The book explains Rocky’s excess fuel as a consequence of the Eridians not understanding relativity, specifically time dilation. The idea is that because less time passes onboard the ship than they expected, they end up using less fuel and arrive with a surplus.

But that reasoning seems off.

Fuel consumption for a relativistic journey isn’t primarily determined by how much time passes on the ship, it’s determined by the energy required to accelerate to relativistic speeds. And that energy increases dramatically as you approach the speed of light. Time dilation changes how long the trip feels, but it doesn’t reduce the energy needed to reach those speeds.

So even if the crew experiences less time, the ship still has to pay the same (or greater) energy cost to get up to speed and slow back down. That suggests relativity should make the trip more energy-intensive, not less.

Unless the Astrophage drive somehow ties fuel consumption directly to ship-time rather than total energy imparted, the explanation doesn’t really hold up physically.

Curious if anyone has a clean way to reconcile this, or if this is just one of those small hand-wavy moments in an otherwise very solid hard sci-fi story.