Voyager 1's transmitter issue may spell doom for the spacecraft

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You probably have seen reports that Voyager 1, the little spacecraft that could, is using a transmitter that hasn’t been used since 1981. This is honestly an amazing thing, that this spacecraft was built in such a robust way that after the coldness and intense radiation environment that Voyager 1 is in, instruments and components that have been off for decades can be turned on and they work. I don’t want to take away from that, because it is absolutely amazing.

But this communication issue with Voyager 1 is actually very serious, to the point where if the team can’t figure out a way to fix it, the Voyager 1 mission will be over. Let’s dive into what’s going on with Voyager 1 and whether this is the end of an almost 50-year mission.

Voyager 1’s difficult year

You may remember a huge communication problem with Voyager 1 that was resolved earlier this year — the spacecraft was sending gibberish back to Earth, and engineers had to figure out how to fix the problem. It was a big deal, and even the Voyager 1 team wasn’t sure they could get the spacecraft operational again.

The short story is that engineers figured out that a computer chip on Voyager 1 had failed and had to send instructions to the spacecraft on how to store its data in chunks to route around it. Once they did that, the probe began sending back real data and the team was able to slowly turn the science instruments back on.

But that wasn’t the end of Voyager 1’s woes this year — the thruster performance was also degrading. The NASA JPL team swapped the thrusters on the probe from 15 billion miles/24 billion kilometers away.

The current communications problem

So, what now, you might be asking!! Well, this was yet another communications issue, but it’s different than what we’ve seen from Voyager 1 before: The spacecraft autonomously switched off one of its two radio transmitters, and the team at JPL is still trying to figure out why it happened.

Here’s what we know and what we think we know:

On October 16, the Voyager 1 team sent a command to turn on the spacecraft’s heaters. I spoke with someone at NASA to find out why, and basically, the circuits in one of Voyager 1’s computers are beginning to degrade because of age and exposure to radiation. The team was trying to warm them up with a heater which they hoped would trigger a process called “annealing” in order to improve performance.

Annealing is a process of heat treatment that can do various things depending on the circumstances in which it’s used, including restore the original properties of materials and therefore reverse radiation damage. The team was flipping on this heater to warm up these specific circuits.

They did the math and they were certain they had enough power available when they sent that command on October 16. Now, every time any instructions are sent to Voyager 1, the spacecraft sends back engineering data describing how it responded to that command. There’s no working model or testbed of Voyager 1’s computers anymore (there’s just no way to model on Earth the conditions the spacecraft is in), so the team is very reliant on this communication to understand how Voyager 1 is executing commands.

(Sometimes, in the past, Voyager 2 has even been used as a test to see how Voyager 1 will respond because Voyager 1 is further into interstellar space, and therefore considered the more valuable spacecraft and mission.)

Round trip travel time for a signal to Voyager 1 is approaching 46 hours, almost 23 hours each way. But on October 18, the NASA-JPL discovered that the Deep Space Network wasn’t picking up Voyager 1’s return signal. They were out of contact with Voyager 1.

The spacecraft usually uses an X-band radio transmitter to talk with Earth, and the Deep Space Network couldn’t find that specific X-band signal. The team then sifted through the signals the Deep Space Network was receiving — and found a lower rate X-band transmission from Voyager 1, which confirmed their suspicions: The command to turn on the heater had triggered Voyager 1’s fault protection system. As a result, Voyager 1 switched to a lower power mode of communication with the X-band transmitter.

Power management is a constant problem

The fault protection system is automatic, and it can be triggered for quite a few reasons. One of them is if the spacecraft overdraws on power, Voyager 1 will automatically turn off systems to prioritize the health of the spacecraft.

The twin Voyager spacecraft are powered by radioisotope thermoelectric generators, or RTGs. The versions on Voyager 1 and 2 are specifically called Multihundred-watt radioisotope thermoelectric generators, and they were developed specifically for this program. Each generator uses 24 pressed plutonium-238 oxide spheres to generate heat that, at the time of launch, provided 157 watts of power. Each spacecraft is equipped with three of these RTGs, for a total of 470 watts at launch.

They’re called generators, but really they’re just nuclear batteries — as the plutonium-238 decays, it creates waste heat that’s converted into energy. It’s a great energy solution for a spacecraft for which fuel cells, chemical batteries, or solar power just aren’t really feasible. But there’s a downside.

Every single year, as the plutonium decays, the twin Voyager spacecraft lose about 4 watts of power. This means that at this point, Voyager 1 has 220 watts available, or about 47 percent of its original power left, according to the person at NASA I spoke with.

This has huge implications for the future of the spacecraft, because the available power to operate science instruments is expected to run out by around 2030, at which point NASA will shut off all science instruments for the twin spacecraft. But as long as Voyager 1 can continue to point itself towards Earth with its thrusters, it will send back telemetry and engineering data hopefully through 2036, at which point it will travel beyond the range of the Deep Space Network’s ability to pick up its X-band transmissions.

A transmitter that hasn’t been used since 1981

Ok, so back to the transmitter — Voyager 1 was sending back an X-band transmission at a lower rate, but the spacecraft appeared to be stable. That is, until October 19, when the X-band transmission stopped entirely. Based on their correct assumption that the original X-band transmission issue had been triggered by Voyager 1’s fault protection system, they concluded that it had happened twice more — and as a result, Voyager 1 had switched to its S-band transmitter, which hadn’t been used since 1981.

The S-band transmitter uses less power than the X-band, but it also sends a weaker signal. That’s why it stopped being used after Voyager 1 completed its primary mission in 1980.

At this point, the Voyager 1 team wasn’t even sure they’d be able to detect the S-band signal. It’s just so weak, and Voyager is 15 billion miles/24 billion km away. But the little spacecraft that could managed to send a strong enough signal with its S-band transmitter that engineers at the Deep Space Network were able to pick it up.

That’s basically where we are now. The Voyager 1 team sent back a transmission on October 22 to confirm that the S-band transmitter is working properly. They received an affirmative response on October 24. Now they have to figure out why the fault protection system triggered and if it’s safe to try and turn the X-band transmitter back on.

It’s amazing that the spacecraft was able to do make this transmitter switch automatically, and that the S-band transmitter is still working. But it’s not good for the long term.

Is this the end of Voyager 1’s mission?

A spokesperson at NASA told me that if they can’t turn the X-band transmitter back on, then the Voyager 1 mission is effectively over. The S-band transmitter isn’t powerful enough to send telemetry, let alone science data. There’s no engineering data to take a look at the health of the spacecraft. All they can really do with it is keep Voyager 1 pointed at Earth and send commands to the spacecraft.

If they can’t get the X-band transmitter working again in the near future, then we will be saying goodbye to Voyager 1.

I don’t want to start predicting the spacecraft’s impending doom, because it seems like every time I start despairing about the spacecraft, the amazing team at NASA figures out a way to keep Voyager 1 going. But I also know the clock is ticking, and that each of these serious problems could be the spacecraft’s last one.

Engineers were hoping to keep Voyager 1 operational through its 50th anniversary in 2027. I’m just really hoping that happens.

I’m going to end with what the NASA spokesperson told me in an email, because I don’t think I could say it any better myself:

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