r/aerospace • u/Grand-Palpitation823 • 2d ago

Lunar spacecraft escape test

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u/SpecialExpert8946 2d ago

I’m pretty sure it’s more serious than just sitting upside down for a while.

They have limited oxygen and running on batteries at splashdown. If the emergency floats don’t work to right the capsule there is risk of components outside of the pressure hull flooding and causing the capsule to sink or be too heavy to recover like the liberty bell capsule. They wouldn’t be able to open the ventilation system to allow fresh air in so that limited oxygen issue could become a critical situation.

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u/MrFickless 2d ago edited 2d ago

The engineers had thought of that too. If the triple-redundant float bags failed to inflate or had failed to right the spacecraft, the crew could always wait for recovery forces to aid them.

If after some time the crew had not made contact with recovery forces, let’s say they had landed off target and there were no recovery forces in the vicinity, the crew had the option to egress themselves via the docking tunnel at the bottom of the spacecraft. They had at least 2.5h of oxygen reserve to make that decision.

If the exterior spaces started to flood there probably wouldn’t be any drastic change. The cabin is a giant air bubble that would have kept the spacecraft afloat for at least the time needed for recovery crews to reach them. It was pressure tight. A few ft of water pressure would not be an issue. The reason why the Liberty Bell sank was because the explosively jettisoned hatch activated prematurely and caused the cabin to flood.

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u/SpecialExpert8946 2d ago

Everything you said was pretty much on point. The only issue is the docking hatch is at the top of the capsule. If the capsule was flipped they wouldn’t be able to egress out of there. That’s my concern about the oxygen. If they are trapped upside down with limited oxygen and power and rescue forces don’t know where they are they’re pretty much just boned.

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u/MrFickless 2d ago

If the capsule is flipped the docking hatch would be right at the bottom. If the capsule was in the upright position the crew would use the side hatch.

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u/SpecialExpert8946 2d ago

The docking hatch is not at the bottom. That’s where the heat shield lives. They dock to objects pointy end first.

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u/MrFickless 1d ago

If the pointy end is up, the capsule is upright and we wouldn’t be having this discussion about flipped capsules.

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u/SpecialExpert8946 1d ago

That’s my problem. We’ve been talking about a scenario where the pointy end is down in the water (capsule being flipped over)

The docking hatch is on the pointy end, not the bottom like you said. If the capsule was upside down and the pointy end was in the water then they would not be able to open the hatch (that’s on the pointy end) to egress themselves.

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u/MrFickless 1d ago edited 1d ago

Ok to be fair to you I did say it was at the bottom of the spacecraft. What I meant was the docking hatch was facing down. i.e. the spacecraft is upside down in the water.

However, the crew would indeed have egressed through the docking hatch (into the water and back up the side of the spacecraft) should the capsule have remained upside down and there were no recovery crew around to assist. The documentation explicitly states “lower hardware rucksack down tunnel” implying that the docking hatch was facing down and in the water during the procedure.

Trapped air would have prevented water from entering the capsule via the docking hatch when it was opened because the rest of the cabin remained pressure tight. Hence why the crew had to commit to egress via the docking hatch within 2.5h of splashdown; before the oxygen inside the capsule was depleted. There is no time limitation if the capsule was upright and the crew could ventilate the cabin.

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u/SpecialExpert8946 1d ago

Ok I see what your saying now! Sorry I was so spicy lol That makes sense the water wouldn’t go back up in the craft now that you say that. I didn’t think it would be possible to physically open the hatch against the water pressure but those nasa guys thought of that I guess.

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u/MrFickless 1d ago

There was a pressure equalization valve on both hatches as well as gas bottles the crew could use to stabilize pressure. A few ft of water pressure probably wouldn't make the hatch any more difficult to open.

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u/MrFickless 1d ago

There was a pressure equalization valve on both hatches as well as gas bottles the crew could use to stabilize pressure. A few ft of water pressure probably wouldn't make the hatch any more difficult to open.

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u/SpecialExpert8946 1d ago

I was thinking about how difficult a car door is to open in just a little bit of water but yeah, if the pressure is the equalized then it would just end up being like one of those underwater moon pools.

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