Author: Tony Greicius

NASA’s Voyager 1 has resumed regular operations 1 following a pause in communication last month. The probe had unexpectedly turned off its primary radio transmitter, called an X-band transmitter, and turned on the much weaker S-band transmitter. Due to the spacecraft’s distance from Earth — about 15.4 billion miles (24.9 billion kilometers) — this switch prevented the mission team from downloading science data and information about the spacecraft’s engineering status.

Earlier this month, the team reactivated the X-band transmitter and then resumed collecting data the week of Nov. 18 from the four operating science instruments. Now engineers are completing a few remaining tasks to return Voyager 1 to the state it was in before the issue arose, such as resetting the system that synchronizes its three onboard computers.

The X-band transmitter had been shut off by the spacecraft’s fault protection system when engineers activated a heater on the spacecraft. Historically, if the fault protection system sensed that the probe had too little power available, it would automatically turn off systems not essential for keeping the spacecraft flying in order to keep power flowing to the critical systems. But the probes have already turned off all nonessential systems except for the science instruments. So the fault protection system turned off the X-band transmitter and turned on the S-band transmitter, which uses less power.

The mission is working with extremely small power margins on both Voyager probes. Powered by heat from decaying plutonium that is converted into electricity, the spacecraft lose about 4 watts of power each year. About five years ago — some 41 years after the Voyager spacecraft launched — the team began turning off any remaining systems not critical to keeping the probes flying, including heaters for some of the science instruments. To the mission team’s surprise, all of those instruments continued to operate despite reaching temperatures lower than what they had been tested at.

The team has computer models designed to predict how much power various systems, such as heaters and instruments, are expected to use. But a variety of factors contribute to uncertainty in those models, including the age of the components and the fact that hardware doesn’t always behave as expected.

With power levels being measured to fractions of a watt, the team also adjusted how both probes monitor voltage. But earlier this year, the declining power supply required the team to turn off a science instrument on Voyager 2. The mission shut off multiple instruments on Voyager 1 in 1990 to conserve energy, but those instruments were no longer in use after the probe flew past Jupiter and Saturn. Of the 10 science instruments on each spacecraft, four are now being used to study the particles, plasma, and magnetic fields in interstellar space.

Voyagers 1 and 2 have been flying for more than 47 years and are the only two spacecraft to operate in interstellar space. Their advanced age has meant an increase in the frequency and complexity of technical issues and new challenges for the mission engineering team.

News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

On Oct. 24, NASA reconnected with the Voyager 1 spacecraft after a brief pause in communications. The spacecraft recently turned off one of its two radio transmitters, and the team is now working to determine what caused the issue.

The transmitter shut-off seems to have been prompted by the spacecraft’s fault protection system, which autonomously responds to onboard issues. For example, if the spacecraft overdraws its power supply, fault protection will conserve power by turning off systems that aren’t essential for keeping the spacecraft flying. But it may take days to weeks before the team can identify the underlying issue that triggered the fault protection system.

When the flight team, which is based at NASA’s Jet Propulsion Laboratory in Southern California, beams instructions to the spacecraft via the agency’s Deep Space Network, Voyager 1 sends back engineering data that the team assesses to determine how the spacecraft responded to the command. This process normally takes a couple of days — almost 23 hours for the command to travel more than 15 billion miles (24 billion kilometers) from Earth to the spacecraft, and another 23 hours for the data to travel back.

On Oct. 16, the flight team sent a command to turn on one of the spacecraft’s heaters. While Voyager 1 should have had ample power to operate the heater, the command triggered the fault protection system. The team learned of the issue when the Deep Space Network couldn’t detect Voyager 1’s signal on Oct. 18.

The spacecraft typically communicates with Earth using what’s called an X-band radio transmitter, named for the specific frequency it uses. The flight team correctly hypothesized that the fault protection system had lowered the rate at which the transmitter was sending back data. This mode requires less power from the spacecraft, but it also changes the X-band signal that the Deep Space Network needs to listen for. Engineers found the signal later that day, and Voyager 1 otherwise seemed to be in a stable state as the team began to investigate what had happened.

Then, on Oct. 19, communication appeared to stop entirely. The flight team suspected that Voyager 1’s fault protection system was triggered twice more and that it turned off the X-band transmitter and switched to a second radio transmitter called the S-band. While the S-band uses less power, Voyager 1 had not used it to communicate with Earth since 1981. It uses a different frequency than the X-band transmitters signal is significantly fainter. The flight team was not certain the S-band could be detected at Earth due to the spacecraft’s distance, but engineers with the Deep Space Network were able to find it.

Rather than risk turning the X-band back on before determining what triggered the fault protection system, the team sent a command on Oct. 22 to confirm the S-band transmitter is working. The team is now working to gather information that will help them figure out what happened and return Voyager 1 to normal operations.

Voyagers 1 and 2 have been flying for more than 47 years and are the only two spacecraft to operate in interstellar space. Their advanced age has meant an increase in the frequency and complexity of technical issues and new challenges for the mission engineering team.

For more information about the Voyager mission, visit:

https://science.nasa.gov/mission/voyager

News Media Contact

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Engineers working on NASA’s Voyager 1 probe have successfully mitigated an issue with the spacecraft’s thrusters, which keep the distant explorer pointed at Earth so that it can receive commands, send engineering data, and provide the unique science data it is gathering.

After 47 years, a fuel tube inside the thrusters has become clogged with silicon dioxide, a byproduct that appears with age from a rubber diaphragm in the spacecraft’s fuel tank. The clogging reduces how efficiently the thrusters can generate force. After weeks of careful planning, the team switched the spacecraft to a different set of thrusters.

The thrusters are fueled by liquid hydrazine, which is turned into gases and released in tens-of-milliseconds-long puffs to gently tilt the spacecraft’s antenna toward Earth. If the clogged thruster were healthy it would need to conduct about 40 of these short pulses per day.

Both Voyager probes feature three sets, or branches, of thrusters: two sets of attitude propulsion thrusters and one set of trajectory correction maneuver thrusters. During the mission’s planetary flybys, both types of thrusters were used for different purposes. But as Voyager 1 travels on an unchanging path out of the solar system, its thruster needs are simpler, and either thruster branch can be used to point the spacecraft at Earth.

In 2002 the mission’s engineering team, based at NASA’s Jet Propulsion Laboratory in Southern California, noticed some fuel tubes in the attitude propulsion thruster branch being used for pointing were clogging, so the team switched to the second branch. When that branch showed signs of clogging in 2018, the team switched to the trajectory correction maneuver thrusters and have been using that branch since then.

Now those trajectory correction thruster tubes are even more clogged than the original branches were when the team swapped them in 2018. The clogged tubes are located inside the thrusters and direct fuel to the catalyst beds, where it is turned into gases. (These are different than the fuel tubes that send hydrazine to the thrusters.) Where the tube opening was originally only 0.01 inches (0.25 millimeters) in diameter, the clogging has reduced it to 0.0015 inches (0.035 mm), or about half the width of a human hair. As a result, the team needed to switch back to one of the attitude propulsion thruster branches.

Warming Up the Thrusters

Switching to different thrusters would have been a relatively simple operation for the mission in 1980 or even 2002. But the spacecraft’s age has introduced new challenges, primarily related to power supply and temperature. The mission has turned off all non-essential onboard systems, including some heaters, on both spacecraft to conserve their gradually shrinking electrical power supply, which is generated by decaying plutonium.

While those steps have worked to reduce power, they have also led to the spacecraft growing colder, an effect compounded by the loss of other non-essential systems that produced heat. Consequently, the attitude propulsion thruster branches have grown cold, and turning them on in that state could damage them, making the thrusters unusable.

The team determined that the best option would be to warm the thrusters before the switch by turning on what had been deemed non-essential heaters. However, as with so many challenges the Voyager team has faced, this presented a puzzle: The spacecraft’s power supply is so low that turning on non-essential heaters would require the mission to turn off something else to provide the heaters adequate electricity, and everything that’s currently operating is considered essential.

Studying the issue, they ruled out turning off one of the still-operating science instruments for a limited time because there’s a risk that the instrument would not come back online. After additional study and planning, the engineering team determined they could safely turn off one of the spacecraft’s main heaters for up to an hour, freeing up enough power to turn on the thruster heaters.

It worked. On Aug. 27, they confirmed that the needed thruster branch was back in action, helping point Voyager 1 toward Earth.

“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 at the Jet Propulsion Laboratory which manages Voyager for NASA.

The spacecraft are exploring interstellar space, the region outside the bubble of particles and magnetic fields created by the Sun, where no other spacecraft are likely to visit for a long time. The mission science team is working to keep the Voyagers going for as long as possible, so they can continue to reveal what the interstellar environment is like.

News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Voyager 1 has resumed returning science data from two of its four instruments for the first time since a computer issue arose with the spacecraft in November 2023. The mission’s science instrument teams are now determining steps to recalibrate the remaining two instruments, which will likely occur in the coming weeks. The achievement marks significant progress toward restoring the spacecraft to normal operations.

In April, after five months of troubleshooting since the original computer issue, the mission was able to get the spacecraft to begin returning usable engineering data about the health and status of its onboard systems, including the science instruments. On May 17, the team sent commands to the 46-year-old spacecraft that enabled it to resume sending science data to Earth. With Voyager 1 located more than 15 billion miles (24 billion kilometers) from its home planet, it takes light over 22 1/2 hours to reach the spacecraft, and 22 1/2 hours for a signal to return to Earth. As a result, the team had to wait nearly two days to see if their commands were successful.

The plasma wave subsystem and magnetometer instrument are now returning usable science data. As part of the effort to restore Voyager 1 to normal operations, the mission is continuing work on the cosmic ray subsystem and low energy charged particle instrument. (Six additional instruments aboard Voyager 1 are either no longer working or were turned off after the probe’s flyby of Saturn.)

Normal operations were interrupted last year when Voyager 1 began sending a signal back to Earth that contained no science or engineering data. The team eventually determined the issue stemmed from a small portion of corrupted memory in the flight data subsystem, one of the spacecraft’s three computers. Among other things, this system is designed to package data from the science instruments as well as engineering data about the health and status of the spacecraft before that information is sent to Earth.

Launched in 1977, Voyager 1 and its twin, Voyager 2, will celebrate 47 years of operations later this year. They are NASA’s longest-operating spacecraft as well as the first and only spacecraft to explore outside the heliosphere. Created by the Sun, this bubble of magnetic fields and solar wind pushes against the interstellar medium, an ocean of particles created by stars that have exploded elsewhere in the Milky Way galaxy. Both probes flew past Jupiter and Saturn, while Voyager 2 also flew past Uranus and Neptune.

News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov