Author: Naomi Hartono

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

NASA’s Voyager 1 spacecraft is conducting normal science operations for the first time following a technical issue that arose in November 2023.

The team partially resolved the issue in April when they prompted the spacecraft to begin returning engineering data, which includes information about the health and status of the spacecraft. On May 19, the mission team executed the second step of that repair process and beamed a command to the spacecraft to begin returning science data. Two of the four science instruments returned to their normal operating modes immediately. Two other instruments required some additional work, but now, all four are returning usable science data.

The four instruments study plasma waves, magnetic fields, and particles. Voyager 1 and Voyager 2 are the only spacecraft to directly sample interstellar space, which is the region outside the heliosphere — the protective bubble of magnetic fields and solar wind created by the Sun.

While Voyager 1 is back to conducting science, additional minor work is needed to clean up the effects of the issue. Among other tasks, engineers will resynchronize timekeeping software in the spacecraft’s three onboard computers so they can execute commands at the right time. The team will also perform maintenance on the digital tape recorder, which records some data for the plasma wave instrument that is sent to Earth twice per year. (Most of the Voyagers’ science data is sent directly to Earth and not recorded.)

Voyager 1 is more than 15 billion miles (24 billion kilometers) from Earth, and Voyager 2 is more than 12 billion miles (20 billion kilometers) from the planet. The probes will mark 47 years of operations later this year. They are NASA’s longest-running and most-distant spacecraft. Both spacecraft 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

For the first time since November, NASA’s Voyager 1 spacecraft is returning usable data about the health and status of its onboard engineering systems. The next step is to enable the spacecraft to begin returning science data again. The probe and its twin, Voyager 2, are the only spacecraft to ever fly in interstellar space (the space between stars).

Voyager 1 stopped sending readable science and engineering data back to Earth on Nov. 14, 2023, even though mission controllers could tell the spacecraft was still receiving their commands and otherwise operating normally. In March, the Voyager engineering team at NASA’s Jet Propulsion Laboratory in Southern California confirmed that the issue was tied to one of the spacecraft’s three onboard computers, called the flight data subsystem (FDS). The FDS is responsible for packaging the science and engineering data before it’s sent to Earth.

The team discovered that a single chip responsible for storing a portion of the FDS memory — including some of the FDS computer’s software code — isn’t working. The loss of that code rendered the science and engineering data unusable. Unable to repair the chip, the team decided to place the affected code elsewhere in the FDS memory. But no single location is large enough to hold the section of code in its entirety.

So they devised a plan to divide the affected code into sections and store those sections in different places in the FDS. To make this plan work, they also needed to adjust those code sections to ensure, for example, that they all still function as a whole. Any references to the location of that code in other parts of the FDS memory needed to be updated as well.

The team started by singling out the code responsible for packaging the spacecraft’s engineering data. They sent it to its new location in the FDS memory on April 18. A radio signal takes about 22 ½ hours to reach Voyager 1, which is over 15 billion miles (24 billion kilometers) from Earth, and another 22 ½ hours for a signal to come back to Earth. When the mission flight team heard back from the spacecraft on April 20, they saw that the modification worked: For the first time in five months, they have been able to check the health and status of the spacecraft.

During the coming weeks, the team will relocate and adjust the other affected portions of the FDS software. These include the portions that will start returning science data.

Voyager 2 continues to operate normally. Launched over 46 years ago, the twin Voyager spacecraft are the longest-running and most distant spacecraft in history. Before the start of their interstellar exploration, both probes flew by Saturn and Jupiter, and Voyager 2 flew by Uranus and Neptune.

Caltech in Pasadena, California, manages JPL for NASA.

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

Engineers have confirmed that a small portion of corrupted memory in one of the computers aboard NASA’s Voyager 1 has been causing the spacecraft to send unreadable science and engineering data to Earth since last November. Called the flight data subsystem (FDS), the computer is responsible for packaging the probe’s science and engineering data before the telemetry modulation unit (TMU) and radio transmitter send the data to Earth.

In early March, the team issued a “poke” command to prompt the spacecraft to send back a readout of the FDS memory, which includes the computer’s software code as well as variables (values used in the code that can change based on commands or the spacecraft’s status). Using the readout, the team has confirmed that about 3% of the FDS memory has been corrupted, preventing the computer from carrying out normal operations.

The team suspects that a single chip responsible for storing part of the affected portion of the FDS memory isn’t working. Engineers can’t determine with certainty what caused the issue. Two possibilities are that the chip could have been hit by an energetic particle from space or that it simply may have worn out after 46 years.

Although it may take weeks or months, engineers are optimistic they can find a way for the FDS to operate normally without the unusable memory hardware, which would enable Voyager 1 to begin returning science and engineering data again.

Launched in 1977, the twin Voyager spacecraft flew by Saturn and Jupiter, and Voyager 2 flew by Uranus and Neptune. They are both exploring interstellar space, outside the bubble of particles and magnetic fields created by the Sun, called the heliosphere. Voyager 2 continues to operate normally.

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

Editor’s note: This blog post was originally published March 13, 2024, on NASA’s Sun Spot blog. Future Voyager blog posts will appear here, on NASA’s Voyager blog.

Since November 2023, NASA’s Voyager 1 spacecraft has been sending a steady radio signal to Earth, but the signal does not contain usable data. The source of the issue appears to be with one of three onboard computers, the flight data subsystem (FDS), which is responsible for packaging the science and engineering data before it’s sent to Earth by the telemetry modulation unit.

On March 3, the Voyager mission team saw activity from one section of the FDS that differed from the rest of the computer’s unreadable data stream. The new signal was still not in the format used by Voyager 1 when the FDS is working properly, so the team wasn’t initially sure what to make of it. But an engineer with the agency’s Deep Space Network, which operates the radio antennas that communicate with both Voyagers and other spacecraft traveling to the Moon and beyond, was able to decode the new signal and found that it contains a readout of the entire FDS memory.

The FDS memory includes its code, or instructions for what to do, as well as variables, or values used in the code that can change based on commands or the spacecraft’s status. It also contains science or engineering data for downlink. The team will compare this readout to the one that came down before the issue arose and look for discrepancies in the code and the variables to potentially find the source of the ongoing issue.

This new signal resulted from a command sent to Voyager 1 on March 1. Called a “poke” by the team, the command is meant to gently prompt the FDS to try different sequences in its software package in case the issue could be resolved by going around a corrupted section.

Because Voyager 1 is more than 15 billion miles (24 billion kilometers) from Earth, it takes 22.5 hours for a radio signal to reach the spacecraft and another 22.5 hours for the probe’s response to reach antennas on the ground. So the team received the results of the command on March 3. On March 7, engineers began working to decode the data, and on March 10, they determined that it contains a memory readout.

The team is analyzing the readout. Using that information to devise a potential solution and attempt to put it into action will take time.

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

Editor’s note: This blog post was originally published Dec. 12, 2023, on NASA’s Sun Spot blog. Future Voyager blog posts will appear here, on NASA’s Voyager blog. A previous version of this post identified the TMU as the telecommunications unit. It is the telemetry modulation unit.

Engineers are working to resolve an issue with one of Voyager 1’s three onboard computers, called the flight data system (FDS). The spacecraft is receiving and executing commands sent from Earth; however, the FDS is not communicating properly with one of the probe’s subsystems, called the telemetry modulation unit (TMU). As a result, no science or engineering data is being sent back to Earth.

Among other things, the FDS is designed to collect data from the science instruments as well as engineering data about the health and status of the spacecraft. It then combines that information into a single data “package” to be sent back to Earth by the TMU. The data is in the form of ones and zeros, or binary code. Varying combinations of the two numbers are the basis of all computer language.

Recently, the TMU began transmitting a repeating pattern of ones and zeros as if it were “stuck.” After ruling out other possibilities, the Voyager team determined that the source of the issue is the FDS. This past weekend the team tried to restart the FDS and return it to the state it was in before the issue began, but the spacecraft still isn’t returning useable data.

It could take several weeks for engineers to develop a new plan to remedy the issue. Launched in 1977, the spacecraft and its twin, Voyager 2, are the two longest-operating spacecraft in history. Finding solutions to challenges the probes encounter often entails consulting original, decades-old documents written by engineers who didn’t anticipate the issues that are arising today. As a result, it takes time for the team to understand how a new command will affect the spacecraft’s operations in order to avoid unintended consequences.

In addition, commands from mission controllers on Earth take 22.5 hours to reach Voyager 1, which is exploring the outer regions of our solar system more than 15 billion miles (24 billion kilometers) from Earth. That means the engineering team has to wait 45 hours to get a response from Voyager 1 and determine whether a command had the intended outcome.

Launched in 1977, NASA’s twin Voyager spacecraft are the agency’s longest-operating and farthest-flung probes. Voyager 1 visited Jupiter and Saturn, revealing new features of both planets and their moons. Voyager 2 followed its twin to Jupiter and Saturn before changing its trajectory to fly by Uranus and Neptune. It remains the only spacecraft to visit our solar system’s two ice giant planets.

Continuing their legacy as science pioneers, the Voyagers are the only two probes to journey into interstellar space – the space between stars. This region lies outside the heliosphere, the protective bubble of particles and magnetic fields emitted by our Sun. By directly sampling the interstellar environment, the Voyagers are providing data that spacecraft closer to Earth can’t replicate. This helps scientists study both the shape of the heliosphere and its interaction with the ocean of interstellar material that the Sun is traveling through.

Readers of this blog can find occasional updates on mission science, the health of the spacecraft, and the creative solutions engineers have needed to come up with in order to keep the venerable spacecraft operating after nearly 50 years.

For more about Voyager, go to www.nasa.gov/voyager and follow along on X (formerly Twitter) at @NASAVoyager. Take Voyager’s Grand Tour with NASA’s Eyes.

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