posted 03-28-2011 04:00 PM            

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Originally posted by Sceptic1:
How vital was the lunar module...

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posted 04-21-2011 11:30 AM               

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Originally posted by SpaceAholic:
Snoopy and Aquarius descent stage carried almost identical propellant loads...

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Everything I have heard indicates that the consumables (O2, water, etc.) on board Snoopy would only have lasted for about 10 hours for a two-man crew. Assuming, as on Apollo 13, they had nothing to work with at all from the SM.

posted 09-15-2021 05:31 AM               

555520
CDR I believe we've had a problem here.

555529
CAPCOM This is Houston. Say again, please.

555535
CDR Houston, we've had a problem. We've had a MAIN B BUS UNDERVOLT.

CAPCOM OK 8, we're looking at it.

What might they try to do? Do they throw caution to the wind and blast the SPS immediately and desperately try something whilst homeward bound?

Or do they just accept the crew is lost?
Do the crew suffocate, or freeze to death, or throw open the hatch and end it quickly?

posted 09-15-2021 08:48 AM               

In this case, about the Apollo 13 explosion, it is really a discussion about the capabilities of the command and service modules, as well as what state the Apollo 13 spacecraft was by the time the crew returned to Earth.

posted 10-04-2021 04:51 PM            

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Originally posted by schnappsicle:
Had it stayed on Apollo 10...

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The problem was not simply that the O2 tanks had been built with inadequately rated thermostats, but that the tank (as part of the complete "oxygen shelf") had been subject to a mechanical shock when it was inadvertently dropped during its removal from SM-106. It was hypothesized by the Apollo 13 Review Board that this shock loosened an internal joint in the fill/drain tube (or exacerbated an already ill fitting joint) on that tank which subsequently prevented the tank from being drained after the CDDT using the "normal" de-tanking procedure. This led to the (somewhat ill thought out) "special" de-tanking procedure that relied on the thermostats, which were inadequate, etc, etc, etc.

posted 10-04-2021 10:17 PM               

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Originally posted by pterodactyl;
The reply was quick and unequivocal, "Apollo 8 would NOT have had that failure."

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For a start there is no checklist procedure that required the crew to monitor the AC Volts gauge reading (which is way down on the lower right of Panel 3) during a cryo stir and also, even if it had been monitored, it would have required in the case of Apollo 13, the associated monitor switch to be positioned to one of the available phase selections for AC Bus 2 (not AC Bus 1).

The normal EPS System Check checklist states:

• H2 PRESS (2) - 225-260 psia
  
• O2 PRESS (2) - 865 - 935 psia
  
• SURGE TK PRESS -865-935 psia
  
• H2 QTY (2) - record
  
• O2 QTY (2) - record
  
• CRYO FANS - OF; ON as req'd

The following information was sourced from the "Report Of The Apollo 13 Review Board - Appendix B" and "Part 4." of the "Final Report."

The activation of the fans in O2 Tank 2 at 55:53:20 initially produced indications of a fuel cell current increase of 1 ½ amperes and a drop in AC Bus 2 volts of 0.6 volts that were similar to the turn on values for O2 Tank 1, i.e. normal indications.

Approximately three seconds later, the first of three anomalous voltage spikes occurred with an approximately 2 volt transient drop and a 11 amp current increase followed by a much larger spike 15 seconds later and another 3 seconds after that.

Due to the nature of timing of telemetry received, it is possible that if a larger spike of less than 0.1 seconds duration had occurred it may have not been recorded - let alone been observable.

It was concluded that low level combustion started with the first spike so it is reasonable to assume that turning the fan motors OFF at that particular point would not have stopped the subsequent failure of Tank 2.

After the "bang" and C&W - MAIN B UNDERVOLT, Jack left the left hand seat and floated over to the right hand side and observed that Main B had normal voltages, normal amps and normal fuel cell flows and concluded that it was a transient spike that had generated the C&W and he asked Fred if he recalled the 80 amp spike that had occurred in training.

Jack was therefore, more concerned with a LM hull beach and wanted to get the hatch closed.

Fred reported to Mission Control that "the voltage is - is looking good" and also that he recalled MAIN B had indicated an amp spike on it once before however, by the time that Fred got into position, the instrumentation was no longer "normal."

posted 10-04-2021 11:40 PM               

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Originally posted by Paul78zephyr:
The problem was not simply that the O2 tanks had been built with inadequately rated thermostats...

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Once the tanks were installed in the service module, access to the internal components of the O2 tanks was not possible without the tank being removed, and the modification of the tank systems required that the tanks be returned to the contractor to have the work done. The tanks needed to be cut open to facilitate the modification and welded shut after the work was done.

The O2 tanks were, I understand, manufactured by Beech, and there has always been some question over how the thermostat wiring modification was not completed during the time it was returned to the contractor. I do not know having if the tank returned with damage created a distraction for the repair venue or if the documentation never called ou for the thermostat system to be changed, or, it was just plain missed. The investigation board determined that the probability of the tank systems being damaged by the fall during the tank removal was minimal.

The investigation into the tank damage was well documented and the decision to allow the tank to remain in service has been well covered. The problem of draining the tank contents and the workaround of using the tank heater to "boil off" the remaining oxygen, causing damage to the electrical wiring insulation, was a theory that was tested to confirm the scenario possibility.

There was the previous tank stirs carried out during the Apollo 13 mission that did not result in an explosion, it was not the first time that the tank fans had been powered during the flight. The post-flight investigation never determined the exact cause of the failure, it produced a theory that was accepted by the board. There is a possibility that a pressure vessel simply failed at that exact moment, or that an unknown failure point was never identified. The program could not have moved forward without attributing the failure to a cause.

Each heater is protected with a thermostatic switch, mounted on the heater tube, which is intended to open the heater circuit when it senses a temperature of 80° F. In tests conducted at MSC since the accident, however, it was found that the switches failed to open when the heaters were powered from a 65 V dc supply similar to the power used at KSC during the detanking sequence. Subsequent investigations have shown that the thermostatic switches used, while rated as satisfactory for the 28 V dc spacecraft power supply, could not open properly at 65 V dc.

The investigation board also interviewed technicians and engineers involved in the use of the tank heaters to boil off the liquid oxygen.

Many of the principals in the discussions were not aware of the extended heater operations. Those that did know the details of the procedure did not consider the possibility of damage due to excessive heat within the tank and therefore did not advise management officials of any possible consequences of the unusually long heater operations.

posted 10-05-2021 05:19 AM            

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Originally posted by pterodactyl:
"Apollo 8 would NOT have had that failure."

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Pilots tell themselves, and each other this kind of thing all the time; and sometimes it’s even true. Seriously though, in a risky business it’s a normal defence mechanism that allows you to keep on going up.

Oh and if it was Borman, remember that he absolutely didn’t suffer from space sickness on Apollo 8 until about 40 years later when you know maybe, perhaps he did. That wrong-footed more than one of his colleagues who were still towing the absolutely no-way party line.

posted 10-05-2021 12:08 PM               

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Originally posted by pterodactyl:
...and seen the short circuit when the heater switch was actuated.

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posted 10-07-2021 08:39 PM               

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Originally posted by Andy Anderson:
I wonder what was said that implied the Apollo 8 crew would have been closely monitoring the "voltmeter" during a cryo stir or how they believed the cryo stir should have been carried out.

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Another factor: this was only the second flight of the CSM, and it was a day or more away from Earth when in this scenario, the stir occurred. They may have been more cautious than later flights and monitored the ammeter.