CAPE CANAVERAL, Fla. -- Maverick millionaire Dennis Tito floated toward the midway point of an International Space Station vacation Thursday, but his Soyuz taxi flight is much more than a $20 million orbital sightseeing trip.
In fact, the wealthy California space tourist wouldnt be on board the frontier complex if his Soyuz crewmates didnt have a time-critical job: maintaining a safe way for the stations resident crew to abandon ship in an emergency.
Heres the situation:
Parked at the outpost since last November, the stations first Russian Soyuz rescue craft is rapidly nearing the end of its service life.
Toxic rocket fuel is slowly degrading within an engine system, diminishing its ability to safely propel station astronauts and cosmonauts on a hasty return to Earth.
Whats more, the highly corrosive propellants are gradually eating away at engine valves, seals and fuel lines, making replacement of the craft a crucial necessity.
"It fundamentally gets down to when the warranty expires on a Soyuz spacecraft," said NASA lead station flight director John Curry. "We needed to have a taxi crew mission where we essentially brought up a change-out vehicle."
Launched Oct. 31, 2000, from Baikonur Cosmodrome in Kazakhstan, the stations original Soyuz spacecraft ferried its first full-time tenants to what long had been a vacant complex.
Designated Soyuz TM-31, the ship served as an emergency lifeboat for the so-called Expedition One crew, which included U.S. astronaut Bill Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev.
The three of them returned to Earth aboard shuttle Discovery March 21, having been replaced by the Expedition Two crew, which includes Russian cosmonaut Yuri Usachev and American flight engineers Susan Helms and Jim Voss.
The original Soyuz, meanwhile, remains in place as a station lifeboat. Service time to date: 184 days. Its warranty: 200 days.
Advanced versions of spacecraft that first debuted in 1967, Soyuz taxis are equipped with a main engine and four steering thrusters powered by caustic propellants that gradually lose their propulsive punch.
"Its very nasty, toxic stuff, so its not good for the metals, the seals and the materials within the engines," said Dennis Newkirk, a Russian space program expert and author of the highly acclaimed Almanac of Soviet Manned Space Flight.
"Once you expose pipes, valves and seals to the propellants, they have a limited lifetime before they develop leaks."
Any propellant leak is potentially explosive, and any leak could cause engine or thruster problems. Consequently, the three-seat Soyuz spacecraft must be swapped out at the station every six months.
Only a commander and a flight engineer, however, are required to ferry a fresh Soyuz up to the outpost and then return to Earth in the craft being replaced. And that essentially leaves a custom-made couch open for another cosmonaut or a fare-paying passenger.
The first of what will be semi-annual Soyuz taxi flights to the international station blasted off from Baikonur last Saturday.
On board the Soyuz TM-32 ship: commander Talgat Musabayev, flight engineer Yuri Baturin and Tito, the "cosmonaut-tourist" who is paying the Russians a fee that works out to about $2.5 million a day.
The three-man crew arrived at the outpost early Monday and Tito, 60, has been spending his days listening to opera music, taking photographs and watching the blue orb Earth spin below.
Musabayev and Baturin, meanwhile, have more critical things to do: The veteran cosmonauts are conducting key check-out tests on the stations original Soyuz, making certain it's safe to fly back to Earth this weekend.
With Tito in tow, the taxi flight commander and his flight engineer are scheduled to depart the station at 10:19 p.m. EDT Saturday (02:19 GMT Sunday). A crucial engine firing will follow two hours later, leading to a 2 a.m. EDT (06:00 GMT) landing on the arid steppes of central Asia.
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