Ellen Ripley seems to complete the deactivation of the request either physically or via a voice command, and Mother rejected accomplishing the task. She didn't want to or wasn't able to?

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    It’s not made totally clear in the movie but I recall an implication that the window to disable the self destruct closed before Ripley could complete the disabling procedure. That’s why she’s pushing those columns down to try to make them go faster because she knows she might not finish in time. Commented Sep 30, 2022 at 1:31
  • As comment: because of the answer of @K-H-W, the things is now centered if Ripley did the right procedure or mother malfunctioned. AFAIK. the levers are a switch overprotected to avoid a detonation by mistake, but when she turned it off, it should deactivate the reactor/meltdown/explosive process
    – riccs_0x
    Commented Sep 30, 2022 at 13:39
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    I am sure I am not the first to ask why there is any period in which the countdown can't be stopped except, and this is pretty lame, you have an intelligent opponent who you want unable to force you to stop the countdown.
    – releseabe
    Commented Sep 30, 2022 at 20:50
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    @releseabe Is that so lame? When would you activate a ship's autodestruct sequence? When the ship has been compromised. You wouldn't want pirates to be able to take over and cancel the countdown. Even a security code could be worked around with something like "Put in the code or I'll blow your head off." I'm skeptical that a system would be designed this way in the real world, but I can see the logic behind it. Commented Oct 2, 2022 at 0:22
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    @KefSchecter: I guess a period long enough to allow escape with an unknown subperiod in which even stopping the explosion could indeed have its uses. Keeping it secret could be key -- a heroic captain could even kill the pirates by pretending he or she could still stop the sequence seconds before the end. The ship's computer blabbing about it would be something I would disable in my design.
    – releseabe
    Commented Oct 2, 2022 at 0:45

3 Answers 3


TL&DR version: Ripley missed the window to disarm it by seconds.

If you look at the system when she's arming it, it makes it clear that there's a 5 minute window to deactivate

Image of the Scuttle instructions When she approaches the 5 minute cutoff, you can hear Mother counting down; As Todd-Wilcox mentions in the comments, you see her pushing down on the columns to try to make it go faster, since she can see that she's right at the edge of the time... and she doesn't make it.

She finishes what she's doing at one console, and runs over to push the levers back up to finish the abort... and you hear mother say that "The Option to Override detonation procedure has now Expired." Ripley was still pushing the levers up when mother starts making the statement, which occurs right at the 5 minute mark. 5 minute mark (First, you see it hit 5 minutes, then it switches back to Ripley pushing the lever up.) Pushing the Levers (One is still all the way down, and she's partway pushed the other up, when 5 minutes hits and Mother makes the announcement.)

She finishes the override steps as Mother hits the word "Now" in "The Option to Override detonation procedure has now Expired."

If it's still up, you can watch the whole deactivation process here, where I got the screencaps. She misses it by seconds, but she does miss it.

Why should mother not help anyway? It's been a while since I've seen the movie, and it might be mentioned somewhere else, but I assumed that since her next comment was "Mother? I've turned the cooling unit back on. Mother?!", that the self-destruct was basically allowing the ship reactor to meltdown (although, for some reason the ship would detonate), and 5 minutes was the point-of-no-return; Mother wasn't trying to be unhelpful, it just wasn't possible to abort, at that point.

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    I don't know how reliable it is, but the AVP Fandom seems to back this up at this page -- "The emergency destruction system aboard the USCSS Nostromo operated on a ten-minute delay, with an initial five-minute fail-safe window during which the process could be aborted. However, after these five minutes had elapsed, the meltdown of the ship's core was irreversible and could not be stopped. When the ten minutes ended, the ship's core would explode with tremendous force, utterly destroying the spacecraft."
    – K-H-W
    Commented Sep 30, 2022 at 2:25
  • Very valuable answer, It sprunged more questions on my mind. Biut I will take into another questions.
    – riccs_0x
    Commented Sep 30, 2022 at 13:32
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    What's the caution labels say? No pinching the screen ?
    – Mazura
    Commented Oct 1, 2022 at 2:50
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    – benrg
    Commented Oct 1, 2022 at 5:57

In the original screenplay, the self-destruct doesn't appear to be an intentional self-destruct system, it was just Ripley using her knowledge of the ship's engine to cause the power core to explode.

MOTHER'S VOICE: (o.s.) Attention. The cooling units for the light-plus engines are not functioning. Engines will over-load in four minutes, fifty seconds...

When she tried to remediate her actions less than two minutes later, the damage she'd already caused was sufficient to result in the ship becoming a ticking timebomb. Again, note the absence of a strict cut-off time limit.

MOTHER'S VOICE: (o.s.) Attention. Engines will overload in three minutes, twenty seconds.

INT. ENGINE ROOM - CUBICLE The door crashes open, Ripley comes pounding in.
The chamber filled with smoke.
Engines whining dangerously.
Ripley breaks out in perspiration from the intense heat.
She runs to the controls.
Begins throwing the cooling unit switches back into place.
The sirens continue sounding.

MOTHER'S VOICE (o.s.) Attention. Engines will overload in three minutes.

Ripley pushes a button and speaks into it.

RIPLEY: Mother, I've turned all the cooling units back on.

MOTHER'S VOICE: (o.s.) Too late for remedial action. The core has begun to melt. Engines will overload in two minutes, thirty-five seconds.

The official novelisation also strongly agrees. Mother advises her that the process is simply too far gone to rectify.

Gasping for breath, she leaned against the hot wall as she jabbed a button. 'Mother, I've turned all the cooling units back on full!'
'Too late for remedial action. The drive core has begun to melt. Reaction irreversible at this point. Implosion incipient, followed by uncontainable overload and subsequent detonation. Engines will overload in two minutes, fifty-five seconds.'

It would appear that the film's makers realised that audiences need a more explicit explanation of why the ship is going to blow up and put in place a handy-dandy self-destruct sign to explain what's happening. Having done so, they also then put nice round numbers in place to make it easier for audiences to realise why it wasn't fixable after she'd changed her mind.

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    I'm glad they did, that Emergency Destruction System instruction plate is such a nice touch making the Nostromo seem real.
    – Schwern
    Commented Sep 30, 2022 at 20:21
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    @Schwern - Plus it improves the tension and explains what's happening to audience members just getting back from the toilet or looking up from shovelling popcorn into their faces.
    – Valorum
    Commented Sep 30, 2022 at 20:23
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    I'm not glad. I'm always bugged by the idea that Sci-Fi ships need a full-fledged self-destruct system. If it was a military vessel of some tactical importance, I could more reasonably understand it but in a long range civilian/corporate freight hauler pulling an ore refinery, I just don't see it. The WY corp explicitly places more value on money than human life and allowing just one of those lowly, easily replaceable humans to blow up tens of millions in starship and who know how much in ore and refinery doesn't gibe. It just doesn't make sense from a financial or insurance standpoint.
    – CitizenRon
    Commented Sep 30, 2022 at 21:29
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    @CitizenRon - That sounds like an excellent question to ask; "Why does the Nostromo even have a self-destruct"
    – Valorum
    Commented Oct 1, 2022 at 8:34
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    @Mazura - Except that this is basically a space hauler. It would be like installing a self-destruct in a tugboat.
    – Valorum
    Commented Oct 2, 2022 at 7:27

Why should mother not help anyway?

The out-of-universe explanation is a countdown adds tension, and they needed to show Ripley being unable to turn off self-destruct. They don't need to explain why, explaining why would be distracting, it's enough that she tries but she can't.

K-H-W's answer is good, there is a physical point where self-destruct cannot be stopped. While it may be true that there is such a point, having it a exactly 5 minutes is a bit too neat. This isn't Star Trek where they can calculate everything down to the last second. The Alien universe is gritty and messy. Even if 5 minutes was determined at the factory, with the state of repair of Nostromo it's hard to believe anything works to factory spec.

An alternative, or additional, explanation is that the 5 minute mark is a security mechanism: Mother is programmed to not allow any override.

Why would Nostromo, a civilian cargo vessel, have a self-destruct mechanism in the first place? Because there are situations when leaving the ship intact are far, far worse. For example, if your ship is out of control, drifting towards an inhabited planet, and carrying disease or very dangerous cargo, you really want to make sure its reactor blows up before it gets too close; you don't want any panicking crew to stop the process. Or maybe your ship is being boarded; you don't want any plucky heroes turning self-destruct off with 1 second remaining after you've left.

The Emergency Destruct System describes it as a "Failsafe Warning" and cancelling the self-destruct as a "Cut-off system" implying self-destruct is an active process which can be stopped.

enter image description here

If you set self-destruct and let it tick down to T-5 minutes, the people who programmed Mother assumed that everyone is leaving or has already left and that you absolutely do indeed want to blow up the ship wholeheartedly. They didn't contemplate you'd be blocked from the escape pods by "something never recorded once on over three hundred surveyed worlds".

When Ripley tells Mother she's turned the cooling units back on, she doesn't expect Mother to do anything. Mother doesn't have voice commands, you need to go into a special room full of blinking lights and type on a keyboard. Mother can't hear her, and Ripley knows that. She's just doing what we all do; she's yelling at a computer in frustration.

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    And before someone points out that Starfleet self-destruct mechanisms can be turned off with 2 seconds remaining, Starfleet knows their captains will set self-destruct just to prove a point.
    – Schwern
    Commented Sep 30, 2022 at 19:38
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    This seems like guesswork. Can you offer any evidence to back this up?
    – Valorum
    Commented Sep 30, 2022 at 19:56
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    @Valorum There are some implications from the wording of the self-destruct instructions, but this is just as much speculation as the other answer. 5 minutes is just too neat.
    – Schwern
    Commented Sep 30, 2022 at 20:04
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    It's a round number, sure, but life is full of those
    – Valorum
    Commented Sep 30, 2022 at 20:07
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    The shuttle had an 'abort'. Every time it launched it was someone's job to stand by the button that would kill everyone onboard, so that if it was going to hit Tampa it wouldn't all still be in one piece.
    – Mazura
    Commented Oct 1, 2022 at 2:55

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