NASA's 49-year-old probe crosses a symbolic distance where even radio signals need 24 hours to arrive, as engineers work to stretch its fading power into the 2030s

At 5:16:07 a.m. EST on Wednesday, Nov. 18, NASA's Voyager 1 will become the first human-made object to sit one full light-day from Earth, according to NASA. That distance is 16,094,799,096 miles (25,902,068,356 kilometers), the span light covers in 24 hours.

Nothing about the spacecraft physically changes at that moment — the milestone is a yardstick that makes the scale of space easier to picture. Sunlight reaches Earth in about 8 minutes and 20 seconds, and light from Neptune takes a little over 4 hours. A radio command to Voyager 1 now takes a full day to arrive, and the reply another full day to return.

It also arrives as engineers are working hard to keep the probe alive. Voyager 1 lost contact for about 48 hours in October and is running on a power supply that shrinks every year, so the countdown is as much about endurance as distance.

A 16-Billion-Mile Yardstick for Light

Voyager 1 launched on Sept. 5, 1977, and will reach the light-day mark after 49 years, 2 months, and 11 days of travel. It crossed the heliopause, the edge of the Sun's sphere of influence, in August 2012 and now moves through interstellar space at nearly 38,000 miles per hour (about 61,000 kilometers per hour).

In early October, the probe was about 15.98 billion miles away, and its signal took 23 hours, 52 minutes and 30 seconds to reach Earth, EarthSky reported. The extra few minutes to a full day close as it keeps moving outward. Its twin, Voyager 2, is about 2 billion miles closer and should reach a light-year in November 2035.

For perspective, light from the Moon reaches Earth in about 1.3 seconds, and light from Mars takes 3 to 22 minutes depending on where the planets sit. Even at a full light-day, Voyager 1 has covered only a tiny fraction of the 4.24 light-years to Proxima Centauri, the nearest star beyond the Sun. The milestone shows how far the probe has gone and how empty the space between stars really is.

Several early estimates gave different dates for the crossing. The Voyager team confirmed Nov. 18 to IFLScience, and NASA's own page lists the exact second.

Two-Day Conversations Through the Deep Space Network

Every command and every byte of data travels through NASA's Deep Space Network, large radio antennas at three sites spaced around the globe so at least one can always see the spacecraft. At one light-day, a simple instruction becomes a 48-hour round trip.

Voyager project manager Suzanne Dodd at NASA's Jet Propulsion Laboratory described the routine plainly: engineers send a message and "you go home, and you wait two days," she said, according to a JPL release published on ScienceDaily.

That delay makes problems harder to solve. The network failed to hear Voyager 1 during scheduled contacts on Oct. 18 and 19. The signal returned Oct. 20, and engineers found that one set of thrusters had stopped working, prompting the spacecraft's fault protection to switch to backups. The cause has not been determined — a reminder that a 49-year-old machine at this distance can fail without warning.

Running on Fading Plutonium Power

Voyager 1 runs on radioisotope thermoelectric generators, which turn heat from decaying plutonium into electricity. Each Voyager loses about 4 watts of generating capacity per year, which has forced NASA to switch instruments off one at a time. The probe launched with 10 science instruments. NASA turned off its cosmic ray subsystem in 2025 and its low-energy charged particle instrument on April 17, 2026, leaving the magnetometer and plasma wave subsystem as its working science instruments as of that update, NPR reported.

In early September, engineers completed a power-saving swap the team calls the "Big Bang," replacing three devices with lower-power alternatives in a single operation, about six weeks after a similar procedure on Voyager 2. JPL said the upgrade should extend the life of the remaining instruments beyond earlier expectations. Without it, another instrument could have been shut off as soon as summer 2027.

Those remaining instruments matter because they sample interstellar space directly, a region no other active mission can currently measure. Each year of extra power means more data on the magnetic fields and plasma that fill the space between stars.

NASA has not set an end date. The team's goal is to keep at least one science instrument running on each spacecraft into the 2030s. Exactly when power runs too low depends on how the aging hardware behaves, and that is the central uncertainty for the mission.

Flashing Morse Code at the Sky on Nov. 17

NASA is inviting the public to mark the milestone through a "Shine Bright" event, asking people to flash V-G-R in Morse code toward the sky after sunset on Tuesday, Nov. 17, local time. An automated flasher is available on NASA's website for those who do not know the code.

Both Voyagers also carry a golden record with sounds and images of life on Earth. In about 40,000 years, Voyager 1 should pass within about 1.7 light-years of the star Gliese 445.

There is nothing for readers to prepare for, and the crossing poses no risk. The things to watch are NASA updates around Nov. 18, any report on the cause of October's thruster problem, and future decisions about which instrument is switched off next.

What Readers Want to Know

When exactly does Voyager 1 reach one light-day? At 5:16:07 a.m. EST on Wednesday, Nov. 18, 2026, according to NASA.

How far is a light-day? About 16.09 billion miles (25.9 billion kilometers), the distance light travels in 24 hours.

Does anything happen to the spacecraft? No. The milestone is symbolic. It simply means signals now take a full day each way.

Which instruments still work? NASA's April update left the magnetometer and the plasma wave subsystem operating.

How long can Voyager 1 keep going? NASA has not set an end date. Engineers hope to keep at least one instrument running into the 2030s.

How can I take part? NASA invites people to flash V-G-R in Morse code at the sky after sunset on Nov. 17.