In the movie Apollo 13 there's a scene when the LEM is losing power; when they switch the module on, one of the astronauts reads the levels and says that one battery has no Volts but 2 Amps. What did he mean?
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$\begingroup$ I will defer to the official script, but I remember having the same question after watching the movie. $\endgroup$– hazzey ♦Commented May 10, 2016 at 17:57
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1$\begingroup$ I think he meant it's not dead yet. Makes sense, Hollywood style at least. The real transcript is actually quite interesting: apollo13.spacelog.org/search but sadly the movie seems to have no real correlation in this technical aspect, at that point in the story at least. $\endgroup$– JayyCommented May 10, 2016 at 20:02
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1$\begingroup$ It might just mean that either the volt or the ampere meter has been damaged. The readings disagree, as a battery with 0 volts would hardly give 2 amperes current. Considering the damage the spacecraft suffered, damaged cables/meters wouldn't be surprising. $\endgroup$– jpaCommented May 11, 2016 at 9:36
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1 Answer
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The part of the movie transcript you're talking about (taken from here) is where Fred Halse says:
Batt B, no volts, amps are okay. Batt C, s***. No volts, only two amps. They may die before the main chutes open.
To make sense of it, I think we need to ground ourselves with the real Apollo 13 and basic electronics. A battery can have zero volts across it and current flowing if it is being short circuited. Compare this to the actual Apollo transcripts which mention "volts": there are moments shortly following the catastrophy where zero volts is mentioned:
- d02 h07, m55, s20: I believe we've had a problem here.
- d02 h07 m58 s07: Okay, AC 2 is showing zip. I'm going to try to reconfigure on that, Jack.
- d02 h07 m58 s33 It's reading about 25-1/2, MAIN B is reading zip right now.
From what I gather, those are due to the destruction of the fuel cells (batteries). So no current would be flowing either.
But they quickly swap around connections between fuel cells, main buses and AC inverters, and I cannot find any further mention of zero volts. The voltages are usually around 30V, which makes sense since they were designed to be nominally at 28V DC. (Aside: What caused the accident in the first place: at some point parts of the design were changed from 65V DC. Explanation here).
From the movie transcript, your quote is said straight after:
KEN MATTINGLY - Re-entry interface in one minute and thirty seconds.
Interestingly, the zero volt 2 amp movie quote vaguely corresponds in content and timing with the real transcript where battery and parachutes are mentioned shortly preceeding reentry:
So I think that is your answer. Hollywood was trying to give the impression of the batteries having just about enough juice left. Technically it had little to do with volts and amps, but rather amp-hours; the energy left in the batteries.
