I was watching the HISHE clip on youtube today about the movie Aliens (one of my favourite films) when it got me wondering, what would really happen if someone opened an airlock into space like Ripley does at the end?
Would the air be sucked out like the movie shows, would it be more of an explosion of air from the airlock, would someone really be able to hold on to the rungs of the access ladder or not?
Need answer fast! 
I don’t think you could hold on to the access ladder. But.
Even using a simplistic calculation using just air pressure and area, depressurization would not be completely instantaneous. In college my friends and I calculated that even using this naive equation it would take more than a second to depressurize the space shuttle from a tiny hole, and I think that the proportion of air to hole size in this example is about the same since Ripley’s vessel is much larger.
However, there’s also the fluid dynamics side of the equation, since the air will not neatly behave and instantaneously occupy the newly vacated space. I don’t know the specifics of this but it will slow down the depressurization even further.
On the third hand, Ripley is closer to the hole than most of the vessel. So while the entire vessel will not undergo explosive decompression, I’m not sure if Ripley would.
Well, she was standing on it, too. The queen had a grip on Ripley’s right ankle, but Ripley’s left foot was on a lower rung, in at least some of the shots.
Can’t a fat guy get sucked out of a tiny airplane window if it breaks? Or is that just in the movies, too?
Assuming the Sulaco was pressurized at 1 atmosphere, that’s about 15 lbs. of pressure per square inch.
The hatch looked to be roughly 18 feet square, for an area of ~324 ft = 46,656 square inches.
The volume/momentum of air per second rushing through that hole, given those peramiters… well, someone will have to do the math. But I’ll bet it’s a lot.
ETA: Fluid dynamics on a gas, as opposed to a liquid like water, would act much faster as liquid doesn’t compress and creates far more drag. Yet, the expulsion of air wouldn’t be instantaneous, but probably more explosive than seen in the flick.
Movie myth.
Assuming your calculations were right and the decompression would be more forceful than shown, is it possible that there are safeguards in that room to protect the ship? Ripley didn’t do anything special to open both doors, so she wasn’t overriding any controls.
Could the ship have automatically opened several emergency vents to diffuse where the gas is escaping, creating less danger for the ship and crew and acting as was shown in the film? Or would that not really make that much of a difference?
Obviously this is a fanwank, but it seems possible. In real life, I doubt they’d make it that easy. And it’s fun to try to come up with “why” something happened the way it happened.
It was always strange to me that vaccuum is used to kill the alien in three of the movies.
However, Aliens is the only one where the airlock is oriented “down” relative to the artificial gravity of the ship. I wonder to what extent the alien is “falling” versus being “sucked out.” Probably best not to think too much about the movie physics.
Interesting to contrast is 2001, which depicts much more of a sudden explosion rather than a steady suction.
In case somebody does do the math, the hatch is more like 6’x10’ at a minimum. The narrow side is longer than Ripley is tall. More like 520,000 in[sup]2[/sup]
I thought for sure that Cecil had covered being sucked out of an airplane window but can’t find it in the archives.
Here’s his take on explosive decompression. He’s specifically talking about 2001 here and says in a vacuum you would only have 10-15 seconds of consciousness. Of course air was still rushing out so Ripley wasn’t in total vacuum so that may not apply here.
This article (warning: PDF) talking about drag on a human says a human has an approximate cross sectional area of .68 m[sup]2[/sup] which is just over 1000 square inches. At 15 psi, that’s 15,000 pounds of force. And yeah, I know it’s a lot more complicated than that, but I wouldn’t want to try to hold on outside of the power loader.
It’s even more complicated than that. Any bay with an airlock isn’t going to be wide open to the rest of the ship. Doors leading into it would logically be airtight when closed, and there seems little reason to think they’d opened more than one, so the size of that door would constrain airflow into the bay. Other hatches throughout the ship might be closed, but not airtight, further slowing the pressure loss. We can’t even assume they maintained 1 atmosphere–they could easily run at lower pressure with elevated oxygen content, though the use of open flame on board makes that seem unlikely.
What I’m getting at is that there are enough potential variables in play that you could probably come up with a combination that would produce the results in the movie.
Ahh, I was going from memory – as usual, my memory decieves me! I was thinking it was more or less a square hole in the floor with a hatch acting as the floor about the size of a typical household room. But if the dimensions are closer to 6’x10’, that gives an area of 60 square feet, or 8,640 sq. inches.
Also, good point, Balance. Still I’m curious about what kind of rush of air a hole like that would give to a vacuum (all else being equal).
Its been a long time since I saw the original Alien, but IIRC, the Alien isn’t killed by the vacuum, but because it tried to take refuge inside the engines when they fired.
I always thought that an Alien could survive in space, possibly going into some sort of hibernation state. If so, its possible that the Queen from Aliens isn’t dead at all, but still alive floating around in orbit of LV-426
Nitpick from memory: Dave Bowman set off the explosive bolts to destroy the pod and use the explosion to force him into the airlock rapidly.
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We should ask the crew of the Prometheus. They’ll be here soon.
Kill? Victory was just moving the alien to Somewhere That’s Not Inside The Ship. The first bug was still thrashing after engine ignition burned up the line tethering it to the Narcissus, and while we can assume the Queen was not going to survive re-entry, she certainly didn’t seem to be slowed down much by the spacing.
This part is especially weird because of the implications it makes as to the mass of the Queen. She’s huge! Dramatic stompy sound effects notwithstanding, she must be pretty light on her feet for Ripley to have been able to support her weight in the artificial gravity. The a-grav clearly extends to the bottom of the airlock, as the loader’s pinning the queen down prior to opening. So…yeah.
It’s best not too look too closely at that scene, methinks.
As many folks have observed, Alien owes a lot to a 1950s low-budget and generally unappreciated science fiction film called It! The Terror from Beyond Space*, written by Jerome Bixby**. At the end of that, the Evil Beastie is killed by opening the airlock. But, in good SF mode, the situation was analyzed and understood as the creature needing air to survive, as it had on its native Mars, and they basically suffocated it (It was stuck in an inner ship hatchway, and wasn’t “sucked out” into space by opening the airlock). The Alien franchise decided to repeatedly use this element, only with the “expulsion into s;pace” part added, apparently because the damned Beast was so powerful and destructive (Acis Blood!) that they couldn’t figure out any other way to get rid of it.
(I note that, in the original Ridley Scott film, the Alien is just barely hanging on by its fingertips as it’s getting sucked out, until Ripley shoots the damned thing. At the conclusion of Scott’s next film, Legend, Tim Curry’s Devil-like character is also being sucked out into the outer Darkness and just barely holds on by his fingertips. Scott seems to like his weirdly iconic images, and uses them repeatedly. There are other examples in his ouevre.)
*There are people who will claim that Bixby, in turn, ripped off A.E. van Vogt’s Black Destroyer, but I think the only real similarity is that we’ve got a Alien Aboard the Starship. Black Destroyer and It are a helluva lot more different than It and Alien are.
**Bixby is underappreciated, too, but you probably know his work – he’s the one responsible for the story about the magic little boy who can do anything and puts people he doesn’t like “in the cornfield” (“It’s a GOOD Life”). It was eventually made into a much-recalled episode of the original Twilight Zone (As well as being redone for the TZ movie, and with a sequel in one of the later TZ series on televcision). He also wrote The Lost Missile and the pretty awful Curse of the Faceless Man. He wrote several episodes of the original Star Trek, and his Man from Earth was filmed five years ago, prompting a thread on this Board.
While true, that doesnt really tell you anything about the aerodynamic forces on Ripley as the air rushes out of the airlock. The 15psi would only be relevant if it was 15psi on her front side and magically near 0 just on the other side. The flip side of this would be how fast would a rocket with 15,000 pounds of thrust push Ripley through the air? (pretty damn fast, probably supersonic and I doubt the air rushing ou of the airlock is near that fast).
Without doing the technically correct calculations here is one back of the envelope way to get a rough feel of how fast air would be flowing out. Imagine a car tire. Imagine yanking out the whole valve stem quickly. About a 30 PSI differential. Deflates in two seconds give or take a factor of 2 say? Calculate the volume and figure out how fast the air has to be flowing out of that hole.
Great story. I have it in a collection of “monster” short stories that my uncle had when he was a kid in the 50s.
It’s also in Healy and McComas’ clasic anthology Adventures in Time and Space.
More importantly, it’s in A.E;. van Vogt’s Voyage of the Space Beagle, a “fix-up”, as van Vogt called it, where he took a group of short stories and connected them together into a longer narrative. VotSB also included a story called “Discord in Scarlet”, that was, AFAIK, the first account of an alien creature implanting eggs in a human body, to hatch and develop into young by eating their host. (Just as “Black Destroyer” is, AFAIK, the original >Monster loose on a star ship" story). That this theme, too, showed up in Alien is suggestive, although I have the feeling that Dan O’Bannon and co-scripters , who seem more attuned to movie SF than literary SF*, got their inspiration from the film * Night of the Blood Beast*, the first sf film AFAIK that includes this gruesome idea.
*Alien also has influences from other flicks, such as Planet of Vampires, but not notably from sf literature.
People have a hard time understanding what is happening. You aren’t sucked into space. You’re blown into space by the air in your compartment. The air is pressurized to 1 atmosphere (more or less), and when you open a hole to a place where the pressure is zero atmospheres, the air will push itself through the hole into space.
One atmosphere is 14 pounds per square inch. That is the maximum force that the air inside a spaceship can exert. Could you push a cow through a small hole with that amount of force? No you can’t. You could block a small hole in a spaceship by putting your hand over the hole. Your hand might get bruised and frozen, but it’s not going to be crushed.