I hate science reporting

[elfs]

Okay, so why is it that every report about Cassini starts with one of the following:

"The 3.3 billion dollar space probe Cassini..."

"About the size of a bus, the nuclear-powered space probe Cassini..."

Does it really matter, now, that Cassini cost that much money, or that it has a nuclear power source? I suppose it does, but it's not really the big first thing when talking about space probes now, is it? Why do they have to put that in the first paragraph, often the first sentence?

Is it that they're easy targets, simple fnords ("your tax money", "nuclear power") that the writer can hang a story off of, whereas details of the hydrocarbon-rich oceans and organic molecule-laden clouds don't resonate with a scientifically illiterate population?

Comments

Not all plutonium is created equal

[neowolf2.livejournal.com]

Not to lend support to the radiophobes, but comparing plutonium by mass is not the correct thing to do here.

What matters for the radiological toxicity is activity (decays/time). The isotope in RTGs, 238Pu, has a much shorter halflife (87.7 years) than the main isotope used in fission bombs (24,100 years for 239Pu).(*) Short halflife means a proportionally greater activity. The energy of the alpha particles from 238Pu is also somewhat greater, but that's less important.

This is consistent with the observation that, unlike the oxide in RTGs, the cores in nuclear bombs do not visibly glow from the decay heat. The rate of production of decay energy per mass of Pu is much less in the bomb core.

You might argue that centuries in the future, the bomb plutonium will still be around radiating people, but by that time any remaining Pu will have been sequestered in sediments or soils, not suspended in the atmosphere as it was after it was released.

(*) 241Pu has a halflife of 14.4 years, but it's a beta emitter, and there's not much of it in weapons-grade Pu anyway.

Re: Not all plutonium is created equal

[elfs.livejournal.com]

True, but I think the point is still made. If we agree that 238PuO₂ is the nuclear ingredient in RTGs, then the chemical properties of 238PuO₂ make it a reasonably safe component to launch on a rocket. It is insoluble and its frangibility does not lend itself to easy vaporization or pulverization; a catastrophic launch event powerful enough to crack a case that survived head-on train collisions and drops from 10 kilometers onto a hard surface would most likely only kill someone if a chunk of it fell on them.

Re: Not all plutonium is created equal

[neowolf2.livejournal.com]

That's true, but remember Cassini also did a couple of flybys of Earth to pump up the orbit. If it had reentered due to malfunction/trajectory error, the RTGs would likely have burned up while reentering at above escape velocity (especially if the trajectory was near-vertical.)

What's really needed for outer planet missions are nuclear _reactor_ powered spacecraft, with 235U that is almost completely innocuous until after the reactor is turned on.