After bombing a base from orbit, you may need to land troops to take control of what's left. Alternatively, you may want to try and take a base intact, in which case infantry and supporting forces are the only option. An invasion force can be made up of six different types of units, each with their own advantages and disadvantages.

Icon	Unit	Cost	Description
	Riflemen	5	Basic infantry units
	Engineer	5	Specialist infantry
	APCs	5	Used to carry infantry
	Tanks	10	Armoured fighting vehicles
	Gunships	15	VTOL or other airborne forces
	Artillery	15	Long ranged heavy weapons

All these need to be carried down to the surface. It is assumed that they can all operate in either an atmosphere or vacuum environment, but can't operate in the depths of space.