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At the time of launch what was the air pressure in the Apollo LM, and the spacecraft-LEM adapter section (SLA)? Was the air vented from the SLA as the vehicle entered orbit?

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    $\begingroup$ I can't find any authoritative reference, but I would guess that the SLA had to be open to ambient pressure at all times, thus venting from sea level pressure to vacuum as the vehicle flew to orbit. On Apollo 6, one of the SLA panels failed because of increasing pressure inside the honeycomb-sandwich structure of the panel. As the SLA is made up of multiple separating panels, and has a number of access ports, it would be hard to pressure-seal it if you wanted to, and I don't think you'd want a lot of overpressure there. $\endgroup$ – Russell Borogove Aug 8 '18 at 15:44
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    $\begingroup$ I couldn't find a reference either but I am also sure there were vents. Next time I drive by the Saturn V at JSC I'll stop in and take a look at the SLA to see I if I can see them. Although I'm not 100% sure it is a real SLA. $\endgroup$ – Organic Marble Aug 8 '18 at 18:13
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    $\begingroup$ @OrganicMarble The Saturn V at Marshall probably has a real SLA. Do you ever go there? You'd probably need a telescope to check for the vents: that Saturn V is upright! $\endgroup$ – Tom Spilker Aug 9 '18 at 0:58
  • $\begingroup$ @TomSpilker I have been to the visitor center there once. It's pretty awesome. My highlights were seeing the Shuttle-Centaur and the MPTA boat-tail, sitting beside each other outside. $\endgroup$ – Organic Marble Aug 9 '18 at 1:27
  • $\begingroup$ The Field Guide to American Spacecraft says it's a real SLA, SLA-22. The page is a tad out of date though, the booster is displayed indoors now. I'll try and stop by tomorrow. americanspacecraft.com/pages/booster/sv-jsc.html $\endgroup$ – Organic Marble Aug 9 '18 at 1:33
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I was able to answer this by taking some pictures of the Saturn V displayed at Johnson Space Center. Despite my skepticism, it is a real Spacecraft Launch Adapter (SLA), just as the Field Guide to American Spacecraft states.

We can see what are clearly a number of vents inside the SLA. (the crossed brace is not flight hardware, it merely supports the aft end of the SLA for display).

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A closeup of one of the vents

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The outside of the vents on this SLA are covered with metal disks because it was displayed outside for many years. But knowing what to look for, we can see the vents on a stacked Saturn on the pad.

enter image description here


As far as the Lunar Module (LEM) goes, we know that operationally it had a ~ 5 psi pure oxygen atmosphere. It's inconceivable that the light weight LEM structure could have withstood 10 psi crush loads, so the LEM must have been pressurized to 14.7 psi on the pad with pure O2, which then bled down through the positive pressure relief valves during ascent.

Reference (page 3-58)

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  • $\begingroup$ I know that some of the ports on the SLA were for loading propellants to the service module, though: heroicrelics.org/space-ctr/csm-sla/dsc49568.jpg.html -- I still haven't seen anything that's unmistakably an open pressure vent. $\endgroup$ – Russell Borogove Aug 10 '18 at 20:01
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    $\begingroup$ Those round circles on either side of the hinge on the side away from the tower certainly were not used to load anything, and match up with the vents in the picture I took. $\endgroup$ – Organic Marble Aug 10 '18 at 20:06
  • $\begingroup$ You can see the connections in that link you posted in your comment in the first picture I took. They go into that pillow looking thing at the back of the SM. In fact, if you click on the "oxidizer service connection" in the link you posted, you'll see that exactly. $\endgroup$ – Organic Marble Aug 10 '18 at 20:20
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    $\begingroup$ Very nice detective work, must be handy to have a space center nearby ;-) $\endgroup$ – uhoh Sep 10 '18 at 0:56
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    $\begingroup$ @uhoh Somewhat surprisingly, Rocket Park where the Saturn and other rockets are displayed is open to all for free - no pricey Space Center Houston tickets or NASA badge required. Just roll up to the main gate and tell the guard you're going to Rocket Park. Stop in when you're in Houston next. $\endgroup$ – Organic Marble Sep 10 '18 at 19:41

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