Thrusta is an early 16K ZX Spectrum game written by Patrick Richmond and published in 1983 by Software Projects.
You control a spaceship that can move in four directions and is subject to the downward pull of gravity. The aim of the game is to push a boulder off platforms in order to kill the aliens below. The aliens hatch from eggs at the bottom of the screen and three secondary enemies also fly randomly around, re-spawning when killed. If any enemies touch you you’ll lose a life. Your ship also has a laser that can fire horizontally, but this only works against secondary enemies – not the hatched aliens. When the boulder hits the bottom of the screen it re-spawns on the top platform in a random position for you to go again.
If hatched enemies move above you you cannot drop the boulder on them, and you can’t shoot them either, so you have to wait for them to move below you again, which can be tedious. Thankfully the game doesn’t have a timer, so you’re at least free to wait as long as you need to.
Thrusta unfortunately only has one screen, which repeats over and over, but the alien sprites do change every level. And that’s really the only variety you get. The layout of the platforms doesn’t change and the only real motivation to keep playing is a high score, but at least there’s a high score table where you can enter your name.
The game is playable but is more difficult than it looks, and if you’re not concentrating properly it’s easy to lose a succession of lives quickly. It also has a weird, constant churning sound effect that may get on your nerves after a while, and you can’t turn it off.
Thrusta is a simple, repetitive, challenging game that was obviously an attempt to recreate the thrills of the arcades of the early ’80s. It succeeds to some degree, but is limited because it’s squeezed into just 16K of RAM.