After nearly 50 years in space, Voyager 1, the farthest human-made object, continues its journey through interstellar space.
Despite its age, the spacecraft remains operational, but recent issues with its thrusters posed a major challenge to keeping it aligned with Earth. Engineers at NASA's Jet Propulsion Laboratory (JPL) successfully switched to a backup set of thrusters, ensuring that the spacecraft can continue its mission to send data back to Earth from more than 24 billion kilometers away.
Thruster Clogging: A Threat to Voyager’s Alignment
One of the most critical systems on Voyager 1 is its hydrazine-fueled thrusters, which generate small bursts of gas to adjust the spacecraft’s orientation. This alignment is crucial for keeping the probe’s antenna pointed toward Earth, enabling it to send and receive signals despite being more than 24 billion kilometers away. Each day, the thrusters are fired in short bursts, requiring about 40 pulses to maintain this alignment. However, as the spacecraft aged, its primary thrusters became less efficient due to clogging in their fuel tubes.
The clogging is caused by silicon dioxide, a byproduct of the spacecraft's aging rubber components. Over the years, the fuel tubes have narrowed to just 0.0015 inches (about 0.035 millimeters), making it difficult for the thrusters to generate sufficient force. This led the engineering team to switch to backup thrusters that had previously been used during Voyager 1’s planetary flybys. These backup thrusters have been inactive for decades, but after careful planning, they were successfully brought online in late August 2024.
Suzanne Dodd emphasized the importance of these thrusters for keeping Voyager operational: “The thrusters are what keep the spacecraft pointed at Earth, and without them, Voyager would drift out of communication range.” By successfully switching to the backup thrusters, NASA has ensured that Voyager 1 can continue its mission for the foreseeable future.
Power Management and the Challenge of Cold Thrusters
Switching to the backup thrusters was not a straightforward task. One of the major complications was the fact that the backup thrusters had become extremely cold after years of inactivity. Since Voyager 1's power supply has been gradually diminishing over the decades, many of the spacecraft’s non-essential systems, including heaters, have been turned off to conserve energy. This has caused various components, including the thrusters, to cool to temperatures that could damage them if they were activated without proper preparation.
NASA engineers devised a plan to carefully warm the thrusters by temporarily turning on non-essential heaters. However, this posed another challenge: Voyager 1’s power supply is so limited that powering the heaters required turning off another system. After extensive analysis, the team decided to briefly shut down one of the spacecraft’s main heaters, which freed up enough power to warm the thrusters safely. This delicate operation was carried out successfully, and on August 27, 2024, NASA confirmed that the backup thrusters were operational and maintaining Voyager 1’s alignment with Earth.
“This was a very careful balancing act,” Dodd said. “We had to figure out how to allocate power without compromising other critical systems. Every watt of power is precious at this stage of the mission.”
Voyager 1’s Journey Beyond the Solar System
Voyager 1 crossed the heliopause—the boundary where the Sun’s influence ends and interstellar space begins—in 2012, making it the first human-made object to do so. Since then, the spacecraft has been traveling through the space between stars, sending back data about the interstellar environment. Voyager 1’s data is invaluable to scientists, as it provides a unique glimpse into a region of space that no other spacecraft has reached.
Despite the incredible distance—over 24 billion kilometers from Earth—Voyager 1 continues to transmit data, although with significant delays. Signals from the spacecraft take over 21 hours to reach Earth, highlighting the challenges of operating such a distant probe. The mission's ability to collect data from beyond the heliosphere offers insights into the structure and composition of interstellar space, which was previously uncharted territory for scientists.
“Voyager is truly on the frontier of space exploration,” said Dodd. “No other mission has provided us with data from such a distant and unknown region.”
Extending Voyager’s Mission as Long as Possible
With power levels steadily dropping, NASA faces tough decisions on how to manage Voyager 1’s remaining energy. The spacecraft’s power supply, generated by decaying plutonium, is expected to last until around 2030. Until then, engineers will continue to turn off non-essential systems and instruments to conserve energy and prolong the mission. This includes shutting down some of the scientific instruments, a process that has already begun, though NASA hopes to keep the most critical instruments running for as long as possible.
The thruster swap is just one of many engineering challenges the Voyager team has overcome in recent years. In 2018, a similar issue arose when another set of thrusters began clogging, prompting the team to switch to the trajectory correction thrusters, which had not been used since Voyager 1’s flybys of the outer planets. These creative solutions have kept Voyager 1 operational far longer than its designers initially anticipated.
Dodd underscored the importance of careful planning for each new step: “All future decisions will require even more analysis and caution than they once did. The spacecraft is old, and every action we take now has to be weighed carefully.”