Launched in 1977, the Voyager probes are the longest-serving spacecraft in history, capturing data from Jupiter, Saturn, Neptune and Uranus before continuing their journeys beyond the heliosphere to interstellar space. Voyager 1 is now almost 22 billion km from the Sun, while its sibling is a mere 18 billion km.
Each of the probes is powered by three radioisotope thermoelectric generators, or RTGs, which produce heat via the natural decay of plutonium-238 radioisotopes and convert that heat into electrical power. Because the heat energy of the plutonium in the RTGs declines and their internal efficiency decreases over time, each spacecraft is producing about 4 fewer watts of electrical power each year. That means the generators produce about 40 per cent less than at the time of launch nearly 42 years ago, limiting the number of systems that can run on the spacecraft.
The mission's new power management plan explores multiple options for dealing with the diminishing power supply on both spacecraft, including shutting off additional instrument heaters over the coming years.
"It's incredible that Voyagers' instruments have proved so hardy," said Voyager project manager Suzanne Dodd, from 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."
Voyager 2 continues to return data from five instruments as it travels through interstellar space. In addition to the cosmic ray subsystem (CRS) instrument, which detects fast-moving particles that can originate from the Sun or from sources outside our solar system, the spacecraft is operating two instruments dedicated to studying plasma and a magnetometer for understanding the sparse clouds of material in interstellar space.
Taking data from a range of directions, the low-energy charged particle instrument is particularly useful for studying the probe's transition away from our heliosphere. Because CRS can look only in certain fixed directions, the Voyager science team decided to turn off that instrument's heater first. Decisions had to be made sooner for Voyager 2 than Voyager 1 because the former has one more science instrument collecting data - and drawing power - than its sibling. On the back of the new power management plans, NASA believes that both spacecraft should continue to send valuable data back to Earth for years to come.
"Both Voyager probes are exploring regions never before visited, so every day is a day of discovery," said Project Scientist Ed Stone, who is based at Caltech. "Voyager is going to keep surprising us with new insights about deep space."
Nanogenerator consumes CO2 to generate electricity
Whoopee, they've solved how to keep a light on but not a lot else.