Forty-seven years and eight months after its launch, Voyager 1 continues to push the limits of what seemed possible.
Voyager 1 is currently over 24.88 billion kilometers from Earth—about 166 times the distance between Earth and the Sun—making it the most distant human-made object in space.
Launched in 1977, both Voyager spacecraft are now cruising through interstellar space at nearly 35,000 miles per hour. To maintain communication with Earth, they use small thrusters to orient their antennas precisely toward our planet for sending and receiving signals.
Each spacecraft is equipped with a set of primary thrusters that manage movement in various directions, including a separate set for controlling a motion called “roll.” From Earth, this roll resembles the antenna spinning like a vinyl record—a subtle but crucial movement that helps lock onto a guide star to stay aligned.
Voyager also carries backup roll thrusters. A third set of thrusters, originally used during planetary flybys, was reactivated in 2018 and 2019. However, these are not capable of handling roll control, which is vital for maintaining contact with Earth.
To address clogging issues in the thruster systems, engineers alternate between the primary, backup, and trajectory thrusters. On Voyager 1, the primary roll thrusters stopped working in 2004 after two small internal heaters failed. With the heaters likely unrepairable, the team relied exclusively on the backup roll thrusters.
But if the backup thrusters were to clog completely, Voyager would lose its ability to control roll—and potentially lose contact with Earth. This prompted engineers to revisit the 2004 failure. They suspected that a disturbance in the heater power circuits had flipped a virtual switch, cutting power to the heaters. If they could reverse that switch, the heaters might come back online, allowing the primary roll thrusters to be reactivated.
Racing Against Time
Restarting the heaters was risky. Engineers had to power on the dormant thrusters and attempt a heater reset. However, if the star tracker lost lock on the guide star during this process, the roll thrusters would automatically fire. If they did so while still cold, it could cause a small explosion. Precise alignment of the star tracker was critical.
Complicating matters, the team faced a tight timeline. From May 4, 2025, to February 2026, Deep Space Station 43 (DSS-43) in Canberra, Australia—the only antenna powerful enough to send commands to the Voyagers—would be mostly offline for upgrades, with only brief availability in August and December.
Though NASA’s Deep Space Network has three global sites (Goldstone, California; Madrid, Spain; and Canberra), only DSS-43 can transmit signals strong enough to reach Voyager.
A Delicate Success
On March 20, the team’s careful planning paid off. Because Voyager is so distant, its radio signal takes over 23 hours to reach Earth, meaning any response is nearly a full day old by the time it’s received.
Within 20 minutes of receiving the expected signal, engineers saw the temperature of the heater rise—clear evidence that the primary roll thruster system had been successfully reactivated. A risky move under tight constraints had paid off, potentially extending the mission’s life and preserving humanity’s connection with its most distant emissary.
