On November 18, 2026, Voyager 1 will reach a remarkable milestone—it will become the first human-made object located one light-day from Earth. That means a radio command sent from Earth, traveling at the speed of light, will require 24 hours just to reach the spacecraft. NASA Space Shuttle Discover. Smithsonian Visit Photo by 19FortyFive.com And any reply will take another full day to return. The boundary serves as a reminder of the extraordinary distances involved in deep-space exploration.