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#41
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"blow the hatches" on Gemini
Jorge R. Frank wrote: The time doesn't matter; the certainty of detecting the fault does. You snipped my comparison with a pad abort, in which the countdown is halted after T-6 seconds. Nevertheless there is practically a zero chance of actually launching with only two SSMEs running. Like that "practically a zero chance" part, brings back memories of an ocean liner and an iceberg. My pet disaster scenario is that all three SSMEs come up to full power, the command is given to light the SRBs... and only one SRB lights. Pat |
#42
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"blow the hatches" on Gemini
On Sat, 03 Jun 2006 15:11:37 -0500, Pat Flannery
wrote: By and large these are mainly minor glitches- but there are a hell of a lot of them cropping up on one mission, and that should have been a warning to all involved. One reason that these myriad problems weren't taken as a warning sign fleet-wide is that they were all on Columbia, which was coming off a two year overhaul. And Columbia had the "Penguin" and "Hangar Queen" reputation anyway, so the glitches were just taken to be Columbia being her usual Murphy's Law self. That, and considering that 51J, 61A, and 61B had all gone off very smoothly over the previous few months, made the "oh my God, the program's at the edge of disaster" viewpoint very hard to justify. Brian |
#43
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"blow the hatches" on Gemini
Brian Thorn wrote: They don't start to pressurize the LOX tank for flight until T-2:55. So really, there was about 2 minutes for the system to figure out there was a problem and abort. Probably during that time, Launch Control was looking at the readings, trying to figure out if the LOX tank was draining or if it was a sensor glitch. Then the computers aborted the launch from them automatically at T-31, which is the generic abort point (handover from ground control to vehicle control) if things aren't right. Here's the official NSA anomoly report: "Tracking No Time Classification Documentation Subsystem MER - 0 None MET: Prelaunch GMT: Prelaunch Problem FIAR SPR None IPR None IFA STS-61C-V-01 UA PR MPS Manager: Engineer: Title: Main Propulsion System Liquid-Oxygen (LO2) Inboard Fill-And-Drain Valve Did Not Close. (This resulted in about 2000 pounds per minute of LO2 draining from the vehicle through the 8-inch LO2 fill and drain line.) (ORB) Summary: DISCUSSION: At launch minus 4 minutes 40 seconds, the closed-switch indication for the main propulsion system (MPS) liquid-oxygen replenish valve was not received. Even though the replenish-valve closed-switch indication was not available, the auto sequencer continued operation using the valve position indication, the flowrate, and the actuator pressure to status the position of the replenish valve. At launch minus 4 minutes 20 seconds, the command to close the liquid-oxygen inboard fill and-drain valve was blocked in the liquid-oxygen loading sequencer by the failure of the prerequisite control logic to receive the mission facility replenish-valve closed switch indication. This resulted in the auto sequencer initiating a launch hold. A continue command was issued at launch minus 2 minutes and 55 seconds that allowed the liquid-oxygen terminal-count sequencer to open the tail-service-mast vent and drain valves without closing the Orbiter inboard fill-and-drain valve. This unknowingly permitted the offloading of liquid oxygen until the Orbiter inboard fill-and-drain valve was noted to be open and manually closed. Liquid-oxygen prepressurization was initiated; however, the ground helium-gas supply was unable to satisfy the control-band pressure requirement because of the ullage-volume increase resulting from the rapid offloading of liquid oxygen. The tank ullage pressure decreased to -0.12 psid, at which time the fill-and-drain valve closure allowed repressurization to begin again. During the liquid-oxygen offloading, the low-level cutoff sensors temporarily indicated dry. This was probably caused by the termination of the helium feedline antigeyser injector approximately 20 seconds after the tail-service-mast drain valve was open. A hold was initiated at launch minus 31 seconds to review the previous out-of-sequence loading termination and obtain a 5-minute liquid-oxygen drain through the main engines. During the hold, the liquid-oxygen main engine temperature dropped below the engine start requirement of 168.3 deg R by approximately 3 degrees. The engine limit was exceeded because the amount of liquid oxygen lost overboard through the fill-and-drain valve caused the colder, more-dense liquid oxygen to be drawn in from the external tank. The countdown was recycled to launch minus 20 minutes and oxygen replenish flow was reestablished. The launch was scrubbed when it was determined that the vehicle could not be recycled within the allowable launch window. A liquid-oxygen ullage-pressure of -0.12 psid was experienced when the liquid-oxygen vent valve was closed, and the helium supply terminated during liquid-oxygen drain back. Subsequent visual examination of the liquid-oxygen tank revealed no cracks or debonded areas. Analysis indicated that with the 98-percent level propellant load present at the time of occurrence of the negative pressure (-0.2 psi used for analysis), a safety factor of greater than 1.25 was maintained. There was no effect on tank cycles. Review of the above-nominal surge pressure at the engine inlet and the liquid-oxygen manifold was evaluated because the fill-and-drain valve was closed during flow conditions (valve not certified to be closed under flow). The surge pressures observed and the valve opening/closing times all were deemed acceptable for flight. CONCLUSION: The MPS liquid-oxygen inboard fill-and-drain valve was not commanded closed because the liquid-oxygen loading sequencer did not receive the closed-switch indication from the replenish valve as required by the prerequisite control logic. The operator verified replenish-valve closure, but did not close the inboard fill-and-drain valve prior to issuing the resume command to the automatic sequencer. CORRECTIVE_ACTION: 1. The prerequisite control logic that blocked the close command to the liquid-oxygen inboard fill-and-drain valve was overridden for STS 61-C and STS 51-L. This eliminated the inconsistency between the liquid-oxygen loading sequencer software and the prerequisite control software. 2. The launch commit criteria (LCC) will be changed to verify that the liquid-oxygen inboard fill-and-drain valve is closed after replenish valve closure and prior to tail-service-mast vent and drain opening. The count will be held if the fill-and-drain valve closed-indication is lost during the remainder of the count down until T-31 seconds. 3. The helium repressurization "pulse purge" will be turned on if less than 0.25 psi is read on the liquidoxygen low-range pressure transducers. The monitoring will be done automatically with a manual call to pressurize, if required. 4. The minimum external tank (ET) ullage pressure rise rate will be verified at T-120 seconds. This rate was established at 0.85 psi/second as a check on tank-ullage volume, and therefore, liquid level. The existing ET ullage pressure check has been removed from T-125 to T-133 seconds to assure compliance with ET liquid-oxygen tank structural requirements. EFFECTS_ON_SUBSEQUENT_MISSIONS: NONE Pat |
#44
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"blow the hatches" on Gemini
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#45
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"blow the hatches" on Gemini
In article ,
Geert Sassen wrote: ...As each hatch actuator finished its stroke, the movement of the piston uncovered vent ports which released hot gas into the igniters of the seat propulsion system. Now that was a novel set-up! It didn't always work in the correct sequence, i remember reading a story about one of the seats slamming straight *through* the hatch during a test... They did have some debugging to do. :-) That one, if I recall correctly, resulted from a hot-gas leak, fixed by redundant seals and more careful quality control on some of the components. The final system was believed reliable, but it still wasn't anything you'd use unless your life was at stake... -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#46
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"blow the hatches" on Gemini
In article ,
Pat Flannery wrote: How'd you like to eject straight up into the fouled parawing? That wouldn't be fun either. My understanding is that the operational parawing would have used the same deployment concept as the parachute, meaning that it would deploy with the capsule nose-up -- putting the ejection path well clear of any possible snarls -- and the capsule would then flop down into nose-forward position. Simpler setups were used for some of the development testing but I don't think they were meant for operational use. (I could be wrong -- it's been a long time since I read about this.) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#47
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"blow the hatches" on Gemini
In message , Henry Spencer
writes In article , Geert Sassen wrote: ...As each hatch actuator finished its stroke, the movement of the piston uncovered vent ports which released hot gas into the igniters of the seat propulsion system. Now that was a novel set-up! It didn't always work in the correct sequence, i remember reading a story about one of the seats slamming straight *through* the hatch during a test... They did have some debugging to do. :-) That one, if I recall correctly, resulted from a hot-gas leak, fixed by redundant seals and more careful quality control on some of the components. The final system was believed reliable, but it still wasn't anything you'd use unless your life was at stake... Doesn't that apply to _any_ ejector seat? ;-) |
#48
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"blow the hatches" on Gemini
In article ,
Jonathan Silverlight wrote: ...The final system was believed reliable, but it still wasn't anything you'd use unless your life was at stake... Doesn't that apply to _any_ ejector seat? ;-) Yes, but for somewhat less emphatic values of "apply". :-) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#49
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"blow the hatches" on Gemini
Henry Spencer wrote:
In article , Geert Sassen wrote: ...As each hatch actuator finished its stroke, the movement of the piston uncovered vent ports which released hot gas into the igniters of the seat propulsion system. Now that was a novel set-up! It didn't always work in the correct sequence, i remember reading a story about one of the seats slamming straight *through* the hatch during a test... They did have some debugging to do. :-) That one, if I recall correctly, resulted from a hot-gas leak, fixed by redundant seals and more careful quality control on some of the components. The final system was believed reliable, but it still wasn't anything you'd use unless your life was at stake... Didn't John Young once remark about the chances of the seat's use causing (paraphrasing) a very bad, but very short, headache? -- .. "Though I could not caution all, I yet may warn a few: Don't lend your hand to raise no flag atop no ship of fools!" --grateful dead. __________________________________________________ _____________ Mike Flugennock, flugennock at sinkers dot org "Mikey'zine": dubya dubya dubya dot sinkers dot org |
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