing requirements. Usually microgravity experiments were gravity gradient. Thermal requirements could have also been a reason for not using gravity gradient.
Andy
How accurate was the pointing capability of the Shuttle, and how frequent were the thruster firings to accomplish it?
There's really multiple parts to the first question. First, how accurate was the shuttle's attitude determination? The shuttle used IMUs to maintain its attitude reference, and the IMU platforms slowly drifted over time. Flight Rules required the IMU misalignment be maintained <0.5 deg for safe entry, so to protect for extended loss of comm, an IMU alignment would be performed if the misalignment exceeded 0.25 deg. This was done using the star trackers. The star trackers were accurate within 1-2 hundredths of a degree. The original KT-70 IMUs required alignment about every 12 hours. The HAINS IMUs used at the end of the program could go 48 hours between alignments, and sometimes as much as 96.
Second, how precisely could the shuttle hold attitude? This was a function of the attitude deadband setting in the digital autopilot (DAP). Minimum attitude deadband was 0.033 deg using the vernier RCS thrusters. 0.5 deg for primary RCS, I think.
Obviously there is no simple answer to your second question; thruster firing frequency depended on the deadband width, which thrusters were used, and the environmental torques acting on the vehicle (which in turn were a function of attitude, mass properties, and altitude).
Excellent answer - the only thing I'd add is that if you made the deadband tighter, you would use more propellant. So, there was a tradeoff for keeping the deadband too tight. Also if you were running microgravity experiments, you might want a wider deadband to minimize the microgravity-disturbing jet firings.
Andy
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#2353
by
Malderi
on 05 Oct, 2011 15:07
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Quick question re: orbiter attitude, was the gravity gradient attitude SOP for all Spacelab/Spacehab research flights?
No, Spacelabs like Spacelab 2 were astronomy releated and had strict pointing requirements. Usually microgravity experiments were gravity gradient. Thermal requirements could have also been a reason for not using gravity gradient.
Andy
How accurate was the pointing capability of the Shuttle, and how frequent were the thruster firings to accomplish it?
There's really multiple parts to the first question. First, how accurate was the shuttle's attitude determination? The shuttle used IMUs to maintain its attitude reference, and the IMU platforms slowly drifted over time. Flight Rules required the IMU misalignment be maintained <0.5 deg for safe entry, so to protect for extended loss of comm, an IMU alignment would be performed if the misalignment exceeded 0.25 deg. This was done using the star trackers. The star trackers were accurate within 1-2 hundredths of a degree. The original KT-70 IMUs required alignment about every 12 hours. The HAINS IMUs used at the end of the program could go 48 hours between alignments, and sometimes as much as 96.
Second, how precisely could the shuttle hold attitude? This was a function of the attitude deadband setting in the digital autopilot (DAP). Minimum attitude deadband was 0.033 deg using the vernier RCS thrusters. 0.5 deg for primary RCS, I think.
Obviously there is no simple answer to your second question; thruster firing frequency depended on the deadband width, which thrusters were used, and the environmental torques acting on the vehicle (which in turn were a function of attitude, mass properties, and altitude).
Excellent answer - the only thing I'd add is that if you made the deadband tighter, you would use more propellant. So, there was a tradeoff for keeping the deadband too tight. Also if you were running microgravity experiments, you might want a wider deadband to minimize the microgravity-disturbing jet firings.
Andy
I guess that's one of the things I was getting at - Station uses CMGs to both keep precise pointing as well as microgravity. Shuttle doesn't have those, so could you do both astronomy-related experiments and microgravity work at the same time? Or would all the microgravity stuff have to wait until periods of free drift?
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#2354
by
Jim
on 05 Oct, 2011 16:17
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I guess that's one of the things I was getting at - Station uses CMGs to both keep precise pointing as well as microgravity. Shuttle doesn't have those, so could you do both astronomy-related experiments and microgravity work at the same time? Or would all the microgravity stuff have to wait until periods of free drift?
It depends, but astronomy-related experiments and microgravity work were usually not manifested on the same mission, however, there were exceptions like STS-9/Spacelab-1. The shuttle used gravity gradient for microgravity missions. Astronomy payloads had their pointing systems so the orbiter didn't require to have tight deadbands.
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#2355
by
TJL
on 18 Oct, 2011 02:27
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Does anyone notice a difference in the appearance of the plume of STS 129's launch.
In this view from the VAB roof, it seems that the shuttles exhaust sort of curves to the north before straightening out (26 to 30 seconds into the video).
Anyone know if the wind was blowing from the south?
See clip:
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#2356
by
DDG40
on 18 Oct, 2011 02:44
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Does anyone notice a difference in the appearance of the plume of STS 129's launch.
In this view from the VAB roof, it seems that the shuttles exhaust sort of curves to the north before straightening out (26 to 30 seconds into the video).
Anyone know if the wind was blowing from the south?
See clip:
Per weather undergrund winds were 12 mph NNW at launch time. I remember there was a low cloud ceiling the morning of the launch, But it cleared up around noon.
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#2357
by
alk3997
on 18 Oct, 2011 23:13
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Let me see if I can understand your question a bit better. First, the tail of the orbiter faced south. At the roll manuever, the orbiter turned at least 90 degrees (to the east in other words) and for ISS continued another approximately 21 degrees (total roll of 111 degrees apprx). In other words the roll maneuver put the vehicle on a ENE direction.
Now given that, which direction and which plume did you mean (SSME or SRB)? The SSME plume went south (mostly) and SRB plume went north (mostly). If the ground wind was from the east, then the SSME plume would head south out of the flame duct and then the east wind would blow it towards the west.
The photographers who setup remote cameras would try to take into account which way the wind was predicted to blow when setting up remote cameras. The cameras would have to be setup about a day before launch, so figuring out which way the wind *would* blow was important.
Now if you are talking higher up during ascent, then that would be upper level winds (or winds aloft) and that would be a completely different subject.
Andy
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#2358
by
TJL
on 19 Oct, 2011 01:52
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Andy, I was referring to the plume created by the SRB's.
If you look at the video between 25 and 30 seconds in, you will see that the plume is not vertical as it appears in all othe shuttle launches...it actually curves to the north (left) and then straightens out.
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#2359
by
Jorge
on 19 Oct, 2011 02:09
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Andy, I was referring to the plume created by the SRB's.
If you look at the video between 25 and 30 seconds in, you will see that the plume is not vertical as it appears in all othe shuttle launches...it actually curves to the north (left) and then straightens out.
That's the roll program. You're wrong, it happens every launch. The camera angle is not always optimal for seeing the effect of the roll on the plume.