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I just finished watching The Farthest, a great documentary about the Voyager spacecraft, launched in 1977 and still operational today.

It got me wondering about those people shown in the documentary sitting at consoles monitoring the two Voyager spacecraft. Are the consoles (or some more-modern version thereof) still staffed? During the intervening 4-plus decades has there always been one or more staff person on duty 24/7, 365? If so, what are they doing? If not, what level of staffing is required to monitor the spacecraft?

Stu Smith
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    I have scripts here that create various plots using data from JPL Horizons. You can find the current distance to the Voyagers, and make an interactive 3D plot of their trajectories. The IDs of the Voyagers are -31 & -32. For trajectories, I recommend a time span of a decade or two, with a time step of 1 year. I like to include an outer planet in the plot to give a sense of scale. (Saturn ID=6, Uranus ID=7). – PM 2Ring May 02 '23 at 09:31
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    You need to read https://www.nytimes.com/2017/08/03/magazine/the-loyal-engineers-steering-nasas-voyager-probes-across-the-universe.html. – Peter - Reinstate Monica May 04 '23 at 11:27
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    Thank you Peter - a wonderful read! "Over decades, the crew members who have remained have forgone promotions, the lure of nearby Silicon Valley and, more recently, retirement, to stay with the spacecraft." – Stu Smith May 04 '23 at 15:31

2 Answers2

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Continuously? No, for several reasons.

Most significantly, it just isn't possible. Both Voyagers are now so far away that only the 70-meter antennas of the Deep Space Network can communicate with them. Each DSN site only has one of these antennas, and the two Voyagers are both on the same side of the Earth, so there are times when only one antenna is available for the two of them. That antenna can only point in one direction, so except in the rare case of multiple spacecraft close together, it can only talk to one at a time*.

There also isn't any need. The round-trip signal time for Voyager 1 is around 44 hours; for Voyager 2, it's 36 hours. Both spacecraft are pretty much in the middle of nowhere, doing nothing but recording data and periodically forwarding it to Earth. There's no expectation of anything surprising happening, so losing a few hours of data if something goes wrong is no big deal.

Both spacecraft are routinely monitored, but this takes the form of periodic, scheduled communication sessions rather than continuous monitoring.

*Right now, antenna 25 at Goldstone is talking to Mars Odyssey, MAVEN, and the Trace Gas Orbiter, all in orbit around Mars.

Mark
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    It would still be good to mention that both Voyagers are routinely monitored, and that just because the round trip light time is longer than a day, that doesn't mean that there couldn't be messages sent every day and received every day. After all, DSN is not necessarily having an in-depth conversation with them. They can just "check in" with each other assynchronously. – uhoh May 02 '23 at 09:29
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    I don't have time to do it right now, but for anyone interested, one can query DSN to see how often they talk to the Voyagers Understanding the information contained in the Deep Space Network XML data? and Power and frequency units used in Deep Space Network XML data? – uhoh May 02 '23 at 10:46
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    in case anyone reading hasn't seen it before, this page (DSN Now) shows what NASA's massive antennas are currently doing. As I write this it actually shows two of the smaller antennas (DSS 34 and 35) at Canberra receiving data from Voyager 2. I guess maybe they use some form of synthetic aperture or whatever. – user253751 May 02 '23 at 20:45
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    @user253751, with the end of the Pioneer and Galileo programs, the Voyagers are the only spacecraft that need the big antennas. I know that DSN has been experimenting with using antenna groups in place of a single big antenna; I don't know if it's reached the point where they can decommission the 70-meter dishes. – Mark May 02 '23 at 21:41
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    @Mark see Tradeoffs between using two 34 m and one 70 m Deep Space Network dish? and Why does DSN sometimes uses two dishes at the same time to receive Voyager-1? and links therein. – uhoh May 03 '23 at 01:45
  • @user253751 ditto – uhoh May 03 '23 at 01:46
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    Good answer! One thing you might want to add is the speed at which data is sent. I don't know for Voyager specifically, but in general spacecrafts that go this deep into space have very low data rates. Less than 1 bps is common. So if we assume 0.5bps, then it would take 16 seconds to see 1 character pop up on your screen. It's not very useful to have someone continuously stare at a terminal waiting for the characters to pop up. – Opifex May 03 '23 at 15:40
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    @Opifex, current data rates for the Voyager spacecraft are 160 bps. For text data, that would be 20 characters per second; binary system-status data would be considerably more compact. – Mark May 03 '23 at 23:19
  • Thanks for that info @Mark! Do you perhaps have a source for that? I'm particularly interested in how for the voyager it's still relatively high, even though they are the furthest away from Earth. – Opifex May 04 '23 at 08:19
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    @Opifex, I got it from the tracking schedule at the bottom of the spacecraft status page, confirmed by looking at a communications session on the DSN Now status page. Wikipedia suggests that it could be boosted to 1.4kbps for readout from the tape recorder, but I don't know if this is actually possible. – Mark May 04 '23 at 22:20
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    @Opifex, as for how, the Voyagers have larger antennas than Pioneers 10 and 11 (3.7 meters versus 2.7 meters) and three times the RTG output, which presumably allows for a more powerful transmitter. The Voyagers are also actively steered where the Pioneers are spin-stabilized, which may permit better antenna pointing. – Mark May 04 '23 at 22:24
  • JPL probably just pages the on-call guy if something bad happens... :D – RonJohn May 05 '23 at 05:22
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    They had a 1.4 kbit/s comms session this year. This requires all of the antennas at a DSN station to be arrayed together. – Hobbes Aug 15 '23 at 11:52
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The Voyagers are not monitored continuously.

On average, there is a communications session with each spacecraft every day. For up to 8 hours at a time, science and operations data is received and the occasional command is sent. This is handled by the Deep Space Network operations personnel. Those sessions are planned using visibility data (Voyager 2 is out of reach of the Goldstone and Madrid complexes, so its comms sessions have to be when Voyager 2 is visible from Canberra) and have to fit in the other uses of the DSN (all other interplanetary missions).

They forward the data to the Voyager team, which analyzes it, plans upcoming operations, and prepares new command uploads. I suspect they do this during normal work hours instead of looking at the data as it comes in: there's no benefit in looking at the data immediately when it takes 18 hours to send a command anyway.

From a recent interview:

“The Voyager science isn’t something you need to monitor constantly,” Calla Cofield, a JPL spokesperson, told WIRED via email. “They’re studying this region of space over long distances, so a gap of a few weeks won’t hurt those studies.”

Hobbes
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