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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.
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.
Tea and kung-fu. Life is good. Rising Phoenix
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?'
this: http://en.wikipedia.org/wiki/R...
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.
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."
Hi there, I'm Bruce Halberstadt, the chief scientist involved in the Philae lander design. If only we knew of this option when we were designing our lander!
Would you like to come work for us on the next lander? We need more people like you.
We've been hiring all of the top internet commenters for our next project, I think it's going to be spectacular. I can't confirm it just yet, but from recent meetings, it looks like the next project will be a giant robot that searches for extra-terrestrial boobies, with devices on-board to send back relevant cat videos. With your help, maybe we can make this thing nuclear powered.
Bruce Halberstadt
Np, it would not have mattered.
Numerous times RTG-powered spacecraft had their main rocket "explode" or "fail" and the RTGs were just recovered. Early models, packed without any precautions at all, basically contaminated some small area.
http://en.wikipedia.org/wiki/R...
Then again, if you are worried about RTGs contaminating things, you should probably pull all your hair out over the nuclear weapon tests that occurred and all the stockpiled weapons, ready to be deployed at moment's notice. Weapon testing contaminated ALL soil around the world with detectable amounts of plutonium. Amount of the substance in RTGs is negligible by comparison.
This is one of my primary goals in life. Get nuclear more accepted in the US, then start building Thorium reactors across the country.
Soon
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.
No matter how you build them, nuclear Radioisotope Thermal Generators are heavy.
That's totally inaccurate. I went into details about this a couple days ago when Philae was discussed here. In that case someone said that because it took 10 years to arrive at the comet, an RTG couldn't have been used. I'll just copy/paste my other post since it already covers your statement.
The lander only uses 32 watts of power. The MMRTG used in Curiosity provides 125 watts of power initially, and 100 watts after 14 years. The mass of that specific RTG (the MMRTG, 45kg) would be too great for use in Philae, but then it also produces 3 times more energy than needed (even after 14 years). RTGs have been made in many sizes for many different applications, so it would simply have been a matter of designing an RTG that produces 40-45 watts of power after 10 years.
However, one of the main uses of the 32 watts of power required by Philae is just to keep the batteries warm so they don't fail. RTGs produce more "waste" heat than they do electricity. For example, the MMRTG used in the Curiosity rover produces 2 kW of heat, of which 125 W is converted to electricity. The extra heat is used to keep the various temperature-sensitive parts of the rover nice and warm so they don't fail. With Philae, a good portion of the 32 watts of the solar power it requires is just to keep the battery warm. So if an RTG were used, it wouldn't even need to produce 32 watts of electricity since it can keep the lander warm directly.
Looking at the mass and wattage produced, the RTGs ("SNAP-19") in the Pioneer probes would have been just about perfect for Philae. They produce 40 watts of power and weigh 13.6 kg. Philae's current electrical system weighs 12.2 kg, so that's at least in the ballpark. The RTGs on the surface of the moon, as manually placed by Apollo astronauts's would have been a bit heavy at 20 kg. One of those RTGs was still producing 90% of its power after 10 years.
The SNAP-9A used in the Transit 5B-2 navigation satellite launched in 1963 weighed 12.3 kg and produced 25 watts of power. That looks about like a perfect fit for Philae, and I'm sure more efficient thermocouplers are available today that could further reduce the weight.
Better known as 318230.
Due to several sources closely linked with the Rosetta program, Philae will be getting a whole lot of sun come May 2015 due to the position of the comet as it adjusts it's precession around the sun and moves that particular part of the comet in to near-constant daylight. Expect more news at that point from Philae. You heard it here first, folks.
moox. for a new generation.
I get the mission design, and I think most people here get the idea, too. But ESA seems to have missed the boat on the PR and public affairs front.
The demise of the lander after a complete primary mission is being portrayed as a huge failure. As near as I can tell, it did exactly what it was supposed to do for about as long as it was supposed to. Anything beyond that was "if possible".
Additionally, the mission is being shown as a "lander mission" instead of an orbiter with a small lander tacked on. Rosetta is still doing the mission as intended, and most of the objectives are being met very nicely. I see all sorts of comments in the press (and particularly in the European media and media comments section) as another Beagle "cock-up".
I think it's a very nicely done mission that is working very well. It's a shame that it is not coming across like that.
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.
we don't want plutonium-powered reactors on an exploding rocket
Back up a bit, who's the "we"?
I recall seeing testing footage for the RTG in the Cassini probe, among other things the tests involved a large artillery gun and a steel wall a few feet thick. Cassini was particularly controversial because it made a 'sling shot' flyby of earth at a much greater speed than escape velocity. From the tests I saw in the doco decades ago the worst thing that could possibly happen with an RTG is that it falls from the sky directly onto someone's head. Far from being anti-nuke, I'm actually interested the idea of "pebble bed" reactors (materials research is what's needed there). I'm also in favour of "full life cycle" nuclear power as practised in some parts of the EU. I don't know of a -science based- environmentalist/hippie/greenie who thinks otherwise. I've held these views since the early 90's, I'm not alone either, James Lovelock and some other influential greenies expressed similar opinions in the early 2000's
I speak to you today as a scientist and as the originator of Gaia Theory, the earth's system science which describes a self regulating planet which keeps its temperature and its chemical composition always favourable for life. I care deeply about the natural world, but as a scientist I consider that the earth has now reached a state profoundly dangerous to all of us and to our civilisation. And this view is shared by scientists around the world. Unfortunately, governments, especially in Europe, appear to listen less to scientists than they do to Green political parties and to Green lobbies. Now, I am a green myself, so I know that these greens are well intentioned, but they understand people a lot better than they understand the earth, and consequently they recommend inappropriate remedies and action. Lovelock 2005.
Disclaimer: According to my parents I became a Hippie back in 1976. Like any other social group, "Hippies" in general are reasonable people if you stop insulting them and feeding them on bullshit.
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
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.