Interstellar space probe Voyager 2 is back in action after a technical glitch required immediate attention. Mission operators reported a few days later that the 42-year-old exploration craft has been fixed remotely from Earth – an engineering triumph.
Astronomers realized that the late 1970s offered the rare opportunity to send remote-controlled spacecraft equipped with sensors to fly by Jupiter, Saturn, Uranus, and Neptune, which were all aligned from Earth’s point of view.
The Voyager program began in 1977 with the launch of Voyager 2 on August 20, followed by its twin, Voyager 1, on September 5. Voyager 1 would visit two of our solar system’s outer planets (Jupiter and Saturn) whereas Voyager 2 would take a longer path to enable it to reach two additional outer planets, Uranus and Neptune.
This so-called Grand Tour, orchestrated by the federal National Aeronautics and Space Administration (NASA), used planetary gravitation forces to sling-shot the probes further into space, saving fuel and reducing the cost of the data collection program.
Voyager 2’s primary mission was a complete success, reaching the Jovian system in 1979, the Saturnian system in 1981, the Uranian system in 1986, and the Neptunian system on October 2, 1989.
Now in its extended mission phase, Voyager 2 continues its heading and left the Solar System on November 5, 2018, at a distance of 119 astronomical units (11 billion miles) from the Sun. This miracle of modern engineering has been operational for 42 years, 5 months, and 21 days as of February 10, 2020 – longer than any other spacecraft in history.
Concerns about the Voyager 2 mission were raised in late January 2020 when mission operators noted that one of the spacecraft’s autonomous fault protection routines had been triggered.
NASA’s Jet Propulsion Laboratory (JPL), a division of Caltech in Pasadena, California, explained the problem:
“On Saturday, Jan. 25, Voyager 2 didn’t execute a scheduled maneuver in which the spacecraft rotates 360 degrees in order to calibrate its onboard magnetic field instrument.”
The craft’s unexpected failure to roll caused two systems to consume fairly high levels of power while they were functioning at the same time. Voyager 2 overdrew its available power supply.
The onboard fault protection software did its job and shut off non-essential systems, including its scientific instruments, to make up for the power drain caused by the failed rotational calibration maneuver.
Voyager 2 has a very limited amount of power onboard and uses radioactive fuel to generate heat that is then converted into electricity. As the fuel in the radioisotope thermoelectric generator (RTG) decays naturally, it provides less and less power over time.
The natural decay of the radioactive material inside the RTG lowers Voyager 2’s power budget by approximately 4 watts each year. That may not sound like much, but it adds up over the decades.
Repairing the craft from Mission Control here on Earth was essential – and challenging. It takes 17 hours for terrestrial commands to travel outside the solar system and reach Voyager 2. The return transmission takes another 17 hours before the ground team can analyze the craft’s response.
As of Jan. 28, Voyager engineers succeeded in switching off one of the high-power systems and turned the science instruments back on. No data was being received, however. The team began to check the status of the rest of the spacecraft to restore its regular operations.
On Feb. 5, NASA mission operators reported that Voyager 2 was in stable condition and transmitting scientific information again from interstellar space. NASA Voyager tweeted:
“Good vibes! Voyager 2 continues to be stable, and communications between Earth and the spacecraft are fine. My twin is back to taking science data, and the team at NASA JPL is evaluating the health of the instruments following their brief shutoff.”
This wasn’t the first time Voyager engineers powered down equipment hurtling through space to preserve the craft’s power supply. A key component of both Voyagers is the heaters that warm them despite the coldness of deep space. In 2019, according to NASA, “engineers turned off the primary heater for the Voyager 2 cosmic ray subsystem instrument in order to compensate for this power loss and the instrument continues to operate.”
Voyager 1 and Voyager 2 are currently about 13.8 billion miles and 11.5 billion miles from Earth, respectively. That’s more than 122 times the distance between the Earth and the sun.
The Heliophysics Division of the Science Mission Directorate in Washington, D.C. sponsors the Voyager missions as a part of the NASA Heliophysics System Observatory. Visit the official NASA Voyager website to share the program’s unique discoveries about the mysterious nature of space.