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Could waste heat drive Stirling engines? Web says they were explored by NASA but also has a lot of yea... nah comments.

If there was an acceptable efficiency to concentrate the heat into mass, you wind up at ion engines and shed heat physically for thrust.

I think he hasn't done his sums, or maybe we need a "show your workings" moment over the Fermi numbers on this.

I'm sceptical.

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yes and also no ;) Think of stirling engines as driven by "heat differentials" as opposed to "heat." At first when you fire up the GPU, it's hotter than everythign else and can start driving a stirling...but eventually everything heats up to the same temp and it stops moving. To get it moving again, requires a heat differential, so part of it would need to radiate, which is blatantly difficult in a vacuum(1), such as space.

In case it's not clear: Little-St. James Wannabe Invitee, Nazi-Saluter, Musk's full of it again, but to recognize it requires being halfway through college physics to understand it, so all the elites will be glazed over thinking they're onto the next big thing. grift, grift, grift, grift.

(1) a giant flipping vacuum.

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