NASA’s Voyager 1 Resumes Regular Operations After Communications Pause

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.

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Calla Cofield
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