But this record feat would not be possible without the engineers who had to make crucial decisions to keep the double spacecraft running. Now, they have a new plan that will keep Voyager 1 and 2 in the waking state and allows scientists to continue to receive vital data on some of the space that we've never had explored.
One of the difficulties is to maintain the current, necessary to operate the scientific instruments as well as the radiators that will prevent them from freezing in the deepest spaces. Both probes are now more than 11 billion kilometers from the sun, making it a crucial element for maintaining functions. If the fuel fails to power the thrusters ensuring that both probes direct their antennas to Earth, engineers will not be able to receive data or communicate with the probes.
Over time, the efficiency of the power system has decreased and the generators produce 40% less than at the time of their launch.
The thrusters of both spacecraft are also degraded. They send small bursts that point the spacecraft, which means that their antennas are always directed towards the Earth. Voyager 2 will soon launch a new series of thrusters last used during its flight over Neptune in 1989. Engineers did the same with the Voyager 1 thrusters in 2017.
Voyager 2 is the main priority for receiving new plans as it collects more data with an instrument that does not operate on Voyager 1. It also consumes more energy. The engineers therefore deactivated the heating of the Cosmic Ray subsystem. This instrument has dropped to minus 74 degrees Fahrenheit, but it still sends data. This is remarkable considering the fact that the instrument was initially tested at a temperature not exceeding 49 degrees Fahrenheit.
"It's amazing that Voyagers' instruments have proven so robust," said Suzanne Dodd, Voyager Project Leader, in a statement. "We are proud that they have stood the test of time." The long life of the spacecraft means that we are faced with scenarios that we would never have imagined. We will continue to explore all the options we have to keep Voyagers doing the best science possible. "
The Cosmic Ray subsystem was essential for communication when Voyager 2 entered interstellar space last year.
This boundary between the hot solar wind and the cold interstellar space is called heliopause. The mission scientists compared the Voyager 2 instrument data to determine that the crossing date was November 5th, when the solar wind particles around the probe plummeted.
"There is still much to be learned about the region of interstellar space just beyond the heliopause," said Ed Stone, Voyager project scientist, in a statement.
However, it is not because the probes have left the heliosphere that they have left our solar system. This boundary is the outermost edge of the Oort Cloud, a group of small objects influenced by the gravity of our sun.
Mission scientists estimate that it would take 2,300 years for Voyager to reach the inner edge of the cloud and 30,000 years to fly over it completely.
Voyager 2 contains something unique: two Plasma Science experiment instruments. Voyager 1 has one and stopped working in 1980.
They will be able to take unprecedented observations in this part of the interstellar space and send them back to the scientists of the mission. Scientists can still communicate with Voyager 2, even in interstellar space, but it takes about 16.5 hours for the data to go to Earth.
Learning more about interstellar space also helps to better understand radiation, which is essential to inform inhabited missions more deeply in our solar system.
Voyager 2 returns data from its five operational instruments, which provide information on particles, plasma and clouds of rapidly moving materials in interstellar space. Voyager 1 also returns data from similar instruments.
With the new plan to save energy and steer the satellite, engineers expect Voyager 1 and 2 to return data for at least the next few years.
"The two Voyager probes explore areas never visited before, so every day is a day of discovery," said Voyager project scientist Ed Stone. "Traveling will continue to surprise us with new ideas about deep space."