I'm preparing a talk on data storage for an ASME meeting. Given that it's 20 billion km away, I want to quote Voyager I as the "largest control loop" in existence. I'm guessing the tape recording capability is no longer used, but is it still true that someone here on earth could press a button and 18 hours later the tape would start running and 18 hours after that we could pick up the data with the deep space network. I want a "gee-whiz" start to the talk so appreciate any help on interesting aspects or anecdotes, etc. (I see the discussion on angular momentum, for example) - Roger


Edit: The Spacecraft operations schedule contains the answer. On December 18, 2021, we see an item 'PLAYBACK' show up in the schedule for Voyager 1.


S/C 31 is Voyager 1. The 'PLAYBACK' label is the data playback itself, this takes about 6 hours at 1.4 kbit/s. Before playback you can see 'X/B HI POWER', which switches the transmitter to high power mode (18 instead of 12 W).

'31 DSN Coverage' shows the antennas that are used. '55' is DSS 55, one of the antennas at the Madrid station. They're using 4 antennas (at Madrid) in an array: DSS 63 is the 70-m antenna, the others are 34 m diameter (DA = downlink pass in an array, R is the array reference antenna).

At various other times in the schedule you'll see 'TAPPOS', which I'm guessing is a Tape Position command, in preparation for recording PWS data.

This part was written in 2016. The tape recorder on Voyager 1 is still in use:

Science data are returned to earth in real time at 160 bps. Real time data capture uses 34 meter Deep Space Network (DSN) resources (see below) with the project goal to acquire at least 16 hours per day of real time data per spacecraft. This goal is not always achieved due to the competition for DSN resources with prime mission projects and other extended mission projects.

Once a week per spacecraft, 48 seconds of high rate (115.2 kbps) PWS data are recorded onto the Digital Tape Recorder (DTR) for later playback. An additional 48 seconds are recorded each week on Voyager 1. These data are played back to Earth once every 6 months per spacecraft and require 70 meter DSN support for data capture.

The Deep Space Network (DSN) is a series of large dish antennas used by NASA to communicate with deep-space missions like Voyager. The DSN includes dishes with a diameter of 34 m and a few with a diameter of 70 m. There are only a few antennas this large in the world, so they are shared between various deep-space missions.

On Voyager 2, DTR operation was ended in 2007:

Voyager 2 DTR operations was no longer needed due to a failure on the high waveform receiver on the Plasma Wave Subsystem (PWS) on June 30th, 2002.

The JPL site lists a cutoff date in approx. 2018:

limited by ability to capture 1.4 kbit/s data using a 70 m/34 m antenna array. This is the minimum rate at which the DTR can read-out data.

I'd expect it to be possible to play back some data from the DTR into Voyager's RAM, then transmit at a slower rate from RAM. The JPL site doesn't mention this possibility, though.

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    $\begingroup$ What's a 34 meter Deep Space Network? $\endgroup$ May 16 '16 at 4:36
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    $\begingroup$ That is really astounding! This is an actual tape recorder? Magnetic tape? I'm imagining an 8-track cassette and other "stuff" from the 1970's, but any chance you can find a picture of what it actually looked like? $\endgroup$
    – uhoh
    May 16 '16 at 6:01
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    $\begingroup$ @BurhanKhalid here's one $\endgroup$
    – uhoh
    May 16 '16 at 6:03
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    $\begingroup$ More info on Voyager DTR: space.stackexchange.com/questions/2053/… , photo of Galileo DTR: space.stackexchange.com/questions/2272/… , I searched for photos or drawings of the Voyager DTR for one of these questions but couldn't find any. $\endgroup$
    – Hobbes
    May 16 '16 at 7:21
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    $\begingroup$ Well you can't really spool much tape into RAM because Voyager's computers have 32kbytes RAM, a good chunk of which is program code. $\endgroup$
    – Joshua
    May 16 '16 at 15:22

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