The New York Times's When Voyager 2 Calls Home, Earth Soon Won’t Be Able to Answer explains that because Voyager 2's trajectory has taken it way below the ecliptic, of the three 70 meter dishes in the DSN only Canberra's can talk to it. So when it undergoes renovation soon, there'll be no more talking.

However, the article points out that reception of Voyager's transmissions will still possible.

Question: Why exactly was this so? Was it only the 70 meter dish's transmitter that's being fixed? Why can't a pair of 34 meter dishes do the task but at a lower data rate? What was the technical explanation for receive-only?

While the team won’t be able to command Voyager 2, they will still be listening to the spacecraft. By combining the power of the other antennas in Canberra, they will be able to collect its scientific observations.

“The Canberra site will still be getting data back from the spacecraft,” Ms. Dodd said. “The science data will still be coming down.”

Being able to only listen could prompt some anxiety. While Voyager 2 will keep collecting and sending back science data, should something go wrong, members of the team will be powerless to help it, and will just have to watch with their hands tied.

“We’ve been planning on this for over a year,” Ms. Dodd said. “I think like any good planning, we’re prepared for it. And we’ve done our best, you know, we’ve done the best that we can.”

note aspherical cows in foreground:

Antennas belonging to the Deep Space Network complex in Canberra, Australia

Antennas belonging to the Deep Space Network complex in Canberra, Australia. Credit: Canberra Deep Space Communication Complex, By Shannon Stirone

From here:

below: data for the Sun, planets, Pluto, Voyager 1 and Voyager 2, from January 1, 1969 (a good year to start things) until now. Dots are now. Data is from NASA JPL Horizons. Reposted from this question, where additional details are given.

enter image description here

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    $\begingroup$ "note aspherical cows in foreground" What do you mean? They look spherical enough to me! $\endgroup$
    – JiK
    Commented Mar 5, 2020 at 12:28
  • 10
    $\begingroup$ @JiK They're only spherical to two terms in the Fourier expansion $\endgroup$ Commented Mar 5, 2020 at 12:54
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    $\begingroup$ @CarlWitthoft You say that as if there were more than two terms in a Fourier expansion. $\endgroup$
    – JiK
    Commented Mar 5, 2020 at 12:56
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    $\begingroup$ @MichaelSeifert that's udderly obvious $\endgroup$ Commented Mar 5, 2020 at 19:02
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    $\begingroup$ @MichaelSeifert They're not actually spherical, so the question is mooo-t. $\endgroup$
    – bta
    Commented Mar 5, 2020 at 19:37

1 Answer 1


As per the March 4 JPL News story, only DSS43 has the right S-band transmitter, enough power and is in the right hemisphere to talk to Voyager:

Moreover, a special S-band transmitter is required to send commands to Voyager 2 - one both powerful enough to reach interstellar space and on a frequency that can communicate with Voyager's dated technology. The Canberra 70-meter antenna (called "DSS43") is the only such antenna in the southern hemisphere.

It goes on to say:

As the equipment in the antenna ages, the risk of unplanned outages will increase, which adds more risk to the Voyager mission. The planned upgrades will not only reduce that risk, but will also add state-of-the art technology upgrades that will benefit future missions.

I would also speculate that digging out a low signal-to-noise ratio signal from Voyager received by the 34-meter dishes is easier with the more modern hardware available on the ground than for Voyager's 40+ year old radio and computer to correctly decode the super weak signals transmitted by the same 34-meter dishes. This is somewhat supported by the information in Deep Space Telecommunications Systems Engineering book at JPL's DESCANSO site. Page 350 (368 in the PDF) says:

...spacecraft missions have employed(...) and a single-channel digital command detector (Viking Heritage). A new single-channel digital command detector (NASA standard) has been developed and will probably be used on new missions of the near future.

(note that the book is from 1983). It then says:

The Viking Heritage command detector was originally developed for the Viking Mission, and was later adopted by the Voyager and Galileo Projects.

(emphasis mine). Section on page 387 in the book (405 in the PDF) talks more about the S/X-band transponder (S-only for uplink, S and X-band for downlink) and again discusses the two versions - a Voyager version and the newer NASA standard version. This likely again means that the newer 34-meter dishes don't have transmitters that can talk to the old Voyager-style transponders.

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    $\begingroup$ I'm not sure what you are saying that the reason that Voyager 2 can not receive signals from Canbera's 34 meter dishes. Is it because they do not have the correct S-band transmitters, or they have NO S-band transmitters, or they don't have enough power, or enough gain? fyi there's more about the link budget and Voyager's systems in these: 1, 2, 3, 4, 5. $\endgroup$
    – uhoh
    Commented Mar 5, 2020 at 6:59
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    $\begingroup$ more about the Descanso series and just for fun Why is the operating temperature for the Voyagers' receiver noise calculation about 1550K? is currently unanswered. $\endgroup$
    – uhoh
    Commented Mar 5, 2020 at 7:00
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    $\begingroup$ As far as I can tell (e.g. Chapter 7 of Large Antennas of the Deep Space Network), the 34-m antennas support S, X and Ka-bands. I think it's more that the newer 34-m antennas can't do the old Viking/Voyager-style modulation and there isn't enough SNR link budget. $\endgroup$ Commented Mar 6, 2020 at 4:22
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    $\begingroup$ Not really. The news items mention the S-band transmit/receive needed for Voyager vs the more common X-band today but looking at e.g. the page for the 34-m DSS 36 at Canberra it seems both it and DSS34 have S-band transmitters that overlap the frequency range of the 70m DSS 43. So I still think that it's down to coding details on the transmissions or the possible SNR needing the bigger 70m dish but would need a DSN engineer to confirm (try @nascom1 on Twitter?) $\endgroup$ Commented Nov 4, 2020 at 19:16
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    $\begingroup$ or if the Sun would be strong enough to saturate it, but this is related to that: Why is the operating temperature for the Voyagers' receiver noise calculation about 1550K?. I assume the designers were optimistic that Voyager might survive this long and designed the system to be able to pick out transmissions from Earth from the Sun's output, but I'm not quite able to put the whole puzzle together yet. I guess I just need to ask How bright is the Sun in S-band? $\endgroup$
    – uhoh
    Commented Nov 4, 2020 at 23:48

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