Mind the gaffe
In reply to the feature “The fictional science of science fiction” by Rhett Allain about scientific bloopers in movies (November 2019).
Allain gets it absolutely right about the poor science in science-fiction films. But he singles out the TV series The Expanse for particular praise regarding the use of acceleration to produce “gravity” on a spaceship. I agree that it is wonderful that this series gets this right, for a change. It knows that you accelerate with the engines firing, or you coast with the engines off. As the spaceships are mostly firing their engines, the crew can have “gravity” onboard.
Unfortunately, the engines used to produce 1g travel simply don’t (yet) exist. Simple calculations using, for example, Space Shuttle main engines and external fuel tanks, show that an acceleration of 1g (9.81 m/s2) could only be sustained for a few minutes before the fuel runs out (even when you allow for the decreasing spacecraft mass as the fuel is used up, so that the engines throttle-down to maintain a constant 1g.) Furthermore, there is no solution involving many tanks and many engines, due mainly to the mass of the fuel.
I don’t know how those Expanse engines are supposed to work, but they must remain in the realm of science fiction
So although it would be nice to go to the Moon in 3.5 hours having full Earth gravity – which could be achieved by accelerating for the first half of the journey and decelerating for the second half – in practice, using current chemical rockets, it just can’t be done. I don’t know how those Expanse engines are supposed to work, but they must, unfortunately, remain in the realm of science fiction.