Fuel consumption should be tied to acceleration

When you hold down the W key, your ship accelerates from zero to 300m/s. During this acceleration, obviously the ship consumes fuel (in the form of hydrogen or energy). This makes sense.

The moment your ship hits 300m/s, your ship stops accelerating, you're capped at speed, the ship will not go any faster. However, if you continue to hold down the W key, you continue to consume fuel as though you were still accelerating. The ship will not go any faster.

The amount of fuel used should tie to acceleration. When the ship hits a threshold where it cannot go any faster, the fuel burn should stop even if you're holding W You might want to hold W while going 300m/s to maintain the inertial dampeners, such as if you're flying through a gravity well briefly as a shortcut. Obviously you're still 'accelerating' when the dampeners are counteracting said gravity and that should consume fuel, but if you're doing 300m/s ahead at the same time, this should not unless you want to get rid of the cap on top speed. Then simply increase the mass of the grid as you approach c until the thrust simply can't measurably make you go faster. :)

Or, just make it so that you don't burn extra fuel when you hit the artificial space speed limit.