23

The extremely cool NASA JPL video Triumph at Saturn (Part I) is really worth a watch and/or listen.

At about 17:40 it discusses Cassini's RTG and at 18:36 there is a shot of four RTGs in a row being checked for radiation levels.

RTGs have been in short supply, and because they start degrading as soon as they are assembled (or as soon as the radioisotope has been refined) they're not something one might just have a stock of laying around, or so it seems to me.

Question: Why are there four RTGs in a row sitting in this room? What are they waiting for? Were they built together and stored for separate launches?

screenshot from the extremely cool NASA JPL video "Triumph at Saturn (Part I)"

cued at 17:40

uhoh
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    I like the monoliths behind the RTGs too. Cue "Also sprach Zarathustra" – Organic Marble Oct 25 '21 at 22:04
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    @OrganicMarble I saw the movie when it first came out in theaters (which somewhat dates me) and when I had learned to read better I read the book. I discovered math not in school, but in the dimensions of the monolith: the squares of the first three prime numbers. They pulled it off in Seattle back in 2001 (also here) and again more recently. These are better looking, but a bit on the thin side for Clarke's tastes. – uhoh Oct 27 '21 at 00:29
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    Yeah, I bugged my parents to take me to see it when it first came out. My dad slept blissfully through most of it. The soundtrack is the first vinyl LP I bought too. https://i.imgur.com/3syd5pL.png – Organic Marble Oct 27 '21 at 01:17
  • I wouldn't stand that close if they were loaded. – James Ervin Oct 28 '21 at 01:37
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    @JamesErvin a radiation safety-trained person knows what to expect, and (as shown) carries instrumentation to check radiation levels, as well as a personal dosimeter. 238Pu is primarily an alpha particle emitter and those have a very short range (microns). In that sense it's like the 241Am alpha sources in smoke detectors, but a lot more powerful. There is a small neutron background, so you would not want to stand that close for a long time. My guess is that this is a unoccupied storage area to minimize large doses of thermal neutrons, and folks only visit for short periods of time. – uhoh Oct 28 '21 at 06:46
  • @JamesErvin see for example Does curiosity's RTG generate neutrons as this NASA CheMin X-ray detection system webpage suggests? If so, how? Since I'm just guessing about this, you might consider asking how these are stored and how much time people spend in the room with them as a new question! – uhoh Oct 28 '21 at 06:47
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    @uhoh it was a joke that I wanted to make but didn't have quite the right wording, regardless, I'm going to take a look into what you sent me. It looks very interesting! – James Ervin Nov 02 '21 at 23:36
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    @JamesErvin yep got it! Historically there has been some public pushback about launching spacecraft with RTGs due to safety concern, both in public discourse and in protests, e.g. "What if it blows up on the launch pad, will we all die?" In the video they show a clip of a press event before launch where some members of the panel even attest that they have brought family members to the launch as a way of showing confidence that the RTG does not itself pose a safety risk. So I'm just covering the bases here for future readers. https://youtu.be/SY-hQJ5pMd4?t=1114 – uhoh Nov 02 '21 at 23:42

1 Answers1

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There were seven General Purpose Heat Source - Radioisotope Thermal Generators (GPHS-RTGs) assembled (there were parts for an eighth).

The seven would eventually fly in space on four different spacecraft.

Perhaps we are looking at the 3 Cassini flight units and the New Horizons one.

The flight units used by mission, with power levels at launch, were:

  • Galileo: Flight Units 1 (289 We) and 4 (288 We)

  • Ulysses: Flight Unit 3 (289 We)

  • Cassini: Flight Units 2 (296 We), 6 (294 We) and 7 (298 We)

  • New Horizons: Flight Unit 8 (245.7 We at bus instead of connector pins)

The listed power levels are electrical power levels in watts (We),

Sources

Organic Marble
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