There is no room for romance on board the cosy confines of the International Space Station, a NASA space shuttle commander said today when asked what would happen if astronauts had sex in space.

"We are a group of professionals," said Space Shuttle Discovery commander Alan Poindexter during a visit to Tokyo, after a reporter asked about the consequences if astronauts boldly went where probably no others have been.

"We treat each other with respect and we have a great working relationship. Personal relationships are not ... an issue," said a serious-faced Poindexter. "We don't have them and we won't."

Poindexter and his six crew members, including the first Japanese mother in space Naoko Yamazaki, were in Tokyo to talk about their two-week resupply mission to the International Space Station.

The April voyage broke new ground by putting four women in orbit for the first time, with three female crew joining one woman already on the station.

Sex in space may appear out of bounds, but astronauts have been known to succumb to earthly passions.

In 2007 former NASA astronaut Lisa Marie Nowak allegedly wore adult diapers when driving hundreds of miles across the United States without bathroom breaks to confront a suspected rival in a romance with a fellow astronaut.