Voyager's Journey: The Fading Power of NASA's Twin Interstellar Spacecraft

For nearly five decades, NASA's twin Voyager spacecraft have pushed the boundaries of human exploration, sending back groundbreaking data from the outer planets and beyond. Launched in 1977, Voyager 1 and Voyager 2 are now hurtling through interstellar space, but their power sources are slowly running out. This Q&A explores the challenges they face, the strategies to extend their mission, and what the future holds for these iconic explorers.

• What are the Voyager spacecraft, and when did they launch?
• Where are Voyager 1 and Voyager 2 today?
• How do these spacecraft generate power?
• Why is their power declining after almost 50 years?
• What steps has NASA taken to conserve power?
• How much longer can the Voyagers keep sending data?

What are the Voyager spacecraft, and when did they launch?

NASA's Voyager program consists of two identical probes: Voyager 1 and Voyager 2. They were launched in 1977, just a few weeks apart, with a primary mission to study Jupiter and Saturn. Their remarkable discoveries included volcanic activity on Jupiter's moon Io and intricate ring structures around Saturn. After completing their primary objectives, they continued on to explore Uranus and Neptune—making Voyager 2 the only spacecraft to visit these ice giants. Now, after nearly half a century, they remain humanity's most distant active probes, currently exploring the uncharted region of interstellar space.

Where are Voyager 1 and Voyager 2 today?

Both Voyager spacecraft have left the protective bubble of our Sun's influence, known as the heliosphere, and entered interstellar space—the vast, empty region between stars. Voyager 1 crossed this boundary in 2012, becoming the first human-made object to do so. Voyager 2 followed in 2018. As of now, Voyager 1 is about 15 billion miles (24 billion kilometers) from Earth, while Voyager 2 is roughly 12 billion miles (19 billion kilometers) away. They are moving outward at speeds of around 38,000 miles per hour, carrying a Golden Record with sounds and images of Earth, just in case any intelligent life might one day find them.

How do these spacecraft generate power?

Unlike solar-powered spacecraft, the Voyagers rely on radioisotope thermoelectric generators (RTGs). These devices convert heat from the natural decay of plutonium-238 into electricity. Each RTG contains a solid plutonium oxide fuel pellet that generates heat, which is then converted to electrical power by thermocouples. This design allows the probes to operate far from the Sun, where sunlight is too weak for solar panels. At launch, each RTG produced about 470 watts of power. The system is simple, rugged, and has no moving parts, which is critical for a mission that must survive decades in deep space.

Why is their power declining after almost 50 years?

The decline is due to the constant decay of the plutonium-238 isotope. Plutonium-238 has a half-life of about 87.7 years, meaning that after that time, half of its atoms will have transformed into other elements. As the fuel decays, it produces less heat, and the thermocouples that convert heat to electricity also degrade over time. The result is a steady loss of power—roughly 4 to 5 watts per year. Originally generating 470 watts, the spacecraft now have only about 220 to 240 watts of power available. This dwindling supply forces NASA to make difficult choices about which scientific instruments to keep running.

What steps has NASA taken to conserve power?

To stretch the available power, NASA engineers have gradually shut down non-essential systems and heaters. They've also turned off some scientific instruments. On Voyager 1, three of its original ten science instruments are now operating; on Voyager 2, four remain active. The spacecraft's heaters are being turned off one by one, relying on the heat from the RTGs themselves to keep critical components warm enough. Additionally, engineers have optimized the power usage by adjusting the voltage thresholds and modifying software to reduce energy consumption. These careful power management strategies have already extended the mission by several years beyond initial expectations.

How much longer can the Voyagers keep sending data?

It's difficult to predict an exact end date, but experts estimate the probes can continue operating some instruments until around 2025 to 2030. Once the power drops below about 200 watts, there won't be enough electricity to run even a single instrument. After that, the spacecraft may still be able to send limited engineering data for a few more years, but the scientific return will be over. By the mid-2030s, the RTGs may produce too little power to maintain communication. However, the Voyagers will sail through interstellar space for billions of years, silently carrying their Golden Records as time capsules of human civilization.