Space Sentry was the 3rd place winner of the Spectral Associates Machine Language Game Programming contest (1st place was Whirlybird Run and 2nd place was Storm Arrows. This got its author John Nakoski a $200 prize plus his game got published by Spectral Associates. (He also created his own software company that published 6 games for the Coco, first called Color Software and later renamed to Challenge Software).
The game features 9 skill levels (this determines how long the player has to wait to use their shields after firing - 1 is the shortest), and uses the right joystick to fly through space (analog required as the player can vary their speed a bit in all directions) and destroy 20 enemy alien ships. The player fires in the direction that they are traveling by tapping the joystick button; holding down the fire button will raise the players shields to block enemy shots - it does not help against collisions with enemies or mines. The ability to use shields is controlled by the player's amount of fuel left; once it gets below 10, the shields don't work and if it drops down to zero, even firing lasers no longer works. All the player can do at this point is fly the ship and find the refueling station to get refueled (done by flying into the station, after which it randomly reappears elsewhere in space). Each shot the player does costs 1 fuel point. Space mines can destroy a player in two ways - 1) running into them, and 2) shooting them. While the game is generous with lives (10 to start) it is easy to shoot a mine coming in from off screen while flying and/or firing. It should be mentioned that both the space mines and the refueling station are stationary and don't move in space, but the alien ships are constantly moving.
The main part of the game screen shows the player's immediate surroundings (the player's ship is always in the center) and has 3 radar screens at the bottom of the screen, each detecting specific things:
Left radar screen - this shows the positions of space mines.
Middle radar screen - this shows the position of the refueling station.
Left radar screen - this shows the positions of the alien ships. NOTE: I believe that they can only move horizontally or vertically.
It takes practice to be able to monitor multiple radars at once and prevent the player from accidentally shooting a mine or running into an alien unprepared, and monitoring these is what makes the game challenging, especially on higher levels.
Title: Space Sentry
Author: John Nakoski
Publisher: Spectral Associates
Released: April 1983 (written by November 15, 1982)
Requires: Color Computer 1,2,3, 16K RAM, tape or disk, joystick.