The Absence of Airlocks

[Jason Thompson]

I know that. But if they had used an airlock they would have needed one, and added to the weight. Another reason they didn't use  one.

Why would they need a pump? An airlock between atmosphere inside and vacuum outside only requires valves. When leaving the ship the airlock starts full of air and opening a valve to the outside will cause it to bleed out. When re-entering the airlock starts in vacuum and opening a valve to the inside will cause it to fill with air from inside the ship. The ambient pressure differences on either side of the doors will serve the function perfectly well without any active pumping of gas.

You only need a pump if there is something other than a vacuum on the other side and you need to exchange one atmosphere for another, or the ambient pressure outside your tiny ship is significantly greater than that inside, where just opening the valves will fill your ship with whatever is outside at similar pressure. So in a submarine you'd need an active pump to remove the water prior to opening the interior door, or if you were on Venus, for example. The only reason for having a pump on a spacecraft would be to avoid losing precious oxygen to the outside, by pumping it back into the cabin from the airlock, but it's more likely to be considered OK to lose that volume of gaseous oxygen a few times than add the complexity of a pump where one is not needed for normal airlock operation.

[JayUtah]

If one of the reasons you want an airlock is to recover the gas in the lock by pumping it down to vacuum and storing it for later use, then you have to consider that a vacuum pump and its related plumbing and wiring would cost more mass than the equivalent additional volume of atmospheric gases required for several full recharges of the LM interior.  And it's a lot less complex that way.  In contrast, if you're willing to waste the gas in the airlock by venting it to space, then you have to consider that an appropriately sized airlock wouldn't be a significant savings of that gas over simply venting the entire volume.  In order for that to look attractive to engineers, the airlock would have to be an order of magnitude smaller than the volume whose atmosphere you're trying to preserve.  The only reason to require an airlock in such a scenario is if you need to preserve a shirtsleeve environment for people not ingressing or egressing.  That's not a requirement for Apollo.

[Britmax]

And once you realise that this is the only reason you'd have a pump, and there is no way the net saving of atmosphere will make up for the weight penalty incurred by fitting an eccentrically mounted walk in fridge, the case for an airlock really disappears over the horizon, does it not? 

[JayUtah]

It does.  There's really no engineering reason to even attempt to fit an airlock to the Apollo LM.  For that design, it's universally easier to provide a different solution for problems you think an airlock would solve.

[HyperOreo]

It has always amazed me why a conspiracy theorist would pose a genuine question when they are convinced they already have the answer.

[Allan F]

It has always amazed me why a conspiracy theorist would pose a genuine question when they are convinced they already have the answer.

Because that is how they make themselves feel smart. It gives them the warm fuzzy feeling inside. To show all the eggheads with their edjukasjon how stupid they are.

[smartcooky]

It has always amazed me why a conspiracy theorist would pose a genuine question when they are convinced they already have the answer.

I think its an attempt to try to show how "superior"^TM they are, and how they "know"^TM the "truth"^TM and have "special knowledge"^TM that the rest of us sheeple and shills don't.

[JayUtah]

Yes, there's at least one neuroscientist out there who's studying the electrochemical payoff that happens when someone believes he has hidden knowledge.  It's pure ego reinforcement.  The Powers That Be have taken great pains to keep something hidden, but the conspiracy theorist is so smart to have figured it all out anyway, and to have had the open mind and imagination to have considered conspiracy and hoax in the first place.  This is what I believe Jr Knowing is trying to accomplish.  He wants to be given credit for being "woke," but with this crowd he can't make his alleged wokenness (sorry, Gillianren) take the place of actual knowledge of the events, the relevant sciences, and the specific engineering solutions.

[Jason Thompson]

And once you realise that this is the only reason you'd have a pump, and there is no way the net saving of atmosphere will make up for the weight penalty incurred by fitting an eccentrically mounted walk in fridge, the case for an airlock really disappears over the horizon, does it not? 

Indeed, whistling merrily and arm in arm with a whole bunch of other 'common sense' engineering 'solutions' held up by conspiracy theorists as being necessary for a successful lunar mission.

[gillianren]

Yes, there's at least one neuroscientist out there who's studying the electrochemical payoff that happens when someone believes he has hidden knowledge.  It's pure ego reinforcement.  The Powers That Be have taken great pains to keep something hidden, but the conspiracy theorist is so smart to have figured it all out anyway, and to have had the open mind and imagination to have considered conspiracy and hoax in the first place.  This is what I believe Jr Knowing is trying to accomplish.  He wants to be given credit for being "woke," but with this crowd he can't make his alleged wokenness (sorry, Gillianren) take the place of actual knowledge of the events, the relevant sciences, and the specific engineering solutions.

You should be sorry!  There should be only one "n" in "wokeness," in my opinion.

[bknight]

If one of the reasons you want an airlock is to recover the gas in the lock by pumping it down to vacuum and storing it for later use, then you have to consider that a vacuum pump and its related plumbing and wiring would cost more mass than the equivalent additional volume of atmospheric gases required for several full recharges of the LM interior.  And it's a lot less complex that way.  In contrast, if you're willing to waste the gas in the airlock by venting it to space, then you have to consider that an appropriately sized airlock wouldn't be a significant savings of that gas over simply venting the entire volume.  In order for that to look attractive to engineers, the airlock would have to be an order of magnitude smaller than the volume whose atmosphere you're trying to preserve.  The only reason to require an airlock in such a scenario is if you need to preserve a shirtsleeve environment for people not ingressing or egressing.  That's not a requirement for Apollo.

Indeed as you point out that the system dumped the oxygen in the LM to the Lunar atmosphere and thereby negated a reason to have an airlock.  Plus nobody was left inside to be in a shirtsleeve environment. 

[Britmax]

Two more things occur to me. Firstly, as the windows on the LM are positioned to enable the pilot to see when landing, and watch the command module through the window, any airlock would probably impinge on the vision when docking and undocking. But also, what exactly happens to it on takeoff from the moon? Do you carry the extra weight, which means a bigger engine and more fuel use, or do you jettison it, whether separately or part of the descent stage, either of which need guillotines and additional seals which are a further complication and more weight?   

[Abaddon]

Two more things occur to me. Firstly, as the windows on the LM are positioned to enable the pilot to see when landing, and watch the command module through the window, any airlock would probably impinge on the vision when docking and undocking. But also, what exactly happens to it on takeoff from the moon? Do you carry the extra weight, which means a bigger engine and more fuel use, or do you jettison it, whether separately or part of the descent stage, either of which need guillotines and additional seals which are a further complication and more weight?   

Putting on an engineers hat...

One could, I suppose, include an airlock in the LM, but why? What benefit would there be to maintaining an atmosphere in the LM? There are no people there. There are no systems there dependent on an atmosphere. (beyond things like scrubbers, which are redundant if nobody is there) so why exactly would one desire to maintain a breathable atmosphere in the LM when there is nothing in it that breathes?

Perhaps a safe haven in the event of an unexpected suit puncture by some misadventure? That dog don't hunt. Astronaut be dead long before returning and cycling an airlock.

Maybe a minor leak? Well, pressurising the LM would take the same or less time than cycling an airlock, no?

In a way, the LM itself IS the airlock. All that has happened is an elegant economy of design. The suit itself is, in effect, a spacecraft in its own right. Suit and LM form together a rather efficient airlock. Why add a load of clunky hardware to that? Not to mention the weight cost.

[Obviousman]

In a way, the LM itself IS the airlock.

I like that.

[Abaddon]

In a way, the LM itself IS the airlock.

I like that.

So do I. One can run it on to lunar rendezvous with the CM. Once again the LM is the airlock. The simple engineering elegance is a joy.

Weellll. I say simple in a relative sense, but you catch my drift.