You are in charge of a remote asteroid refuelling base, vitally important to Earth's space exploration program. Deep below the base lie four giant silos, each containing millions of litres of liquid oxygen.

So far your tour of duty has been uneventful - but suddenly you become aware of an alien spacecraft in orbit high above. It has detected your presence and is about to send down drones to plunder your fuel supplies - unless you cn zap them first. Your only defence is a powerful laser cannon. It's fast, deadly and uses a mirror to angle your fire power in any direction. Muttering "No free gas for Ganymede!", you hurtle to the controls, eager to destroy the drones and pulverise the pirates!

How long can you hold out before your defences crumble?

The first screen displayed is the title page - press any key to continue. The next screen allows you to specify the keys for Fire, Go Left and Go Right. Press the key you want to use as each option is displayed in turn on the screen.

Pressing the joystick fire button in response to any of the options will let the computer know that you will be using the joystick.

Next, you can choose whether you wish to have the sound on or off.

If the program is left unattended, it does into autoplay. Use the BREAK key to return to the title page.

The Go Left or Right key (or corresponding joystick movement) will cause the cannon to move in that direction until:

a) another key is pressed, or
b) the Fire key/button is pressed

Your laser cannon is automatically replenished with energy whenever it is connected to the energy bank at the extreme left of the screen. The energy level indicator shows how much energy remains to you - as this level falls, your laser beam becomes shorter and slower.

When the drones penetrate the plasti-steel roof of the base, they start to build fuel siphons on the top of each silon. The screen flashes to warn you this is happening and you see the top of each silo changing colour in turn. When all four silos have been covered, you lose a life. You have three lives in each game.

The drones attack in waves. Advanced players will encounter a wave of high-speed super-drones at the end of each level. If you manage to survive this, you progress to the next level - the screen changes to a different colour combination and the level number changes on the display. The time check shows how long you've lasted!

You gain higher scores as you go further into the game. At the first level the drones are worth ten points each, at the second, twenty each, and so on. Bonus points are awarded for hitting a drone near the top of the screen and also for hitting drones in the advanced attack wave at the end of a level.

Move your cannon for greater fleixibility and more points. It is impossible to zap all the drones by staying in one place - by the energy bank, for example. Move out to fire at a sharper angle and get yourself a bigger score.

The highest score so far is given at the start of the game. If you manage to beat this, you can enter your own name. You are allwed up to fifteen characters and can use DELETE if you make a mistake. Press RETURN to register it.

N.B. Pressing BREAK will restart the game! Pressing CTRL-BREAK clears the memory and returns you to BASIC.

Game Written by John Colin, Program by Jon Malone and Graphics by Mike Masters