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Without Plutonium, Deep-Space Probe Missions May Sputter Out
cold fjord writes with this excerpt from Wired: "Most of what humanity knows about the outer planets came back to Earth on plutonium power. ... The characteristics of this metal's radioactive decay make it a super-fuel. ... there is no other viable option. Solar power is too weak, chemical batteries don't last, nuclear fission systems are too heavy. So, we depend on plutonium-238, a fuel largely acquired as by-product of making nuclear weapons. But there's a problem: We've almost run out. 'We've got enough to last to the end of this decade. That's it,' said Steve Johnson, a nuclear chemist at Idaho National Laboratory. And it's not just the U.S. reserves that are in jeopardy. The entire planet's stores are nearly depleted. ... what's left has already been spoken for and then some. ... Political ignorance and shortsighted squabbling, along with false promises from Russia, and penny-wise management of NASA's ever-thinning budget still stand in the way of a robust plutonium-238 production system." The plutonium shortage has been deepening for a long time, leading to some creative solutions. The Wired article alludes to the NASA project underway to create more, but leans toward gloom.
Mass doesn't disappear just because something is in outer space. That mass carries with it a certain amount of inertia, and the heavier something is on earth, the more energy will be required to manipulate it with any kind of acceleration, even in space.
File under 'M' for 'Manic ranting'
Launch price.
Shoving something out of ye olde gravity well is always expensive, if you go over the weight/size limit of one of the reasonably-commodified launch systems, things go from 'expensive' to 'heroically expensive'.
Depending on exactly what trajectory you have in mind, a more massive craft may also require more fuel/more powerful thrusters if you are making any course corrections along the way.
there are alternative isotopes, with much longer half lives even if battery weight is three or five times what a pu-238 one would be. not the heaviest thing in a spacecraft...anyway, the equipment to make the pu-238 exists, just a matter of getting serious about making the stuff
Fire up Rocky Flats and Hanford again to start building the next generation of nukes! That way we can get enough Pu-238 to power our deep space ambitions! I read on "The Onion" that the North Koreans are already building their deep space probe Kim Il Wang 1 which will reach out and spread communism to our neighboring galaxies! We can't afford to have a deep space probe power gap! We must contain the Red Menace!
Frankly with all the carcinogens in our air, amoebas in our water and a third of us with Toxoplasmosis, what's a little radiation folks?
Harrison's Postulate - "For every action there is an equal and opposite criticism"
That's the wrong kind of Plutonium. RTGs need Plutonium-238. That stockpile is Plutonium-239, 240, 241, and a bit of 242.
upon the advice of my lawyer, i have no sig at this time
A very long time ago I was in the Navy, sailing about in a nuclear submarine.
The power plant of that submarine outmassed the ISS.
"I do not agree with what you say, but I will defend to the death your right to say it"
Tapping undersea cables.
A design concern for nuclear reactors is cooling. Nuclear subs are conveniently surrounded by an infinite heat sink of cold water, so cooling them is easy. A nuclear reactor desgined for space would need a completely different cooling system, which is a major part of the design.
The problem is that the Dept. of Energy, although hugely wasteful, cannot "afford" to make plutonium for NASA/JPL. Yet another way this and previous admin is trying to gut planetary science: http://www.planetary.org/blogs/casey-dreier/2013/20130913-the-doe-is-full-of-wasteful-spending-but-forbidden-to-help-nasa-make-plutonium-for-space-missions.html
We are not creating any new ones is the point he was making. It had nothing to do if we were still maintaining them. Maintaining them doesn't give the fuel that is needed.
But I should think the minimum safe distance from an unshielded reactor would preclude anybody actually getting near enough the spacecraft to prep it for launch.
A fission reactor that has been assembled, but never operated, does not produce much radiation. Enriched uranium and/or pure plutonium are not particularly dangerous (unless inhaled or ingested). It is the fission byproducts from actually operating the reactor that are dangerous. Even this minimal radiation could be avoided by using temporary shielding that is removed (possibly by a robot) immediately before the launch.
Pu-238 isn't usable for nuclear weapons. The only use to which it is put is power generation. The only connection between Pu-238 and nuclear weapons, in fact, is that weapons production facilities naturally make good production facilities for Pu-238.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
I thought NASA struck a deal with DOE back in March to do 2 kilos per year of Pu-238 back in March. Did it get de-funded or something? http://www.universetoday.com/100875/u-s-to-restart-plutonium-production-for-deep-space-exploration/
[RIAA] says its concern is artists. That's true, in just the sense that a cattle rancher is concerned about its cattle.
WHAT WOULD HAPPEN?
The reactor would mostly likely fall into the ocean, where it would be retrieved intact. RTGs are designed to survive a launch failure, and several accidents have
already happened, without any significant release of radiation.
Consider it costs from $2000 (Falcon 9) to $30,000 (Pegasus) per lb. to launch a payload from Earth. And the present maximum launch capability is, IIRC, about 150 tons. Anything bigger has to be launched in pieces. For probes going anywhere besides Earth orbit, that 150 tons has to include the additional rocket stage to push the probe out of the Earth's gravitational influence. So the probe itself is likely to be under 1/2 ton. Now, make a reactor that fits.
Having said that, I've been casually wondering if a small MSR (Thorium) reactor could be used. It provides both heat and power, and its characteristics make it plausible that an under-10-ton reactor could be made. Such a reactor could provide the heat for propulsion of the probe, plus lots of electricity, and it can be turned on and off at will, or throttled. So this might work in a large vehicle. Of course nobody has even started on the engineering required to make a liquid reactor work in microgravity (no convection, no heat conduction to dump waste heat).
It's easier to be a result of the past, but more fun to be a cause of the future! http://www.spacefinancegroup.com/
Many other isotypes and generator types.
Strontium-90 is a good substitute for shorter trips. Americium-241 is very close to being a reality for longer trips. There is also the Safe Affordable Fission Engine project https://en.wikipedia.org/wiki/Safe_Affordable_Fission_Engine
But there is another type of electro-mechanical rotating generator designed for Russian craft, TOPAZ-II, but, unfortunately, it's far too heavy.
Kriston
Neither of those substances are overly dangerous or radioactive. It's the stuff with shorter half lives that you have to worry about. It decays faster, and pound-for-pound will release a greater amount of radioactivity in a shorter time scale.
PU-238 has a half life of 87.7 years. It will be cold and inert thousands of years before entering another star system.
I want peace on earth and goodwill toward man.
We are the United States Government! We don't do that sort of thing.
Most probes use a boom rather than a tether. Look at pictures of pretty much any probe, like Voyager, Galileo, Pioneer and you'll see RTGs mounted out on booms away from the main body of the probe.
When our name is on the back of your car, we're behind you all the way!
Not correct - the plutonium in nuclear weapons is Pu-239, not the Pu-238 that we desire for RTGs. You can't extract useful quantities of Pu-238 from a nuclear weapon. Conversely, you can't use Pu-238 to make a nuclear (fission) weapon. You could make a dirty bomb, I suppose, but that's more due to plutonium being a toxic heavy metal than its radioactivity.