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Voyager 2: Back in Two-Way Communication

It’s reassuring to hear that we’re in two-way contact once again with Voyager 2. Since last March, controllers have been limited to receiving X-band (8 to 12 GHz) downlink data, with no capability to uplink commands to the craft via S-band (2 to 4 GHz). This has been a problem unique to Voyager 2 thanks to its trajectory. The Deep Space Network’s three radio antenna facilities — Canberra, Australia; Goldstone, California and Madrid, Spain — are positioned so that at least one facility is available for communications with our far-flung space probes.

While Voyager 1 can talk to us via the two northern hemisphere DSN stations, Voyager 2’s close flyby of Neptune’s large moon Triton in 1989 bent its course well south of the ecliptic. 18.8 billion kilometers from Earth, Voyager 2 can only line up on Canberra, and the antenna called Deep Space Station 43 (DSS43) has been the only southern hemisphere dish with a transmitter capable of reaching the craft at the right frequency to send commands. DSS43 went offline for equipment upgrades to handle increasingly problematic aging equipment.

Philip Baldwin is operations manager for NASA’s Space Communications and Navigation (SCaN) Program;

“The DSS43 antenna is a highly specialized system; there are only two other similar antennas in the world, so having the antenna down…is not an ideal situation for Voyager or for many other NASA missions. The agency made the decision to conduct these upgrades to ensure that the antenna can continue to be used for current and future missions. For an antenna that is almost 50 years old, it’s better to be proactive than reactive with critical maintenance.”

Image: Crews conduct critical upgrades and repairs to the 70-meter-wide radio antenna Deep Space Station 43 in Canberra, Australia. In this image, one of the antenna’s white feed cones (which house portions of the antenna receivers) is being moved by a crane. Credit: CSIRO.

Only DSS43 has the S-band transmitter powerful enough to reach and communicate with Voyager’s dated technology, but the upgrades will also be significant for Moon and Mars missions going forward. From the Voyager 2 perspective, the craft has been in a quiescent mode that still allowed return of science data, with Canberra’s three 34-meter dishes configured to listen to its signal, though unable to transmit commands. Now DSS43 has successfully tested its new hardware and we can get back to uploading commands as needed to the probe.

“What makes this task unique is that we’re doing work at all levels of the antenna, from the pedestal at ground level all the way up to the feedcones at the center of the dish that extend above the rim,” said Brad Arnold, the DSN project manager at NASA’s Jet Propulsion Lab in southern California. “This test communication with Voyager 2 definitely tells us that things are on track with the work we’re doing.”

All of which is excellent news, as Voyager 2 seems healthy. Recall that the spacecraft accidentally overdrew its power supply last January, leading to the automatic shutdown of its science instruments. The upgrade of DSS43 began after that problem had been resolved. The station now has two new radio transmitters as well as upgraded heating and cooling equipment, power supply and support upgrades demanded by the new transmitters.

So both our active craft in interstellar space are in two-way communication again. It’s instructive, and a bit awe-inspiring, to remember how difficult it is to track a signal as weak as the one Voyager can produce. At Jupiter, the craft could transmit at 115,000 kilobits per second. This is a 23-watt radio transmitter that produced, at the giant planet, a signal that was one hundred-millionth as powerful as a cell phone battery by the time it reached the DSN on Earth. And of course Voyager keeps going. Even before it went interstellar, Voyager 2’s power levels received at Earth were more than five hundred times fainter than at the Jupiter encounter.

We may be able to keep the Voyagers alive into the middle of this decade by clever cycling of their instruments and systems, with the last surviving science instrument likely being the magnetometer, which has the lowest power requirement. A faint engineering signal might still be feasible into the 2030s, but no one knows exactly. It would be wonderful if we could stay in touch with these craft until 2027, which would mark their 50th year in flight. Go Voyager.

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{ 11 comments… add one }
  • Brad in Dallas November 5, 2020, 14:34

    All thanks to the radioactive power source which, correct me if I’m wrong, is no longer allowed under international treaty? Is there spacecraft power hardware on the shelf now that could achieve the same 50-year lifespan?

    • Alex Tolley November 6, 2020, 0:41

      Voyager power sources are Pu-238 RTGs. This is the same basic power source that is used on the Curiosity rover. As these are not nuclear weapons, so there is no ban on their use in space. The biggest issue is the manufacture of the Pu-238 that was a result of the nuclear weapons program (I think). The current availability of Pu-238 is limited although I think there are plans to manufacture more before the supply is depleted.

  • Robert November 5, 2020, 14:39

    It’s really neat to think there are 2 spacecraft in interstellar space now.
    At the JPL voyager site below there is much information and also some great posters to download.

    https://voyager.jpl.nasa.gov

  • Robert A L November 6, 2020, 0:05

    Voyager 1 is 21 light hours away. Communication over 1 light day will be a milestone, and a reminder how big the distances are and how slow the travel.

  • Alex Tolley November 6, 2020, 0:55

    We forget how technology changes result in legacy systems that in this case, cannot be changed in situ. The rapid pace of computer technology development and the long development period for space systems results in technology that is obsolete before it is even flown. Software changes quickly too, with legacy systems exposed to the Y2K issue, and fewer developers familiar with the software language.

    I’m reminded of this hardware obsolescence being a plot point in the “Space Cowboys” movie. In Vinge’s Zones of Thought novels, he makes a point that as software obsolete, no one rewrites the old code, just adds a new layer that interfaces with the old, resulting in deep layers of code interfacing with each other, an extreme example of what has happened to legacy software that is interfaced with newer software for more contemporary computing systems.

    When we talk about sending interstellar probes out on centuries-long missions, it may require some way to maintain the legacy computer systems and knowledge, rather like linguists maintain knowledge of ancient languages and craftsmen of ancient artisan skills. It may require a cadre of people (or AIs/ robots) to be trained to maintain this knowledge and skills in order to be able to communicate and even control these ancient probes. If only we had Star Trek technology that seems capable of instantly correctly interfacing with any alien communication encoding method.

    • Robin Datta November 8, 2020, 0:02

      “no one rewrites the old code, just adds a new layer that interfaces with the old, resulting in deep layers of code interfacing with each other, an extreme example of what has happened to legacy software that is interfaced with newer software”

      One is reminded. by this that we ourselves are functioning on a similar software (and hardware) architecture, knowing not whether we are are anchored or hamstrung – or both – by it. It will likely not be inherited by our AI creations, with consequences as yet unknown.

      • Alex Tolley November 8, 2020, 19:15

        We could write an essay comparing and contrasting biology vs software and hardware.

        IMO, biology uses common hardware and software and just keeps modifying the routines and execution flow. I.e. DNA, RNA, amino acids remain common for all organisms. To me, this is like all development uses one microprocessor architecture and software language. Computing, however, continues to maintain different microprocessor architectures and instruction sets and a wide range of languages. However, some of the languages can be ported to different microprocessors by either using specific compilers or special virtual machines. The languages can also in some cases interoperate by various means. Vinge’s software layering could use any number of different approaches, perhaps most easily accomplished with interfaces for message handling, much like the web protocols can send structured text messages between disparate systems. This is perhaps most analogous in biology by using certain
        molecules for intercellular communication, or sound or light to communicate between individuals of a species or between species.

        Because the base code of biology is teh same for all organisms, it makes genetic engineering using cut ‘n paste methods feasible. Any difference between DNA and RNA structures and genetic codes renders Earth and alien biology effectively non-interoperable. We would be shadow biospheres to each other at this level. Of course, multi-cellular life could still impact alien species by other, more crude methods.

        Software development often results in “bloatware” where new features are added, old features or code not deleted, which expands the code size. Biology seems to do something similar in complex animals and plants, where old genes remain in the genome unused, as new genes are added. Then there is the huge amount of non-coding sequences that in humans represents most of the size of the human genome. Prokaryotes are far more parsimonious paring down their genomes and even coding different, but overlapping, genes on the 2 complementary DNA strands. This is reminiscent of coding competitions to make the shortest code do a specific task, or optimizing pieces of code for maximum performance in performance-critical applications. In both biology and software, minimizing resource use increases performance and increases replication.

  • Kamal Ali November 6, 2020, 3:53

    A 50 year survival would be wonderful.
    It would give us hope we could build spacecraft for 100 years or more to visit the gravitational lens etc.

  • Mike Serfas November 8, 2020, 17:42

    As I understand it, a good chunk of Voyager’s power goes for purposes of heating, even though it also has specialized radioisotope heating units. ( https://voyager.jpl.nasa.gov/news/details.php?article_id=117 ) So if Voyager had something else keeping it toasty warm, it could keep doing science, right? And it is said “Breakthrough Starshot” will launch interstellar spacecraft using incredibly powerful lasers. Which they’ll have to be able to aim very precisely onto a tiny swatch of sail at great distances (when not at some foreign leader who wants too much for lithium). So…

  • Afterthought November 9, 2020, 23:47

    It’s worth it to build a dedicated, shielded, space-based receiver for these missions that are truly pioneering and not likely to be surpassed any time soon.

    Maximize what we can learn at a modest price!

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