March 5 (UPI) -- Engineers at NASA's Jet Propulsion Laboratory have conserved energy supplies on the record-setting Voyager 1 & 2 deep space probes nearly 50 years after their missions launched to extend them further.
NASA launched the probes in 1977, which rely on a diminishing radioisotope power system that uses the heat from decaying plutonium to generate electrical power.
Each probe loses about 4 watts of power every year, but NASA has extended their respective missions by shutting down some of its instruments to conserve their remaining power sources.
"The Voyagers have been deep space rock stars since launch," Voyager project manager Suzanne Dodd said. "We want to keep it that way as long as possible."
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Dodd said the probes' electrical power is [running low](https://www.nasa.gov/centers-and-facilities/jpl/nasa-turns-off-2-voyager-science-instruments-to-extend-mission/) and only would have a few more months of power before shutting down and ending their missions without taking steps to reduce power consumption.
Each spacecraft contains identical sets of 10 scientific instruments, some of which are designed to collect data during planetary flybys.
The instruments for the flybys have been turned off after each probe completed exploratory missions of the solar system's gas giants.
Other instruments have remained under power while studying the solar system's heliosphere, which NASA describes as a "bubble of solar wind and magnetic fields created by the Sun."
The remaining powered instruments also will help the probes explore interstellar space, which is the region located outside the heliosphere.
The Voyager 1 and Voyager 2 probes reached the edge of the heliosphere and began entering interstellar space in 2012 and 2018, respectively.
They are the only man-made spacecraft that have operated in interstellar space.
NASA engineers in October shut down an instrument that measures the amount and direction of electronically charged atoms called plasma on Voyager 2.
Engineers shut down the same instrument on Voyager 1 years ago due to degraded performance.
Mission engineers last week shut down the cosmic ray subsystem on Voyager 1, which was used to study cosmic rays, including protons, by measuring their energy and flux.
The cosmic ray subsystem used three telescopes to accomplish its mission and determine when and where the probe exited the heliosphere.
Mission engineers also are preparing to deactivate Voyager 2's low-energy charged-particle instrument that measures ions, electrons and cosmic rays that originate from within the solar system and galaxy.
"The Voyager spacecraft have far surpassed their original mission to study the outer planets," NASA Voyager program scientist Patrick Koehn said.
"Every bit of additional data we have gathered since then is not only valuable bonus science for heliophysics, but also a testament to the exemplary engineering that has gone into the Voyagers - starting nearly 50 years ago and continuing to this day."
The NASA engineers say the probes should operate for another year before each will require another system to be shut down to preserve more power and extend their missions.
The power-conservation plan for the Voyager 1 and 2 probes should enable them to remain active into the 2030s.
Each probe has suffered deep-space weathering for 47 years, which might lessen their service lives.
Each probe is the most distance man-made object ever built with Voyager 1 traveling more than 15 billion miles from Earth and Voyager 2 more than 13 billion miles, according to NASA.
"Every minute of every day, the Voyagers explore a region where no spacecraft has gone before," Voyager project scientists Linda Spilker said.