Encounter One is a system of miniature rules governing spaceship-to-spaceship combat in a "hard" or "realistic" science fiction setting. Rules allow for different "races" and alliances, as well as a system designed to simulate three dimensional movement. Ships move based on last turns speed, with additions or subtractions due to acceleration and deceleration, respectively. Mass and gravity play a role as well. Otherwise, other parts of the system remind the player of a complicated Star Trek-style system that includes fighters, with lots of charts to use to figure out "to hit," "damage," and "hit locations."