Voyager 1, NASA’s deep-space probe, could soon become the first spacecraft to reach a historic milestone. In November 2026, the probe will be one light-day from Earth.
Launched in 1977, Voyager 1 is the farthest spacecraft from our planet, currently exploring interstellar space 15.8 billion miles away.
The term light-day refers to the distance at which it will take 24 hours for a signal or command traveling at the speed of light to reach the spacecraft from Earth, said Suzy Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory. One light-day is equivalent to 16 billion miles (26 billion kilometers).
So if Voyager’s team is asking the spacecraft to do something once it reaches that point, it will take another day for Voyager to respond.
“If I send a command and say, ‘good morning, Voyager 1,’ at 8 a.m. on a Monday morning, I’m going to get Voyager 1’s response back to me on Wednesday morning at approximately 8 a.m.,” Dodd said.
Voyager 1 and its twin, Voyager 2, are the only spacecraft to operate beyond the heliosphere , the sun’s bubble of magnetic fields and particles that extends well beyond the orbit of Pluto. After decades in space, both have had to turn off several instruments, but they are using their remaining tools to study this uncharted territory and provide data that could inform future missions.
There are many challenges that come with staying in communication with such far-reaching probes, but Dodd and her team are taking necessary steps to ensure that their “senior citizens” reach their 50 th anniversary in 2027.
Staying in touch over cosmic distances
Launched on a journey to explore Jupiter and Saturn, Voyager 1 has been traveling away from Earth on the same trajectory and at the same speed — 38,000 miles per hour — since its flyby of Saturn in November 1980.
With an understanding of Earth’s location relative to Voyager 1, the spacecraft’s speed and its trajectory, engineers are able to calculate how long it takes a signal to reach the probe.
