Why a Nuclear Submarine Wouldn’t Work As a Spaceship

As part of their “What If?” series, Randall Munroe of xkcd and Henry Reich of MinutePhysics explained via very minimal animation why a nuclear submarine would not work as a spaceship despite its sturdy, airtight, watertight hull.

This question comes from Jason, who asks: How long could a nuclear submarine last in orbit? The answer is “not very long,” but not for the reason I expected.

The problem is the onboard nuclear reactor. When the submarine is used as designed, the external water keeps the reactor cool. Unfortunately, the relative dry warmth of space would cause the reactor to meltdown.

…a nuclear submarine isn’t just carrying humans – it’s carrying a 200 megawatt nuclear reactor… around half of the reactor’s energy – or around 100 megawatts – is lost as heat. This heat is normally dissipated by seawater, but again, there’s no water in space. – the submarine would become too hot for human survivability within an hour.