Month: October 2024

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

Mission engineers at NASA have turned off the plasma science instrument aboard the Voyager 2 spacecraft due to the probe’s gradually shrinking electrical power supply.

Traveling more than 12.8 billion miles (20.5 billion kilometers) from Earth, the spacecraft continues to use four science instruments to study the region outside our heliosphere, the protective bubble of particles and magnetic fields created by the Sun. The probe has enough power to continue exploring this region with at least one operational science instrument into the 2030s.

Mission engineers have taken steps to avoid turning off a science instrument for as long as possible because the science data collected by the twin Voyager probes is unique. No other human-made spacecraft has operated in interstellar space, the region outside the heliosphere.

The plasma science instrument measures the amount of plasma (electrically charged atoms) and the direction it is flowing. It has collected limited data in recent years due to its orientation relative to the direction that plasma is flowing in interstellar space.

Both spacecraft are powered by decaying plutonium and lose about 4 watts of power each year. After the twin Voyagers completed their exploration of the giant planets in the 1980s, the mission team turned off several science instruments that would not be used in the study of interstellar space. That gave the spacecraft plenty of extra power until a few years ago. Since then, the team has turned off all onboard systems not essential for keeping the probes working, including some heaters. In order to postpone having to shut off another science instrument, they also adjusted how Voyager 2’ voltage is monitored.

Monitoring Results

On Sept. 26, engineers issued the command to turn off the plasma science instrument. Sent by NASA’s Deep Space Network, it took 19 hours to reach Voyager 2, and the return signal took another 19 hours to reach Earth.

Mission engineers always carefully monitor changes being made to the 47-year-old spacecraft’s operations to ensure they don’t generate any unwanted secondary effects. The team has confirmed that the switch-off command was executed without incident and the probe is operating normally.

In 2018, the plasma science instrument proved critical in determining that Voyager 2 left the heliosphere. The boundary between the heliosphere and interstellar space is demarcated by changes in the atoms, particles, and magnetic fields that instruments on the Voyagers can detect. Inside the heliosphere, particles from the Sun flow outward, away from our nearest star. The heliosphere is moving through interstellar space, so at Voyager 2’s position near the front of the solar bubble, the plasma flows in almost the opposite direction of the solar particles.

The plasma science instrument consists of four “cups.” Three cups point in the direction of the Sun and observed the solar wind while inside the heliosphere. A fourth points at a right angle to the direction of the other three and has observed the plasma in planetary magnetospheres, the heliosphere, and now, interstellar space.

When Voyager 2 exited the heliosphere, the flow of plasma into the three cups facing the Sun dropped off dramatically. The most useful data from the fourth cup comes only once every three months, when the spacecraft does a 360-degree turn on the axis pointed toward the Sun. This factored into the mission’s decision to turn this instrument off before others.

The plasma science instrument on Voyager 1 stopped working in 1980 and was turned off in 2007 to save power. Another instrument aboard Voyager 2, called the plasma wave subsystem, can estimate the plasma density when eruptions from the Sun drive shocks through the interstellar medium, producing plasma waves.

The Voyager team continues to monitor the health of the spacecraft and its available resources to make engineering decisions that maximize the mission’s science output.

For more information about NASA’s Voyager missions, 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