The space romance Passengers has faced a mudslide of criticism for its conflation of Stockholm syndrome and romance and for taking a heady plot with scientific inaccuracies and intellectually lazy ideas about 24th-century culture. Still, it has one thing going for it that NASA never has: sex.

Sex in space isn’t new to pop culture. It has been imagined with aliens, robots, Jane Fonda, and a considerable percentage of the Star Trek: Deep Space Nine cast. But Jim Preston (Chris Pratt) and the ludicrously named Aurora Lane (Jennifer Lawrence) cavorting does re-raise the question at the core of a future kink. What would intercourse in space be like?

The basics first: Passengers portrays two humans in a heterosexual relationship. Nowhere is a condom spotted. STDs are never mentioned. The positions in question seem to be exclusively doggy-style and missionary. All the sexual action portrayed takes place in gravity controlled, pressurized chambers that (spoiler alert) are slowly breaking down, which means the pressurization and gravity levels are occasionally a bit off — and this is a critical point. Gravity is an important reason why sex in space might be more difficult than we can imagine, especially when we consider dicks in space. Erections are caused — the psychosexual stuff aside — by a rush of blood to the penis that causes hardening and “lift.” In a location where gravity isn’t steady, that rush of blood to the nether regions can be tough, because blood is concentrated up top around the head and chest, where your vitals are housed. It’s not to say that a boner can’t be achieved, so much as that it will take some coaxing. Passengers works around this problem, however, by having all the steamy scenes occur in spaces that have some gravity.

Not that Aurora is having a perfectly smooth time getting her O on; lady boners require the same rush of blood to the genitals. It takes two to tango, and if a woman’s clitoris doesn’t swell when she’s aroused, intercourse won’t turn out as advertised. Not only that, but a lady’s going to want to have her vagina be slippery and wet for intercourse. Moist secretions — like sweat and tears — tend to just glob up in Zero-G. Vaginal secretions would not be spread evenly, which would create discomfort.

What makes confirming how space travel will affect our sex lives especially difficult is the fact that NASA keeps its lips zipped on the subject. While NASA has studied gender and biology in space, it’s coy about discussing sex in space, and we’re not exactly sure how much — if anything at all — NASA knows about how sex works in space. That doesn’t mean we don’t know a few things about sex in space. For one, while we might think of sex in microgravity as adventurous, it’s not, according to NASA bioethicist Paul Root Wolpe. As he told Motherboard:

“A lot of people think that sex in microgravity will be great because by losing gravity you can move in ways you can’t terrestrially. The [scientists] who’ve thought about this aren’t so sure about that at all. One of the things that gravity helps us do is stay together, so sex in microgravity might actually be more difficult because you’re going to have to make sure that you’re always holding each other so you don’t drift apart. It might be a lot more challenging and a lot less fulfilling than most people think.”

All of this seems to indicate that sex in space will require a set of tools. In 2006, artist Vanna Bonta imagined the very sexily-named “coupling suit,” a garment with velcro strips and “diaphanous inner material” that prevented a space partner from throwing up from nerves or (more likely) space sickness. The suits are designed to allow heat convection for a more Earth-like sexual experience — the slip and slide of sweaty bodies, while kind of gross, is biologically helpful in keeping partners squared off with one another. Microgravity would take sweat and create floating droplets, which would probably be a distraction. Combined with zero gravity, this makes the very emotional core of sex — that intimacy aspect — hard to achieve. Bonta’s fantasy suit allows not only for heat convection but anchors designed to keep one partner on a wall.

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But a lack of gravity isn’t the only potential obstacle. There’s also the concerning issue of cosmic radiation. Specifically, scientists are worried about high-energy protons that are so atomically charged they can shred the biological basis of DNA or rip through the shielding of a spacecraft. On Earth, primate tests have shown that even low levels of radiation terminate pregnancies and if a female is born in space, she will likely be infertile. Men aren’t safe from the effects of radiation either. Sperm doesn’t handle radiation well, which can lead to birth defects or infertility.

In University of Arizona astronomer Chris Impey’s 2015 book, Beyond: Our Future in Space, NASA’s medical director, Norbert Kraft, is quoted as being against the idea of sex and pregnancy in space, particularly because no one has studied how contraceptives may or may not work out there. Kraft has gone so far as to plan to tell astronauts venturing to Mars that they should consider celibacy: To him, the risks and uncertainty of sex in space are just too frightening.

That there might be no sex on Mars is deeply problematic for anyone planning to go there. Elon Musk’s plan to create a city on Mars requires propagation, requires people to have children who in turn have children to create a society. Sex in space might incite sniggers but sex in space is something that will help make space colonization feasible. Without sex in space, there’s no hope for humans to survive, much less thrive, as a multi-planetary species. And while reproductive technology might be able to create a future where conception can occur without a sperm meeting an egg, sex makes us essentially human. To send Earthlings off to space without the possibility of engaging in the most human of acts is a huge ask, and one that will surely alter the course of evolution.

All in all, sex in space — whether it be in a controlled gravitational environment or one that’s leaking space air like Passengers — isn’t exactly hot. But futurists know that humanity’s going to make inroads into living among the stars and on other planets very soon, and sex will help ensure the future of the human species. And the science of sex in space might make it appear to be the least fun thing ever, but former NASA physician Jim Logan offered some hope in the form of carefully choreographed, cinematic sex.

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“It’s a pretty messy environment, when you think about it,” he told the Space Frontier Foundation’s NewSpace 2006 Conference. “And for every action there is an equal and opposite reaction. However… I can well imagine how compelling, inspiring, and quite frankly stimulating choreographed sex in zero-G might be in the hands of a skilled and talented cinematographer with appropriate lighting and music.”

Photos via Vanna Bonta, Sony/NASA/TriStar Pictures/James Grebey