One can appreciate Adam Sandler using his Big Deal with Netflix to try and branch out as an actor, to act in more serious films that the self-described “moron” comedies he’s churned out for decades, keeping himself, assorted family members and legions of his cronies fat and happy.

But one must note how limited his skillset remains, how ill-suited he is in certain guises, how bad he is in “Spaceman” and how gorgeous but indifferent the film surrounding him is.

The Swedish director Johan Renck (TV’s “Chernobyl”) and under-credentialed screenwriter Colby Day adapt Jaroslav Kalfar’s hallucinatory novel of a solo space mission undertaken by a man whose marriage to his very pregnant wife is disentegrating, mid-voyage, and put Sandler in the middle of it.

Jakub, our “Spaceman” cracks up, hallucinating a long debate with an imagined gigantic space spider given the soothing vocal tones of Paul Dano, as the spacefarer’s wife Lenka (Carey Mulligan) tries to end the marriage via phone calls, somewhat supported by her mother (Lena Olin) but blocked from finishing the breakup by a space agency chief played by Isabella Rossellini.

Yes, the deal that got this movie off the ground, involving Netflix, Sandler and a cluster of more accomplished if not more famous screen icons, is more interesting than the movie itself. And yes, it’s entirely possible that they got Sandler’s attention by informing him the spider would repeatedly address him as “Skinny Human.”

It’s a sad, dreamy, impressively-financed space travel tale about the spiritual isolation of a daying marriage, stress and abandonment that presents Sandler’s Jakub struggling with system failures, listening to opera, and explaining opera in a stilted, half-assed attempt at a “European” accent to a giant imaginary spider.

“Skinny Human, I have never heard such silence before.”

The real struggle involves trying to add tools to Sandler’s always-limited repertoire. He shouts a lot in dramas, because that’s all he’s got to lean on that’s “serious.” He doesn’t shout much here, but that doesn’t help. His line readings are creaky affectations that sound so unnatural coming from his mouth that it’s a relief when he has the odd grammatical noun-verb agreement blunder.

His character carries a son’s trauma of his father’s downfall and memories of the dark communist crimes of Czech history. He’s on his way to Jupiter, racing “the Koreans” to get there, grasping at sanity, and desperate to reach his wife before she cuts off contact altogether.

“Whatever” is the only line Sandler delivers with conviction.

The narrative changes points of view, following the spaceman and then his wife, each spiraling into an existential crisis, each crisis driven by loneliness and panic.

And the film skips by the biggest question in the plot with a Carey Mulligan shrug.

“Why can’t you wait until he comes back?”

The best one can say for “Spaceman” is that it’s a trippy curiosity. The worst is that it’s a serious swing-and-a-miss for the Sand Man, and a career low for Carey M.

Rating: R, profanity

Cast: Adam Sandler, Carey Mulligan, Lena Olin, Isabella Rossellini and the voice of Paul Dano.

Credits: Directed by Johan Renck, scripted by Colby Day, based on a novel by Jaroslav Kalfar. A Netflix release.

Running time: 1:47