As Suzanne Dodds When the team transmitted a routine command to Voyager 2 on July 21, the unthinkable happened: They accidentally sent the wrong version, which pointed the interstellar probe’s antenna slightly away from Earth. The next time they expected to receive data, they heard nothing at all. The small glitch almost caused humanity to lose contact with the popular spacecraft, which is now 12.4 billion miles from home. Along with its twin, Voyager 1, it is humanity’s most distant spacecraft still collecting data.
Here’s what happened: Dodd’s team at NASA’s Jet Propulsion Laboratory did indeed spot and correct the error in the command—but then inadvertently sent the erroneous version. “It felt awful. It was a moment of panic because we were off point by two degrees, which was significant,” says Dodd, the project manager for the interstellar mission Voyager.
The team agreed on a solution: issue a “yell” command in the direction of the probe, instructing it to point the antenna back towards Earth. If the signal was strong enough, the vehicle could still pick it up even if its antenna was offset.
On the morning of August 2, they transmitted the strongest signal they could from the high-altitude, 70-metre, 100-kilowatt S-band transmitter at the communications station in Canberra, Australia. The station is part of NASA’s Deep Space Network, an international system of giant antennas managed by JPL. (Due to Voyager 2’s trajectory, it can only be communicated with through telescopes in Earth’s southern hemisphere.)
There was no guarantee of success, and it would take 37 hours to show if the solution had worked: the time it took for their signal to ping the ship and then – if they were lucky – for a signal to come on from Voyager 2 her back.
The team spent a sleepless night waiting. And then relief: It worked. Contact was reestablished at 9:30 p.m. Pacific Time on August 3. “We went from ‘Oh my god, that happened’ to ‘It’s wonderful, we’re back,'” says Linda Spilker, Voyager Project Scientist at JPL.
If the attempt had failed, the team would only have had one backup option: the error protection routine of the on-board software. Several failsafes were programmed into Voyager to automatically take action to deal with circumstances that could harm the mission. The next routine should begin in mid-October. If it had worked it would have generated a correct pointing command and hopefully pointed the antenna in the right direction.
Voyager has been flying since the late 1970s – they’ll be 46 in a few weeks – and as Spilker points out, “That was a two-week period without scientific data, the longest period without it.” In the 2010s, they crossed the heliopause, the boundary between the solar wind and the interstellar wind. Since then, they’ve been collecting data on the edge of the heliosphere, the protective bubble of particles and magnetic fields created by the Sun that interacts with the interstellar medium in unknown ways.
Still, this two-week period of no contact did not interrupt the team’s scientific work. “Voyager science doesn’t need constant monitoring,” Calla Cofield, a JPL spokeswoman, told WIRED via email. “They’re studying this region of space over long distances, so a few weeks’ break won’t hurt those studies.”