According to the movie Apollo 13 (1995) the radio blackout on reentry was quite a bit longer than expected.

Very dramatic, yes, but:

Did that really happen, and if so, why was it so much longer than expected (or was there typically that much variance on Apollo flights)?

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    $\begingroup$ slightly related: Communication Blackout $\endgroup$
    – uhoh
    Commented Jul 17, 2019 at 13:12
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    $\begingroup$ Time is relative, said someone famous... $\endgroup$
    – Criggie
    Commented Jul 17, 2019 at 19:56

2 Answers 2


Apollo 13 Blackout Story, Chuck Deiterich, Apollo 13 Retrofire Officerenter image description here

  • $\begingroup$ Great find thank you! This totally explains it! $\endgroup$
    – davidbak
    Commented Aug 4, 2023 at 19:55
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    $\begingroup$ Welcome to Stack Exchange! "great find" but where did you find it? Screenshots of text are strongly discouraged for several reasons; people using screen readers (text to speech) can't access it, and it can't be searched, either within the site or via search engine. Also, there's no source quoted for this information, which means readers can not confirm it, or read further, and the source is now being use without attribution. Can you provide a link or a citation? Thanks! Also, can you copy/paste the actual text into your answer rather than just leaving a picture of it? Thanks again! $\endgroup$
    – uhoh
    Commented Aug 4, 2023 at 22:00
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    $\begingroup$ The information came from my MCC console log and my Apollo 13 post flight report. I tried to paste but the system scrambled the text. When interviewed by Henry S. F. Cooper, I did not realize what the answer might be until a couple of years ago. $\endgroup$ Commented Aug 5, 2023 at 22:07
  • $\begingroup$ Midcourse correction 7, I'm assuming that was the burn at GET 137:39:51, five hours before entry? I'm looking at Apollo by the Numbers and it only lists four midcourse corrections, so I'm guessing some of the midcourse corrections were skipped as unneeded, or due to the change in mission plan, or perhaps considered too risky for the potential accuracy gain? Also the shallower than expected entry angle, was that known right away after midcourse correction 7, or not until post-flight analysis? $\endgroup$ Commented Jan 5 at 13:24

Sort of, but not for the usual reasons. When you are low on batteries, parachutes are more important than radios.

Remember that they were running off of batteries, everything non-essential was powered off, and those system which were needed were strictly powered on only as needed. There were several communication systems, which all would have been powered in a normal re-entry; many were powered off at various times during 13's re-entry.

In particular, the VHF systems were kept off during the blackout, and had to be turned on manually after the parachutes were confirmed deployed. The radio contact was late because the astronauts had to turn the radio power back on.

From 101:53:00 to 102:02:00 and from 123:05:00 to 123:12:00, the communications system was powered up to the extent necessary to transmit high-bit-rate telemetry data using the omnidirectional antennas. The S-band system was turned on for verification prior to undocking and performed nominally. The VHF/AM and VHF recovery systems were turned on at parachute deployment and operated nominally throughout recovery.

Apollo 13 Mission Report, section 5.4

Update: A typical Apollo blackout lasted about 4 minutes. Due to a shallower re-entry path, Apollo 13's blackout was calculated to last about 4.5 minutes. Flight director Gene Kranz's logs show that it took about 6 minutes to re-establish contact with Apollo 13.

Telemetry was usually the first signal received after the blackout. This article from Smithsonian Air and Space magazine confirms that 13's first signal was telemetry:

With no radio signal, there was "no way to tell" how the crew and ship were faring, Kranz says. "There was no telemetry from Odyssey until the end of blackout," he recalls.

Telemetry would confirm that the spacecraft was intact, and biomedical data would confirm that the crew was alive. However, voice communication would confirm that the crew was conscious and that there were no anomalies. The Air and Space article confirms that there was some relief in mission control upon hearing the crew's voices, but not as dramatic as in the film:

Henry Cooper's 1973 book Thirteen: The Flight That Failed describes the tension: "After three minutes of blackout, Kranz put through a call to [lead retro-fire officer Chuck] Deiterich to find out how much longer they had to wait. Deiterich said it should be over in another thirty seconds. At the end of thirty seconds, there was still no word from the astronauts, and Deiterich began to get concerned. Thirty seconds later, the astronauts still hadn't reported in, and Deiterich was alarmed." Even when they finally heard astronaut Jack Swigert's voice over the radio, confirming that the crew had survived, the controllers didn't say a word, just kept silent until the capsule splashed down in the Pacific nine minutes later, according to Cooper's account.

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    $\begingroup$ @DrSheldon: if it was transmitting telemetry, then is it correct to assume that NASA knew the re-entry worked before the astronauts regained contact? If so that definitely removes a dramatic element from the movie :-P $\endgroup$ Commented Jul 17, 2019 at 15:21
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    $\begingroup$ @davidbak See the Apollo 13 transcripts, seemingly around 098:54. $\endgroup$
    – user
    Commented Jul 17, 2019 at 20:31
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    $\begingroup$ Mission control is always filled with rancorous applause in movies. I don't know how realistic that seems, though. "Excuse me whlie I prance away from these safety critical systems for 3 minutes hugging and high fiving all my friends." $\endgroup$
    – corsiKa
    Commented Jul 18, 2019 at 1:45
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    $\begingroup$ @corsiKa: Maybe not 'accurate', but it's not at all unrealistic: youtube.com/watch?v=7DB60S7BYtA or youtube.com/watch?v=83GyUtktiII $\endgroup$ Commented Jul 18, 2019 at 20:51
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    $\begingroup$ @Joshua: obviously, but most of the people at mission control had just as much influence by the time blackout ended. The point is, it's not unrealistic to portray human beings as doing human behaviors. $\endgroup$ Commented Jul 18, 2019 at 21:04

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