The Voyager Twins: How NASA's Longest-Running Mission Keeps Going on Fumes

Since their launch in 1977, NASA's twin Voyager spacecraft have become humanity's farthest-reaching ambassadors, now cruising through interstellar space. But after nearly 50 years, their power reserves are critically low. In this Q&A, we explore how these legendary probes continue to operate, what science they're still delivering, and when we might finally lose contact.

1. What are the Voyager spacecraft and why are they so important?

Voyager 1 and Voyager 2 are a pair of identical robotic probes launched by NASA in 1977 to study the outer planets. Their original mission was a four-year tour of Jupiter, Saturn, and beyond, but they exceeded all expectations. Voyager 2 is the only spacecraft to have visited Uranus and Neptune, while Voyager 1 delivered stunning images of Jupiter's Great Red Spot and Saturn's rings. After completing their planetary flybys, both probes continued outward, eventually crossing the heliopause—the boundary where the Sun's influence ends—and entering interstellar space. Today, they are the only human-made objects in this uncharted realm, providing direct measurements of the interstellar medium. Their longevity and resilience have made them icons of space exploration.

2. How are the Voyagers powered, and why is their power running out?

Each Voyager carries three radioisotope thermoelectric generators (RTGs), which convert heat from decaying plutonium-238 into electricity. Unlike solar panels, RTGs work in deep space far from the Sun. However, the plutonium naturally decays over time, reducing heat output. After nearly 50 years, each RTG produces about 40% less power than at launch. Combined, the twin probes now generate roughly 250 watts—enough to power a couple of light bulbs. To keep critical systems alive, NASA engineers have had to systematically shut down non-essential instruments and heaters. The declining power threatens both communication and scientific data collection.

3. What steps have engineers taken to conserve power on Voyager?

NASA's Voyager team has implemented a series of power-saving measures over the decades. They have turned off most heaters, allowing the spacecraft to operate at cryogenic temperatures—well below their original design limits. Some instruments that were not essential for interstellar studies, such as the imaging cameras, were deactivated long ago. More recently, engineers began powering down individual subsystems, like the Ultraviolet Spectrometer on Voyager 1 in 2022. In 2024, they also shut off the Low-Energy Charged Particle instrument on Voyager 2. Each shutdown buys a few more years of life. The team carefully prioritizes which instruments remain active to maximize scientific return, focusing on those that measure magnetic fields, cosmic rays, and plasma waves directly in interstellar space.

4. What scientific discoveries have the Voyagers made in interstellar space?

Since crossing the heliopause—Voyager 1 in 2012 and Voyager 2 in 2018—the probes have revealed a completely new environment. They measured the density and temperature of interstellar plasma, finding it surprisingly hotter than expected. They also detected a gradual increase in cosmic rays from outside our solar system, helping scientists map the shape of the heliosphere. One key finding is that the magnetic field direction in interstellar space differs from the Sun's magnetic field, suggesting complex interactions at the boundary. The spacecraft also recorded sudden electron bursts from distant supernovae. These real-time measurements are impossible from Earth and have already rewritten textbooks on the nature of the interstellar medium.

5. How much longer can the Voyager spacecraft continue transmitting data?

There is no exact expiration date, but engineers estimate that Voyager 1 and 2 could lose all power for science instruments by around 2026–2030. The final instrument likely to be turned off is the magnetometer, because it draws very low power and provides crucial data. Even after all science stops, the probes might still be able to send a faint carrier signal for a few years. However, by the mid-2030s, the RTGs will produce insufficient electricity to power even the radio transmitter. At that point, the spacecraft will become silent, floating onward forever. Their trajectories will take them to other star systems—Voyager 1 will pass near a star in the constellation Ursa Minor in about 40,000 years.

6. What is the legacy of the Voyager mission beyond its scientific data?

Beyond science, the Voyagers carry the Golden Record—a time capsule of Earth's sounds, music, and greetings in 55 languages, designed to communicate our existence to any intelligent life that might find them. The record includes images of our planet, life forms, and human achievements. This gesture has made Voyager a cultural icon. Additionally, the mission demonstrated the incredible durability of well-built spacecraft and the value of long-term investment in exploration. The Voyagers have inspired generations of engineers, scientists, and dreamers. Their journey is a testament to human curiosity and our desire to reach out into the cosmos. Even after they fall silent, they will continue as our silent ambassadors for billions of years.

7. Could any future mission catch up to or outlast the Voyagers?

No spacecraft launched so far is faster than the Voyagers. The New Horizons probe, which flew past Pluto in 2015, is traveling at a similar speed but launched later, so it will never catch up. To exceed Voyager's longevity, a future mission would need more efficient power sources, such as advanced RTGs or nuclear fission reactors, and radiation-hardened electronics. Proposals for interstellar probes like Breakthrough Starshot aim for much higher speeds using light sails, but they would sacrifice the ability to slow down and make sustained measurements. For now, the Voyagers remain the longest continuously operating spacecraft and hold the record for farthest human-made objects. Unless a dedicated interstellar mission is launched soon, no other craft will pass them for decades.

8. How can the public follow the current status of the Voyager mission?

NASA provides real-time updates through the Voyager mission status page, which lists which instruments are still active and the current distance from Earth. The Jet Propulsion Laboratory also publishes periodic news releases and social media updates. Enthusiasts can use a live distance tracker to see Voyager's position relative to the solar system. Additionally, the Golden Record's contents are available online. For those who want to dive deeper, the book The Interstellar Age by Jim Bell offers an insider's account. Following Voyager today is like watching a slow, graceful fade—a reminder that even the greatest missions eventually end.