Voyager 1 Went Silent for Two Days, Then Came Back Before Its One-Light-Day Milestone
NASA says the probe's thrusters switched to backups on their own, and a power-saving swap of three heaters has extended the life of its remaining instruments.
NASA's Voyager 1, the most distant human-made object, briefly fell silent in October and then reappeared on its own, the agency's Voyager team announced. The spacecraft, launched in 1977 and now about 16 billion miles (24 billion kilometers) from Earth, missed two scheduled communication attempts with NASA's Deep Space Network on Oct. 18 and 19. Its signal returned on Oct. 20, after the unexpected loss of communication resolved itself about 48 hours in, before engineers sent any commands to troubleshoot.
Engineers are still investigating the cause. So far, the team has determined that one group of thrusters went offline and their backups turned on. Such a swap is programmed to happen automatically if the spacecraft's computers detect something amiss, a response known as fault protection that puts the probe into a safe configuration and pauses normal operations while engineers diagnose the problem. "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. "We're relieved to be back in contact with Voyager 1 and are eager to understand what happened."
The scare came weeks after a separate success. In early September, engineers turned off three devices on Voyager 1 and substituted three lower-power alternatives in an effort nicknamed the "Big Bang." The team had done the same swap on Voyager 2 about six weeks earlier. The Big Bang was unique because the three swaps had to happen simultaneously: the six devices help keep the spacecraft warm enough to operate in the frigid expanse of space, and only by changing all three could the team both reduce power use and ensure heat is properly distributed.
The power budget is the central problem for both probes. The Voyagers draw electricity from radioisotope thermoelectric generators, which convert heat from decaying plutonium into power, and each probe loses about 4 watts a year. Nearly half a century after launch, the margins are thin, which has forced the team to shut off nonessential systems. In recent years, the dwindling supply has forced the team to turn off two science instruments. The mission launched with 10 dedicated science instruments, some of which were turned off after the planetary encounters, and some were left on to study the outer region of the heliosphere, the bubble of particles and magnetic fields created by the sun.
Without the Big Bang swap, the team would have needed to turn off another instrument on Voyager 1 as early as summer 2027, NASA said. Now the Voyagers are traveling through interstellar space, the area outside the heliosphere, and are the only spacecraft ever to study that region directly. The swap should let the remaining instruments keep operating longer than previously expected.
A symbolic distance is next. On Nov. 18, Voyager 1, moving at about 38,000 mph (61,155 kph), will be 16.09 billion miles (25.89 billion kilometers) from Earth, the equivalent of one light-day. Radio waves take 24 hours to reach the probe, and its reply takes another 24 hours to return. "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 when it passes one light-day, and nothing will change aboard it. NASA said the milestone's significance is in demonstrating the vastness of the universe and the endurance of humanity's most distant explorer.
