It is only the second time a U.S. astronaut is returning in a Russian craft and landing on foreign soil. Space officials are hoping for less drama Tuesday than the nerve-racking landing in May, when a computer error sent the Soyuz's American and Russian crew on a wild descent that was 250 miles off-course.
American astronaut Ed Lu, Russian cosmonaut Yuri Malenchenko and the station's eight-day visitor, Spanish astronaut Pedro Duque, are scheduled to thump down in the barren and sparsely populated north-central Kazakh steppe at 5:41 a.m. Tuesday (9:41 p.m. EST Monday).
Lu and Malenchenko are 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 this crew would suffer 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.
The rocky landing in May came just three months after the space shuttle 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 steep landing that subjected the crew to roughly eight times the force of gravity.
"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.
"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 swath 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 possible landing spots, he said.
Thirteen helicopters, four planes and numerous off-terrain vehicles will participate. 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 should still be able to pinpoint and phone in their location.
Lu and Malenchenko are being replaced aboard the ISS by American Michael Foale and Russia's Alexander Kaleri, who arrived at the floating outpost last Monday.
In addition to the worries about the Soyuz that will bring Lu and Malenchenko back to Earth, safety concerns led to objections to sending Foale up to the ISS.
The Washington Post reported Thursday that two officials overseeing health and environmental conditions on the space station didn't sign off on the launch, instead signing a dissent that warned about "the continued degradation" of the environmental monitoring and health maintenance systems and exercise equipment vital to the astronauts' well being.
An agency spokesman says NASA concluded that sending a fresh crew to the ISS was "well within the parameters of safety" despite warnings about unreliable medical equipment and air and water monitoring devices.
Robert Mirelson said there was a full discussion by mid- and management-level engineers before the decision was made to send the new crew to the orbiting lab.
That decision was preceded by several pre-launch meetings in Moscow, Washington and the Johnson Space Center involving NASA engineers and experts from the International Space Station partner nations, he said.
The officials considered the concerns expressed by engineers about the air cleaning equipment, water supplies and the "quality of life equipment," which would include medical supplies, and concluded the launch would be safe.
NASA Administrator Sean O'Keefe told the Post that, as he understood it, there was no immediate hazard to the crew but that conditions could deteriorate in the next six months and force the crew to abandon ship.
Since the February shuttle disaster, NASA critics have questioned the value of the work done aboard the space station.
According to the space agency, Foale and Valeri will receive several shipments of supplies, upgrade the station's software, test the robotic arm and possibly conduct a spacewalk to prepare part of the space station for a delivery of supplies next year.