Following the messages from some who want BFG to have a 'proper' movement thing (i.e., stop and you stay stopped, etc.) I propose the following changes:
Movement
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At the start of the game, make a note of each ships' speed. In the movement phase, this speed can be increased or decreased by the ships' movement value.
All Ahead Full: You can only increase your speed using this order. Burn Retros: Immediately decrease your speed by movement + 4d6cm (with the usual things - improved thrusters give +1d6 to this, etc). If you hit 0, you can stay there if you like.
If the ship turns, it continues moving in the direction it was going previously, along with any new speed in another direction. I'll leave it to your knowledge of trigonometry to work out it's proper speed.
Note that if a ship passes 0.1 times the speed of light, it becomes affected by the laws of relatively. For every full 0.1 past 0, the ship takes twice as long to do things (i.e., moves at the same speed, but can only turn, fire, etc. half as much).
Ships which leave the table may not return, even if you didn't mean it.
Ships which enter an asteroid field may decreases their forward speed by 5cm for every additional hit they take (savable by shields as normal). Every blast marker a ship comes into contact with decreases it's speed by 1cm.