Oddly enough nuclear rockets aren't particularly powerful and tend to be extremely heavy. Their strength is that they're highly efficient, so they can just keep

Oddly enough nuclear rockets aren't particularly powerful and tend to be extremely heavy. Their strength is that they're highly efficient, so they can just keep going with relatively little fuel. Chemical rockets, by contrast, tend to be extremely high power but also extremely inefficient. Here's a few comparisons: ---- NERVA [1] / Nuclear / 1969 / 246kN thrust / 18,000 kg mass, 841s ISP (seconds of specific impulse - higher is better/more efficient, a little is a lot) / The only completed possibly launch viable nuclear rocket engine, as far as I know. F-1 [2] / Chemical / 1959 / 7,770kN thrust, 8,400 kg mass, 263s ISP / Powered the Apollo rockets Merlin [3] / Chemical / 2007 / 981kN thrust, 470 kg mass, 282s ISP / Powers the SpaceX Falcon 9 in a group of 9 Raptor [4] / Chemical / ?? / 2,640kN thrust, 1,600 kg mass / 327s ISP / Powers the SpaceX Starship in a group of 33 ---- So what really matters in a rocket, for getting off Earth, is its thrust to weight ratio. NERVA isn't inefficient because it's dated (which was part of the reason I included the F-1), but simply because nuclear itself has an inherently poor thrust to weight ratio. However it just keeps going and going and going, which makes it absolutely awesome for travel once you're already in space. It's even "fast" in space, because of how travel in space works. You don't just keep thrusting in space; instead you make a limited burn and then coast to where you're going, making a final reversal burn towards the end. So even if it takes hundreds of times as as long to reach a higher cruising velocity, it'll end up getting to the destination long before a chemical rocket, for any sufficiently distant destination. ---- [1] - https://en.wikipedia.org/wiki/NERVA https://en.wikipedia.org/wiki/NERVA [2] - https://en.wikipedia.org/wiki/Rocketdyne_F-1 https://en.wikipedia.org/wiki/Rocketdyne_F-1 [3] - https://en.wikipedia.org/wiki/SpaceX_Merlin https://en.wikipedia.org/wiki/SpaceX_Merlin [4] - https://en.wikipedia.org/wiki/SpaceX_Starship https://en.wikipedia.org/wiki/SpaceX_Starship