Table 7-11 on page 7-9 of MSC-00171 Apollo 11 Mission Report lists the CSM/S-IVB separation occurring 3 hours, 17 minutes and 4.6 seconds into the mission, at an altitude of 4110.9 nautical miles, at 31.16ºN 88.76ºW, at a space fixed velocity of 24456.8 ft/s.

Table 4-3 on page 4-9 of NASA-TM-X-62558 Saturn 5 Launch Vehicle Flight Evaluation Report AS-506 Apollo 11 mission lists the same event as occurring at range time 11723 (3 hours, 15 minutes and 23 seconds) at an altitude of 3815 nautical miles, at 31.883ºN 64.147ºW, at a space fixed velocity of 24962.6 ft/s

Why are the documents using different figures, and which is more accurate?

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    $\begingroup$ Air-to-ground transcript supports the 3:17 version. "00 03 16 59 CDR / Houston, we're about to SEP. / 00 03 17 02 CC / This is Houston. We copy. / 00 03 17 09 CDR / SEP is complete." hq.nasa.gov/alsj/a11/a11transcript_tec.html $\endgroup$ Commented Jun 11, 2018 at 3:09
  • $\begingroup$ It's not an erroneous copy from the Apollo 10 report; CSM sep on that flight was 10962.4 seconds. $\endgroup$ Commented Jun 11, 2018 at 3:29
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    $\begingroup$ I note that 3:17:04 is 11824 seconds versus 11723; a one digit slip in the hundreds place would bring the figures within one second of agreement. $\endgroup$ Commented Jun 11, 2018 at 3:56
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    $\begingroup$ Excellent example of a neutrally phrased “why the discrepancy” question, by the way. $\endgroup$ Commented Jun 11, 2018 at 4:31
  • $\begingroup$ Thanks for looking into those possibilities @RussellBorogove, and thanks for the compliment on the question. Glad I didn't mess my first one up, at least not too obviously. $\endgroup$
    – user20636
    Commented Jun 11, 2018 at 12:13

2 Answers 2


The two times are for DIFFERENT events. The CSM physically separated from the S-IVB at 003:15:23.0. The 003:17:04.6 time is for the CSM separation maneuver ignition, which, by the way, had cutoff at 003:17:11.7.

These times are documented in "Apollo By The Numbers" (page 106) and "Apollo: The Definitive Sourcebook" page 321

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    $\begingroup$ Hi, that's an interesting claim. Can you add some more details to explain why you think this is the case and/or references to support it? $\endgroup$
    – TooTea
    Commented Jul 19, 2020 at 16:10
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    $\begingroup$ I wrote "Apollo By The Numbers" 30+ years ago, and no longer have my material. The data came either from a NASA or contractor document. If I recall correctly, the initial sep was mechanical, followed by a burn. So there were three times associated with the sep -- the mechanical sep, a burn ignition which increased the sep, and a burn cutoff after the desired sep was achieved. The three times are on page 106 of "ABTN", and also on page 321 of "Apollo: The Definitive Sourcebook", on which David Harland and I collaborated. Sorry I can't be more helpful. But you've got me thinking! $\endgroup$
    – PAD39C
    Commented Jul 22, 2020 at 21:20
  • $\begingroup$ Yes, the first source lists trajectory changes, and the second separation events. $\endgroup$
    – user20636
    Commented Jul 22, 2020 at 22:02
  • $\begingroup$ I don't see how to reconcile this claim with the annotated transcript, which discusses coordinating the separation (triggered by Aldrin pressing a button) with the distancing maneuver (flown by Collins), well after 3:15. $\endgroup$ Commented Jul 23, 2020 at 4:09

TL;DR: Someone probably erroneously transcribed a timestamp and I believe the correct answer is more likely 3:17, but am not certain.

I made the mistake of checking one more reference in preparation to write this answer, and now I am somewhat uncertain about what the actual time of CSM separation was.

In addition to your two sources, I also found:

003:16:55 Armstrong (onboard): Okay, Houston; we're about to Sep.

003:16:58 Collins (onboard): Thrusting...

[Mike thrusts forward in the plus-X direction with the small Reaction Control System engines, so that when Buzz pushes the Sep (Separation) button on Panel 2, the CSM immediately starts to move away from the S-IVB stage and the jettisoned panels.]

003:16:59 Armstrong: Houston, we're about to Sep.

003:17:00 Armstrong (onboard): Sep!

003:17:02 McCandless: This is Houston. We copy.

003:17:03 Aldrin (onboard): Look at that trash.

003:17:05 Armstrong (onboard): Sep complete.

003:17:07 Aldrin (onboard): Got Delta-V?

003:17:08 Collins (onboard): Okay, got 0.7; I'm going to stop there and - -

003:17:09 Armstrong: SEP is complete.

Note that in the latter table, the altitude is given as 23,181,538 feet, which works out to 3815 nautical miles, matching the figure from the LV Flight Eval.

Even though these tables stop at 11723 sec, we can cross-check the other altitude figure from here! From 11600 seconds to 11700 seconds, the altitude increased by 1770214 feet (291 nautical miles), so we're ascending at roughly 291 nm per 100 seconds. The 3:17 figure of 4110 nm is 101 seconds later and 295 nm higher, as expected, so the altitude, velocity, and other position figures there are probably correct for the timestamp.

The production dates and origins of the reports aren't much help:

  • Flight Eval Report (MSFC, September '69) says 3:15
  • Postflight Trajectory Report (Boeing, October '69) says 3:15
  • Mission Report (MSC, November '69) says 3:17.

3:17:04 is 11824 seconds; the fact that the timestamps differ by 101 seconds suggests strongly to me that at some point, someone's fingers slipped on a typewriter keyboard and hit the wrong digits -- 11723 versus 11824 -- and that error was transcribed into other reports later.

The Mission Report has a fractional-second timestamp, which suggests that the number came from telemetry data. The timestamps on the transcripts would not have come from that telemetry, but from an independent clock source, so I am inclined to treat 3:17 as the correct time despite the fact that the 3:15 sources were produced earlier.

I know that some raw telemetry data for Apollo is available online; the best primary source for this would be to find the actual CSM sep telemetry event on a strip chart somewhere.

Listening to the recordings of the air-to-ground loop with a stopwatch at hand and checking the intervals between the TLI burn (2:44), CSM sep, and first docking (3:24) would also provide additional evidence if you had an hour to kill.

  • $\begingroup$ One of the reports is from JSC (MSC back then) and one is from MSFC, so probably totally different teams put them together. I wonder if "Range Time" is different from "Ground Elapsed Time", like one starts at ignition and one starts at liftoff/tower clear/or something silly like that. $\endgroup$ Commented Jun 11, 2018 at 16:15
  • $\begingroup$ @OrganicMarble I'd blow off a 2-second discrepancy as being something like that, but this is 101 seconds; I can't attribute that to different time bases or clock drift. Good point about the different origins though. $\endgroup$ Commented Jun 11, 2018 at 16:21
  • $\begingroup$ Ah, thanks, I had misremembered it from last night as 10 seconds. $\endgroup$ Commented Jun 11, 2018 at 16:22
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    $\begingroup$ And, good grief, the third source is Boeing! But it references another document... $\endgroup$ Commented Jun 11, 2018 at 16:26
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    $\begingroup$ Boeing would have been an MSFC contractor, so it makes sense that their reports agree. $\endgroup$ Commented Jun 11, 2018 at 17:57

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