NASA shuts down plasma device to save spacecraft 20.5 billion kilometers away

NASA engineers shut down one of Voyager 2's key scientific instruments to extend the spacecraft's life as its power supply dwindles.

Voyager 2 launched on August 20, 1977, and left the Solar System on November 5, 2018. It is currently 12.5 billion miles from Earth and is using four scientific instruments to study the space outside the heliosphere, the bubble of charged particles and magnetic fields that surrounds the Solar System. NASA believes Voyager 2 has enough power to keep one scientific instrument running until the 2030s, but that will require choosing which instruments to turn off.

Simulation of Voyager 2 entering interstellar space.

The mission team had been trying to delay the shutdown because Voyager 1 and Voyager 2 are the only two probes operating in interstellar space, making any data they collect precious. Six of the spacecraft's original 10 instruments have been shut down so far. Now, shutting down a seventh instrument was inevitable, and this time it was the spacecraft's plasma science instrument. Engineers sent the shutdown command on September 26.

The Plasma Science Instrument consists of four cups that collect information about the amount of plasma, a stream of charged particles, moving through Voyager 2 and its direction. Three cups are angled toward the Sun, tracking charged particles in the solar wind while in the heliosphere. The fourth cup is angled in the other direction, observing plasma in the planet's magnetic field and interstellar space. The instrument played a key role in detecting a drop in the amount of charged particles from the Sun, indicating that Voyager 2 crossed the boundary between the heliosphere and interstellar space in 2018.

"Engineers working on the mission carefully monitor changes to the 47-year-old spacecraft's operations to ensure they do not create any unintended side effects," a representative from NASA's Jet Propulsion Laboratory said. "The team confirmed that the shutdown command was processed without incident and the probe is operating normally."

The usefulness of the plasma science instrument is limited because the three Sun-facing cups stop collecting plasma after leaving the heliosphere and moving beyond the influence of the solar wind. In addition, the orientation of Voyager 2 means that the data collected over the past few years is more limited. The one functioning cup only provides useful data once every three months, as the spacecraft rotates 360 degrees on its axis. This led to the decision to shut down the plasma instrument to conserve power rather than shut down the other instruments.

Both Voyager 1 and Voyager 2 run on decaying plutonium and lose about 4 watts of power per year. In the 1980s, some of their instruments were turned off after the spacecraft finished exploring the giant planets in the system. That freed up power for the probes, extending their lifespans. A few years ago, the spacecraft also turned off all nonessential instruments. Voyager 1's plasma instrument was turned off in 1980 and turned off in 2007.

NASA engineers are closely monitoring Voyager 2's power supply so they can decide which science instruments to turn off next to ensure the interstellar probe can provide scientific data for as long as possible.