Voyager 1 was first launched in 1977 on a path that eventually led both it and its sister spacecraft, Voyager 2, outside the solar system altogether.

But in recent years, Nasa said that fuel residue has been accumulating inside narrow tubes in some of the thrusters on both spacecraft. Voyager 1 has also faced problems with sending junk data back home after it suddenly began routing its telemetry data through a derelict onboard computer for unknown reasons.

The thrusters on Voyager 1 and Voyager 2 are primarily used to keep the spacecraft antennae pointed at Earth in order to communicate. As spacecraft can rotate in three directions, Voyager’s thrusters automatically fire to reorient itself.

Each time a thruster fires, it adds tiny amounts of propellant residue, leading to gradual build-up of material over decades. To slow that build-up, the mission has begun letting the two spacecraft rotate slightly farther in each direction before firing the thrusters...