The opening sequence of Stowaway, a new science fiction thriller by director Joe Penna that's much heavier on the "science" than "thriller", is a top-notch bit of space travel filmmaking that calls to mind all the best examples of the form from Apollo 13 to First Man; the last sequence is ginned-up sentimental horseshit that lets the film off the hook for having to do a single thing about the difficult and insoluble challenges it has raised; and in between those two sequences there is something close to an uninterrupted falling line of quality. This means a few things, one of which is that there is a point at which Stowaway ceases to be "a good film" and instead becomes "a bad film", and I think it is largely a matter of how far along its 116-minute running time you set that point that dictates whether you consider this to be a frustrating movie that's still worth watching (which is the side I come down on), or a movie that's worth avoiding but it does have its moments. It also means that it's very, very hard to be generous towards the film, since any story that ends on its shittiest beat is going to leave an awfully sour taste in the mouth that's perhaps disproportionate to how much it actually does that's bad.

But let us at least try to be generous, and do so by returning to that opening sequence, which depicts the launch of MTS-42, a two-year scientific research mission to an existing Martian post (the exact nature of the Martian colony is unclear; one of the subtler strengths of Penna and Ryan Morrison's screenplay is that they let the exposition happen more or less naturally through the conversations of four people who would have very little reason to talk about the exposition). The film opens by closing in on the anonymous, helmet-clad head of Zoe Levenson (Anna Kendrick), the mission's medical scientist, but we hear the voice of mission commander Marina Barnett (Toni Collette), tersely communicating with the fellas down at mission control; we also hear the bangs and roars of a very fucking massive rocket firing the blazing wrath of hell as it shoves those two and plant biologist David Kim (Daniel Dae Kim) into space at the fastest speeds theoretically available, for a five-month trip to the red planet. The sequence is almost solely made up of massively loud, vicious sounds, and rattling cinematography of Kendrick's head; it is practically minimalist in suggesting the chaos of a rocket launch, though I defy anyone to sit through the shriek of sound designer Jan Petzold and sound editor Andreas Hildebrandt's sonic assault and actually come up with the word "minimalist" to describe it. Most importantly, though, it is very effective dropping us without ceremony into a tense moment and letting that tension soak into our bones until we understand the visceral panic of space travel.

Stowaway never hits that level again, and never even really comes close, though it is quite a smart piece of filmmaking for a decent stretch of its running time. The title gives away the game: a fourth individual, launch support crewman Michael Adams (Shamier Anderson), has managed to wind up unconscious and trapped in a bulkhead, and between his weight, his oxygen consumption, and his need to ingest calories, he has instantly cast doubt on every aspect of the mission's success. Worse yet, Michael had been position just right to damage the all-important carbon dioxide scrubber, without which there won't be enough breathable air for anybody. And thus do we get a film-length philosophical dispute over what happens when a space that was already overtaxed with three people now has four people in it, and if one of those people isn't killed, all four of them will surely die. Trolley Problem: The Movie, basically, except that all of the characters are among those tied to the tracks.

We also do get the first inkling of what will ultimately kill Stowaway, unfortunately, which is that Penna and Morrison are much too eager to come up with the most contrived, bullshitty ways imaginable to heighten their stakes. Michael having just happened to lose consciousness in a place where nobody would see him for hours is one thing; the film doesn't have a scenario without that. But that place also meaning he damaged the one mission-critical system without redundancies? That's starting to feel a little bit like filmmakers who just want to make sure that the worst possible thing always happens, and this will continue to be a niggling, and increasingly gnawing problem with the film's script: it's not enough to be difficult, things must be catastrophic, even when this would seem to violate the rules and logic already established (most notably a perfectly-timed "deadly solar radiation" storm that runs up against a ticking clock that has a different deadline than the ticking clock the film had previously established).

And so it is that the film eventually descends into ludicrous melodrama, a great disappointment for a film that, at its best moments, is ruthlessly spare and stripped down. Stowaway is basically a rocket science procedural, with the four characters defined and written solely in terms of their ability to solve the immediate problems facing the mission, relying entirely on the four actors to provide whatever human emotions will be there to fuel the moral dilemma. And they are all great at this (Colette is the most consistently steady presence, while Kendrick has to deal with the worst writing, but otherwise it's an awfully well-balanced four-hander), so the film doesn't feel entirely dry and hyper-intellectual. It's good for the film that it can rely on this, since it allows Penna to emphasise the businesslike precision of the mission and the crew, in a film that strips down space travel to the matter of an earthlike atmosphere being preserved in a flimsy can in the middle of billions of miles of vacuum. Even something as simple as how he stages conversations with people back on Earth gets at this: we never see the screen the crew is talking to, and they're all wearing earphones, so we never hear what the people back home are saying: it's just watching half of a conversation and having to scramble for context clues to figure out what is going on. It's pretty brilliant, in fact, training us to remain alert and wired while watching the film even before its actual plot kicks in.

All of this, plus the inherent strength of the bleak scenario, gives Stowaway a lot of momentum to power through a large chunk of its arguably bloated running time (though I do think the slowness it enables helps remind us that space travel involves a whole lot of doing nothing in the emptiness imaginable location), the intellectual chilliness and the existential terror sitting well next to each other. Penna is very good at ripping out the sentimentality from his filmmaking, much as he did in his feature debut, the survival thriller Arctic (which was apparently conceived as a kind of sequel to Stowaway, with the action moved from Mars back to Earth when it got financing first), and the brusqueness of Stowaway is very much its strongest element.

But there comes a point where it starts leaning into the random crush Zoe apparently develops on Michael, turning the moral dilemma into more of a personal drama than an ethical puzzle; and then it starts flinging nonsense at the characters to try and ease the burden of having to make tough choices when they could just be living through a tragedy. Whether that's enough to ruin the film, I leave as an exercise for the individual viewer. Let us at least say that it sure as hell doesn't do the film any good.