The team decided to turn off another scientific instrument of the Voyager 2 probe to save energy and prolong the mission in interstellar space
NASA mission engineers have worn out lo scientific instrument plasma aboard the space probe Voyager 2, due to the progressive reduction of the probe’s electrical power supply, to save energy. Traveling more than 20.5 billion kilometers from Earth, the space probe continues to use four scientific instruments to study the region outside our own, the protective bubble of particles and magnetic fields created by the Sun. The probe has enough power to continue to explore this region with at least one operational scientific instrument until 2030. Mission engineers have taken measurements on another scientific tool to preserve the probe for as long as possible: the scientific data collected by the twin Voyager probes are unique, no other man-made craft has operated in interstellar space, the region outside the heliosphere.
Turning off plasma detection
The plasma science instrument measures the amount of plasma (electrically charged atoms) and the direction in which it flows. It has collected limited data in recent years due to its orientation relative to the direction plasma flows in interstellar space. Both probes are powered by decaying plutonium and . After the two Voyager probes completed their exploration of the giant planets in the 1980s, the mission team turned off several scientific instruments that would not be used in the study of interstellar space.
This gave the probe a lot of extra power until a few years ago. Since then, the team has shut down all onboard systems not essential to the probes’ operation. To postpone having to shut down another science instrument, they also changed how Voyager 2’s voltage is monitored. On September 26, engineers gave the command to shut down the plasma science instrument. Sent by NASA’s Deep Space Network, , and the return signal took another 19 hours to reach Earth.
In 2018, the plasma science instrument proved critical in determining that . The boundary between the heliosphere and interstellar space is demarcated by changes in atoms, particles and magnetic fields that instruments on Voyagers can detect. Inside the heliosphere, particles from the Sun flow outward, away from our nearest star. The heliosphere is moving through interstellar space, so at Voyager 2’s location near the front of the solar bubble, the plasma is flowing almost in the opposite direction to the solar particles.
Constant monitoring
Mission engineers always carefully monitor changes made to the 47-year-old spacecraft’s operations to ensure they do not generate unwanted side effects. The team confirmed that the shutdown command and that the probe is functioning normally. The scientific plasma instrument consists of four “cups”. Three cups point in the direction of the Sun and observed the solar wind while inside the heliosphere. A fourth points at right angles to the direction of the other three and has observed plasma in planetary magnetospheres, the heliosphere, and now interstellar space.
When Voyager 2 exited the heliosphere, the plasma flow in the three facing cups dropped dramatically. The most useful data from the fourth cup arrives only once every three months, when the probe makes a 360-degree turn on the axis pointing towards the Sun. This factor influenced the mission’s decision to shut down this instrument before others. The plasma science instrument on Voyager 1 stopped working in 1980 and was turned off in 2007 to save energy. Another instrument aboard Voyager 2, called the plasma wave subsystem, can estimate plasma density when eruptions from the Sun drive shocks through the interstellar medium, producing plasma waves.
The Voyager mission team continues to monitor the probe’s health and available resources to make engineering decisions that maximize the mission’s scientific outcomes.
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