Rockets are used to deliver supplies all the way from Earth or bring colonists which have applied for a life on Mars. They are reusable, and once having refueled on Mars, can bring Rare Metals back to Earth for monetary gains. Players start with five rockets that can be used simultaneously.
Space rockets have a far greater role to play in the mission of establishing a permanent colony on Mars then merely bringing the first colonists there. Until the colony can truly sustain itself, it will always be dependent on Earth for vital resources and the flow of colonists.
Although quite expensive, reusable rocket technology has already been mastered to a degree such that agencies can have a rocket back in space within the same day of landing on either world.