Human spaceflight launched April 12, 1961. A historic flight of the first human to lift off into space, orbit Earth and return, is celebrated as Yuri Gagarin Day. Gagarin spent 108 minutes on Vostok 1. His orange flight suit and surprise appearance frightened two people who witnessed his planned parachute float back to the ground. “Don’t be afraid,” he told them, “I am a Soviet citizen like you, who has descended from space, and I must find a telephone to call Moscow!”

Now, it’s been a generation since humans began living amongst the stars. The International Space Station (ISS) has been inhabited for the last 26 years. Over 290 people have lived in space aboard the ISS. Twelve have walked on the Moon, and four more astronauts are aiming once again to see the Moon as no human can witness from Earth.

The far side of the Moon beckons, and with it, a constant technological challenge: escape Earth’s gravity within a timely launch window and safely rendezvous with the Moon’s ever-shifting position.

Low Earth satellites, like Vostok 1, have short launch windows because they navigate Earth’s motion, then settle into a low, stationary plane. Artemis II mission has a more complicated window due to traversing from low Earth orbit into high Earth orbit. Then with a gravity assist, slingshots to and around the moving lunar target.