One of the most delicate and secret topics of the space age is beginning to go public, at least a bit: sex in space.
Astronauts duck questions about it, and officials of the National Aeronautics and Space Administration often wince at its mention, fearful of appearing to condone eroticism in the heavens at public expense.
For years they have avoided the topic in public, even while struggling with it in private.
Though experts say intercourse itself has yet to occur on a spaceship of any kind, rumors abound.
And despite the space agency's unease and reticence, the topic of celestial intimacy is starting to emerge from private meetings because of a number of major plans and preparations it has been undertaking in recent years.
The most immediate is the world's first space mission by a husband and wife, who are scheduled to fly aboard the shuttle in September.
That plan has already prompted hundreds of calls about the sexuality issue to the space agency from news organizations around the world, and more are expected as the flight draws nearer.
More generally, the agency is moving toward an era of long-duration missions with crews of men and women. Space Station Freedom is to be completed this decade, putting four astronauts into orbit for possibly as long as six months at a stretch.
And early next century, the agency wants to send astronauts to explore Mars, a voyage that could take two or more years to complete.
In this environment, experts say, romantic couplings are all but inevitable. As a result, they say, a number of serious issues of science, engineering, medicine and psychology need to be openly discussed and the results incorporated into NASA's planning.
"It's foolish and perhaps dangerous to pretend that a long-duration space mission will differ from any office where you have men and women working together," said Dr. Patricia A. Santy, a psychiatrist at the University of Texas in Galveston and a former flight surgeon at the agency. "Sex is a normal part of human behavior. It happens in offices. It happens in the Antarctic. It happens wherever you have males and females together."
She added that physical intimacy in the weightlessness of space would probably be enjoyable, perhaps more so than on Earth. "You're going to have lots of freedom of movement," she noted.
Dr. Lynn M. Wiley, a reproductive biologist at the University of California at Davis who sits on several advisory panels at the agency, said NASA was beginning to discuss the issue more openly in its internal deliberations and that the agency was beginning to reflect on its implications for mission planning.
"NASA until very recently played ostrich," she said. "Any time you said "reproduction' or "sex,' the head went into the sand. But there are definite signs that things are opening up. These are big issues. I'm relieved to see that people are starting to talk about them."
The discussion is not likely to be overly public, however, because the agency is loath to sully its reputation for charting new worlds with anything that could be construed as exploring new realms of sensuality.
Until the onset of planning for long-duration missions, the topic of intimacy between astronauts of opposite sexes was generally moot. The space capsules of the Apollo era were little more than big cans and were inhabited only by men.
The space shuttle, first flown in 1981, is far more spacious, yet its crew compartment has only about 2,300 cubic feet of space _ less than that of a good-sized living room.
"It's like camping out with your seven best friends in a tent _ and you can't go outside," said Barbara Schwartz, a spokeswoman at NASA's Johnson Space Center in Houston. "The living quarters are close. There's no privacy."
So far, 124 men and 14 women have flown aboard shuttles, with no serious public interest in the sexuality issue. But that began to change last year, when the agency announced that Air Force Lt. Col. Mark C. Lee, 38, and Dr. N. Jan Davis, 37, a mechanical engineer, had married and would fly together this September.
Schwartz said the planned flight of the married couple did not represent a trial run of space sexuality or a reversal of the agency's long-standing policy to fly astronaut spouses on separate missions.
In fact, she said, the couple had been assigned to the mission well before they were married. NASA officials waived their policy regarding spouses because it would have been too disruptive to reassign the pair.
Though romantic encounters will be difficult to arrange on the shuttle, the possibilities for seclusion and intimacy will increase markedly with the advent of the Space Station Freedom. If the shuttle is a tent, the station is a hotel.
The $30-billion, 350-foot-long outpost is meant to be lofted and assembled beginning in 1996. It is to have 23,000 cubic feet of inhabitable space, with much attention being given to making crew quarters as comfortable as possible to help offset possible depression and health risks that can arise from prolonged periods of confinement.
Beyond the station, in the agency's plans and those of the Bush administration lie proposals to send astronauts on long-duration missions to the Moon and Mars, and these are flights in which long isolation and monotony would greatly increase psychological pressures on astronauts.
Wiley of the University of California said the topic of sexuality on a Mars mission was discussed at an advisory panel meeting at agency headquarters in November.
Among the topics, she said, was the question of contraception and how little was known of its chemistry, biology and general effectiveness in the weightlessness of space.
"You're probably going to have to design new types of contraception that are foolproof," she said. "If you have a pregnancy, it could endanger a Mars mission. It's a big deal. But they clearly hadn't thought ahead to those kinds of issues."