NASA's Voyager 1 Conserves Power, Resolves Brief Communications Pause

This image, taken on April 27, 1977, shows one of the Voyagers in the 25-Foot Space Simulator thermal vacuum chamber at NASA’s Jet Propulsion Laboratory in Southern California.

The agency’s longest-running mission is approaching a historic distance milestone as its team members implement creative engineering solutions to keep it going.

NASA’s Voyager team is celebrating two recent developments with the Voyager 1 spacecraft: In September, they successfully completed a months-long effort to stretch the spacecraft’s diminishing power supply. Then, on Oct. 20, an unexpected loss of communication with the spacecraft resolved itself after 48 hours, before the team sent commands to the spacecraft to troubleshoot the issue.

In early September, engineers successfully turned off three devices on the Voyager 1 spacecraft and substituted them with three lower-power alternatives. Nicknamed the “Big Bang,” the energy-saving effort was completed about six weeks after the mission team performed the same swap on Voyager 2. The Big Bang will enable Voyager 1’s remaining science instruments to operate longer than previously anticipated.

The Voyagers get their power from radioisotope thermoelectric generators, which convert heat from decaying plutonium into electricity. With the plutonium supply continually depleting, both probes lose about 4 watts of power each year. Almost a half-century since Voyager launched, the spacecraft power margins have grown thin, requiring the team to conserve energy by shutting off nonessential devices and systems.

The Big Bang was unique because it required the swaps to occur simultaneously. The six devices help keep the spacecraft warm enough to operate in the frigid expanse of space, and only by swapping all three could the team both reduce the amount of power Voyager 1 uses and ensure that heat is properly distributed on the spacecraft.

In recent years, the dwindling power supply has forced the team to turn off two science instruments. The mission launched in 1977 with 10 dedicated science instruments, some of which were turned off after the spacecraft’s planetary encounters. Some instruments were left on to study the outer region of the heliosphere, a bubble of particles and magnetic fields created by the Sun. Now, the Voyagers are traveling through interstellar space, the area outside the heliosphere, and are the only spacecraft to ever study this region directly. Without performing the Big Bang, the mission would have needed to turn off another instrument on Voyager 1 as early as summer 2027.

But between now and summer 2027, the team is at the ready for more surprises like the one they recently encountered when they briefly lost contact with Voyager 1 on Oct. 18 and 19. NASA’s Deep Space Network — large antennas at three facilities around the globe used to communicate with spacecraft at the Moon and beyond — was unable to detect a radio signal from the probe, which is 16 billion miles (24 billion kilometers) from Earth, during two scheduled communications attempts, 24 hours apart. The spacecraft’s signal reappeared 24 hours later, on Oct. 20, and the team has maintained communication with it since then.

Engineers still are investigating what caused the communication loss. The team has so far determined that one group of thrusters went offline and their backups turned on. Such a swap is programmed to occur automatically if the spacecraft computers detect something amiss with the active thrusters. This automatic response is known as fault protection and directs the spacecraft to put itself in a safe, or stable, configuration and pause normal operations, giving engineers time to diagnose the issue and take action.

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“This is the first time we’ve seen the spacecraft do something like this, but we are also at a point in the mission where we have to expect the unexpected,” said Kareem Badaruddin, Voyager mission manager at NASA’s Jet Propulsion Laboratory in Southern California. “We’re relieved to be back in contact with Voyager 1 and are eager to understand what happened.”

As the investigation continues, Voyager 1 is speeding at 38,000 mph (61,155 kph) toward a major milestone: On Nov. 18, the spacecraft that has traveled farther than any other human-made object will be 16.09 billion miles (25.89 billion kilometers) from Earth — the equivalent of one light-day, or the distance that light can travel in one day. That means that the radio waves used to communicate with the probe take 24 hours to reach it, and the radio waves carrying the spacecraft’s return message take another 24 hours.

“If you want to say ‘hello’ to Voyager, you send your message and then you go home and you wait two days before you finally get a response,” said Suzanne Dodd, Voyager project manager at JPL.

The spacecraft will not detect any change in its environment when it passes one light-day, nor will anything change aboard the spacecraft. The milestone’s significance is in its demonstration of the vastness of the universe and the endurance of humanity’s most distant explorer.

For more information about NASA’s Voyager mission, visit:

Jet Propulsion Laboratory, Pasadena, Calif.

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