Rear Guard

Rear Guard is a horizontally scrolling shooter written for the TRS-80 and released in December 1981 by Adventure International. It is a side-scrolling space shooting game, a bit like Defender, in which you must blast enemy drones and their missiles before they can destroy the mothership you're protecting. Five ships come at you from the right and are worth between 25 and 200 points. A freighter flies in the same direction as you (left to right) and is worth 300 points. In addition, a satellite identified by an F on its side that later changes to an S flies by. Hitting the satellite while it displays an F gives you a fuel recharge, while hitting it with an S gives you a shield recharge.