Adam Sandler, we can all agree, is a serious actor — at times a great one. His comic DNA will often thread its way through his performances, but not always. In “Uncut Gems,” he had a frantic aggro desperation worthy of a Scorsese crime film. In “Hustle,” the crowd-pleasing Netflix sports drama he made after that, he played a pro-basketball scout with a menschy mouthiness that carried the audience right along. So when you sit down to watch “Spaceman” (also made for Netflix), in which Sandler plays a morosely bearded and tired-looking Czechoslovakian astronaut who is six months into a solo mission to the far side of the solar system, you give him the benefit of the doubt. We’ve seen space operas about stranded voyagers before (like Matt Damon’s red-planet Robinson Crusoe in “The Martian”). If any actor has the resources to hold down the center of a movie like this one, it’s probably Adam Sandler.

But “Spaceman,” it’s my duty to report, is a glum and meandering science-fiction fairy tale of a movie. It premieres today at the Berlin Film Festival, and you can see why it was programmed there ­— it’s got an austere dystopian vibe that allows it to pass for an art film. Sandler certainly does what he can with the role. But the director, Johan Renck, adapting the 2017 novel “Spaceman of Bohemia” (the script is by Colby Day), does not know how to carry the audience along. He does a fine job of establishing the spatial dynamics of the ship, which inside looks very 1970s Eastern European (old metal painted in drab shades of tan and chartreuse; aging equipment; lots of storage-unit clutter). The casual dystopian atmosphere, abetted by a soundtrack of eerie modernist effects, could almost be something out of a TV-drama version of “Solaris.”

Sandler, speaking in a faint accent, plays Jakub, who floats around the ship in his sad-sack stupor, killing time as he heads toward a massive psychedelic lavender nebula. It’s known as the Chopra Cloud, and it will be his job to explore what it’s made of. But the movie isn’t really about his mission. It’s about his despair, which is fueled by the fact that his marriage, back on earth, to Lenka (Carey Mulligan) is coming apart. That’s something he can sense even before Lenka, who is pregnant, sends a message to him announcing that she’s leaving him.

Jakub’s commanding officer, played by a ruthless Isabella Rossellini, will not allow Lenka’s message to be transmitted. She fears, quite correctly, that it would undermine the voyage by pulling the plug on Jakub’s will to complete it. He’s already a forlorn customer, going through the motions of commitment to his mission. Even so, the whole situation of a woman with doubts about her marriage choosing to break up with her astronaut-hero husband while he’s off on a high-profile space mission feels fundamentally rigged. You can’t say that this couldn’t happen, but the script of “Spaceman” is too thin to support what does happen.

What’s Lenka’s problem with Jakub? It’s that he’s overly isolated — too committed to flying off alone into space. Well, sure, but it’s not exactly like she didn’t know she was signing on for that. And the movie never fills in the texture of their faltering communion, at least not in a satisfying way. “Spaceman” is oblique and abstract, all murmurs and suggestions. We have to do the filling in ourselves.

Jakub is out there by himself, but there’s another character — sort of. One night, Jakub faces the bathroom mirror and observes what looks like a small tarantula crawling around under his skin, until its legs pop out of his nose and mouth. He wakes up; it was just a nightmare. But the spidery dream continues — or is it real? — when, a few scenes later, he observes an oversize tarantula, about 10 feet across, occupying one chamber of the ship.

How did this creature get in there? We assume that it’s a hallucination, a byproduct of Jakub’s cabin fever. But once the creature starts talking to him, in a voice of the most soothing camaraderie provided by Paul Dano (who does soothing like nobody’s business), it’s as if it’s become real. The bony hairy legs, the six eyes like stacked marbles — it certainly looks authentic enough. The creature has a name, Hanus, and refers to Jakub by a nickname: “skinny human.” The truth is that it almost doesn’t matter whether this is Jakub’s imaginary friend, like Wilson the volleyball in “Cast Away,” or an actual invader. Either way, the effect is that of watching our hero get counseled by a benign comrade/therapist, a kind of stuffed animal for adults who happens to look like a monster out of a ’50s nuclear horror film. And no, in case you’re wondering, that’s not a spoiler. It’s basically the whole damn movie.

Paul Dano’s tranquil voice performance as Hanus often brings to mind the voice of HAL in “2001: A Space Odyssey.” That film hovers over this one, because Kubrick was the director who demonstrated that you could make a science-fiction drama about the emptiness of space — the void of it, the non-drama — and still hold an audience in thrall. That seems to be the intent behind “Spaceman.” But Kubrick, beneath his loftiness, was an instinctive entertainer who knew that you needed conflict and a villain. “Spaceman” gets lost in space and mostly just sits there, limply, because everything that happens is too soft, right down to the healing of Jakub and Lenka’s relationship. We’re watching a Hallmark card in slow motion.