NASA sacrifices plasma instrument at 12 billion miles to let Voyager 2 live longer

Forty-seven years ago, Voyager 2 embarked on a journey that has expanded our understanding of the cosmos.

Voyager 2 has traveled over 12.8 billion miles (20.5 billion kilometers), making it the most distant spacecraft from Earth alongside its twin, Voyager 1.

As Voyager 2’s power supply dwindles, the mission team has made the difficult decision to turn off the Plasma Science Experiment.

Designed and built at MIT, the Plasma Spectrometer (PLS) has been the eyes and ears of Voyager 2, measuring the charged particles that shape our solar system and beyond.

On September 26, the plasma instrument transmitted its final message from a distance of 12.7 billion miles before being deactivated. This shutdown is necessary to ensure the spacecraft’s continued operation.

NASA’s Deep Space Network sent the command to Voyager 2, which took 19 hours to reach the spacecraft. The confirmation signal traveled back to Earth in another 19 hours.

Plasma instrument role

The Plasma Science Experiment has played a vital role in our understanding of the solar system and the interstellar medium.

The instrument gathered data on charged particles found in the magnetic fields of planets, the solar wind, and the space between stars.

Interestingly, PLS was instrumental in determining the exact moment Voyager 2 transitioned from the heliosphere into interstellar space.

The plasma science instrument is designed with four detector “cups” for the measurement of plasma flow.

When Voyager 2 left the heliosphere, the solar wind flow to the three cups facing the Sun decreased a lot. The fourth cup’s (used to study planetary magnetospheres) best data is only collected every three months, so it was turned off last.

Saving power for further exploration

Voyager 1 entered interstellar space first. It crossed the heliopause, the boundary between the heliosphere and interstellar space, in August 2012. Voyager 2 followed suit in November 2018.

After traveling for nearly half a century, the probe’s power system is weakening, leading NASA to deactivate various science instruments to prolong its mission.

The probe is powered by three Radioisotope Thermoelectric Generators (RTGs). These devices convert the heat produced by the radioactive decay of plutonium-238 into electricity. The probe’s power output diminishes by about 4 watts per year.

Following their exploration of the giant planets in the 1980s, the Voyager mission team turned off several instruments that were not relevant to their interstellar space mission. This provided extra power to operate.

The Voyager 2 spacecraft carries 10 instruments, of which four are still operational for further collection of interstellar data.

These instruments will study the space beyond the heliosphere, which is the Sun’s sphere of influence created by particles and magnetic fields.

“The probe has enough power to continue exploring this region with at least one operational science instrument into the 2030s,” a NASA release noted.

“Mission engineers have taken steps to avoid turning off a science instrument for as long as possible because the science data collected by the twin Voyager probes is unique,” it added.

Even as its instruments are turned off, Voyager 2 will continue its journey, carrying the message of humanity to the stars.

The mission team continues to track the spacecraft’s health and remaining resources to strategize how to collect scientific data from the remaining instruments in the future.