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article imageNASA uses 'Plan B' to reorient Voyager 1 in interstellar space

By Karen Graham     Dec 3, 2017 in Technology
NASA scientists needed to reorient the 40-year-old Voyager 1 - the space agency's farthest spacecraft so its antenna would point toward Earth, 13 billion miles away. Their first option, thrusters for reorienting the probe were wearing out. Enter Plan B.
Voyager 1 was launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System. On November 22, 2017, the probe was approximately 13 billion miles (21 billion kilometers), from the Sun. Voyager 1 is also the first human-made spacecraft to leave the solar system.
In its 40 year journey into interstellar space, Voyager 1 completed the objectives of its mission, including flybys of Jupiter, Saturn and Saturn's large moon, Titan. It studied the weather, magnetic fields and rings of the two planets and was the first probe to provide detailed images of their moons.
NASA scientists have been relying on small thrusters, called "attitude control thrusters," on the spacecraft to turn the probe so it can communicate with Earth. The thrusters fire in tiny pulses, or "puffs," lasting mere milliseconds to turn the spacecraft.
Spacecraft that are on trajectories to leave the Solar System. (Note: Voyager 1 left the solar syste...
Spacecraft that are on trajectories to leave the Solar System. (Note: Voyager 1 left the solar system in 2012).
NASA/ Photo ID: ACD97-0036-1.
Main thrusters are wearing out
However, after 40 years, the main thrusters have started wearing out, with scientists noticing it was taking more "puffs" to move the craft into position. However, Voyager 1 does have a set of four backup trajectory correction maneuver thrusters that haven't been used since the 1980s.
The Voyager team assembled a group of propulsion experts at NASA's Jet Propulsion Laboratory, Pasadena, California, to study the problem and come up with a "Plan B." Chris Jones, Robert Shotwell, Carl Guernsey and Todd Barber analyzed options and predicted how the spacecraft would respond in different scenarios.
Saturn and its main rings as seen in this NASA photo are among the wonders visited as part of the Vo...
Saturn and its main rings as seen in this NASA photo are among the wonders visited as part of the Voyager space probe missions
NASA/JPL-Caltech, NASA/JPL/Space Science Institute/AFP
The propulsion experts ended up agreeing on an unusual solution - to try using four "trajectory correction maneuver" (TCM) thrusters, located on the back side of Voyager 1.
"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.
Plan B works perfectly
On November 28, 2017, Voyager engineers fired up the four TCM thrusters for the first time in 37 years, using 10-millisecond pulses. Then they set back and waited for the test results to travel through space. It took 19 hours and 35 minutes for the results to reach an antenna in Goldstone, California,
The Great Red Spot as seen from Voyager 1 This dramatic view of Jupiter s Great Red Spot and its sur...
The Great Red Spot as seen from Voyager 1 This dramatic view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1 on February 25, 1979, when the spacecraft was 5.7 million miles (9.2 million kilometers) from Jupiter. Cloud details as small as 100 miles (160 kilometers) across can be seen here. The colorful, wavy cloud pattern to the left of the Red Spot is a region of extraordinarily complex and variable wave motion. To give a sense of Jupiter's scale, the white oval storm
NASA
And on the next day, November 29, the Voyager team had their answer - The TCM thrusters worked perfectly. "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.
"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, California.
The plan right now is to switch to the TCM thrusters in January.
More about Voyager 1, NASA, attitude control thrusters, Habitable planets, backup thrusters