I love project Orion. But, let's be honest, it will never overcome the politics of Earth. For as far in the future as we can see, nuclear weapons will be a tricky issue. Putting a few thousands of them on a spaceship will be (and it currently is) against international treaties. And for good reason: how would you feel about an entity (either a government, or a private corporation like SpaceX) say that they intend to manufacture a few hundred thousand nuclear bombs, but, you know, pinky promise, they will never be used for anything else but space travel?
I read The Starship and the Canoe after it was mentioned in a reply to me [1], what a great book.
The theoretical physicist father, Freeman Dyson, champion of Orion, pretty much said that the idea was crazy and he wouldn't have pursued it further by the 70s IIRC. Of course, other scientists' options may have differed.
And NASA is going to do this how? NASA is currently in the process of being gutted. Sure, there's a chance that they will be reconstituted in the future, but I wouldn't hold my breath.
I wrote a piece on this in 2017 - (hadn't even been familiar with NERVA at that point, only having had a passing awareness of Orion). It was very much inspired by a Kerbal Space Program-inspired graphic.
Would add fusion propulsion to the list. Fusion propulsion is inherently easier than fusion power since you can get away with lower efficiency. (Chemical rockets are pretty inefficient.)
Fusion rockets can not get away with lower efficiency. Either you are using the fusion reaction as a direct propulsion source, in which case it needs to beat chemical rockets at producing thrust, or you are using it as a power source for electric propulsion, in which case it needs to beat other power sources for energy efficiency. In fact, the problem is so much worse for propulsion, because not only are you concerned about fuel efficiency, you are also concerned about mass.
Right now it takes a building the size of 3 football fields to house the only machine that has ever achieved ignition of a controlled fusion reaction (ie the energy released by the fusion fuel exceeds the energy put into the fuel). This is several orders of magnitude below the point where the energy produced by fusion exceeds the energy needed to run the machine, which is the absolute bare minimum you need to do anything useful. Fusion power output scales with size - keep making your reactor bigger, and you will eventually reach any desired level of power output. The challenge of fusion for power production is making a big enough power plant while remaining economical. Luckily economics is relative - so long as a massive power plant is preferable to the drawbacks of other power sources like pollution or limited fuel, it can be justified.
But for propulsion, you don't just need to satisfy investors, you must overcome gravity. Make your reactor bigger and your mass increases. More mass demands more propulsive power demands a bigger reactor. This is especially the case for launching from planets, where thrust to weight ratio is king, but even for deep space propulsion mass budget is a chief concern (and you still need to get that thing into space somehow). Not only do you need to make a fusion reactor that is competitive with other power sources in terms of efficient power generation, you need to do so with a comparable power density. Further, the only thing fusion really has going for it over fission - that it doesn't produce long lived radioactive waste - is entirely useless when you are flinging stuff out into the void, so you can't even justify a low power density reactor with reduced fuel mass.
No matter how much fusion advances, fission will always be decades ahead and fundamentally simpler. The only form of fusion propulsion that realistically could find practical application is the one form of fusion power humanity has already learned to harness - thermonuclear explosives.
> you are using the fusion reaction as a direct propulsion source, in which case it needs to beat chemical rockets at producing thrust
Yes.
> Right now it takes a building the size of 3 football fields to house the only machine that has ever achieved ignition of a controlled fusion reaction
Compare the size of a jet engine to a power plant of a similar size. Size shrinks dramatically when you can blow the heat out of your ass in propellant product.
> you don't just need to satisfy investors, you must overcome gravity
Why? Burn it in vacuum?
> No matter how much fusion advances, fission will always be decades ahead and fundamentally simpler
Why. Fusion precursors are more plentiful than fissionable elements. And fission produces heavy nuclei; fusion doesn’t.
It's OK, but it's not "vastly" superior down here on Earth. Sun's a fusion reactor we don't need to build.
In space… again, there's uses for nuclear, but it's not a slam-dunk for everything. Space is a very good insulator, so there's a limit how hot and for how long you can run your power source — for a lot of scenarios, being closer to the sun than about Mars means that even with PV, too much heat is more of a problem than too little.
(On Mars itself, you probably do want nuclear anyway: global dust storms happen and can last ages, so you can't just geographically distribute solar farms, but on Deimos and Phobos you should just use PV).
You could use some sort of beamed power/powersat eventually at those distances (using a sending station from a place with a lot of solar power, like Mercury) but that's signifficant infrastructure and ways of right now.
Nuclear propulsion and not even a mention of Freeman Dyson's project Orion?
https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
8 million tons to orbit in one lauch. Mindboggling.
I love project Orion. But, let's be honest, it will never overcome the politics of Earth. For as far in the future as we can see, nuclear weapons will be a tricky issue. Putting a few thousands of them on a spaceship will be (and it currently is) against international treaties. And for good reason: how would you feel about an entity (either a government, or a private corporation like SpaceX) say that they intend to manufacture a few hundred thousand nuclear bombs, but, you know, pinky promise, they will never be used for anything else but space travel?
I read The Starship and the Canoe after it was mentioned in a reply to me [1], what a great book.
The theoretical physicist father, Freeman Dyson, champion of Orion, pretty much said that the idea was crazy and he wouldn't have pursued it further by the 70s IIRC. Of course, other scientists' options may have differed.
https://news.ycombinator.com/item?id=44596988
And NASA is going to do this how? NASA is currently in the process of being gutted. Sure, there's a chance that they will be reconstituted in the future, but I wouldn't hold my breath.
I wrote a piece on this in 2017 - (hadn't even been familiar with NERVA at that point, only having had a passing awareness of Orion). It was very much inspired by a Kerbal Space Program-inspired graphic.
https://walkabout165.blogspot.com/2017/07/freely-zipping-aro...
Glad to see that nuclear thermal propulsion is getting attention, and there's buzz of more nuclear-propelled technologies on the horizon.
I'll probably convert it into a substack and link here.
Would add fusion propulsion to the list. Fusion propulsion is inherently easier than fusion power since you can get away with lower efficiency. (Chemical rockets are pretty inefficient.)
Fusion rockets can not get away with lower efficiency. Either you are using the fusion reaction as a direct propulsion source, in which case it needs to beat chemical rockets at producing thrust, or you are using it as a power source for electric propulsion, in which case it needs to beat other power sources for energy efficiency. In fact, the problem is so much worse for propulsion, because not only are you concerned about fuel efficiency, you are also concerned about mass.
Right now it takes a building the size of 3 football fields to house the only machine that has ever achieved ignition of a controlled fusion reaction (ie the energy released by the fusion fuel exceeds the energy put into the fuel). This is several orders of magnitude below the point where the energy produced by fusion exceeds the energy needed to run the machine, which is the absolute bare minimum you need to do anything useful. Fusion power output scales with size - keep making your reactor bigger, and you will eventually reach any desired level of power output. The challenge of fusion for power production is making a big enough power plant while remaining economical. Luckily economics is relative - so long as a massive power plant is preferable to the drawbacks of other power sources like pollution or limited fuel, it can be justified.
But for propulsion, you don't just need to satisfy investors, you must overcome gravity. Make your reactor bigger and your mass increases. More mass demands more propulsive power demands a bigger reactor. This is especially the case for launching from planets, where thrust to weight ratio is king, but even for deep space propulsion mass budget is a chief concern (and you still need to get that thing into space somehow). Not only do you need to make a fusion reactor that is competitive with other power sources in terms of efficient power generation, you need to do so with a comparable power density. Further, the only thing fusion really has going for it over fission - that it doesn't produce long lived radioactive waste - is entirely useless when you are flinging stuff out into the void, so you can't even justify a low power density reactor with reduced fuel mass.
No matter how much fusion advances, fission will always be decades ahead and fundamentally simpler. The only form of fusion propulsion that realistically could find practical application is the one form of fusion power humanity has already learned to harness - thermonuclear explosives.
> you are using the fusion reaction as a direct propulsion source, in which case it needs to beat chemical rockets at producing thrust
Yes.
> Right now it takes a building the size of 3 football fields to house the only machine that has ever achieved ignition of a controlled fusion reaction
Compare the size of a jet engine to a power plant of a similar size. Size shrinks dramatically when you can blow the heat out of your ass in propellant product.
> you don't just need to satisfy investors, you must overcome gravity
Why? Burn it in vacuum?
> No matter how much fusion advances, fission will always be decades ahead and fundamentally simpler
Why. Fusion precursors are more plentiful than fissionable elements. And fission produces heavy nuclei; fusion doesn’t.
Nuclear energy is vastly superior to every other form of green energy and is vital for a true space based future.
It's OK, but it's not "vastly" superior down here on Earth. Sun's a fusion reactor we don't need to build.
In space… again, there's uses for nuclear, but it's not a slam-dunk for everything. Space is a very good insulator, so there's a limit how hot and for how long you can run your power source — for a lot of scenarios, being closer to the sun than about Mars means that even with PV, too much heat is more of a problem than too little.
(On Mars itself, you probably do want nuclear anyway: global dust storms happen and can last ages, so you can't just geographically distribute solar farms, but on Deimos and Phobos you should just use PV).
Depends on your definition of vastly, and superior but:
How is nuclear energy superior to solar energy?
Within the context of space, solar doesn't work to well when you move away from earth. By mars, you're already down almost 30%!
You could use some sort of beamed power/powersat eventually at those distances (using a sending station from a place with a lot of solar power, like Mercury) but that's signifficant infrastructure and ways of right now.
With the difficulties of cooling things in space, satellites sending/absorbing massive amounts of energy seems like a hard problem.
Solar energy is nuclear energy! ;-)
But it is used, recycled. We only want pristine first order energy sources.