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What Would Have Happened If Philae Were Nuclear Powered?
StartsWithABang writes After successfully landing on a comet with all 10 instruments intact, but failing to deploy its thrusters and harpoons to anchor onto the surface, Philae bounced, coming to rest in an area with woefully insufficient sunlight to keep it alive. After exhausting its primary battery, it went into hibernation, most likely never to wake again. We'll always be left to wonder what might have been if it had functioned optimally, and given us years of data rather than just 60 hours worth. The thing is, it wouldn't have needed to function optimally to give us years of data, if only it were better designed in one particular aspect: powered by Plutonium-238 instead of by solar panels.
Basically the US has exhausted its meager supply. And the few supplies existing elsewhere are being jealously hoarded.
There's ways to MAKE more, and improve nuclear power at the same time. But nobody wants to talk about it.
Because nukes = bombs. M'kaaay?
Chas - The one, the only.
THANK GOD!!!
NASA is almost out of Plutonium. With the end of the cold war the US stopped refining uranium and producing plutonium. There's not much left and it's becoming a real problem for the designers of long term space missions, especially ones that are far enough that solar power isn't a viable option.
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this: http://en.wikipedia.org/wiki/R...
It's a question of weight. No matter how you build them, nuclear Radioisotope Thermal Generators are heavy. This mission was heavily mass-constrained. What they wanted it to do was at the limit of what the rockets were capable of.
Add a several-hundred-kilogram RTG to to mix, and the 'rocket equation' kills you. You just cannot get the probe to the comet. Solar panels were the only option.
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Correct me if I'm wrong, but wouldn't it have been really bad if there had been a boatload of plutonium-238 on the Challenger?
Uh, no.
A boatload of Pu-238 won't explode, and RTGs are designed to stay together even in a launch explosion. If I remember correctly, one RTG was involved in a launch explosion, and it was recovered, refurbished, and used again.
http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
"One example is the RTG used by the Voyager probes - 23 years after production, the radioactive material inside the RTG will have decreased in power by 16.6%, i.e. providing 83.4% of its initial output; starting with a capacity of 470 W, after this length of time it would have a capacity of only 392 W. A related (and unexpected) loss of power in the Voyager RTGs is the degrading properties of the bi-metallic thermocouples used to convert thermal energy into electrical energy, the RTGs were working at about 67% of their total original capacity instead of the expected 83.4%. By the beginning of 2001, the power generated by the Voyager RTGs had dropped to 315 W for Voyager 1 and to 319 W for Voyager 2."
The writer of the article didn't do his research. The designers did not expect the instruments to survive the approach to the Sun. So this could not have gone on for years and years.
From: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions "In any case, by March 2015, when the comet is closer to the Sun, it is likely that the lander will become too hot to operate."
And if that comet then hit earth, do you know what a huge catastrophe that would have caused?
Then we would be saying 'ah but couldn't they just use solar power?'
The mass of the Churyumov---Gerasimenko comet is roughly 1 x 10^13kg. Should it ever fall to earth, I wouldn't expect the dispersal of U-238 from an aging Rosetta-class probe to be my biggest concern.
Philae was a European project, and they didn't have expertise in space-capable RTGs. Plutonium fuel is also difficult to source. And the fuel depletes even when you're not using it, so after a 10 year idle while travelling to the comet it would have lost a significant amount of fuel, requiring a larger amount to start with. They'd also need significant heatsinks to keep the waste energy from melting everything. RTGs aren't always superior in every situation.
About 8% in 10 years; planners need to know about it, but that's hardly a big concern.
Given the many missions they've been used on successfully, that doesn't seem to be a major problem. And if you're willing to fold out big solar panels, you obviously have the budget for heat sinks.
They are by far the best known battery technology for robotic space exploration, satellites, and probes.
Philae does not have fold out solar panels. It is covered with panels but nothing to fold out. So not mass budget there.
The whole thing has a mass of about 100kg. There is not much to spare in it.
Stop being so completely foolish. The plutonium is encased strongly enough that is will survive unexpected reentry let along a launch explosion. It is purely a thermal source and the biggest risk would be burning yourself on it.
Everything else is just knee jerk uneducated scare tactics.
Sad really. And rather pathetic.
The first is that if something goes wrong on takeoff you risk what is effectively a 'dirty bomb' going off somewhere in the Earth's atmosphere which is not good.
Its not nearly as bad as you think. The biggest impact of a dirty bomb in a city would be psychological.
In the atmosphere, less important.
had better make sure that the craft does not return for Earth for a few billion years otherwise, again, it is like a dirty bomb going off in the atmosphere.
Uh, nuh. Pu238 half-life is 88 years. Here is the most basic clue about radioactivity: radiation intensity is inversely related to halflife. If it has a billion-year half-life, it is barely radioactive at all. A dirty bomb needs something with lots of radiation, and so a short half-life.
I don't think you realise just how indestructible a nuclear battery is, the one on Cassini was designed to withstand a crash that might have occurred on it's slingshot flyby of earth (fortunately we didn't get to test that claim). Testing is done by firing the battery from an artillery gun directly into a solid steel wall several feet thick. What happened to Antares would have merely burnt the paint off the outside a nuclear battery. Basically the only way to get hurt by one of them is to be unlucky enough to be hit on the head with it.
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
Rosetta/Philae returned to Earth three times for gravity boosts. Each time it was going at speeds which would guarantee its destruction if it hit the deeper parts of the atmosphere. Had this happened and Philae had carried an RTG, it would have been the end of ESA due to the public outcry, and NASA would likely be in public relations trouble too.
There are places for RTGs, but Rosetta was not it. Philae may have died prematurely, but ESA is alive to try again.
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I was speaking generically, since the parent made a generic point. Let's look at Philae in particular. The probe gets about 32W peak at 3AU. Insolation (W/m2) is roughly 1300W at 1 AU outside the atmosphere. At 3 AU, it's about 150 W. At 20% efficiency, in order to get roughly 30W, the probe needs to have a minimum 1 m2 facing the sun. But since only about 1/3-1/4 of the probe is exposed to sunlight when plastering the panels to the probe's body, there are about 3m2 surface area. That's also what we get from its dimension (about 1m x 1m x 0.8m). A 32W RTG would generate about 600W of waste heat, something that is easy to radiate over 3m2 into space, assuming reasonable operating temperatures for the probe (and actually, a smaller RTG is sufficient).
In fact those numbers generalize: no matter how large or small you scale this, radiating heat from an RTG is going to require less surface area than getting the same amount of power from solar cells.
And there doesn't need to be. Philae contains a 1000Wh disposable battery, a 140Wh rechargeable battery, and 32W-peak solar cells. The 1000Wh battery is intended to discharge 60h at an average of 16W. That tells you that pretty much the entire electrical system could be replaced with a 16W RTG (and a small rechargeable battery or supercapacitor for peak loads if needed).
At typical RTG efficiencies of 3-5W / kg, that means you're somewhere around 3-5kg for an RTG capable of powering the entire probe for a few decades (that includes maybe 100-200g Pu238), generating about 150W of waste heat.
The conclusion is that an RTG would likely have been technically superior to the current power design in pretty much every respect: weight, surface area, reliability, simplicity. The only reasons for not using an RTG are cost and politics (and the cost part itself is largely due to politics too).
I was ignorantly assuming that they'd do everything they could to insure the accomplishment of the mission. I realize how foolish I was now.
Yes, that is a very foolish assumption. Even if they spent a quadrillion euros, they still could not do everything to ensure success. Real life involves tradeoffs. Most people learn this by the time they are adults.
Precisely, no plan in the history of planning has survived contact with reality undamaged. He should brush up on the concept of diminishing returns which is basically what you are talking about. There are other interesting places to visit and blowing your budget on one mission is dumb.
The entire system is designed to operate in peak loads much of the time with long idle periods between, you can't downsize the battery that much.
And RTGs are heavy compared to their output in the inner solar system. A SNAP-19 fits the generation bill (30 watts at beginning of life) but that's 12 kilograms, which is almost certainly heavier than the solar panels.
But the real reasion is, what others have mentioned, cost. And no, it's not a case of "the cost part itself is largely due to politics", it's that plutonium-238 is simply expensive, period. You're talking a product only produced in a few parts of the world from a raw material (neptunium-237) that's only extracted in a few parts of the world in very small quantities from a raw material (nuclear fuel rods) that's already very expensive and difficult to transport. The neptunium takes years to accumulate in its reactor and must be handled with extreme safety protocols during the extraction, and properly secured against misuse. It then must be irradiated for long periods of time, converting it one atomic collision at a time to plutonium 238 using a tremendous amount of energy. Only then can the plutonium be extracted - and once again, you're talking the need for extreme safety protocols during the process, and proper security. None of that is "politics", it's simply the way it is plus very rational handling procedures.
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Except that you are missing the fact that a nuclear battery is not the same think like a nuclear reactor. You can build a nuclear battery with something around a cup full of material, whereas a nuclear reactor needs a significant larger amount of material. Also it is funny how you mention Fukushima, the health effects in this incident where rather minor. There are chemical industrial accidents with significant higher casualty rates than that. If you mentioned Chernobyl you may have had a point, but not with Fukushima.