As space agencies consider sending crews on long missions to the Moon or Mars, they have to face up to the social aspects of such trips. Some aspects, such as personal hygiene or social rituals, can be adapted pretty easily. One of those aspects is almost certainly going to be sex. Whether people are procreating or not, it's generally accepted that somebody, somewhere, is going to have sex in space.

In fact, the most questions fielded by astronauts focus on the more personal aspects of space exploration. Usually, they aren't asked outright about sex, although they do get the "how do you go to the bathroom in space?" question a lot. But, people want to know: has anybody "hooked up" in low-gravity conditions? Lots of speculation exists about whether or not two people have had sex in space, but so far as anyone knows, no one has gotten away with it. Yet (or, if they have, nobody's talking.) It's certainly not part of their astronaut training (or if it is, it's a well-kept secret). However, as humans venture out on those months- and years-long missions, sex in space is going to happen. Humans are human after all, even "out there."

Is Sex in Space Possible?

From a physics standpoint, sex in space looks as though it might be difficult to achieve. The microgravity environment that astronauts experience on the International Space Station, for example, causes all kinds of problems for living and working in space. Eating, sleeping, and exercising are all more complicated acts in space than they are on Earth, and sex would be no different.

For example, look at the regulation of blood flow, important for both sexes, but particularly for men. Low gravity means that blood doesn't flow throughout the body the same way it does as on Earth. It will be much more difficult (and perhaps even impossible) for a male to achieve an erection. Without that, sexual intercourse is going to be difficult—but of course, many other forms of sexual activity are still possible.

The second problem is sweat. When astronauts exercise in space, their sweat tends to build up in layers around their bodies, making them sticky and wet all over. This would give the word "steamy" a whole new meaning and may make intimate moments slippery and uncomfortable.

Since blood doesn't flow the same way in microgravity as it does on Earth, it is not a reach to assume that the flow of other vital fluids would be inhibited as well. However, this may only be important if the goal is to make a baby.

The third and most interesting problem relates to the motions involved in sexual activity. In a microgravity environment, even a small push or pull motion sends an object hurtling across the craft. This makes any physical interaction quite difficult, not just intimate ones.

But there is a fix for these difficulties—the same fix used to overcome the difficulty of exercise in space. When they exercise, astronauts strap themselves into harnesses and fasten themselves to the spacecraft walls. This would presumably allow couples to engage in sexual activity as long as everything else is working smoothly (see discussion of blood flow regulation above.)

Astronaut Sunita Williams exercising aboard the International Space Station. NASA

Has Sex in Space Happened?

For many years, rumors claimed NASA sanctioned sexual experiments in space. These stories have been categorically denied by the space agency and the astronauts. If other space agencies have done this, they've been keeping that information a closely guarded secret. One thing's for sure: even if two (or more) people managed to have intercourse in space, someone would know. Unless they unhooked all their heart monitors and found a truly private place, people at mission control would see an uptick in heart rates and respiration. Plus, space travel takes place in close quarters and is anything but private. And astronauts work on very tight schedules and have few free moments to squeeze in unauthorized activities.

Will Sex in Space Ever Happen?

Of course, it will. People living and working in space for long periods of time will certainly hook up. Space sex is an inevitable outcome of longer-term exploratory missions. It's a staple of science fiction writers, and they have often looked at human activity in space as part of their stories. No one expects crew members on a long-term voyage to abstain from all sexual activity, so it would be wise for mission planners to come up with sensible guidelines.

A related issue is the possibility of pregnancy in space, which is much more complicated. As humans pursue longer trips to the Moon and planets, future generations will also wrestle with issues related to pregnancy and childbirth. It's a difficult thing to "test out" in advance, since experimentation on human beings isn't considered ethical. But, someday, a child will be born on orbit, or on the Moon, or in a habitat on Mars. Its health and growth will be of immense interest to people back on Earth.

Edited by Carolyn Collins Petersen.