As he steps out onto the marbled surface, a shoesized area reaches up to meet his foot. Each step raises to exactly the same level, creating the illusion of a perfectly flat floor that only appears when he's about to step on it. If he stumbles, the floor changes to lessen the stumble.

The imposing airlock door hinges outward, attached to the top of the door. It's designed to be opened manually, so there is a counterbalancing mechanism that he's likely seen a schematic of in passing during his studies. This means he just has to move the mass, and not also hold its weight up against the slightly higher than earth gravity the entire time, which should make this entirely doable.

Well, if he could get started. While the mechanism seems fine, the early part of the descent, before the hull ruptured and could equalize the pressure inside and outside, put a lot of pressure on this door. This wedged it in place, misshaping the edges.

As he pulls the lever, he can hear a seal open and air rush into the airlock, but he doesn't manage to move the door at all.  The floor near the bottom of the door ripples in response to his actions. Does he keep straining?

He considers trying something elaborate. But first: MORE BRUTE STRENGTH.

He puts all his weight on pulling the door. Does it bulge?

Yeah, no, he's not moving this on his own, at least not like this.

As he keeps pulling, two bulges in the floor appear under the door off to the side, vaguely spaced like his hands.

Oh, yeah, the membrane thing.

"Uuuuh. Can you hear me?" This is silly, but. "Can you help me open this door?"

There is no response, at least no words. But the motion of the membrane stills when it is addressed, and then a couple moments pass where nothing happens, followed by a rippling near where he was standing.

Slowly, a pair of appendages grow out of the ground, and the tips form into what you would get if you draped a cast of Mark's hands with an extra layer of marbled skin. The arms tentatively mimic the motion you would get if you just looked at Mark's arms when he was straining, but seemingly without applying any force at all to the lever.

Welp. That is less than fully helpful.

Can he get to any other airlock while staying inside The Membrane?

The space he finds himself in is a tube that connects a tight fitting shell around the spaceship to a seal around the pod. He can walk around a bit in any direction but it's not much larger than required to connect the vehicle size airlock to the pod.

If he wants to go to another side of the ship, the only real chance would be by squeezing himself between the Membrane and the ship for perhaps a fairly long distance. Maybe?

When the membrane sees him not be satisfied with its action, it morphs and imitates his current thinking stance with an amorphous blob. And then the walk from the pod to the air lock. Then it hesitates. It does not at all seem incorporeal. 

Ok, so, it imitates him. But when it imitated him pulling the lever it didn't apply enough force.

It did sustain him while he was walking, so it can definitely apply at least 70 kilograms of force, and do that in a precise way even.

He tries to touch it, trying to imagine how it would feel to squeeze between the membrane and the spaceship to get to the next airlock.

The membrane reaches out a bump to make itself available to be touched when he reaches out. It feels hard and like it has many interlocking pieces, behind a softer surface. Roughly the same as when touching the back of his own hand, with bones and cartilage behind a layer of skin.

It is, of course, still humid, but it seems like it has been drying over time.

If he holds his hand to it for a longer moment, he can feel the subsurface parts slowly rearrange. It seems like it's being careful not to pinch him.

If he applies some force with his palm, he can not deform the hard parts at all. They seem very strong. The soft surface layer squishes though.

This is going to suuuuuuuuuuuuuuuuuuuuuck.

He tries to squeeze between the membrane and the spaceship to get to the next access point.

As he nears the intersection of membrane and ship, the membrane first reaches out to allow itself to be touched again. When Mark then walks around the bump, and starts trying to squeeze through, the membrane starts to adjust to give him more space. It's slow though, so the first few meters are icky close contact moments where the moisture of the membrane and the ship ends up on the vacuum suit. Then it starts opening up to a shuffling area. Then a walking area. It caps out somewhere about a meter away from the ship, which is not roomy but enough to get around without touching either surface.

The ship is not that large in walking distance terms, so he doesn't have to walk that far to find the next interesting part - a huge gash in the side of the ship, where the hull ruptured on the way down. The entrance has loads of pointy metal pieces, all pointing inward from the water pressure, but there are some nasty sharp edges on all sides. The surfaces that are not sharp look slippery from moisture.

Behind the gash is an atmospheric turbine engine, mounted on a structure that holds it slightly away from the hull. Its shape indicates that this is port side of the ship. The engine seems in fairly good shape compared to anything that would have held pressure for a while.

The membrane here has patches of something that looks slightly different. It's slimy and with a vaguely orange color. The shape of the membrane's blue part tend toward shapes that hinder him from touching the orange bit, with barriers extending as far as it can, and contracting around it, decreasing the surface area. If he reaches for it, bits of blue try to intercept his hand and gently push him away, although slowly enough that he could win a contest of speed.

The membrane keeps the start of both the direction he was walking and the reverse open for him, but the areas farther away from him has returned to their previous shapes of very tight squeeze width.