Why didn't HAL use the pod to kill Bowman too?

Question

In "2001: A Space Odyssey" movie, HAL kills Poole using the pod he used, why didn't it kill Bowman using the pod too?

Was HAL too sure that Bowman couldn't make it without the helmet? What Bowman does to rescue himself doesn't seem very intelligent or unexpected, and HAL is supposed to be a very intelligent computer.

Answer 1

The most plausible explanation to me is that HAL had to be specifically enabled to control a pod. It was plausible for Poole to enable HAL to do this when taking a spacewalk to replace the AE-35 unit, as he did not expect HAL to do what it did and needed HAL to be able to control the pod to rescue him in case of an emergency or to ease reentering the pod.

Alternatively, as Hypnosifl stated in a comment, it is plausible that Bowman could have easily overriden any attempt by HAL to control the pod while he’s still inside it, so it would not have made sense for HAL to attempt this at that point. As Bowman directly left the pod for the Discovery, the only way for HAL to use the pod afterwards was to damage the Discovery and thus to endanger itself, which it might not have wanted to do.

Even if HAL had full control of the pod, I only see three ways for it to neutralise Bowman:

• Ramming the discovery (see above).

• Steering the pod away from the Discovery. We do not know on what distance HAL could communicate with the Pod and it is conceivable that this distance is very short. Once communication has ceased, Bowman could regain control and possibly would need to give control back to HAL manually. When Bowman goes to fetch Poole, we briefly see the following screen:

  

  While the displayed information may refer to Poole, it may also refer to the Pod itself, indicating in particular that the pod’s comlink to HAL is broken, which would enable Bowman to freely steer the pod afterwards under the above assumptions.

• Keeping the pod in distance until Bowman runs out of air, water or food. If overriding HAL’s control from within the pod was possible, this would have given Bowman plenty of time to do so.

• Depressurising the pod (see below).

What Bowman does to rescue himself doesn't seem very intelligent or unexpected, and HAL is supposed to be a very intelligent computer.

When coming to think of it, HAL might not have so many ways at hand to kill or neutralise Bowman that do not allow him to grab a spacesuit and disable HAL. Actually, the only other way I can think of at all would be to evacuate the ship. However, why would it be able to do this? Yes, it can probably control the airlocks, but I expect them to have independent, mechanical failsafes that avoid a depressurisation of the whole ship.

So, when Bowman heads for the pod and forgets his helmet, it seems not implausible to me that HAL coöperates and lets him go simply because this is the most promising strategy.

Finally, in the movie, HAL may very well be malfunctioning in some way and thus its decisions do not need to be fully logical.

Answer 2

If you look at the movie, and the sequence in which events occur, it becomes clear.

• HAL reports a fault in the AE-35 unit.
• Bowman retrieves the "faulty" unit.
• After examination, no fault is found.
• They contact mission control, who state that HAL must have been in error.
• Bowman and Poole discuss this in a Pod and agree on the option of disconnecting HAL.
• Poole puts the unit back to let it fail.
• At this point HAL panics and kills Poole.
• Bowman goes out to try rescue him.
• Further events ensue.

So the conclusions are:

• During Bowman's EVA to retrieve the AE-35 first time around, HAL had incorrectly reported a fault. This was an honest error; there was no fault.
• HAL therefore had no reason to kill Bowman at this time.
• Subsequently HAL is under suspicion of being in error about the fault.
• And during Poole's EVA he was (and knew that he was) under threat of disconnection and so took action to prevent that.

As HAL himself said:

I know that you and Frank were planning to disconnect me, and I'm afraid that's something I cannot allow to happen.

So it was the threat of disconnection that pushed HAL over the edge; until that point in time there was no reason to kill anyone, after it there was every reason.

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This of course is a different story to that in the book, and the sequels (movie and books) also retcon the reason differently. That's just part of the complex relationships between the various versions of the story; as Kubrick himself says (source):

There are a number of differences between the book and the movie. The novel, for example, attempts to explain things much more explicitly than the film does, which is inevitable in a verbal medium. The novel came about after we did a 130-page prose treatment of the film at the very outset. This initial treatment was subsequently changed in the screenplay, and the screenplay in turn was altered during the making of the film. But Arthur took all the existing material, plus an impression of some of the rushes, and wrote the novel. As a result, there's a difference between the novel and the film … I think that the divergences between the two works are interesting.

Clarke himself acknowledges these discontinuities in the prologues to each book in the series, so this lack of consistency is something that's recognised by both authors of the original and is something we have to accept. This isn't like the Star Wars EU where everything must be retconned to be consistent and have a reason; this is a series where the story evolves and inconsistencies with previous or alternate tellings are accepted as part of that evolution.