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#640
by
northanger
on 26 Dec, 2006 04:16
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Cape51.
What is disengaging earlier? The shuttle? (I'm wondering if I misread your question, hopefully you've figured I'm no expert here. Just curious).
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#641
by
fdasun
on 26 Dec, 2006 05:21
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landofgrey - 26/12/2006 12:42 PM
... Sadly funny, Graham PERSONALLY SCRUBBED the STS-51L launch attempt on Jan. 27, 1986 because the weather forecast predicted rain. Instead the weather was perfect and warm and had Challenger not been scrubbed on that day, the accident wouldn't have happened on the 28th...
It might not be his fault. Challenger disaster was doomed to happen, when there were so many mistakes existing in NASA and contractor partners, both technical and management.
By the way, is there any abort operation mode between deorbit burn and landing ? ... ... For many years, we have assumed that re-entry and landing is safe. Nevertheless, after STS-107, TPS safety becomes the most important issue for each flight. Can the orbiter abort its landing process during or after the deorbit burn ? Thanks .
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#642
by
shuttlefan
on 26 Dec, 2006 13:14
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fdasun - 26/12/2006 12:04 AM
landofgrey - 26/12/2006 12:42 PM
... Sadly funny, Graham PERSONALLY SCRUBBED the STS-51L launch attempt on Jan. 27, 1986 because the weather forecast predicted rain. Instead the weather was perfect and warm and had Challenger not been scrubbed on that day, the accident wouldn't have happened on the 28th...
It might not be his fault. Challenger disaster was doomed to happen, when there were so many mistakes existing in NASA and contractor partners, both technical and management.
By the way, is there any abort operation mode between deorbit burn and landing ? ... ... For many years, we have assumed that re-entry and landing is safe. Nevertheless, after STS-107, TPS safety becomes the most important issue for each flight. Can the orbiter abort its landing process during or after the deorbit burn ? Thanks .
No, it cannot abort the landing once the deorbit burn gets underway. Once the Orbital Manuevering System engines begin firing, the orbiter starts slowing down right away, just enough that its orbit will decay in order for it to return to Earth. Once they fire the OMS engines, they are committed to land at a precise time and location. That's why, before the go-for-deorbit-burn is given, the weather at KSC, Edwards, or Northrup must be forecast GO.
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#643
by
Jim
on 26 Dec, 2006 13:35
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Some corrections
As mkirk has stated in previous posts, "landing" can be aborted during deorbit burn (and maybe a little after). Another burn is required to put the shuttle back in a stable orbit. Fuel state of the shuttle determines if this is possible.
Also there is a "fast sep" scenario where the orbiter disengages from the ET while the SRB's are still burning. The ability for the orbiter to do this is marginal and some say the orbiter aft attachments (ball joints) would hang up and flip the orbit into the airstream, which would break it up
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#644
by
elmarko
on 26 Dec, 2006 15:05
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Speaking of SRBs, I was wondering today, you know how some SRBs burn "hot" and some burn "cold"
What happens if one side SRB was burning a little more than the other side, resulting in unequal thrust. You'd get a yawing motion to one side, right? Is there any way to compensate for this?
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#645
by
Jim
on 26 Dec, 2006 15:23
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The SRB TVC compensates for unequal thrust. As part of burn out, there is some imbalance.
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#646
by
mkirk
on 26 Dec, 2006 16:06
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Jim - 25/12/2006 4:30 PM
elmarko - 25/12/2006 3:55 PM
And also, can someone tell me the plus x stuff in more detail please, because I can never remember which direction X actually is 
http://spaceflight.nasa.gov/shuttle/reference/index.html
Plus X is towards the cabin roof or up in the payload bay
Let me try and clarify some of the answers and recent questions.
I know Jim actually knows this so I guess he just got the two translation maneuvers confused.
At ET SEP there are normally two translation maneuvers performed a –Z and a +X.
ET SEP occurs at 20 seconds after MECO (main engine cutoff); at structural separation the orbiter’s down firing jets will ignite briefly to initiate a separation from the tank at a rate of 4 feet per second.
The –Z direction is up thru the roof of the cabin or payload bay.
Once the onboard GPCs (general purpose computers) transition the software to Major Mode 104 (the orbital maneuver display) from Major Mode 103 (2nd stage ascent trajectory display) - this transition occurs when the IMUs(inertial measurement units) sense the 4 feet per second acceleration – the Commander will push in on the Translation Controller for 11 seconds to initiate the +X maneuver.
The translation controller (THC) is located on the left side of the cockpit and is used to move the orbiter forward (push in), back (pull out), up/dn (push up/dn), and left/right (push to left or right side). See the attached photo, the THC is the black handle located to the left of the control stick (under the red cover) and above the speed brake handle.
The +X direction is Nose Forward.
The plus X burn allows the cameras in the ET umbilical wells to photograph the length of the fuel tank from bottom to top. It also aids in vehicle separation from the tank and helps set the orbiter up for the ET PHOTO maneuver (which wasn’t done on this last flight since they were in darkness). The ET PHOTO maneuver is a pitch around of the orbiter that allows the crew to take pictures of the tank out of the overhead windows.
Part of the confusion on this subject stems from the fact that the shuttle fly’s in numerous reference frames (or coordinate systems). At MECO the shuttle is in the LVLH (local vertical local horizontal) reference frame which is the most “airplane like” and therefore the most intuitive for the pilots.
Mark Kirkman
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#647
by
shuttlefan
on 26 Dec, 2006 16:25
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elmarko - 26/12/2006 9:48 AM
Speaking of SRBs, I was wondering today, you know how some SRBs burn "hot" and some burn "cold"
What happens if one side SRB was burning a little more than the other side, resulting in unequal thrust. You'd get a yawing motion to one side, right? Is there any way to compensate for this?
Was there not some issue in 1993 that arose with the SRBs, involving some sort of a pressure spike in one SRB , which ocurred on STS-54 in Jan.'93? If so, can someone provide more details on that and how it was resolved. I seem to recall a news report about it, calling it the " 1 minute, 7 second mystery ", because it ocurred 1 minute and 7 seconds into launch.
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#648
by
mkirk
on 26 Dec, 2006 16:27
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fdasun - 26/12/2006 12:04 AM
By the way, is there any abort operation mode between deorbit burn and landing ? ... ... For many years, we have assumed that re-entry and landing is safe. Nevertheless, after STS-107, TPS safety becomes the most important issue for each flight. Can the orbiter abort its landing process during or after the deorbit burn ? Thanks .
Aborting the Deorbit Burn:
The Deorbit Burn can be stopped if the orbiter altitude is above “Safe HP”. HP is the perigee altitude of a given orbit. Safe HP is the altitude that will allow the shuttle to remain in orbit for at least 24 hours before aerodynamic drag effects begin to cause the orbit to decay. For the shuttle this altitude is usually set at 85 nautical miles. This critical altitude is called out in the flight control room on the flight loop and usually PAO will announce it as well.
When the Deorbit OMS burn is underway the crew will watch the HP begin to count down on the Deorbit Maneuver CRT display, if a systems problem occurs prior to going below 85 nm (safe HP) then the burn can be stopped and the problem evaluated. If the orbiter is below Safe HP then the orbiter is committed to Entry.
Mark Kirkman
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#649
by
elmarko
on 26 Dec, 2006 16:43
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Thanks for the answers, I was confused about the directions. I mean, you see X, you think upwards on a graph, right?
I have a few other questions whizzing about in my head, but to give someone else a chance, and also so as not to abuse the priviledge, I'll hold off for a few days. Maybe even word them correctly before committing to the submit button
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#650
by
ichilton
on 26 Dec, 2006 17:35
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That's why, before the go-for-deorbit-burn is given, the weather at KSC, Edwards, or Northrup must be forecast GO.
But what happens if the weather changes between the GO/de-orbit burn and landing, which is about an hour isn't it? - would they just have to land anyway but it would be difficult if the weather turned bad?
Also, at what point does it enter the earths atmosphere (and can burn up like Columbia)? - is that between deorbit burn and landing?
Is there still a radio blackout like the Apollo 13 film?
Thanks
Ian
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#651
by
Chris Bergin
on 26 Dec, 2006 17:44
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ichilton - 26/12/2006 6:18 PM
Is there still a radio blackout like the Apollo 13 film?
Thanks
Ian
Yes, although they pretty much have it all scheduled out now. On the STS-115 full re-entry video you hear "We'll be hearing from Houston very soon" and they then hear a call about status pretty much soon after and its a regular call (in the style they know they can communicate).
Don't know if the Apollo 13 film grandstanded the "we should have heard from them by now" on the re-entry, or if it happened like that for real.
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#652
by
elmarko
on 26 Dec, 2006 17:57
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And don't forget, thanks to TDRS, the comm dropouts aren't anywhere near as long (I guess, anyway...)
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#653
by
bernse
on 26 Dec, 2006 18:26
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Chris Bergin - 25/12/2006 11:27 PM
Don't know if the Apollo 13 film grandstanded the "we should have heard from them by now" on the re-entry, or if it happened like that for real.
According to an interview I saw with Jim Lovell, the blackout lasted longer than normal due to them being quite a bit shallower on reentry than planned (quite a bit being relative, I suspect!). So, from this comment he gave I'd say the blackout did last longer than expected.
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#654
by
Jim
on 26 Dec, 2006 18:39
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Thanks, Mark. I looked at the figure too quickly. I don't quote from my memory anymore since I have deal with other LV's and spacecraft. FYI most spacecraft and LV do not use the same axis.
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#655
by
Jim
on 26 Dec, 2006 18:43
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Actually, depending on the orbit and the orbiter attitude, there isn't a blackout. The plasma sheath envelops the bottom of the orbiter prevent comm. But TDRS can "see" thru the hole in the top
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#656
by
bernse
on 26 Dec, 2006 18:50
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Question about Orbiter retirement. I believe it has been mentioned that Atlantis only has 4 flights left in it before its due for refurbishment, but because of the STS program retirement date, they aren't going to do it.
Why only "4" flights left? I understand that there are finite lifespans for some of the equipment, but surely they would not simply "fail" if they are flown again, would they? Or, could just the "questionable" equipment get replaced, or even inspected or recertified again as opposed to a full-blown Orbiter overhaul?
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#657
by
Jim
on 26 Dec, 2006 18:57
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bernse - 26/12/2006 2:33 PM
Question about Orbiter retirement. I believe it has been mentioned that Atlantis only has 4 flights left in it before its due for refurbishment, but because of the STS program retirement date, they aren't going to do it.
Why only "4" flights left? I understand that there are finite lifespans for some of the equipment, but surely they would not simply "fail" if they are flown again, would they? Or, could just the "questionable" equipment get replaced, or even inspected or recertified again as opposed to a full-blown Orbiter overhaul?
there is a thread called "4 more flights" that goes into this issue
It isn't just refurbishment, but also detailed structural inspections
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#658
by
bernse
on 26 Dec, 2006 19:04
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Thanks for the quick reply! I'll look for that thread. Appreciate it.
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#659
by
DaveS
on 26 Dec, 2006 19:29
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elmarko - 26/12/2006 7:40 PM
And don't forget, thanks to TDRS, the comm dropouts aren't anywhere near as long (I guess, anyway...)
Nope. Comm and telemetry is pretty solid throughout entry, except for some minor drops when the tail blocks the view of TDRS-W until MILA can take over.
