When I asked the team live on Google Hangout chat why they didn't use RTG, for a mission where solar power is a risky bet, their answer was that there were too many political obstructions to getting any reasonable amount of fissile material on-board. I'm certain RTG would greatly increase the chances of mission success, given the reactors proven reliability and capacity, just like they serve our Voyagers.
I appreciate that science cannot operate in isolation of the rest of the world, what with all the economic and political realities and such. However, learning that politics was the reason to use an inferior power source for Philae makes me sad.
Can anyone shed more light on what type of political problems would using RTG create? Something about weapons grade plutonium, perhaps? Or this being an European project, and we cannot possibly source the materials from the US? Or (and I hope this is not it) green “solar good, nuclear bad” dogma?
My understanding is that it's primarily a safety issue: these long-duration missions tend to have to get delta-V boosts by slingshotting around the Earth. (Rosetta did this three times. And a slingshot around Mars once.) While the RTG capsule is robust enough to survive a launch failure intact, it's not robust enough to survive reentry at interplanetary speeds if the slingshot goes wrong. It's not like we don't have tonnes of vapourised plutonium in the atmosphere anyway, but that's no excuse for adding more.
Plus, the kind of plutonium that goes into an RTG is fabulously expensive, not just because it doesn't occur in nature and has to be made via transmutation, but because it makes handling so much more complicated.
They'll have done the cost-benefit analysis and decided it simply wasn't worth it.
(Also, RTGs are big and heavy. New Horizons, which is a really small spacecraft, has a 50kg RTG. Philae only massed 21kg.)
From what I gathered that was actually a major reason, considering that the plan was to land the probe unharmed on the comet. More weight for power generation would likely have meant more weight to make whatever is involved in landing stronger and ultimately probably less weight dedicated to instruments.
Do RTG's need to be big, heavy and require large amounts of plutonium? I recall reading about plutonium pacemakers. Depending on power needs, could something smaller like this be used as a trickle charge to power limited essential systems ongoing or for bursts of access?
RTGs are incredibly well built and designed to survive a launch accident (indeed, they have done so) without releasing radioactive material. A road accident would be nothing in comparison. As for theft, that seems very unlikely, the parts are well guarded and not just put on a truck and sent across country.
Nuclear missiles, fissile material, reactor cores, etc are transported on public roads - where else would they go? We haven't invented transporters yet so transportation is still roads, rail, sea, air - these things don't just magically appear at the launch site or at the power station. Someone needed to drive the semi that gets it there.
There is absolutely a chance of fissile materials being stolen in transport - that's why there's multiple levels of security and multilateral treaties with most countries around the world about this kind of issue.
The concern was that performing a slingshot around Earth with a RTG-equiped probe has risks. If early in the mission the probe loses the ability to guide itself, then the probe may be off course enough to hit Earth.
The Cassini mission to Saturn did this with an RTG, and there was a significant outcry about the plan.[1]
"Had there been any malfunction causing the Cassini space probe to collide with the Earth, NASA's complete environmental impact study estimated that, in the worst case (with an acute angle of entry in which Cassini would gradually burn up), a significant fraction of the 33 kg of plutonium-238 inside the RTGs would have been dispersed into the Earth's atmosphere so that up to five billion people (i.e. almost the entire terrestrial population) could have been exposed, causing up to an estimated 5,000 additional cancer deaths (0.0005 per cent, i.e. a fraction 0.000005, of 1 billion cancer deaths expected anyway from other causes), but the chance of that happening were less than one in one million."
Would it be true to say that your loved ones are thousands of times more likely to die in a car crash than in the worst-case scenario of this project?
What about "Let's add risk to strangers' lives so we can look at a comet slightly longer"?. Throw in that 'one in one million' is a number pulled from the air to represent an opinion, not calculated mathematically, and that launching probes happens multiple times, not as a once-off event. Let's keep things in perspective here.
What happens if that burnup happens over a country like Russia or China?
And if you're going to make the "well, only 5000 people would die" argument, then you've lost already. Out of the global population that live and work in buildings, the World Trade Center attacks killed fewer than 5000 people. Overzealous police shooting people in the streets? Bah, it's hardly anyone, by the numbers. Wildfire sweeps through the state, killing 50 people? Drop in the ocean compared to car deaths, why is anyone concerned? "They were going to die anyway" is a pretty callous argument that can be used against anything.
I mean, if we're arguing for science here, then we should also be pointing out the flaws in the quoted paragraph - it doesn't matter how many other deaths are attributable to cancer (and doubly so because cancer isn't a single thing anyway). Mentioning that statistic in this context is purely political and poor science.
I say all this because the process of cutting edge science is necessarily political. You see it in academia, you see it in industry, and you see it in government funding.
Yes I agree. Science has no opinion whatsoever about the ethics of this, it can merely predict possible outcomes. The actual decision has to be about more than the statistics and include other factors. It may be worth the risk sometimes and not others. But public deaths is categorically unacceptable however you make the decision.
There’s a huge antiscience group of people out there. Let’s just not give them yet another excuse to attack science. They could inflate numbers and make it sound like NASA is endangering the health of millions of people for generations to come. We’ve heard crap like that before.
Sadly, the particular antiscience group that tried to stop the Cassini launch was more or less led by a popular, (then) well-respected physicist, Michio Kaku. [1]
For that reason, his name should not be forgotten by posterity, the way it was almost forgotten by me until this thread popped up.
If I read that correctly that there's a one-in-a-million chance of killing 5k people, the expected number of deaths over all alternative universes is 1/200.
Additionally, one has to consider the non-plutonic fallout and its consequences of NASA as an agency and space exploration in general.
> I appreciate that science cannot operate in isolation of the rest of the world
I can't. It's absolutely atrocious they're limited because of the shortsightedness people have. I get it, we can't live in a moral vacuum, but I'm not talking about human experimentation but the best method of producing energy is unavailable because some people are idiots. /rant
To be fair, there are real world safety considerations when putting radioactive material into orbit. It's not just a knee jerk reaction, in all likelihood. The risk for Cassini was calculated at 1:1400 (For context, humans have launched something like 8000 man made objects into orbit). That's certainly acceptable when there's no other reasonable way to provide the power that the mission profile requires, but it makes sense that they would go with a more conventional source where possible.
ESA is multinational and some member countries are very opposed to nuclear technology in any form. Aside from the fact that Europe generally lacks the ability to manufacture Pu-238 or RTGs in general. Britain is looking at developing RTG technology on its own, possibly using Am-241, which might shake things up. It's still a hard problem with so many member countries involved.
> Nuclear material isn't going to 'fly' in Europe ever again
France (which is in Europe and part of the EU, obviously) is the biggest pro-nuclear energy nation in the world, and (together with the USA) has been on the forefront of exploration and development in that region.
It's not pestering, it's getting the opportunity to speak with scientists directly. I would ask the same thing. It doesn't matter if I "already know the answer" - I have no place at the table and assumptions that you're right are so often wrong.
I'm german and live approximately 30 miles away from a very big nuclear waste disposal site, which is one of the reasons I prefer solar/wind/etc. energy over nuclear. I don't see why anybody would be against using it for scientific purposes though (especially stuff happening in space).
Because it's fissile material that somehow has to get into space, and the mechanism for that is 200tons of explosives controlled by 2 million movable parts each procured from the lowest bidder :)
Thanks to trade treaties, ESA always has to use the cheapest available hardware that fulfils the requirements – no matter if other hardware is more reliable.
This has been part of many discussions before – and it doesn’t just affect ESA.
From government agencies which have to buy pencils that break after every use and are practically useless, to contractors building Autobahnen where the asphalt melts in the summer sun away.
You're bringing up a non issue. Add reliability constraints into your requirements. Airplane components are also made of the cheapest materials that satisfy the constraints required by the engineers and they don't randomly fall apart.
Perhaps you should use actual statistics for launch and slingshot failures, because those numbers are actually available. Also consider that the design of an RTG probably takes those risks into account.
I think we'd probably all long since accepted that was the inevitable end for Philae. Although it's a little bit sad that they didn't get the perfect landing and imagery they were after, the whole project's just been staggering - even if the interpretation that they 'aimed for the first landing on a comet but got the first two instead' became so widespread as to be a gag, it doesn't make it any less true...
Philae was a great mission. Flying into space, linking up with a comet, then landing a probe is the stuff of science fiction. 60 hours of data really pushed the science forward quite a bit. I'm missing why people think it wasn't a success.
My guess is that most laymen compare it to the highly successful Mars rover (Curiousity and Opportunity) missions which have lasted for years and still continue to be operational.
Does anybody know of any decent layman-oriented summary of the successful measurements performed by Philae & Rosetta? And any interesting and/or surprising findings and conclusions? After quick googling I've found this: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Scie... from July 2015 (e.g.: "[CONSERT] results show that the small lobe of the comet is consistent with a very loosely compacted (porosity 75–85%) mixture of dust and ice (dust-to-ice ratio 0.4–2.6 by volume) that is fairly homogeneous on the scale of tens of metres") but I'd be interested in more, more recent, and with more explanations and details.
