By Irene Klotz
CAPE CANAVERAL, Fla. (Reuters) - A NASA astronaut and two Russian cosmonauts were preparing to head for the International Space Station in a Russian Soyuz rocket on Friday as replacements for a crew that ended a year-long flight earlier this month.
U.S. astronaut Jeff Williams and cosmonauts Oleg Skripochka and Alexey Ovchinin are scheduled to blast off from the Baikonur Cosmodrome in Kazakhstan at 5:26 p.m. EDT (2126 GMT). They are due to arrive at the station about six hours later.
The men will spend about six months living and working aboard the $100 billion research laboratory that flies about 250 miles (400 km) above Earth.
NASA and Russia have not yet assigned crews for additional year-long missions following the March 1 return of astronaut Scott Kelly and cosmonaut Mikhail Kornienko from a 340-day spaceflight.
Williams, 58, who will be serving aboard the station for a third time, is expected to return to Earth with a career total of 534 days in space. This would surpass the current U.S. record, which is Kelly’s cumulative 520 days.
The world record belongs to Russian cosmonaut Gennady Padalka, who returned from his fifth flight last September and has spent a total of 879 days in space.
Scientists are interested in seeing how the human body fares during longer stays in space as the United States and other countries being planning for multi-year missions to Mars.
In addition to more exposure to radiation, astronauts experience bone and muscle loss and changes in their cardiovascular, immune and other systems.
Williams, Skripochka and Ovchinin will join a three-man crew already aboard the station. The crew has been preparing for the arrival of an Orbital ATK cargo ship, which is scheduled to blast off from Florida on Tuesday.
(Reporting by Irene Klotz; Editing by Colleen Jenkins and Chizu Nomiyama)