Cosmic coitus. NASA denies it exists, Russians are rumored to be its pioneers, and a little-known French astronomer's new book on the subject has everyone involved a little hot under the collar.

When Pierre Kohler last week released "The Last Mission: Mir, the Human Adventure" - which alleges that U.S. and Russian astronauts have had sex in space, and cites a "secret" NASA publication documenting the 10 best zero-gravity lovemaking positions - the American space agency was quick to say the work was a fraud and that astronauts and sex simply don't mix.

"We are not, have not and do not plan to conduct any sex experiments," NASA spokesman Ed Camption told Reuters last Wednesday.

The Americans' omission is somewhat surprising in light of the extensive medical research being done in preparation for the International Space Station flights, scheduled to begin in 2012, which will launch men and women - and potentially married couples - into states of weightlessness for nearly three years at a time.

But for a human activity that some consider as essential as eating and sleeping, sex has gotten surprisingly short shrift among researchers exploring the physical and psychological effects of long-term space travel.

"The issue of sex in space is a serious one," Kohler writes. "Scientists need to know how far sexual relations are possible without gravity."

Kohler's allegations that galactic intimacy has already been achieved - albeit between guinea pigs - have been hotly denied by NASA but eagerly discussed by analysts and the media.

According to the Frenchman, 20 coital positions were tested by computer simulation to obtain the best 10. "Two guinea pigs then tested them in real zero-gravity conditions. The results were videotaped but are considered so sensitive that even NASA was only given a censored version," he writes.

Six of the experiments apparently involved artificial aids such as elastic harnesses and inflatable tunnels. The others apparently relied on muscle strength to overcome the effects of zero gravity. The guinea pigs were graded for tenderness, endurance and satisfaction, he wrote.

"One of the principal findings was that the classic so-called missionary position, which is so easy on earth when gravity pushes one downward, is simply not possible," Kohler said.

Kohler's research leaves a bit to be desired. The document around which he builds his case, for example, was located on the Internet and is widely believed to be a hoax designed to poke fun at NASA's inability to admit to the existence of sexual relations.

The document, full of typographic errors and overblown scientific descriptions of lovemaking, rates experiments as "satisfactory" or "frustrating." It notes that "entry was difficult" in several of the positions and that the elastic-belt options could easily be associated with bondage, a subject that potential interplanetary lovebirds might not find "particularly appealing."

Finally, the document ends with NASA allegedly recommending that "non-procreative marital relations" would prove the most satisfactory.

NASA has said the story and documents are false. "The story's not true. The document cited is fraudulent," Kirsten Willions, a spokeswoman at NASA Washington headquarters told Reuters.

The agency has also noted that the document number cited in Kohler's book does not even correspond to the numbering system used by the agency to identify its publications.

"It's one of those urban myth things," NASA spokesman John Ira Petty said on MSNBC News last week.

Another one of those "urban myth things" concerns the Russians' alleged achievements in space sex. Although the Russian Aviation Space Academy press center has repeatedly denied it, rumors continue to spread that Russians were the first to practice interstellar lovemaking.

Most fingers point to cosmonaut Svetlana Savitskaya, who is rumored to have "docked" with an colleague who was identified aboard the Salyut-7 space station in 1982.

There were no official records of the incident and no independent confirmation. The Moscow Times was unable to reach Savitskaya by telephone.

When asked whether she was aware of any sexual activities on her missions, cosmonaut Yelena Kondakova said simply that she "doesn't understand what all the talk is about."

The last time NASA was forced to address the matter was in 1992, when married partners Mark Lee and Jan Davis flew together on Endeavor Space Shuttle mission STS-47. Officials at NASA refused to comment on whether any "procreative marital relations" took place during the 8-day mission.

In 1991, British commercial astronaut Helen Sharman told reporters that she had received "fantastical experience" on board the Russian Mir station with Russian cosmonauts. On a videotaped segment of the mission shown on Russian national television, the 28-year-old cosmonaut, dressed in a pink evening gown, gave viewers reason to believe she was about to embark on a brave international mission in orbit - but it was only a hint.

Not all NASA officials recoil at the mention of sex.

Former astronaut Michael Collins, in his book "Liftoff," said, "I don't think any astronauts have yet been privileged to sample the ultimate use of weightlessness, but having no gravity to crush bodies together offers exquisite possibilities."

These "new sensations may someday allow 'a space Kamasutra' to be written by a 'lucky couple' living in the future," he added.

With the scheduled maiden voyage of the International Space Station just 12 years away, NASA and other aeronautic organizations may have to face up to the reality of sexual desire sooner than they think.

"NASA's stated position of not being interested in the private lives of its employees may seem satisfying to [American] culture, which values privacy ... but the inherent dangers demand some sort of framework to guide the process of sexual relations in space," writes John Sturgeon a member of Space.Edu, an Internet space studies program partially funded by NASA.

"Ultimately, NASA will need to give up its puritanical views and begin studying sexual behavior and reproduction."