Scientists are closer to learning even more about the universe after astronauts started fixing a £1bn lab to the International Space Station (ISS).
In an eight-hour spacewalk, astronauts Stan Love and Rex Walheim attached the lab - called Columbus - to the main structure of the ISS.
The lab could help scientists make breakthroughs in medical science and other exciting discoveries.
Another spacewalk on Wednesday will do more to get Columbus up and running.
As the astronauts ventured out on their first spacewalk, Walheim said: "Welcome to spacewalking, buddy,"
Love replied: "It's awesome."
The job took longer than expected, but the commander, Stephen Frick, was really pleased with them, saying: "Man, you guys have done an amazing job."
The Columbus lab was made in Europe and is an important part of a project to get Europe more involved in the international space programme.