Voyager 1 fires up some of its thrusters
15 billion miles away from Earth, well beyond the heliosphere (The region surrounding the Sun and the solar system filled with the solar magnetic field and the protons and electrons of the solar wind -This extends well beyond Pluto’s orbit). A 47-year-old spacecraft is still making its way through interstellar space. It is the furthest away spacecraft ever but when it lifted off to space on September 5th 1977, it was never planned to still be operating today.
Due to this unexpectedly long mission, Voyager 1 is inadvertently experiencing problems due to parts ageing, especially in the extreme conditions that being in space exposes it to. The sheer distance between us and Voyager 1 also makes any communications and remote repairs difficult for the team at NASA’s Jet Propulsion Laboratory (JPL) in California.
Earlier this year, engineers detected an issue with one of the thrusters on the Voyager spacecraft. The problem was that a fuel tube inside the thruster became clogged with silicon dioxide, a byproduct from the ageing of the fuel tank’s rubber diaphragm. Thrusters on spacecraft like Voyager work by expelling fuel to generate force, which is necessary for controlling the spacecraft's orientation and movement.
The thrusters are powered by converting liquid hydrazine to a gas and expelling it in short “puffs” about 40 times a day to ensure that Voyager is orientated correctly.
If a fuel tube is clogged, it means the thruster can't expel fuel as effectively, reducing the amount of force it can generate. This is a big concern because the thrusters are responsible for keeping the spacecraft properly oriented in space. Orientation is crucial for Voyager because its antennas need to be pointed precisely towards Earth to maintain communication. If the thrusters can’t do their job, Voyager might drift out of alignment, making it difficult or even impossible to send data back to Earth. “If the thrusters that keep the antenna pointed at Earth get clogged, that would be end of mission,” says Calla Cofield, media relations specialist at JPL. Although the team sent commands to the spacecraft to switch to another set of thrusters, that was not the end of the fix.
Over recent decades Voyager has had to switch over to different sets of thrusters, of which it has 3 sets:
two sets of attitude propulsion thrusters
one set devoted to trajectory correction manoeuvres.
Unlike its time spent exploring around the gas giants, it is now on an unchanging path away from our solar system, meaning it only needs 1 set of these thrusters to allow the antenna to be pointed towards us.
In 2002, the team instructed Voyager 1 to switch to its second set of attitude control thrusters after the first set began showing signs of clogging. Then, in 2018, they switched to the trajectory correction thrusters when the second set also seemed to be clogged.
However, when the team recently checked the status of the trajectory correction thrusters, they found that these thrusters were even more clogged than the previous two sets.
When Voyager was initially switched to the trajectory correction thrusters six years ago, the tube opening measured 0.01 inches (0.25 millimetres) across. But now, due to clogging, the opening has shrunk to just 0.0015 inches (0.035 millimetres)—half the width of a human hair, according to NASA.
To conserve power on both the Voyager 1 and 2 missions, NASA has had to turn off nonessential systems, including heaters. This has caused the spacecraft to get even colder and the team could not just send a command to turn on one of the sets of altitude control thrusters without warming them up a bit. However, a problem arises because Voyager 1 does not have enough power to turn on the heaters without shutting something else off, and to stay safe, the team steered clear of shutting off any of the scientific instruments in case they would not be able to come back on again. This is why NASA decided to turn off its main heater for an hour to allow the thruster heaters to come on instead and safely make the switch of thrusters.
Luckily, this plan worked and on August 27th Voyager 1 was once again relying on one of its original thruster sets. Todd Barber, Voyager propulsion engineer. says, “The team has taken steps to use the thrusters less, and it is expecting to get another two to three years out of the original set.”
Voyager 2 has also gone through thruster swaps in 1999 and 2019, and “the situation there is less dire,” Barber said. Voyager 2 has travelled more than 12 billion miles from Earth.
Once Voyager 1 has finished with this set of thrusters its only option will be to go back to the other set of already clogged attitude propulsion thrusters. “All the decisions we will have to make going forward are going to require a lot more analysis and caution than they once did,” said Suzanne Dodd, Voyager’s project manager, in a statement.
