The Lunar Module hatch could not be opened while the cabin was pressurized. The hatch opened inward, and the air pressure inside the Lunar Module (LM) forced the hatch to seal tightly. (This is exactly the same principle that is used in all passenger doors in airliners. It is impossible to open a properly-working airliner passenger door while the plane is at altitude.)
舱neural加压时，月球舱门无法打开。 舱门打开时向内，并且登月舱（LM）内部的气压迫使舱门紧密密封。 （这与在客机中所有乘客门上使用的原理完全相同。在飞机处于高度时，不可能打开工作正常的客机门。）
So the LM had to be depressurized before the hatch could be opened. There was a pressure dump valve in the hatch that vented the cabin atmosphere to space. The air (oxygen) in the cabin was simply lost.
因此，在舱口打开之前，必须先对LM减压。 舱口中有一个泄压阀，该泄压阀将机舱大气排入太空。 机舱中的空气（氧气）就丢失了。
Why waste the air? There were a few reasons that I can think of:
- Weight. In space, Weight is Everything ™. The oxygen that was dumped overboard didn’t weigh very much, but the vacuum pumps to suck the oxygen back into the tanks would have weighed a lot more.
- 重量。 在太空中，重量就是一切。 排放到船外的氧气的重量并不大，但是将氧气吸回储罐的真空泵的重量会更大。
- Complexity. Spacecraft are complicated pieces of equipment, but engineers try to avoid needless complexity. The more complex something is, the more likely it is to fail. A valve to dump oxygen overboard is simple. Vacuum pumps are more complex. Imagine landing on the moon but not being able to go outside because the vacuum pumps have failed. Yikes.
- 复杂。 航天器是复杂的设备，但是工程师们试图避免不必要的复杂性。 事物越复杂，失败的可能性就越大。 将氧气排放到船外的阀门很简单。 真空泵更复杂。 想象一下降落在月球上，但由于真空泵发生故障而无法外出。 Yikes.
- Electricity. Electrical power was always at a premium on the LM. All of the LM’s electrical power came from 4 or 5 batteries (a 5th battery was added starting on Apollo 15). A vent valve requires no electrical power. Vacuum pumps do. No idea if this would have been an issue, however.
- 电力。 LM上的电功率始终很高。 LM的所有电力均来自4或5块电池（从Apollo 15开始增加了第5块电池）。 排气阀不需要电源。 真空泵要。 不知道这是否会成为问题。
- Most importantly, safety. A fun fact about the LM hatches is that the hatches could be operated from either side, making it impossible to be locked out. Both the hatch locking mechanism and the pressure dump valve could be operated from inside or outside. Imagine the astronauts are outside on an EVA (“moonwalk”). The hatch gets closed, and a tiny leak in the pressurization system causes the cabin to become slightly pressurized. When they try to get back in, they find that the vacuum pumps have failed, and they can’t depressurize the cabin. Double yikes! With the cabin pressurized — even partially — they are not going to get the hatch open. So you’re going to need an emergency vent valve anyway.
- 最重要的是安全。 关于LM舱口的一个有趣事实是，舱内舱外都可以操作舱门，因此无法将其完全锁住。 想象一下，宇航员在EVA（“月球漫步”）上在外面。 舱门关闭，增压系统中的微小泄漏导致机舱变得略微增压。 当他们尝试返回时，发现真空泵出现故障，无法为机舱减压。 Double yikes! 在机舱增压（甚至是部分增压）的情况下，就打开不了舱门。 因此，无论如何您都需要一个紧急排气阀。
For all these reasons, it just doesn’t make sense to try to save a little oxygen.、
Here’s a diagram of the LM’s hatch, with the cabin relief and dump valve circled in red:
And here’s a photo, taken just before launch of the Apollo 17 valve on the LM front hatch:
By the way, the LM had two hatches, a front hatch and a top hatch, and
the Command Module also had two hatches. Everything here applies to all
the hatches: the latching mechanism could be operated from inside or
outside, and the pressure dump valves could be operated from inside or
 Thanks to Dragi Raos for reminding me that the cargo doors on some airliners are not plug-type doors, and in fact have resulted in several fatal airliner crashes.
 The interior of the LM was meticulously photographed just before launch, in what were known as “closeout photos.” Before launch the ground crew was supposed to leave every switch in a predetermined position, and the closeout photos were a way to determine that this had been done correctly, and that all equipment had been stowed properly. Each set of closeout photos is available on NASA’s Apollo Lunar Surface Journal website.
 LM的内部是在发射前精心拍摄的，即所谓的“关闭照片”。在发射之前，地面人员应该将每个开关都放在预定的位置， 并且正确存放所有设备。 关闭照片 是一种能确保正确完成了此操作的方法， 每张关闭图都可以在NASA的《阿波罗月球表面期刊》网站上找到。
@ Jonathan Miller 30+ Years NASA Engineer, Johnson Space Center, Houston
So no way to lock the doors and keep those pesky aliens out?
That’s what the phasers were for.
On the moon, who were the aliens?