If you tried to start a car that’s been sitting in a garage for decades, you might not expect the engine to respond. But a set of thrusters aboard the Voyager 1 spacecraft successfully fired up Nov. 29, 2017, after 37 years without use.

Voyager 1, NASA’s farthest and fastest spacecraft, is the only human-made object in interstellar space, the environment between the stars. The spacecraft, which has been flying for 40 years, relies on small devices called thrusters to orient itself so it can communicate with Earth. These thrusters fire in tiny pulses, or “puffs,” lasting mere milliseconds, to subtly rotate the spacecraft so that its antenna points at our planet. Now, the Voyager team is able to use a set of four backup thrusters, dormant since 1980.

“With these thrusters that are still functional after 37 years without use, we will be able to extend the life of the Voyager 1 spacecraft by two to three years,” said Suzanne Dodd, project manager for Voyager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

Since 2014, engineers have noticed that the thrusters Voyager 1 has been using to orient the spacecraft, called “attitude control thrusters,” have been degrading. Over time, the thrusters require more puffs to give off the same amount of energy. At 13 billion miles from Earth, there’s no mechanic shop nearby to get a tune-up.

The Voyager team assembled a group of propulsion experts at NASA’s Jet Propulsion Laboratory, Pasadena, California, to study the problem. Chris Jones, Robert Shotwell, Carl Guernsey and Todd Barber analyzed options and predicted how the spacecraft would respond in different scenarios. They agreed on an unusual solution: Try giving the job of orientation to a set of thrusters that had been asleep for 37 years.

“The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters,” said Jones, chief engineer at JPL.

In the early days of the mission, Voyager 1 flew by Jupiter, Saturn, and important moons of each. To accurately fly by and point the spacecraft’s instruments at a smorgasbord of targets, engineers used “trajectory correction maneuver,” or TCM, thrusters that are identical in size and functionality to the attitude control thrusters, and are located on the back side of the spacecraft. But because Voyager 1’s last planetary encounter was Saturn, the Voyager team hadn’t needed to use the TCM thrusters since November 8, 1980. Back then, the TCM thrusters were used in a more continuous firing mode; they had never been used in the brief bursts necessary to orient the spacecraft.

All of Voyager’s thrusters were developed by Aerojet Rocketdyne. The same kind of thruster, called the MR-103, flew on other NASA spacecraft as well, such as Cassini and Dawn.

On Nov. 28, 2017, Voyager engineers fired up the four TCM thrusters for the first time in 37 years and tested their ability to orient the spacecraft using 10-millisecond pulses. The team waited eagerly as the test results traveled through space, taking 19 hours and 35 minutes to reach an antenna in Goldstone, California, that is part of NASA’s Deep Space Network.

Lo and behold, on Nov. 29, they learned the TCM thrusters worked perfectly — and just as well as the attitude control thrusters.

“The Voyager team got more excited each time with each milestone in the thruster test. The mood was one of relief, joy and incredulity after witnessing these well-rested thrusters pick up the baton as if no time had passed at all,” said Barber, a JPL propulsion engineer.  

The plan going forward is to switch to the TCM thrusters in January. To make the change, Voyager has to turn on one heater per thruster, which requires power — a limited resource for the aging mission. When there is no longer enough power to operate the heaters, the team will switch back to the attitude control thrusters.

The thruster test went so well, the team will likely do a similar test on the TCM thrusters for Voyager 2, the twin spacecraft of Voyager 1. The attitude control thrusters currently used for Voyager 2 are not yet as degraded as Voyager 1’s, however.
 
Voyager 2 is also on course to enter interstellar space, likely within the next few years.

The Voyagers in popular culture
Whether you’re traveling across cities, continents or even oceans this holiday season, there is no long-haul flight quite like that of the Voyagers.

This year, we celebrated 40 years since the launch of NASA’s twin Voyager probes — the two farthest, fastest spacecraft currently in operation. Each Voyager has contributed an enormous amount of knowledge about the solar system, including the unexpected diversity of its planets and their moons. Among their many distinctions, Voyager 1 is the only spacecraft to enter interstellar space, and Voyager 2 is the only spacecraft to fly by all four giant planets: Jupiter, Saturn, Uranus and Neptune.

You might have missed the virtual Voyager party, though, since there was a lot of other space news around the time of the Voyager launch anniversaries. The solar eclipse, visible across America, took place on Aug. 21, just one day after Voyager 2 marked 40 years in flight. Sept. 5 was Voyager 1’s launch anniversary, but space fans were already gearing up to commemorate the finale of NASA’s Cassini mission on Sept. 15.

Don’t worry — it’s never too late to appreciate the far-reaching influence the Voyagers have had. In fact, in addition to the news coverage the spacecraft have received, the spacecraft have also earned a place in popular culture.

So, since you might have some downtime as we head into the holidays, here are some Voyager-related movies, TV shows and songs. (Warning: a few spoilers ahead!)

Voyagers in film, television
Perhaps the most widely recognized pop culture Voyager homage is in the film “Star Trek: The Motion Picture” from 1979.

In the film, a machine called V’Ger — the fictional Voyager 6 spacecraft, its intelligence greatly enhanced by an alien race — seeks the home of its creator, Earth, and threatens to wreak havoc on our planet in the process. In real life, John Casani, who was the Voyager project manager at that time at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., offered to loan a Voyager model to “Star Trek” creator Gene Roddenberry. Although the movie version altered the original design, it still used the mission as an inspiration.

The spacecraft had long passed the planets when a 2004 episode of “The West Wing” — titled “The Warfare of Genghis Khan” — mentioned a major mission milestone: Voyager 1 crossing the termination shock. The termination shock is a shockwave that marks the point at which the solar wind from the Sun, which travels at supersonic speeds up to that point, abruptly slows down and heats up. It represents the innermost part of the boundary of the heliosphere, the magnetic bubble that includes the Sun, planets and solar wind. Due to the termination shock crossing, the character Josh Lyman (mistakenly) declares this Voyager 1 to be the first man-made object to leave our solar system (mistakenly, because the solar system ends well beyond that landmark). “Funny, I’m going through a little termination shock myself,” quips the character Donna Moss.

More recently, Voyager 1 did, in real life, cross into interstellar space in 2012, although technically it has still not left the solar system. In 2013, to talk about that milestone, the mission’s project scientist, Ed Stone of Caltech in Pasadena, appeared on Comedy Central’s Colbert Report.

The golden record
Each Voyager contains a copy of a Golden Record filled with Earth’s sights and sounds, including images, music and audio clips of people and animals. This record has been featured in several works of science fiction. In the 1984 film “Starman,” a race of aliens discovers the record and sends an emissary to Earth to learn more about our planet.

A 1994 episode of the X-Files titled “Little Green Men” also paid homage to Voyager. The episode opens with FBI agent Fox Mulder describing the Voyager mission and the Golden Record, including images, music and a child’s voice saying, “Hello from the children of planet Earth.” Mulder says the Voyagers passed the orbit of Neptune and “there were no further messages sent,” but in reality, the Voyagers still communicate with Earth every day.

The mission wasn’t exempt from fun on “Saturday Night Live.” In episode 64, which aired in 1978, a psychic played by actor Steve Martin says the extraterrestrials had found the record and replied, “Send More Chuck Berry” — referring to the iconic song “Johnny B. Goode” included on the Golden Record. Learn more about the Golden Record and see a full list of its contents at https://voyager.jpl.nasa.gov/golden-record/.

And more
Voyager has proved inspirational to contemporary musicians and songwriters as well. The Academy Award-winning composer Dario Marianelli wrote a Voyager violin concerto that had its world premiere in 2014 in Brisbane, Australia, and was subsequently played by the London Symphony Orchestra in 2015. Artist James Stretton also wrote a song in honor of the Voyagers’ 40th anniversary.

For a deep dive into the history of the mission, the documentary “The Farthest” premiered on PBS in August, featuring numerous interviews with Voyager scientists and engineers, past and present.

And if you get tired of looking at your own vacation photos, there are lots to explore on the Voyager website. Live long and prosper, Voyagers!

The Voyager spacecraft were built by NASA’s Jet Propulsion Laboratory, Pasadena, California, which continues to operate both. JPL is a division of Caltech in Pasadena. The Voyager missions are a part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate in Washington. For more information about the Voyager spacecraft, visit https://www.nasa.gov/voyager or https://voyager.jpl.nasa.gov.