Set in the 21st century, the map depicts the inner Solar system out to Jupiter. Scenarios involve racing, pirating, invasions, and a few others.
Movement involves vector mechanics. Players plot courses using a grease pencil on the map and use fuel to accelerate a maximum of one each turn. Planets and moons are used to modify the trajectory.
There are a limited number of ships. Most are limited in fuel, so making efficient use of gravity is important to reaching a destination.
2nd edition came out in 1981. A 3rd edition was released in 2018 by Steve Jackson Games.
It is fairly easy to extend the game to much more than 3 players, although the board can become cluttered with ship trails (the game is sorta like Crayon Rails in this respect).