Tim Daughters
Tim Daughters asked Neil deGrasse Tyson:

I've been reading "Project Hail Mary." OK, it's science fiction, but there was a part when a character didn't know anything about relativity and was surprised that he had extra fuel at the end of his relativistic travels. That doesn't seem right. OK, there is time dilation, so the trip doesn't take as long as he thought, but doesn't his mass get bigger as he goes faster--needing more fuel to accelerate his ship?

Neil deGrasse Tyson He will find that as he approaches the speed of light his fuel needs will grow exponentially -- we interpret that as a relativistic increase in his mass.

About the extra fuel, I'd have to do the math on this one. It may be that he wouldn't have that extra fuel for those reasons, in spite of the time dilation shortening his trip.

I've friends with Andy Weir, I'll check with him on this, to make sure he did his homework properly.

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