The idea of human sexual activity in the weightlessness or extreme environments of outer space – sex in space – presents difficulties for the performance of most sexual activities due to Newton's third law. According to the law, if the couple remain attached, their movements will counter each other. Consequently, their actions will not change their velocity unless they are affected by another, unattached, object. Some difficulty could occur due to drifting into other objects. If the couple have a combined velocity relative to other objects, collisions could occur. There have been suggestions that conception and pregnancy in off-Earth environments could be an issue.
As of 2009[update], with NASA planning long-term missions for lunar settlements with goals to explore and colonize space, the topic has taken a respected place in life sciences. Scientist Stephen Hawking publicly concluded in 2006 that possibly human survival itself will depend on successfully contending with the extreme environments of space.
Numerous physiological changes have been noted during spaceflight, many of which may affect sex and procreation. Such effects would be a result of factors including gravity changes, radiation, noise, vibration, isolation, disrupted circadian rhythms, stress, or a combination of these factors.
The primary issue to be considered in off-Earth reproduction is the lack of gravitational acceleration. Life on Earth, and thus the reproductive and ontogenetic processes of all extant species and their ancestors, evolved under the constant influence of the Earth's 1g gravitational field. It is imperative to study how space environment affects critical phases of mammalian reproduction and development as well as events surrounding fertilization, embryogenesis, pregnancy, birth, postnatal maturation, and parental care. Gravity affects all aspects of vertebrate development, including cell structure and function, organ system development, and even behavior. As gravity regulates mammalian gene expression, there are significant implications for successful procreation in an extraterrestrial environment.
Studies conducted on reproduction of mammals in microgravity include experiments with rats. Although the fetus developed properly once exposed to normal gravity, the rats that were raised in microgravity lacked the ability to right themselves. Another study examined mouse embryo fertilization in microgravity. Although both groups resulted in healthy mice once implanted at normal gravity, the authors noted that the fertilization rate was lower for the embryos fertilized in microgravity than for those in normal gravity. Currently no mice or rats have developed while in microgravity throughout the entire developmental cycle.
The 2suit (alternately 2-Suit or twosuit) is a garment designed to facilitate low-effort sex in the weightless environments such as outer space, or on planets with low gravity. The flight garment, invented by American novelist Vanna Bonta, was one of the subjects of Sex in Space, a 2008 History Channel television documentary about the biological and emotional implications of human migration and reproduction beyond Earth. The 2suit sparked international discussions in news and political debates as a metaphor for human colonization of space.
The psychosocial implications of in-flight sex and reproduction are at least as problematic as the related physiological challenges. For the foreseeable future, space crews will be relatively small in number. If pairing off occurs within the crew, it can have ramifications on the crew's working relationships, and therefore, on mission success and crew operations.[page needed] Behavioral health, close proximity, compatibility and coupling will all be factors determining selection of crews for long term and off-planet missions.
Lyubov Serova, a specialist with the Russian Institute for Biomedical Problems (IBMP) in the field of procreation in the conditions of spaceflight, says: "After a period of adaptation for weightlessness, people will not need any special devices, like elastic belts or inflatable tubes to have sex in space," and "We study the impact of weightlessness on the reproductive function of male and female bodies by using mammals as test subjects, particularly rats." The overall conclusion is that sex in space is not a physical problem, and that individuals motivated enough to embark on space flight would not be distracted by the need for sex.
In February 2013, Dennis Tito's Inspiration Mars Foundation announced that they were going to send a two-person crew – a man and a woman – on a 501-day, free-return, flyby mission to Mars and back. Jane Poynter stressed the importance of the pre-existing stable emotional bond between the members of the couple. She cited her own experience as being a Biosphere 2 crew member together with her husband Taber MacCallum, who is the chief technology officer of Inspiration Mars.
In June 2015, Pornhub announced its plans to make the first pornographic film in space. It launched a crowdfunding campaign to fund the effort, dubbed Sexploration, with the goal of raising $3.4 million in 60 days. The campaign only received pledges for $236 086. If funded, the film would have been slated for a 2016 release, following six months of training for the two performers and six-person crew. Though it claimed to be in talks with multiple private spaceflight carriers, the company declined to name names "for fear that that would risk unnecessary fallout" from the carriers. A Space.com article about the campaign mentioned that in 2008, Virgin Galactic received and rejected a $1 million offer from an undisclosed party to shoot a sex film on board SpaceShipTwo.
Short of actual space, the adult entertainment production company Private Media Group has filmed a movie called The Uranus Experiment: Part Two where an actual zero-gravity intercourse scene was accomplished by flying an airplane to an altitude of 11,000 feet (3350 meters) and then doing a steep dive. The filming process was particularly difficult from a technical and logistical standpoint. Budget constraints allowed for only one 20-second shot, featuring the actors Sylvia Saint and Nick Lang. Berth Milton, Jr, president and CEO of Private Media Group, says "You would not want to be afraid of flying, that's for sure!"
Science fiction writer and futurist Isaac Asimov, in a 1973 article "Sex in a Spaceship", conjectured what sex would be like in the weightless environment of space, anticipating some of the benefits of engaging in sex in an environment of microgravity.
When Apollo 11 astronaut Michael Collins published his autobiography Carrying the Fire in 1974, a contemporary Time magazine quoted the following passage: "Imagine a spacecraft of the future, with a crew of a thousand ladies, off for Alpha Centauri, with 2,000 breasts bobbing beautifully and quivering delightfully in response to every weightless movement ... and I am the commander of the craft, and it is Saturday morning and time for inspection, naturally." Arthur C. Clarke in turn was quick to point out in a letter to the editor that he had beaten Collins to addressing the matter in the novel Rendezvous with Rama (1973).
On July 23, 2006, a Sex in Space panel was held at the Space Frontier Foundation's annual conference. Speakers were science journalist-author Laura Woodmansee, who presented her book Sex in Space; Jim Logan, the first graduate of a new aerospace medicine residency program to be hired by NASA's Johnson Space Center in Houston; and Vanna Bonta, an American poet, novelist, and actress who had recently flown in zero gravity and had agreed to an interview for Woodmansee's book. The speakers made presentations that explored "the biological, emotional, and ... physical issues that will confront people moving [off Earth] into the space environment." NBC science journalist Alan Boyle reported on the panel, opening a world discussion of a topic previously considered taboo.
"Sex in Space" was the title of an episode of the History Channel documentary television series The Universe in 2008. The globally distributed show was dubbed into foreign languages, opening worldwide discussion about what had previously been avoided as a taboo subject. Sex in space became a topic of discussion for the long-term survival of the human species, colonization of other planets, inspired songs, and humanized reasons for space exploration.
The idea of sex in space appears frequently in science fiction. Among films that include space-sex themes are Moonraker, Moving Violations, Supernova and Cube 2: Hypercube. In the novelization of Alien, Parker tells Brett about an episode of zero-G sex that went wrong. A more recent and perhaps more realistic description of the mechanics of low-gravity intercourse is presented in "Sex in Space: The Video", a short story contained in Susie Bright's The Best American Erotica 2004. The story uses cheating astronauts to describe techniques humans might use to copulate in space without special apparatus. The difficulties microgravity poses for human intimacy were also discussed in an anonymous fictional "NASA Document 12-571-3570" in 1989, where the use of an elastic belt and an inflatable tunnel were proposed as solutions to these problems. A mission patch and other documents were determined to be hoaxes.