Each level of the game is played in two parts. During the surface attack, the player fights enemies in order to delay the construction of the base. "Warning" messages indicate that a fresh wave of enemies is arriving, while an "Alert" tells of an attempt to siphon energy from the planet. If the player can fly through the enemy's energy beam in time, then pass through a charging station, the energy will be returned to the planet; otherwise, it will go into building the base.
