Voyager Command Glitch Causes Unplanned Pause In Communications

Important safety tip: When you’re sending commands to the second-most-distant space probe ever launched, make really, really sure that what you send isn’t going to cause any problems.

According to NASA, that’s just what happened to Voyager 2 last week, when uplinked commands unexpectedly shifted the 46-year-old spacecraft’s orientation by just a couple of degrees. Of course, at a distance of nearly 20 billion kilometers, even fractions of a degree can make a huge difference, especially since the spacecraft’s high-gain antenna (HGA) is set up for very narrow beamwidths; 2.3° on the S-band channel, and a razor-thin 0.5° on the X-band side. That means that communications between the spacecraft and the Canberra Deep Space Communication Complex — the only station capable of talking to Voyager 2 now that it has dipped so far below the plane of the ecliptic — are on pause until the spacecraft is reoriented.

Luckily, NASA considered this as a possibility and built safety routines into Voyager‘s program that will hopefully get it back on track. The program uses the onboard star tracker to get a fix on the bright star Canopus, and from there figures out which way the spacecraft needs to move to get pointed back at Earth. The contingency program runs automatically several times a year, just in case something like this happens.

That’s the good news; the bad news is that the program won’t run again until October 15. While that’s really not that far away, mission controllers will no doubt find it an agonizingly long time to be incommunicado. And while NASA is outwardly confident that communications will be restored, there’s no way to be sure until we actually get to October and see what happens. Fingers crossed.

31 thoughts on “Voyager Command Glitch Causes Unplanned Pause In Communications

  1. I found the article interesting and I’m sure I’ll find the follow-on investigation as to what happened even more so. I just assumed all commands–even simple ones–sent to the real satellite first went through a simulator.

  2. “When you’re sending commands to the second-most-distant space probe ever launched, make really, really sure that what you send isn’t going to cause any problems.

    “According to NASA, that’s just what happened to Voyager 2 last week”

    I’d argue that’s the opposite of what happened. 😉

    (Yes, I know what you meant. Interesting story!)

  3. At least the Voyagers are better than the Pioneer probes in this situation, because the Pioneers were completely remote-controlled. Every single action the Pioneer performed had to be a command radioed up from Earth. A single missed transmission could cause disaster.

    This almost happened to Pioneer 10 while it was on its way to Jupiter. It was taking long almost-360-degree images of the background Zodiacal Light, but the Sun would have fried the phototube at one point of its rotation. So up the DSN went a steady stream of perfectly-time commands of “open shutter”, “transmit photo level to earth” (repeat)…, “close shutter”. From the book “The Depths of Space”,

    “One day a fishing trawler in the Atlantic Ocean accidentally snagged and broke a transatlantic cable, severing the connection between the Pioneer control center at Ames and a DSN station in South Africa…. Pioneer controllers first tried to reroute communications through a satellite, only to find that the satellite’s ground station was also out of commission thanks to the snagged cable. With literally minutes to spare, an alternate teletype line was secured through England, across Europe, and finally down to Johannesburg, and the IPP was closed down just before it would have been totally blinded.”

    That was a hack.

      1. X.25 wasn’t worldwide until the 90s; DATAPAC launched in 1974 and at the time was available in Canada only. The event described would have happened in 1972.

        1. “X.25 wasn’t worldwide until the 90s;”

          Are you sure. I have seen printouts of my father dating back to circa mid-80s.
          He used to call computer databases located in the US via Datex-P from within Germany.

          1. Europe, North America, Hong Kong and Australia were connected through IPSS by 1981, but it took longer to link up the rest of the world.

            Which gets us further from the fact the the original event described occurred in 1972, years before X.25 became available anywhere, much less everywhere in the world.

  4. “The program uses the onboard star tracker to get a fix on the bright star Canopus”

    That’s just a Canopus sensor, which can only tell the difference between ‘pointed at Canopus’ and ‘not pointed at Canopus’. That’s what they used before modern star trackers existed. Canopus was chosen because it’s both distinctively bright and far from the ecliptic, and therefore unlikely to get mixed up with planets or asteroids. A star tracker as used on modern spacecraft is a high-resolution digital camera with built-in machine vision and a database of stars, so you can see why they had to use simpler things decades ago. (Between Canopus sensors and star trackers in time and technological advancement were star scanners, which, I gather, scanned the stars using the spacecraft’s rotation and otherwise worked like star trackers. In my reading, I haven’t seen indications of them ever being very popular, but that term sometimes gets erroneously applied to star trackers on modern spacecraft.)

  5. Oops…

    20 January 2005
    Huygens: the missing data

    Scientists on Huygens’ imaging team only got half of the pictures they had hoped for during the descent. They expected to have more than 700 images from the 2.5-hour flight, and only got about 350. Data from the Doppler-shift experiment, which measured subtle changes in the wind speeds that Huygens experienced, was also lost.

    Most of the probe’s data were duplicated on each channel, like two different radio stations broadcasting the same programme. “The information is so important you carry it twice, it’s a redundant system,” explains David Southwood, director of science for the European Space Agency (ESA), which built and operated the probe.

    That redundancy saved the mission from failure. Cassini had two different receivers to collect the data from Huygens, and one of them did not work.

    Why didn’t the receiver work? The Channel A receiver was simply not turned on during the mission. “There’s no mystery why it didn’t turn on,” says one scientist on the imaging team, who was upset by the loss. “The command was never sent to switch it on.”

    “That’s an ESA responsibility,” admits Southwood. Any instructions that need to be sent to the Cassini spacecraft are compiled as a series of software commands by mission scientists, and these are transmitted to the craft from the Jet Propulsion Laboratory in Pasadena, California. All commands relating to the Huygens probe were programmed by ESA.

    1. And Wordpess Jetpack drops yet another reply to the very bottom of the thread. Now I make sure to always quote who and what I am replying to. This problem has existed since day one here with Jetpack in the loop.

      1. Awful presumptuous the newbie
        crew are not as smart. Not as experienced , yes. Probably better educated, too. Cant recall any physicist back then having a space related degree, you ran what you had

        1. “better educated” isn’t always smarter. I know a lot of people who are college “educated” yet they do not have any real-world experience. What works on paper, doesn’t always work in real life. Plus, in real life, you have to expect and prepared for the unexpected, because nothing ever works exactly as planned.

          As for no physicist having a “space related degree,” see point #1. And even with this “deficiency” these physicists managed to – without a space related degree- put men on the moon with slide rules and the computing power of a Casio watch, all the while using repurposed missiles … yet the geniuses with “space related degrees” haven’t been able to replicate that feat again.

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