CAPE CANAVERAL, Fla. - NASA's next mission to the International Space Station might be postponed until May to avoid having a visiting space shuttle, a Russian Soyuz taxi and 13 space travelers at the outpost at the same time.
As it stands, shuttle Endeavour and seven astronauts are scheduled to launch April 19 on an 11-day mission to deliver a crucial Canadian construction crane to the growing frontier outpost.
A three-man crew including U.S. millionaire Dennis Tito, meanwhile, is scheduled to launch April 28 on a 10-day mission to deliver a fresh Russian Soyuz lifeboat to the station, which now is occupied by Russian commander Yuri Usachev and two American flight engineers.
Senior NASA managers, however, are concerned that launching both missions as planned could result in an unnecessary traffic jam at the station, as well as an overlap of critical operations at the outpost.
What's more, the possibility of 13 people being on the outpost at the same time could tax crucial station life support systems such as oxygen generation machines and carbon dioxide scrubbers.
"They're taking a look at the level of air traffic that's going to be around the station during that multi-week period," said Rob Navias, a spokesman for NASA's Johnson Space Center in Houston, Texas.
A firm decision on the shuttle launch date will be made at a traditional flight readiness review that will be held here at Kennedy Space Center Thursday.One option under consideration: Moving the shuttle launch to May 6 -- the day that the Soyuz taxi crew would be departing the station if that mission gets under way as scheduled on April 28.
That crew includes two Russian cosmonauts -- Talgat Musabayev and Yuri Baturin - and Tito, a wealthy American investment manager who paid the Russian Space Agency an estimated $12 million to $20 million for the round trip to the outpost.
NASA officials have openly opposed the idea of flying Tito to the station, but their Russian counterparts have made clear their intent to launch the self-described "space tourist" in any case.
Musabayev and his crew are scheduled return to Earth in a Soyuz spacecraft that has been parked at the outpost since last November.
That Soyuz is nearing the end of a six-month orbital design life and its replacement is considered a higher priority than the construction work that will be carried out by the visiting Endeavour crew.
"They're anxious to swap out the Soyuz because they have a certain [design] life," Endeavour commander Kent Rominger told reporters here last week. "And in looking at it, I think something will give because it's probably not wise at this point to have a [new] Soyuz come aboard [the station] while we're still there."
One of the concerns, Rominger said, is air traffic control at the station. More precisely, a Soyuz approaching the station would come very close to a shuttle docked at the outpost.
"I think you know it would pass within 20 or 30 feet (6 or 9 meters) of the shuttle tail coming up to a docking port," Rominger said, adding that NASA routinely avoided the same situation during nine shuttle missions to Russia's Mir space station between 1995 and 1998.
"During the Mir time, I think it was looked at in NASA and we never got comfortable with it."
Another potential problem: Temporarily mounting a shuttle-borne Italian moving van - known as a multi-purpose logistics module, or MPLM - on the side of the station so that several tons of supplies and equipment can be unloaded from it.
"We can't actually do our MPLM installation or removal with the Soyuz there," Endeavour mission specialist Scott Parazynski said. "The clearances are within inches, I believe."
Rominger and his crew - which includes a Russian cosmonaut and astronauts from Canada and Italy - will deliver a Canadian-built robot arm that will play a critical role in almost all future assembly work at the international station.
Considered the centerpiece of the Canadian Space Agency's contribution to the station project, the 57-foot (17-meter) construction crane will be capable of "inch-worming" from work site to work site outside the station, crawling to places the shuttle's fixed robot arm cannot reach.
A move to a May 6 launch date, meanwhile, would result in a shuttle landing here on May 17.
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