Voyager 1, the only spacecraft wandering around beyond the limits of our solar system, has responded to a NASA signal despite being extremely far away.
Voyager 1's thrusters are placed at the back of the spacecraft. [Image by NASA - JPL-Caltech]
NASA sent Voyager 1 to space on September 5, 1977, as part of a program intent on studying the outer reaches of our solar system. Now, 40 years later, Voyager 1 is 21 billion kilometers away from Earth, a distance that’s 141 times the distance of the Earth from the Sun. However, in spite of this distance, the spacecraft has shown that it can still follow instructions sent from Earth.
In late November, NASA sent Voyager 1 instructions to fire four trajectory thrusters, which have been lying dormant for 37 years. If Voyager 1 was able to respond accordingly, it would mean that the thrusters are not only still functional, but also able to function for attitude control.
Just 19 hours and 35 minutes after NASA sent the signal, Voyager 1 responded.
Artist's impression of Voyager 1 entering interstellar space.
The four “trajectory correction maneuver” (TCM) thrusters hadn’t been used since November 1980, during the spacecraft’s amazing flyby around Saturn. Now, nearly four decades later, NASA scientists wanted to see if the thrusters were still able to do their job.
Apparently, they were. The thrusters, according to NASA, passed with flying colors.
In August 2012, Voyager 1 became the first spacecraft to enter interstellar space, or the space that is no longer affected by the sun’s material and magnetic field. In short, it was the space beyond the bounds of our solar system. The performance of the thrusters had apparently been getting somewhat worse for at least three years, which is of course not ideal. After all, the thrusters were tasked with orienting the spacecraft in such a way that communication with Earth, even from interstellar space, would be possible.
"The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters," Chris Jones, JPL’s chief engineer.
TCM thrusters are used in a continuously fired mode. Attitude control, however, requires short bursts of activity. NASA’s tests revealed that not only can the thrusters work for their intended purpose, but can also work for attitude control as well.
A window into interstellar space [Image by NASA, ESA, and the Hubble Heritage Team]
"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, Voyager project manager.
Still, the TCM thrusters won’t be in continuous use. TCM thrusters require heat, which requires power, of which Voyager 1 doesn’t have a bottomless supply. Once the power supply gets too low, Voyager 1 will go back to using the actual attitude control thrusters instead of the TCM thrusters.
Voyager 1, if nothing else, is a pioneer. It was the first spacecraft to tour Jupiter, Saturn, Uranus, and Neptune. After it passed these planets, it simply kept on going until it left the solar system and reached interstellar space, becoming the first and so far only spacecraft to be able to do so. Voyager 2, which was launched in 1977 just a few weeks after Voyager 1, will be able to join its pioneering sibling in interstellar space in just a few years.
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