Alien Assault is clearly influenced by Atari Missile Command. The object of the game is similar - missiles rain down from space onto satellites that must be protected by a laser fired by a central base. You start the game with 35 protective lasers, as indicated by the “Energy” counter at the bottom of the screen. The "Destroyed" counter shows how many of the satellites have been destroyed. Unlike Missile Command, only one missile comes down at a time, but the screen can be scrolled “West” and “East” (left and right) to observe the missile and shoot it down. When you shoot down all of the missiles in a set, another set appears with a different colored background, which is another homage to Missile Command. Once all of the bases are destroyed or you run out of energy, your game ends.
Alien Assault was one of the early A/W/A games written before the team had a disk drive. How do we know that? Because the code overwrites the area of the disk drive handler, and therefore doesn’t work if you run it off the disk! It wasn’t until 2017 that Eric Anschuetz discovered this major flaw, and re- wrote the BASIC code so that it runs in a protected area of memory and can now run on disk some 30 years later! The BASIC code listings show both the original code (circa 1983) and the updated code (2017).
The missile coming down from the screen is a Player/Missile graphic, as is the target indicator controlled by the joystick. The laser that is fired at the satellite is another Player/Missile graphic. This game makes use of parallax scrolling, which means that the satellites in the foreground scroll at a faster rate than the mountains in the background. This mirrors the effect in Williams Moon Patrol, and may have influenced the game a bit.