Each ship has a basic thrust value of one, meaning that it can move the head of the vector arrow into one of the six hexes surrounding the hex the ship will move into if it simply coasts along its current vector. Once in orbit, the game mechanics will keep you there indefinitely. There are also minor gravity wells, which have hollow arrows. Mines and torpedoes are launched at the beginning of the turn, and move in the same way ships do. Mines are not very powerful and have no independent thrust capability, but take up only half the mass of torpedoes, so you can carry twice as many.
Torpedoes are deadly and have one thrust point.
In practice, gunfire is rare, some people like mines, most people opt for torpedoes. Overall, Triplanetary has the best rule length to result ratio I have seen in any game. Unfortunately, Triplanetary is currently out of date, although the rights are now owned by Steve Jackson Games, and it is listed as a long-term project.