Two astronauts will venture outside the International Space Station (ISS) on Friday for a planned six-and-a-half hour spacewalk, NASA has said.

Mark Vande Hei of NASA and Norishige Kanai of the Japan Aerospace Exploration Agency are scheduled to begin the spacewalk at 7.10 a.m. to move components for the station's robotic system into long-term storage, the US space agency said on Wednesday.

The spacewalk will be the 208th in support of space station assembly and maintenance and the third in 2018.

The two spacewalkers will move a Latching End Effector (LEE), or hand, for the Canadian-built robotic arm, Canadarm2, from a payload attachment on the station's Mobile Base System rail car to the Quest airlock.

This LEE was replaced during an Expedition 53 spacewalk in October 2017, and will be returned to Earth to be refurbished and relaunched to the orbiting laboratory as a spare.

They also will move an aging, but functional, LEE that was detached from the arm during a January 23 spacewalk and move it from its temporary storage outside the airlock to a long-term storage location.

That LEE will be available as a spare part on the Mobile Base System, which is used to move the arm and astronauts along the station's truss structure.

The spacewalk originally was scheduled for January 29, but was postponed when a new LEE, installed during the spacewalk, encountered startup issues.

Those issues were later resolved through software updates written by Canadian Space Agency robotics specialists.

The spacewalk was rescheduled again to accommodate the February 15 docking of the Russian Progress 69 cargo spacecraft that launched on February 13, NASA said.

The 69P is due to complete its delivery when it docks on Thursday at 5.43 a.m. EST (4.13 p.m. India time).