Astronaut Scott Kelly and cosmonaut Mikhail Kornienko are making final preparations for return to Earth Tuesday evening, closing out a record 340-day stay aboard the International Space Station where they served as medical test subjects to learn more about the long-term effects of weightlessness, space radiation and isolation.

American and Soviet crews were launched today in 1975 for the first handshakes in space between the two superpowers as part of the Apollo-Soyuz Test Project.

The Ariane 5 rocket’s fifth flight of the year launched at 2030 GMT (4:30 p.m. EDT) with the Sky Muster and Arsat 2 communications satellites, designed to deliver broadband Internet to far-flung Australian citizens and broadcast television and networking services to Argentina and nearby countries.