Before building a colony, planets need to first be terraformed using an atmospheric processor. As a planet's population grows, more taxes can be sent to a player's home starbase. However, in order to survive, colonies need to be supplied with food and energy. The player provides food by buying and placing farming stations on the colony or by transferring them on starships as cargo. Energy comes from purchasing orbiting solar satellites, but can be transferred as cargo. Cargo shipments consume fuel, so the player needs to purchase mining stations. Balancing these and similar factors constitutes the main challenge of the game. As the player expands their empire, they must create planetary defenses. Defense is achieved by building and maintaining defensive ground armaments on a world. The ability to attack comes from purchasing a battle cruiser and arming it with combinations of both homing, ballistic missiles and hover tanks, sending the ship to attack an enemy planet's defenses. Planets are taken by eliminating all ground defenses on an enemy world. The only way to win control over a system is to attack and conquer the enemy's starbase in that system. The only way to beat the game is to take the starbase of the last system, Yottsu. Likewise, if the player's home starbase is defeated, the game ends and the player loses. The NES version game allows direct control over missile launch and hover tanks (1 on the map at any given time) on the offensive side, while offering direct control over the plasma cannon defense base and partial control over the pom-pom cannon and lightening field defense bases. The computer versions do not have these units. Differences between versions The NES version is a port of the earlier home computer versions. However, there are several differences between them: The NES version uses fewer screens than its home computer counterparts, even fewer sounds, and much more simplified controls. While the original game uses units of soldiers in platoons which were upgradeable, the NES game condensed the battle elements to missiles and hover tanks against ground defenses, none of which can be upgraded. The message area is much larger in the other versions, and placed along the right hand side of the screen, compared to bottom center of the NES game. The NES game allows a single saved game to be stored, compared to up to four on the home computer version.