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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. (Rose
by david-given 11y ago
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.)
- imglorp 11y agoThere's probably plenty of human risk transporting it to the launcher, as well, such as a road accident or having it be stolen.
- ars 11y ago> such as a road accident No, not really. They are pretty safe - you can hold one in your hand without a problem (barring a burn - they get hot). A road accident would do nothing harmful at all. > having it be stolen That strikes me as pretty unlikely - they don't exactly drive on public roads.
- saboot 11y agoWe drive nuclear missiles on public roads, with enough security anything is doable.
- eco 11y agoYep. An example: https://www.youtube.com/watch?v=bCwlV_94kPE https://www.youtube.com/watch?v=bCwlV_94kPE
- barkingcat 11y agoNuclear 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. http://www.patriotnetdaily.com/wp-content/uploads/2015/11/Nuke-rear-ender-Feds-armored-vehicle-collides-into-truck-with-missile.jpg http://www.patriotnetdaily.com/wp-content/uploads/2015/11/Nu...
- InclinedPlane 11y agoRTGs 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.
- ygra 11y ago> Also, RTGs are big and heavy 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.
- Gustomaximus 11y agoDo 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? https://www.orau.org/ptp/collection/Miscellaneous/pacemaker.htm https://www.orau.org/ptp/collection/Miscellaneous/pacemaker....