4K Video: The launch of Crew 4 as seen from the press site

Now in the home stretch of a complex, multi-year upgrade, two space station astronauts floated outside the lab complex Thursday and pressed ahead with the third of four spacewalks the current crew is carrying out to complete the replacement of aging batteries in the station’s solar power system.

NASA has announced that Astrobotic, Intuitive Machines and OrbitBeyond won contracts to deliver science instruments and technology demonstration payloads to the moon’s surface in the first of a series of robotic missions preceding a human return to the moon.

NASA officials say the International Space Station’s logistics chain was designed to absorb a launch failure like the mishap that destroyed an Orbital Sciences Corp. cargo craft in October, but pressure is on SpaceX to deliver supplies on time this year.