Plutonium: The element that saved the crew of Apollo 13 | Hacker News Reader

Plutonium: The element that saved the crew of Apollo 13

bbc.com

36 pointsroc12311 comments

Not only is the article title misleading linkbait -- it's mostly about the discovery of the actinide elements -- it doesn't make any sense.

The LEM (Lunar Excursion Module) did carry an RTG (Radioisotope Thermoelectric Generator) -- but this was for the ALSEP (Apollo Lunar Surface Experiment Package), which is what the training photograph shows Lovell carrying. The instruments were stored in an equipment bay and weren't even accessible from inside the LEM, and weren't relevant to navigation or communications anyway. The heat output of the RTG was not intended for life support, nor for keeping any LEM systems within safe operating temperatures. I am at a loss as to how plutonium was relevant to the astronaut's survival.

What is an interesting story is the fact that the Apollo 13 RTG is now resting at the bottom of the Tonga Trench in the Pacific Ocean, since the LEM re-entered the Earth's atmosphere after it was jettisoned prior to reentry: http://www.spacesafetymagazine.com/aerospace-engineering/nuc...

I think the idea is that the heat output of the battery (about 1.5kW) may have made the difference between the astronauts surviving and not since they had no other heat source available - the LEM heaters were all shut down to conserve power after the explosion.

Clearly the plutonium heat output was never intended to heat the LEM during ordinary operation, since not all missions carried such experimental apparatus - presumably had the mission gone to plan the normal LEM heaters would have run on a lower duty cycle to compensate for the extra heat input from the plutonium cargo.

I agree that it's a badly written article that doesn't actually follow through on the title, so the above is purely guesswork.

The fuel core for the SNAP-27 generator was stored on the _outside_ of the LM descent stage. It was installed into the generator by the astronauts on the lunar surface. I have chopped an image and some text from the Apollo 13 press kit.

https://www.dropbox.com/s/02px58fhbz0gigt/apollo13.pdf?dl=0

I doubt there would have been much thermal path from the fuel element back into the LM itself - indeed the mount would probably have been designed to minimise that flow since the problem is normally how to reject heat from a spacecraft, rather than absorb it. The story just seems a tag to discuss plutonium.

Thanks for the insight.

One bad thing is that the LEM was never designed to return to earth, so when Apollo 13 came back with the LEM it also brought the RTG back and could have dispersed the 8.5 lbs of plutonium in the atmosphere. In the grand scheme of things this was probably nothing compared to all the atmospheric nuclear weapon tests that were done in the preceeding years (like the 50 megaton Tsar Bomba blast).

Now corrected to "Plutonium: The scary element that helps probe space's secrets". Apollo 13 still mentioned, but with no mention of the fact that the only thing that distinguishes its RTG is that it's at the bottom of the Pacific. Neither does it mention that only the less dangerous isotope is used in space.

Great article on the history and discovery of the actinide elements.

The astronauts lives were apparently saved by the warm Plutonium battery powering the Lunar Module's scientific equipment (not exactly sure how though).

EDIT: I know what Radioisotope Thermoelectric Generators are, but not why the warm battery saved Apollo 13.

Not sure how it generates power? Pu238 is a very strong alpha emitter. Alpha particles (helium nuclei) are really big and charged, so they don't travel very far and deposit all their energy near where the decay occurs (as opposed to decay with e.g. neutrinos that essentially never interact and thus deposit no energy). The alpha decay carries a lot of energy so a chunk of Pu238 gets pretty hot. Couple it with a thermoelectric generator and you have an ideal power source for space applications.

Also, alpha particles have almost no penetrative power in human tissue so they're harmless as long as the source isn't inside of you. Pu238 is almost exclusively an alpha emitter, so it's completely safe to handle for extended periods, at least radiologically. It puts off a ton of heat and is chemically really toxic though. I've dealt with it in the lab before, it's relatively harmless as far as nuclear sources go. It's not suited for weapons either, so it isn't directly a proliferation concern, though producing it is because it is related to weapons grade production. You don't see it used very often mostly because it can only be made in a specially configured reactor, so it's not exactly common.

Thanks for the power generation explanation.

Thermoelectric generators are dead simple means of reliably generating a small amount of power for a very long time without moving parts. What you do is get a lump of radioactive material and stick a bunch of thermocouples around it. The lump of radioactivity stays hot because it's radioactive, and the thermocouples produce a very low efficiency amount of power out of the temperature difference.

http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen...

Pu238 is also in very short supply these days http://www.wired.com/2013/09/plutonium-238-problem/all/

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