The two Voyager spacecraft have been hurtling through space since 1977, powered by decaying pieces of plutonium that produce less and less energy each year.
With less electricity available, NASA has decided to shut down an experiment on Voyager 2, the plasma science instrument. This device measures the amount and direction of ionized particles passing through the ship.
While Voyager 2 still has enough power to power the other four operational instruments, it will likely dwindle to just one by 2030.
NASA said that over the past several years, engineers for the mission have taken steps to avoid turning off any science instruments for as long as possible, since the science data collected by the two Voyager probes is unique.
As the first spacecraft to reach interstellar space – the region outside the heliosphere – this is currently our only chance to study this region.
However, this particular instrument has collected limited data in recent years due to its orientation relative to the direction that plasma flows in interstellar space.
The 47-year-old Voyager 2 is traveling at about 15 km/second (35,000 miles per hour) and is currently more than 20.5 billion km (12.8 billion miles) from Earth.
The remaining four science instruments are studying the region outside our heliosphere and include a magnetometer to study the interplanetary magnetic field, a charged particle instrument that measures ion and electron scattering, a cosmic ray system to determine the origin of interstellar cosmic rays, and a detector of plasma waves.
The Grand Tour
The two Voyagers were both launched in 1977 (August and September), and their different trajectories were designed to take advantage of a rare geometric arrangement of the outer planets in the late 1970s and 1980s, which allowed a tour of four planets for a minimum of thrust and travel time.
The positions of these planets – which only occur every 175 years – took Voyager 2 (which launched first) close to the gas giants Jupiter and Saturn, and then its flight path allowed encounters with the ice giants Uranus and Neptune.
It remains the only spacecraft to have visited one of the ice giant planets.
Voyager 1 made flybys of Jupiter, Saturn, and Saturn’s largest moon, Titan. Both spacecraft made remarkable discoveries of distant planets, and the stunning images sent back to Earth opened up a whole new way of looking at the outer solar system.
Now, they are in the phase of the Voyager interstellar mission, where their data helped characterize and study the regions and boundaries of the outer heliosphere, and now explore the interstellar medium.
Voyager 1 crossed the heliopause and entered interstellar space on August 25, 2012. Voyager 2 entered interstellar space on November 5, 2018, at a distance of 119.7 AU.
Both communicate with Earth through the deep space network. It takes nearly a day for one-way communications to reach each spacecraft and another day for the data to be sent back to Earth.
Declining power
Each Voyager 2 is powered by three multihundred-watt radioisotope thermoelectric generators (RTGs).
At launch, each RTG provided enough heat to generate approximately 157 watts of electricity, and so collectively, the RTGs supplied the ship with 470 watts at launch, and their power halves every 87.7 years.
They were expected to allow operations to continue at least until 2020, but are still providing enough power for some data collection and communications. NASA estimates that they lose about 4 watts of power each year.
After the twin Voyagers completed their exploration of the giant planets in the 1980s, the mission team deactivated several scientific instruments that would not be used to study interstellar space. This gave the ship a lot of extra power until a few years ago.
Since then, the team has turned off all onboard systems not essential to the operation of the probes, including some heaters. To delay the shutdown of another science instrument, they also adjusted how Voyager 2’s voltage is monitored.
The device that was recently shut down, the Plasma Science Instrument, measured the amount of plasma (electrically charged atoms) and the direction in which it was flowing.
In 2018, the Plasma Science Instrument helped determine that Voyager 2 left the heliosphere.
Within the heliosphere, particles from the Sun flow outward, away from our parent star. Since the heliosphere is moving through interstellar space, the plasma flows almost in the opposite direction to the solar particles.
When Voyager 2 exited the heliosphere, the plasma flow in the instrument dropped dramatically.
Recently, the instrument has been used only once every three months, when the spacecraft makes a 360-degree turn on its axis toward the Sun. This limited use influenced the mission’s decision to shut down this instrument before others.
NASA said the same plasma science instrument on Voyager 1 stopped working in 1980 and was turned off in 2007 to save energy.
This article was originally published by Universe Today. Read the original article.