"The Soyuz rocket took off successfully," the Russian space agency Roskosmos announced in a statement on Friday, adding that the ship would dock with the ISS after a six hour flight on Saturday.

Among the crew are the cosmonauts Oleg Skriprochka and Alexey Ovchinin and the American Jeff Williams, who NASA says is expected to "become the American with the most cumulative days in space – 534" after the six month trip is finished. They replace a crew that ended a nearly year-long flight earlier this month.

The crew are expected to join US astronaut Tim Kopra, Russian cosmonaut Yuri Malenchenko and British astronaut Tim Peake already aboard the ISS station. The crew has also been preparing for the arrival of an Orbital ATK cargo ship, which is expected to leave from Florida on Tuesday.

Williams is expected to surpass current US record holder Scott Kelly, who had returned to Earth earlier this month affter having been in space for 520 consecutive days. Kelly was part of an experiment that tested the effects of long-duration spaceflight on the body and mind for potential missions to Mars.

Williams took to Twitter to express his enthusiasm for the launch.

The world record for most consecutive days in space belongs to Russian cosmonaut Gennady Padalka, who spent a total of 879 days in space and returned from his fifth flight last September.

The US and other countries have been planning for long-term missions to Mars, and scientists are curious to understand how to better prepare for long-duration spaceflights. While the astronauts are in space, they experience more exposure to radiation, bone and muscle loss and changes in their cardiovascular, immune and other systems.

smm/bw (Reuters, AFP, AP)