Nshan Kazaryan, the NASA engineer responsible for communicating with the Voyager 1 and Voyager 2 space probes, is younger than the spacecraft he talks to.

At 25, Mr. Kazaryan is among a new generation of engineers at NASA’s Jet Propulsion Laboratory in California working to keep the geriatric but resilient spacecraft going.

“Every time I talk about Voyager, I kind of treat it like my parents,” he said. “As a human gets older, they have all these problems. A spacecraft is similar. The older it gets, the more problems.” (Even Mr. Kazaryan’s parents were not yet born when the Voyagers launched in 1977.)

Working with the aging spacecraft requires ingenuity, doggedness and Zen-like patience.

Each time Mr. Kazaryan sends a command to one of the Voyagers, he has to wait a couple of days for a response.

That is how long it takes a radio signal to make the round trip. Voyager 1 is almost 16 billion miles away; Voyager 2 is a bit closer — about 13.3 billion miles. But that is still more than four times the distance to Pluto.

It has been decades since the heyday of the Voyagers, when they flew past the giant planets, sending back photographs of kaleidoscopic wonderlands, including the reddish clouds swirling around the Great Red Spot on Jupiter and the delicate, shimmering rings of Saturn.

Now, speeding away at more than 30,000 miles per hour, the twin spacecraft have traveled the farthest of any human creation. Voyager 1 entered interstellar space in 2012, and Voyager 2 crossed over six years later.

Space scientists want them to continue collecting unique observations about what lies between stars for as long as possible. There will not be another spacecraft venturing that far out anytime soon.

But that endeavor is becoming harder and, within a few years, will be impossible as the energy from the spacecraft’s plutonium batteries diminishes. To keep the spacecraft alive, the engineers have to take risks that other missions would not dare.

“We’re like pirates,” Kareem Badaruddin, the Voyager mission manager, said. “Nobody likes to be this close to the edge, but we’ve gotten quite comfortable with it, because it’s our only choice.”

In a triumph last month, the team pulled off what it calls the “Big Bang” on Voyager 2 — a juggling of the electrical systems that saved about 10 watts of power. That tiny boost, enough to power a lightbulb or two, could extend the mission by about two years, well into 2031.

In the coming weeks, the engineers will finish the rejuvenation process on Voyager 1, hoping it can last until 2030.

A couple more years may not seem like much, but each day offers the possibility of a new discovery. Compared with the particles that the sun spews out into our solar system, interstellar space contains “a different mixture of gas out there and different behavior,” said Jamie Rankin, a space scientist at Princeton University who now serves as the deputy project scientist.

The engineers know they can only postpone the inevitable demise of the Voyagers, but they remain hopeful — and creative.

“Who knows?” Mr. Badaruddin said. “Maybe we’ll come up with something else.”

But, he added, “This is, I think, the best we can do.”

Diseases of Old Age

Three chronic conditions are slowly killing the Voyagers.

One is that the fuel lines are clogging up with residue dissolved from a silicone bladder that pushes propellant — a liquid known as hydrazine — out of the tank to the spacecraft thrusters.

Think of it as the spacecraft equivalent of cholesterol-clogged arteries.

If too many thrusters on a Voyager fail, it would be unable to keep its antenna pointed at Earth. With communications severed, it would be lost.

To slow the buildup of silicone, the thrusters have been fired less often over the past few years — the antenna is now allowed to drift farther out of alignment before being nudged back in the direction of Earth — and the lines that the propellant flows through are periodically switched.

A second challenge is keeping the fuel lines warm enough. Frozen hydrazine would also block the propellant lines and break the thrusters. There are heaters on the spacecraft designed to prevent that, but they require electrical power.

And that — in the Voyagers’ third chronic condition — is something the spacecraft are running dangerously low on. The plutonium batteries (what NASA calls radioisotope thermoelectric generators, or R.T.G.s.) generate the energy that the Voyagers run on by converting heat from the radioactive decay of plutonium into electricity.

The R.T.G.s originally produced about 470 watts for each Voyager. As the plutonium decayed and power dwindled over the decades, one scientific instrument after another was turned off on the probes. On Voyager 2, which is down to 216 watts, only three of the 10 instruments are still collecting data. On Voyager 1, which is subsisting on slightly less power, there are just two.

The mission team investigated ways to cut back on power. For example, the digital tape recorder on Voyager 1 broke decades ago, but engineers kept it on because it fortuitously warmed nearby propellant lines.

The designers of the Voyagers included a heater to keep the recorder warm in case it needed to be turned off. Why not turn off the broken tape recorder and turn on the heater, which uses fewer watts?

That carried some risks. The tape recorder had never been turned off, and the heater had never been turned on. More crucially, the heater produced less heat than the tape recorder. Analysis indicated that a thruster might become too cold for hydrazine to flow. “It wouldn’t really help us,” Mr. Badaruddin said.

Devising the Big Bang

Out of necessity, the Voyager team had to contemplate something far more ambitious.

An engineer named David Woerner suggested that since piecemeal changes would fail, making a slew of such changes at once could keep the heat and power requirements in balance while reducing the spacecraft’s power consumption.

This undertaking became the Big Bang, and after nine months of analysis, the Voyager engineers became convinced it could work. They decided the benefits outweighed the potential pitfalls.

“Voyager is basically the path of least regret,” Bruce Waggoner, the mission assurance manager, said. “There’s no really right answer.”

They started with Voyager 2, because it is healthier power-wise. The operation was performed in three steps, to minimize the danger of losing the spacecraft.

“There’s always that concern that it might not go correctly,” said Suzanne Dodd, who has served as the project manager for Voyager since 2010.

First, in May, the spacecraft was told to switch to the new configuration for 40 minutes. That was to ensure that systems like the heater near the tape recorder, which had never been turned on before, indeed worked.

A month later, Voyager 2 remained in the new configuration for six hours to check that the temperature predictions were accurate. Finally, last month, the change was made permanent.

The 50th anniversary of their launches is just over a year away. “I’m pretty confident that they both make it,” Ms. Dodd said.

But there are no guarantees. It would not be a surprise if a critical system unexpectedly broke on one of the increasingly frail Voyagers.

That happened four years ago when Voyager 1 started sending gibberish to Earth instead of science and telemetry. It effectively became mute, unable to tell the engineers what was wrong.

“We were just shooting in the dark,” Sun Matsumoto, one of the engineers, said. “We just didn’t have any clue.”

The problem was ultimately traced to a failed memory chip that engineers were eventually able to work around, but Voyager 1 was knocked out of commission for the better part of a year.

‘I Want to Be There’

While the Voyagers no longer capture colorful photographs the way they did while flying past the planets — the last images were taken by Voyager 1 in 1990 of a “family portrait” of the solar system — they are still making discoveries in the uncharted territory of interstellar space.

In the middle of 2020, Voyager 1 observed a large change in the magnetic field in that region of interstellar space, with a large change in the density of the plasma of charged particles around it. That change has persisted through now. “We don’t know why,” Dr. Rankin said. “That’s like a really strange thing.”

That is just one of the mysteries that the additional years of exploration might help unravel.

With the power boost from the Big Bang, the engineers and scientists are considering turning back on some of the spacecraft’s inactive scientific instruments to collect additional insights, even if just briefly.

But that, as with everything they do, could put the spacecraft in peril. One possibility is to wait until after the 50th anniversary.

“We haven’t decided yet,” Dr. Spilker said. “You might lose the mission.”

Dr. Spilker was part of the mission when it launched, her first job out of college. She shifted to NASA’s Cassini mission, which orbited Saturn for 13 years, before returning to Voyager.

When asked what she would do after the 50th anniversary, she said she was undecided. “I have like 10 wonderful grandchildren and other things I like to do and travel and so on,” she said.

She has already reduced her hours to part-time, which helps fit the continuing operations for the Voyagers within a $5 million annual budget, a shoestring compared with many other NASA missions.

The next day, Dr. Spilker followed up with an email saying the question had caught her off guard.

“After sleeping on it, I realized that I want to be there when each Voyager goes silent, and we say our goodbyes as a team,” she wrote. “Following up on Voyager’s scientific discoveries has been a part of my life for my entire J.P.L. career, and I won’t be happy if I leave before their final moments.”