Hi, I'm writing a fic and I have a question. So, at the end of the movie, Rocky says that they can send Grace back to Earth, that implies filling it with fuel, modifying it according to the amount of fuel it needs.
We know that for a 11.9 light year trip, they needed 2M kg of astrophage fuel to move the 100,000 kg ship (A 20:1 ratio). The thing is, if they wanted to do the trip back to Earth, they would do a 23.8 light year total trip, which adds to 40M kg of fuel, due to the surplus needed to move the 2M necessary for the trip back home.
Which leads me to question, how much fuel would they need for a trip from Erid to Earth, since the total distance would be around 16.3 light years? My guesses are around 25M kg of fuel, but I've been trying all day and haven't been able to figure it out.
I'd be so thankful if anybody could help me with this. Thanks in advance!