NASA engineers are conducting an extremely long-range reconfiguring of the space agency's two 42-year-old Voyager deep-space probes to extend their service lives. By cutting back and reallocating heating resources and bringing back online thrusters that haven't been used in decades, the goal is to keep the unmanned spacecraft sending back data from the frontiers of the solar system for several more years.
Launched separately in 1977, the Voyager 1 and 2 missions are not just a spectacular success in the annals of deep-space exploration, but an ongoing one. As they flew on slingshot trajectories that are sending them out of the solar system, never to return, they sent back spectacular images of Jupiter, Saturn, Uranus, and Neptune, and are currently returning instrument data as they pass into interstellar space.
Unfortunately, after more than four decades in service, the two probes are showing their age. According to NASA, they are the oldest operating non-passive spacecraft and now they are suffering from the encroaching cold 11 billion miles (18 billion km) from the Sun as their nuclear power plants run down. Too distant to use solar panels, the Voyager craft rely on radiothermal generators (RTGs) that derive power from decaying plugs of plutonium-238 fuel.
These generators allow the Voyagers to not only run their instruments, but also keep the vulnerable electronics from becoming too cold to operate. The RTGs lose four watts per year and are now running at only 60 percent of their original output. This means that they are expected to fail sometime around 2025.
To ensure that the spacecraft continue to work while power is available, NASA engineers are now deciding which instruments to take heating rations away from to give to others. This is particularly important for Voyager 2, which has an additional instrument drawing power. The Cosmic Ray Subsystem (CRS) subsystem measures the charged particles that bombard the spacecraft, but now its heater is being switched off.
NASA says that this is the first of a series of instrument shutdowns with more to follow in the next few years. Meanwhile, other cosmic ray, plasma, magnetometer, and low-energy charged particle instruments will continue to collect data.
In addition, the space agency has determined that Voyager 2's attitude thrusters have begun to degrade. A similar problem was seen with Voyager 1 in 2017 and, like with Voyager 1, Voyager 2 has been ordered to bring back online a second set of thrusters that have not been used since its 1989 flyby of Neptune.
"It's incredible that Voyagers' instruments have proved so hardy," says Voyager Project Manager Suzanne Dodd at NASA's Jet Propulsion Laboratory in Pasadena, California. "We're proud they've withstood the test of time. The long lifetimes of the spacecraft mean we're dealing with scenarios we never thought we'd encounter. We will continue to explore every option we have in order to keep the Voyagers doing the best science possible."
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