Shannon Walker, Fyodor Yurchikhin, Doug Wheelock, left to right, post before their Soyuz capsule this week. Photo Credit: NASA/Victor Zelentsov

A U.S. and Russian crew will lift off for the International Space Station aboard a Soyuz rocket Tuesday night, initiating a six-month journey to finish the outfitting of the newest station module, watch over dozens of science experiments and await the next to last NASA space shuttle mission.

The spacecraft carrying Fyodor Yurchikhin, the Soyuz commander, as well as NASA astronauts Doug Wheelock and Shannon Walker, is scheduled for launching from the Baikonur  Cosmodrome in Kazakhstan at 5:35 p.m. EDT.

They’ll dock with the orbiting science laboratory on Thursday at 6:25 p.m., EDT. The three newcomers will be greeted by Russian Alexander Skvortsov, the station’s commander, cosmonaut Mikhail Kornienko and NASA astronaut Tracy Caldwell-Dyson. The first members of the station’s Expedition 24 crew arrived in early April, to begin their own six-month tour of duty.

Thursday’s linkup will mark the first time the station has been occupied by three Americans and three Russians at the same time.

Early on, they will set their sights on upgrades to the station’s Russian segment, including the Rassvet mini research and docking module that was delivered and installed by the crew of the shuttle Atlantis in May.

During the first of two July spacewalks, Wheelock and Caldwell-Dyson will attach a U.S. power and data grapple fixture to the station’s Zarya module. The fixture will serve as the only anchor point for Canada’s 58-foot-long robot arm on the Russian side of the outpost.

During a second spacewalk, Yurchikhin and Kornienko will equip Rassvet with power and data cables and other electronics that will permit automated dockings with the new module by Soyuz and Progress crew and cargo transports.

The station’s six astronauts will supervise or serve as subjects in 130 science investigations. Some of the experiments focus on human adaptation to spaceflight, others on fundamental biology, biotechnology, physics, materials sciences, technology development, Earth observations and space science.

“We are test subjects to get a deeper understanding of how bone loss and muscle loss mechanisms  work,” said Walker.

 During extended periods of weightlessness, the bones and muscles of astronauts weaken, even with strenuous daily exercise. Researchers are hopeful that by monitoring the metabolism, diet and activities of the station’s crew they can develop countermeasures that will permit future explorers to travel to more distant destinations.

NASA plans two more missions before retiring its shuttle fleet. Currently planned for mid-September and late November, both flights are likely to be re-scheduled to accommodate changes to the primary payloads. The launching of Discovery with a  storage module is likely to fall within the period that Yurchikhin, Wheelock and Walker are aboard the station.

Yurchikhin, 51, and Wheelock, 50, are veterans of previous spaceflights.

Walker, a 45-year-old space physicist, is flying for the first time.

A private pilot, she is also trained to pilot the Soyuz as a backup to Yurchikhin.

Late last year, Walker agreed to carry a watch worn by Amelia Earhart, who pioneered flight by women in the 1930s. Earhart and her navigator disappeared in 1937 over the northern Pacific, while she was attempting to become the first woman to fly around the world.

Her fate remains a mystery.

The timepiece, which was worn by Earhart during a solo crossing of the Atlantic, was presented to Walker by the Ninety Nines Organization of Women Pilots. The organization includes more than 5,500 members from 35 countries, including Walker.

Once Walker returns from her mission, the watch will be placed on public display at the Ninety-Nines Museum of Women Pilots in Oklahoma City.