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#3100
by
alk3997
on 20 May, 2014 12:37
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How was SRB ignition synchronized? I'm interested in the design of the control system that guaranteed the ignition signals would arrive simultaneously to each SRB. Did it require that the communication wiring from the orbiter to the SRBs be exactly the same length to each one?
What was the maximum acceptable difference in ignition time between the two SRBs?
You want to look up a "Master Events Controller" (MEC), not to be confused with a Main Engine Controller (MEC). The Master Events Controller was the interface between the flight computers and the pyrotechnics on the vehicle. The General Purpose Computers (GPCs) would send an arm / fire sequence to the MEC for the particular pyrotechnic that was the blow. There were redundant channels to each pyro and, yes, the wiring was the same length.
I don't remember the specs for the differences in ignition times but it was small. A bigger key was that the thrust had to build-up at the same rate. But, that's outside of your question.
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-av.html#sts-dps-mec
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#3101
by
wolfpack
on 20 May, 2014 14:42
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How was SRB ignition synchronized? I'm interested in the design of the control system that guaranteed the ignition signals would arrive simultaneously to each SRB. Did it require that the communication wiring from the orbiter to the SRBs be exactly the same length to each one?
What was the maximum acceptable difference in ignition time between the two SRBs?
The only electrical connection between the Orbiter and the rest of the stack is through the ET umbilicals. The SRBs had cables to the ET. Tom Jones recalls in his book STS-98 being rolled back to inspect/replace those cables because there had been a failure on a previous mission (STS-97?) where the primary pyrotechnics on the hold-down nuts did not fire, but the redundant set did.
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#3102
by
DaveS
on 20 May, 2014 15:28
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How was SRB ignition synchronized? I'm interested in the design of the control system that guaranteed the ignition signals would arrive simultaneously to each SRB. Did it require that the communication wiring from the orbiter to the SRBs be exactly the same length to each one?
What was the maximum acceptable difference in ignition time between the two SRBs?
The only electrical connection between the Orbiter and the rest of the stack is through the ET umbilicals. The SRBs had cables to the ET. Tom Jones recalls in his book STS-98 being rolled back to inspect/replace those cables because there had been a failure on a previous mission (STS-97?) where the primary pyrotechnics on the hold-down nuts did not fire, but the redundant set did.
The problem that caused the STS-98 rollback was that on STS-97/4A one of two explosive cartridges called NASA Standard Initiators (NSIs) on the left SRB ETAR that connects the SRB with the ET failed to fire. The second one did fire and SRB sep was successful. The problem was traced to a wiring fault that prevented the separation signal from reaching the NSI.
They did check the wiring on each SRB prior to rollout of STS-98/5A but later while in the VAB following a successful Orbiter/ET Mate, the NSI wiring on the left SRB failed a electrical resistance test, it was traced to a bad connector.
Later on the eve prior to the start of the launch countdown (January 15 2001), when four other SRB cables in inventory were discovered to be defective, SSP managers decided to rollback the STS-98/5A stack to the VAB and X-ray and test the SRB wiring. Due to the fact that the wiring runs along the length of the boosters in so called "systems tunnels" the wiring could only be inspected and tested in the VAB.
The problem with the holddown post bolts occurred on a later Atlantis flight, STS-112/9A in October 2002.
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#3103
by
sivodave
on 20 May, 2014 22:02
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The previous posts about CSS during ascent made thing if instead performing CSS during entry and TAEM would have been more realistic and survivable?
Davide
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#3104
by
wolfpack
on 21 May, 2014 00:46
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The previous posts about CSS during ascent made thing if instead performing CSS during entry and TAEM would have been more realistic and survivable?
Davide
You could certainly fly reentry by hand, from deorbit burn to landing. Crews routinely trained for it.
Engle did most if not all of it on STS-2.
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#3105
by
JAFO
on 21 May, 2014 02:58
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You could certainly fly reentry by hand, from deorbit burn to landing. Crews routinely trained for it.
Engle did most if not all of it on STS-2.
Another reason I'd love to hear General Engle do a talk, or write a book about his career.
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#3106
by
alk3997
on 22 May, 2014 02:21
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The previous posts about CSS during ascent made thing if instead performing CSS during entry and TAEM would have been more realistic and survivable?
Davide
Davide, sure - entry CSS from EI to landing was an available mode and, as pointed out, was used on STS-2. However, except for some intermediate OFT test objectives, the guidance needles were followed. So, it was the crew following what the GPCs indicated but it showed that CSS would work.
The way the vehicle was flown meant that auto was followed to just under Mach 1 (usually Mach 0.95) and before the HAC was entered. This was to allow the GPCs to fly the higher speed parts of entry and then let the crew "get the feel" of the vehicle after going subsonic. A lot of that was the result of the STS-3 landing where the crew took back over at 300 feet altitude. Post landing the crew said that they didn't have a good feel for how the vehicle behaved subsonic, so they didn't think 300 feet was an appropriate time to take over.
So, no real good reason to do CSS from EI to HAC, but it was available. Autoland was tried to 300 feet during the early flights. It wasn't used further, well, because the crew liked to land the vehicle. The official reason was that the MLS signal could disappear just over the runway threshold. STS-53 was scheduled for an autoland DTO but that was cancelled 1-2 months before the flight.
So, CSS entry would have been fine. Ascent CSS - probably a really bad day if you needed that. Also remember that if BFS had been engaged during entry, BFS had no auto mode. You were CSS all the way in.
Andy
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#3107
by
iskyfly
on 22 May, 2014 15:47
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What is the whining sound that I frequently hear on cockpit re-entry video's? To describe it- it sounds like beginning of a Cessna 152 stall warning.
It starts here at 15 seconds and can also be heard at 59 seconds and 1:15.
Also, what is DTI? (or is it PTI 19:41) that triggers the master warning at 20:08.
Finally, note at 1:23 how the crew calls Columbia "it" and "boy".
Thanks!
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#3108
by
mkirk
on 22 May, 2014 16:22
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Yes the correct term is PTI (programmed test input). These were usually flight control inputs (typically done automatically) that were intended to further refine the various aerodynamic coefficients used in modeling the orbiter's flight characteristics. The PTI could be something as simple as a timed control stick deflection at a specific mach number/airspeed and or altitude.
The physics majors can probably provide a more elaborate explanation regarding the noise....but.....You're right, in this video it does sound similar to the Cessna stall warning. In this case it is actually noise/interference over the intercom system caused by the plasma flow outside the orbiter during entry.
Mark Kirkman
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#3109
by
iskyfly
on 22 May, 2014 16:59
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Thank you Mark.
At 29:37 the commander advises the crew, "at 8,000 - 9,000 feet you are going to feel a roll and yaw, don't worry". The maneuver occurs at 30:16. Was that a PTI and what were they testing?
Thanks!
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#3110
by
mkirk
on 22 May, 2014 17:30
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Yes it looks like a stick and a rudder deflection. These were likely a part of a series of inputs that made up a specific DTO (detailed test objective). I would have to see the flight plan notes, entry checklist/cue card to decipher what the exact maneuver(s) were and what the specific objectives were. Generally, as I said before, these were to help derive and validate the exact aerodynamic coefficients used in modeling flight characteristics for the simulators.
Mark Kirkman
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#3111
by
iskyfly
on 22 May, 2014 17:49
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At 17:40 What is a (phonetically pronounced) puckamu swap?
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#3112
by
DaveS
on 22 May, 2014 18:08
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At 17:40 What is a (phonetically pronounced) puckamu swap?
It's PCMMU or Pulse Code Modulation Master Unit.
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#3113
by
iskyfly
on 22 May, 2014 18:21
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Thank you Mark and Dave.
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#3114
by
alk3997
on 22 May, 2014 21:36
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At 17:40 What is a (phonetically pronounced) puckamu swap?
It's PCMMU or Pulse Code Modulation Master Unit.
Purchase Davide's book (and it's a good book) and you can find out more. But, basically they were swapping between units that encoded the telemetry so that it was formatted in a way the ground could decode (commutated and decommutated).
Andy
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#3115
by
alk3997
on 22 May, 2014 21:41
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Yes it looks like a stick and a rudder deflection. These were likely a part of a series of inputs that made up a specific DTO (detailed test objective). I would have to see the flight plan notes, entry checklist/cue card to decipher what the exact maneuver(s) were and what the specific objectives were. Generally, as I said before, these were to help derive and validate the exact aerodynamic coefficients used in modeling flight characteristics for the simulators.
Mark Kirkman
Mark, probably this one (luckily the STS-65 press kit text is online):
DTO 251: Entry Aerodynamic Control Surfaces Test
The DTOs were designed to push the envelope, although usually only by a little bit. I always like the PTIs because we (in the old MCDS cockpit) could see flashing with double-overbright characters. A rare combination that is one of those space-geek type things to remember.
Andy
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#3116
by
psloss
on 22 May, 2014 22:35
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#3117
by
mkirk
on 22 May, 2014 23:20
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Yes it looks like a stick and a rudder deflection. These were likely a part of a series of inputs that made up a specific DTO (detailed test objective). I would have to see the flight plan notes, entry checklist/cue card to decipher what the exact maneuver(s) were and what the specific objectives were. Generally, as I said before, these were to help derive and validate the exact aerodynamic coefficients used in modeling flight characteristics for the simulators.
Mark Kirkman
Mark, probably this one (luckily the STS-65 press kit text is online):
DTO 251: Entry Aerodynamic Control Surfaces Test
The DTOs were designed to push the envelope, although usually only by a little bit. I always like the PTIs because we (in the old MCDS cockpit) could see flashing with double-overbright characters. A rare combination that is one of those space-geek type things to remember.
Andy
Actually the one performed on final appears to be part of DTO 254 "Subsonic Aerodynamics Verification". I wouldn't mind seeing the entry maneuvers cue cards from those flights or something else that breaks down the parameters of the test inputs (timing, magnitude, duration, etc).
Mark Kirkman
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#3118
by
iskyfly
on 23 May, 2014 00:27
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Phillip, thank you! I have not read that article before.
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#3119
by
alk3997
on 23 May, 2014 04:01
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Yes it looks like a stick and a rudder deflection. These were likely a part of a series of inputs that made up a specific DTO (detailed test objective). I would have to see the flight plan notes, entry checklist/cue card to decipher what the exact maneuver(s) were and what the specific objectives were. Generally, as I said before, these were to help derive and validate the exact aerodynamic coefficients used in modeling flight characteristics for the simulators.
Mark Kirkman
Mark, probably this one (luckily the STS-65 press kit text is online):
DTO 251: Entry Aerodynamic Control Surfaces Test
The DTOs were designed to push the envelope, although usually only by a little bit. I always like the PTIs because we (in the old MCDS cockpit) could see flashing with double-overbright characters. A rare combination that is one of those space-geek type things to remember.
Andy
Actually the one performed on final appears to be part of DTO 254 "Subsonic Aerodynamics Verification". I wouldn't mind seeing the entry maneuvers cue cards from those flights or something else that breaks down the parameters of the test inputs (timing, magnitude, duration, etc).
Mark Kirkman
I didn't see that one in the press kit. Doesn't mean it wasn't there - press kits were not FRDs. I seem to remember that most of the item entry PTIs were in the supersonic range. Makes sense since that is where you would be in auto.