Venture into open space

Alexander Gerst and his US colleague Reid Wiseman did maintenance work in open space. They exited the ISS and got started on their separate tasks. Gerst also recorded a video with his helmet camera.

Gerst and Wiseman have enjoyed this view from inside the ISS for four months, but on Tuesday they left the safety of the station. The astronauts floated in outer space for six hours, but probably didn't pay much attention to the spectacular view. Instead, Gerst and Wiseman had to move a failed cooling pump.

The second part of their mission was getting up close to essential parts of the ISS. The two men installed a unit that will allow the station's robotic arm to remain powered even when it is being relocated.

Alexander Gerst was optimistic that he and Wiseman would succeed - and they did. They completed all their planned jobs. Wiseman started out by setting up a new home for the failed cooling pump, which Gerst picked up from its temporary position. Then the two of them fixed the pump to its new position, before working on the robotic arm.

For things to go smoothly during the spacewalk, the astronauts had to prepare rigorously. Nothing was left to chance. In this picture, Wiseman is prepping his spacesuit. During the intense preparation phase, which began two weeks ago, he and Gerst were supported by control centers at Houston and Moscow.

Before the astronauts left the pressurized environment of the ISS for pressure-free space, they had to decompress - just like deep-sea scuba divers who ascend from great depths. Gerst and Wiseman breathed pure oxygen for two hours to remove nitrogen from their bodies.

To get ready for their six hours in open space, the astronauts had to work out on board the ISS. After all, a spacewalk… is no cakewalk. The ISS completes a full circuit of Earth every 90 minutes. So Gerst and Wiseman worked in bright sunlight one moment and in complete darkness the next, with only their helmet lights to guide them.

Even though the two astronauts worked faster than planned, they didn't have time to idly watch Earth from above. Gerst and Wiseman used the extra time to work on tasks planned for future spacewalks, such as rerouting cables and reconfiguring equipment.