[Suicide Junkie]

They do one of three things at various times during the design process.

1) Add X # of engines
2) Add engines until there are Y movement points produced
3) Add one engine for every Z Kt of space on the ship.

The first two relate to "minimum speed" and "desired speed", but I'm not sure which matches up with which anymore. At a guess, I think it was desired speed -> Y movement points.