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Cake day: October 6th, 2023

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  • i’m not sure what the exact reason is why we aren’t doing this already, but i suspect it has a lot to do with ease-of-use and price being significantly on the side of chemicals

    Well the reason we don’t have nuclear thermal rockets boils down to budget cuts at NASA and environmental/safety concerns around nuclear. We made significant progress on two different nuclear rocket designs before they were scrapped for entirely political/budgetary reasons. And by budgetary reasons I don’t mean that the program proved to be too expensive or difficult, I mean that NASA’s annual budget was year after year and they simply had to drop some projects.

    That’s not true for spaceships. for launch, chemicals are available and cheaper / fire up faster. for mid-flight, solar panels are available.

    Chemical propellants are great for launch, but the advantage of nuclear for deep space missions are really immense. The additional efficiency means you can make shorter trips, bring more supplies, and have more redundancy for equipment failures. It also provides the possibility of bringing the entire craft back home for future missions rather than simply expending it.

    And as a power source, solar is fine around earth. But for trips further out, like to Jupiter, well at that distance your panels would only get about 4% of what we get here around earth… That’s just not going to cut it for crewed missions.

    Honestly, spacecraft are probably the absolute best use case for fusion power. They’re one of the few contexts where the energy density is extremely important and the high cost is still worthwhile.






  • Well, it’s not really an “efficiency” number.

    For instance, we’re definitely concerned with efficiency when burning gas, we want to get as much energy as we can out of it per unit of fuel. But with fusion, the fuel cost is negligible, so you can treat it as essential free and in infinite supply. And because maintaining the magnetic containment simply costs electricity, you basically just take the net excess power as the output rating of the plant.

    Probably the most useful way to compare these two technologies is by cost per MW. That said, early fusion reactors will not be in any way cheap. Working fusion may be around the corner, but it will in fact be a long time before fusion is really “a good choice” economically.



  • Well to be honest, I personally think that data centers are a huge waste of this emerging technology, but yeah, I suppose it’s probably a perfect use case for fusion…

    My question, is who can miniaturize their technology sufficiently to put it in a spacecraft? When we get fusion reactors in space we’ll be able to use electric propulsion to make vehicles with insane range. We could send humans to Jupiter in a matter of months and have plenty of propellant for a return trip in a perfectly reusable vehicle. We already have all the tech for this, all except a suitable power source.



  • It’s funny you should mention scaling, because fusion does not scale like that at all, it scales much better. If you can get a small reactor to work at all, a larger reactor designed with the same principles is significantly more efficient. With fusion, bigger is better.

    I do hear what you’re saying though. Sometimes there are just simpler solutions. And I actually think you’re right, in most use cases solar + batteries is a better solution than a fusion plant. That said, solar + batteries has only become truly economical within the last 5-10 years. At this point there’s really nothing “Simple” about photovoltaic or battery technology, lifetimes of study have gone into them. And 25 years ago, solar was cute, it was pie in the sky. And you’d hear these same arguments “shouldn’t we be focusing efforts on something we already know works?”