Voyager 1 will reach one light-day from Earth in 2026. Here’s what that means

Voyager 1, NASA’s space probe, could soon become the first spacecraft to achieve a historic milestone. In November 2026, the probe will be one light day from Earth.

Launched in 1977, Voyager 1 is the most distant spacecraft from our planet, currently exploring interstellar space 15.8 billion kilometers away.

The term light day refers to the distance 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 equal to 16 billion miles (26 billion kilometers).

So if the Voyager team asks the spacecraft to do something once it reaches this point, it will take another day for Voyager to respond.

“If I send a command and say ‘Hello, Voyager 1’ at 8 o’clock on a Monday morning, I will receive the response from Voyager 1 on Wednesday morning around 8 o’clock,” Dodd said.

Voyager 1 and its twin, Voyager 2, are the only spacecraft to operate beyond the heliosphere, the solar bubble of magnetic fields and particles that extends far beyond Pluto’s orbit. 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.

Staying in touch with investigations of this magnitude comes with many challenges, but Dodd and his team are taking the necessary steps to ensure their “senior citizens” reach their 50th birthday.^th birthday in 2027.

Staying in Touch at Cosmic Distances

Launched to explore Jupiter and Saturn, Voyager 1 has been moving away from Earth on the same trajectory and at the same speed – 38,000 miles per hour – since its November 1980 flyby of Saturn.

By understanding Earth’s position relative to Voyager 1, the spacecraft’s speed and its trajectory, engineers are able to calculate how long it takes for a signal to reach the probe.

For example, Voyager 1’s trajectory after the Saturn flyby took it up and out of the plane of the planets after passing Saturn, while Voyager 2 passed over Neptune after its flyby of the ice giant in 1989 and went down and out of the plane of the planets. Neither probe has undergone any trajectory adjustment since their last planetary flybys, meaning both have been on uninterrupted cruises for decades.

Voyager 2 is not expected to reach a light day from Earth until November 2035, and even the most ambitious estimates suggest the spacecraft won’t operate at that time. But the two investigations continue to surprise the team.

Every day, as the longest operating spacecraft, the Voyager probes hold a record just by continuing to operate.

But it hasn’t been an easy process.

The probes send data back at a very low rate of 160 bits per second, a data rate similar to that of a dial-up Internet connection, Dodd said.

“The distance from Earth takes a lot longer to receive a signal there, and the strength of the signal just dissipates,” Dodd said. “It takes several antenna arrays to recover this signal.”

The low data rate means Dodd and his team receive little information about the status of each spacecraft, and if something goes wrong, they are unable to respond quickly.

However, both Voyagers are designed to be autonomous with plenty of autonomy on board so they can save themselves if things go wrong billions of miles from Earth.

“If they have a problem, they can put themselves in a safe state so they can wait until we can talk to the spacecraft, figure out what the problem is and fix that,” Dodd said.

Why the Voyager probes endure

For years, the team made difficult decisions to ensure the probes worked as long as possible, Dodd said. This means turning off engineering systems and instruments to save energy and ensure the spacecraft stays warm enough to operate.

For the Voyager probes to continue communicating with Earth, their antennas must also be pointed toward our planet.

If the propulsion lines freeze on either probe, forcing the antennas to point elsewhere, “we would lose the mission because we would no longer be able to transmit a signal to the spacecraft,” Dodd said.

And it’s not just about keeping the Voyager probes flying: they need to work with scientific instruments.

Before their 50th anniversary in 2027, both spacecraft will likely need to deactivate additional instruments and systems. The team hopes to keep the cosmic ray subsystem operating on Voyager 2, as well as the magnetometer and plasma wave subsystems on both spacecraft. The instruments would allow the two probes to essentially function as weather satellites in interstellar space, sensing the environment they pass through, Dodd said.

Scientists want to understand how the sun’s magnetic field changes and interacts at the heliopause, the boundary of the heliosphere where hot solar wind from the sun meets cold interstellar space.

Think of the heliopause as the shore of an ocean, Dodd said. Wading in water reveals ripples, waves, and other changing factors the further you get from shore, and at some point things become more stable. The Voyager probes measure ripples, or interactions between the heliopause, our sun and interstellar space, as the spacecraft moves away from the sun.

“What’s important is to use these scientific instruments for as long as possible to create a map of what changes as we move away from the sun,” Dodd said.

Dodd is confident that at least one of the spacecraft will be able to continue operating for another two to five years. The process of allowing these unprecedented missions to continue becomes more difficult each year, she said.

But Voyager has a remarkable team behind it, including NASA retirees in their 80s who advise on specific subsystems and team members so young that even their parents weren’t born when the probes took off.

“This kind of intergenerational effort on Voyager is really gratifying to see,” Dodd said. “I love these spaceships. They are our ambassadors here on Earth.”

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