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During the Apollo 11 landing, a misconfiguration caused the guidance computer to activate the 1201 and 1202 program alarms, signifying that the computer was overloaded and dropping low-priority tasks. This was connected to the master alarm system to get the crew's attention; the alarms distracted the crew and may have contributed to the long hover time and marginal fuel state on that landing. In actuality the 1201 and 1202 errors were not extremely serious, though the uncertainty of their cause at the time was a big concern.

In November 1968, NASA engineer Bill Tindall wrote a delightful memo recommending against tying a low fuel warning to the master alarm precisely because it was an expected occurrence: "just at the most critical time in the most critical operation of a perfectly nominal lunar landing mission, the master alarm with all its lights, bells, and whistles will go off."

The film Apollo 13 portrays the master alarm as a red light with a loud repeating buzzer. Is that reasonably accurate? Would that buzzer have gone off during the 1201 and 1202 alarms during the Apollo 11 landing?

Russell Borogove
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2 Answers2

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The Apollo Operations Handbook, Caution and Warning section, identifies the alarm tone as "a square wave that is alternately 750 cps and 2000 cps, changing at a rate of 2.5 times a second"

Perhaps someone can gen that up? It appears to me to be more like an alternating type sound rather than a buzzer. If the Shuttle copied this sound for its master alarm (likely), I've heard that one a bunch. It is indeed kind of a warbling sound that to me sounds like a French police car (at least as they are portrayed in American movies).

Edit: just found the Shuttle spec, and it's 400 Hz for .4 seconds, then 1024 Hz for 0.4 seconds. So roughly similar (alternating) but not the same.

Edit2: Russell Borogove synthesized 5 seconds of each alarm at this link. Very neat!

Edit3: The above information related to the Command Module C&W system, my error, since the question is really about the Lunar Module C&W system. That, in fact, seems to have been a buzzer, although not through a loudspeaker:

A malfunction also activates a 3-kc signal that provides a tone in the astronaut headsets and supplies the PCMTEA with a telemetry signal .

I got this from an incredible resource I just found: the Lunar Module Operations Handbook, 800 pages of Apollo-y goodness.

Organic Marble
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    I wonder if the moviemakers used a buzzer because they thought it would sound too much like an 80s video game to use the real thing, or if they just picked a sound that seemed appropriate. http://tvtropes.org/pmwiki/pmwiki.php/Main/TheCoconutEffect – Russell Borogove Nov 08 '15 at 21:26
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    That's so horrible, was it supposed to wake them up from the dead? "Do you want to hear the most annoying sound in the world?" I would've broken a window to get rid of the air quickly. – LocalFluff Nov 08 '15 at 22:32
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    lol! Yes, it was supposed to get their attention! Their fingers got sore from stabbing the button in the sims to shut it off! – Organic Marble Nov 08 '15 at 22:33
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    It would, in fact, have been designed to awaken them. One of the original drivers for the 3-person Apollo crew was that they could sleep in shifts, but they quickly realized it was hard to sleep while other people were working in the close confines of the CM, and decided it was fine to all sleep at once; ground control would be watching the instrumentation and the alarm would wake them up if anything drastic happened. – Russell Borogove Nov 08 '15 at 22:47
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    The pitch & waveform of the alarm may not be as critically annoying as the loudness. – Fred Nov 09 '15 at 08:45
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    Count yourself lucky I only generated it at 91.5% of the maximum possible loudness. The handbook O.M. links says "although the tone is audible above the conversation level, it does not render normal conversation indistinct or garbled." Also, seems like it wasn't on loudspeakers either -- "an audio alarm tone, sent to the three headsets, aurally alerts the crew." – Russell Borogove Nov 09 '15 at 18:56
  • Looking at the schematic in the Telecommunications section of the Apollo Ops Handbook, I cannot even confirm that there was a speaker at all! – Organic Marble Nov 09 '15 at 19:05
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    @OrganicMarble Looks like it was called the "tone booster", and was a separate unit that was stowed during awake periods. See Apollo Operations Handbook, Systems Data, section 2.10.3, page 2.10-3 (upper half of page 4 in the PDF linked in the answer). – user Nov 11 '15 at 15:03
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    Reading the next paragraph, it sounds like the "tone booster" was triggered by the master alarm light through a photocell. Wow, that sounds kludgey! – Organic Marble Nov 11 '15 at 15:36
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    @OrganicMarble Not half as kludgey as the Apollo 13 mailbox. – user Nov 11 '15 at 15:55
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    @RussellBorogove while reading these comments, I realized that my answer deals with the Command Module C&W system. Your question is really about the Lunar Module C&W system. I've edited it to fix this, and wanted to point it out since you already accepted the answer. – Organic Marble Nov 11 '15 at 15:59
  • Eh, I was curious about both. – Russell Borogove Nov 11 '15 at 22:16
  • @RussellBorogove The audio you synthesized appears to be at half the real speed. To be frank, it's not clear whether the spec refers to the period of the sequence or the period of each tone - anyway, here is the sound that is currently used in NASSP (Apollo simulator): http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=2268.0 – oldmud0 Jun 18 '17 at 23:32
  • @RussellBorogove The link with the synthesized samples is dead now. Any chance you could re-upload them? – Polygnome May 14 '19 at 10:10
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    @Polygnome https://cleverdomain.org/mcws/cm.mp3 https://cleverdomain.org/mcws/shuttle.mp3 – hobbs Jul 10 '19 at 19:23
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I found these three active links on Sound Cloud:

No Nonsense
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ayates
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