American astronaut Ed Lu, Russian cosmonaut Yuri Malenchenko and the station's eight-day visitor, Spanish astronaut Pedro Duque, were scheduled to thump down in the barren and sparsely-populated north-central Kazakh steppe, 35 kilometers (22 miles) south of Arkalyk, at 05:41 Moscow time (0241 GMT) Tuesday.
Lu and Malenchenko were to arrive home in the same Russian Soyuz that propelled them into orbit nearly six months ago, demonstrating NASA's full dependence on Russia -- from launch to landing -- to keep its astronauts flying.
"This essentially completes a cycle of Russia being able to launch our crews to continue a manned presence on the space station," said NASA spokesman Rob Navias in the Kazakh capital, Astana.
Russian aerospace engineers said there was only a slim chance that this crew would suffer from the same computer malfunction that sent the station's previous inhabitants on such a steep trajectory home that their tongues rolled back in their mouths. The May landing was so far off-target that more than two gut-wrenching hours passed before rescuers knew the men were safe.
"There is very little probability of another ballistic landing," said Gen. Vladimir Popov, who heads the team responsible for Russia's space search and rescue operations. "But we must be prepared for any variant, and we are."
Kazakhstan, a former Soviet republic, agreed to a Russian request to close off a wider swathe of airspace than previously, said Mikhail Zotov, the search and rescue spokesman. Rescue crews will fly from three locations instead of one to cover all the possible landing spots, he said.
Thirteen helicopters, four planes and numerous off-terrain vehicles will take part in the operation. The search teams will include flight surgeons from NASA and the European Space Agency.
Additionally, this Soyuz is equipped with satellite phones and a global positioning satellite system _ courtesy of NASA _ so if the crew does land off-course and communications systems are damaged as happened in May, they'll still be able to determine and phone in their location.
The May landing rattled Russian space officials and NASA, which had sent their top administrators to Mission Control outside of Moscow to monitor the maiden return of the new model Soyuz with its first-ever U.S. and Russian crew. It came just three months after Columbia broke apart during re-entry, killing all seven astronauts.
A Russian commission concluded that the Soyuz's guidance system malfunctioned, causing the capsule to revert to a ballistic landing. The ship plunged at a steeper trajectory to reduce flight time and increase atmospheric resistance, thus slowing its speed, but the descent also subjected the crew to roughly eight times the force of gravity.
Russian aerospace engineers made minor adjustments to the Soyuz that blasted off Oct. 18, but the Soyuz coming home Tuesday was already docked in space so no changes were made.
"This Soyuz is still technically susceptible to the same type of problem but the Russians believe they understand it well enough and they've trained the crew ... so they can possibly do something manually to override the computer," Navias said.
Hours before departure, Lu, Malenchenko and Duque were to squeeze into their bulky, airtight spacesuits and bid farewell to the station's new crew, American Michael Foale and Russian Alexander Kaleri. Once the Soyuz starts re-entry, it's a one-way ride that can't be stopped.
The Soyuz resembles a fireball as it plunges through the Earth's atmosphere, parts of the ship melting away to leave only the descent module intact.
Malenchenko returns to Earth a married man, having married Texas resident Ekaterina Dmitriev by proxy while in space. The new bride will be waiting at a military air base near Star City outside Moscow, where the cosmonauts will be flown later Tuesday.
Also waiting will be NASA scientists, eager for water samples and, if there is room, a canister of air from the space station. Monitoring equipment onboard has broken down, leading some NASA officials to reportedly express concerns about keeping crews up there. NASA, along with astronaut Foale, have dismissed the fears, saying there are no indications of a health risk.
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