Voyager Chronology Options

[Liss]

I wonder if anybody has a Voyager chronology with such details as dates of all TCMs or precise times of closest approach to different moons of Jupiter back in 1979. What I've found of pre-Saturn TCMs is here:

Voyager 1

1977.09.05 Launch
1977.09.11 TCM-1
1977.09.13 TCM-1
1977.10.29 TCM-1A
1978.06? TCM-2?
1979.01.04 Jupiter Observatory Phase
1979.01.29? TCM-3
1979.02.21 TCM-4
1979.03.05 Jupiter Flyby
1979.04.09 TCM-5
...
1980.08.22 Saturn Observatory Phase
1980.10.10-11 TCM A8
1980.11.06 TCM A9
1980.11.12 Saturn Flyby

Voyager 2

1977.08.20 Launch
1977.10.11 TCM-1
1978.05.03 TCM-2
1979.04.24 Jupiter Observatory Phase
1979.06.27 TCM?
1979.07.09 Jupiter Flyby
1979.07.09 TCM?
1979.07.23 TCM?
1980? TCM B6?
1981.02.26 TCM B7
1981.06.05 Saturn Observatory Phase
1981.07.19 TCM B8
1981.08.18 TCM B9
1981.08.26 Saturn Flyby

[Doug M.]

So the official NASA extended mission plan for Voyager 1, last updated in June 2014, tells us that this is the year its gyroscope will be shut down: "Discontinue gyro operations (+14.4 W steady state, +3.6 W turn on transient and maneuver) - 2015; TBD. This power load reduction step is currently sequenced to occur on DOY 350, 2015 but could be changed if the RTG output is better than predicted."

I assume DOY 350 would be ooa December 16, 2015... Okay, so does anyone know anything more? Is the RTG output about as expected? And what consequences will there be from turning off the gyroscope?


Doug M.

[jgoldader]

So the official NASA extended mission plan for Voyager 1, last updated in June 2014, tells us that this is the year its gyroscope will be shut down: "Discontinue gyro operations (+14.4 W steady state, +3.6 W turn on transient and maneuver) - 2015; TBD. This power load reduction step is currently sequenced to occur on DOY 350, 2015 but could be changed if the RTG output is better than predicted."

I assume DOY 350 would be ooa December 16, 2015... Okay, so does anyone know anything more? Is the RTG output about as expected? And what consequences will there be from turning off the gyroscope?


Doug M.

AFAIK, the RTG output hasn't really changed from predictions. The exponential decay of the plutonium and degradation of the thermocouples are both well understood. Unless something in the power system fails, the wattage should be accurately predictable for the duration of the mission. But two things come immediately to mind with shutting down the gyros.

First, the periodic antenna repointings will require hydrazine when the gyros are powered down. Voyager 1 had 18 kg of hydrazine left as of September 19, and typical consumption is about 5-6 grams per week. I don't know how much a repointing will cost, or how often it needs to be done (I looked at the weekly 2014 reports, which are current up to September 19, and no repointings were obvious for either V1 or V2 during the year). Science observations on V1 (rolling the spacecraft for particles/fields) take 100-400 grams, it seems, so I'd guesstimate that much for a repointing. But if it's done annually or less frequently, there should be enough hydrazine until the RTGs finally run too low to keep the spacecraft operating.

Second, the gyros make heat. It's amazing that the spacecraft are able to function in the cold. Without heaters and insulation, they'd probably be down to 30-40K by now. It wouldn't be a terrible surprise to me if at some point, an important piece just got too cold to work. (E.g., the hydrazine freezes in the fuel lines, or a piece of electronics fails or something.)

I remember listening to Jay Barbree report the launch of one of the Voyagers in 1977, and was glued to the TV during the flybys. I sure hope to see Voyager 2 break through into interstellar space before either it or I shut down. That both V1 and V2 are still working is virtually miraculous, and a testament to the dedication and talent of the people who designed, built, and operate them.

[Doug M.]

So, do we know whether the gyros shut down on schedule or not?


Doug M.