As humanity basks in the aftermath of the unprecedented success of Artemis II, which took humans back to the Moon for the first time in 54 years and brought them farther from Earth than ever before, many of us can’t help but think about grander goals. As a species, we don’t just dream of returning to the Moon, but of heading to places we’ve never been: other planets, other star systems, or even other galaxies. However, there are big problems we have to solve if we ever want to send humans outside of the Solar System: the problems of distance, time, speed, and fuel efficiency. Interstellar distances are huge, even compared to the vast interplanetary distances we encounter in the Solar System. With current rocket technology, it would take hundreds of human lifetimes to reach even the nearest star, and that’s because we’re limited by speed, which is in turn limited by the efficiency of our fuel sources.…