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A useful document I found - spacecraft power systems
Interesting that the RTGs have power densities of 3-4 W/kg, but are only 5%. Stirling generators are being developed that offer far higher efficiencies, 5-6 times this - the worry is maintenance, which shouldn't be as much of an issue for a crewed base or vessel. We're talking about 20 kWe/tonne, so using an RTG should be viable for a base, and gives us decades to develop in-situ power sources.
Now we just have to persuade people to let them be launched...
Use what is abundant and build to last
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If you take a look at the cost of these systems, you'll see why they're impractical at higher output levels. The Pu238 filled RTG's cost too much because we stopped making that Plutonium isotope many years ago and only recently restarted production. Even if we had tons of the stuff sitting around, the cost to manufacture the isotope is much higher than the cost to make U235 and the potential power density will always be quite low. Current work focuses on using highly enriched U235 to make small, power dense cores for fission reactors. Fission reactors scale from devices weigh about 100kg to devices weighing many tons.
The output level of fission reactors is much higher than RTG's and the only reason the output levels aren't even higher than they already are is the mandate for utter simplicity in space reactor design. A 100We fission reactor has one moving part, which would be the neutron attenuating rod inserted into the center of the core for startup and shutdown. This is one more moving part in comparison to what a RTG has, not counting the Stirling generators that produce electricity. The ASRG RTG's also used Stirling generators to increase electrical power output, so apart from radiation levels that's the only real difference between an advanced RTG and a low-output fission reactor. The fission reactor has far fewer total parts count and is far less expensive to manufacture than a RTG, as a function of the abundance of U235 (even highly enriched U235) in our supply chain and the low cost of the rest of the components (shielding, heat pipes, Stirling generators).
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Why are you talking about Plutonium? The Russians use the far more plentiful and much cheaper Strontium.
Use what is abundant and build to last
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I'd take no issue at all with NASA using Strontium, but there's this little NIH issue NASA must first move past. For them, NIH is a "thing".
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Well, if NASA isn't the one leading the project, will that be such an issue?
Use what is abundant and build to last
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In most countries, nuclear things are government monopolies. It takes an act of congress in the US to allow a private company access to nuclear power, excepting only those entities that build and operate Earthly power plants. Even for them, the permitting process is extreme.
It is rules like that which prevent Spacex or any other outfit, essentially nobody but NASA, from fielding nuclear power supplies in space. Fix THAT, and things like Safe-400 will immediately get used and incorporated into many projects.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I'd take no issue at all with NASA using Strontium, but there's this little NIH issue NASA must first move past. For them, NIH is a "thing".
The two isotopes that have been most frequently used are Pu-238 and Sr-90. Each has their advantages and disadvantages that make them preferable for certain types of applications.
This web page answers the question for the use in an RTG: https://atomicinsights.com/rtg-heat-sou … materials/
In nature, strontium is present in igneous rocks as celestite (SrSO4) and strontianite (SrCO3) but no Radioactive strontium, Sr 89 and Sr 90, as they do not occur in nature.
Still looking up reactor uses....
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