Repton

This is Repton, the classic side scrolling shoot-em up influenced by Defender. An endless onslaught of alien ships work to construct their base on your nearly conquered colony planet. You must defend your planet until reinforcements arrive. Quick thinking and fast reflexes are needed to pilot the very well armed Repton Armageddon Ship. And with luck may just be enough to defeat the alien hordes.
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Video : http://www.youtube.com/watch?v=F_GKyx1-EI0
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Repton Mission Orders
They came out of nowhere and destroyed the mining operations in Farsystem. The attacks overwhelmed meager planetary defenses designed for rougers. Unified Colony response has been quick. The Repton Armageddon Ship is our newest defensive weapon system. The RAS incorporates turbo pulse lasers, the new Mark III hyperdrive, tactical fusion weapons, auto shields, and in-dash music player.
We have very little strategic information, and only the following tactical information.

Worker
Moderately armed. Workers build the enemy base. Do not let them complete the base!

Spy

Sensor platform with no known weapons. They can seemingly disappear among buildings when at low altitude.

Drain
Able to tap planetary power grid. The RAS can recover power by intercepting the beam. Power can be returned to the grid via the Power Tube, or in a pinch it can be used in place of a nuke bomb.

Beamer
Very dangerous with long range energy beam weapons, but limited to short duration periodic fire.

Minelayer
The Minelayers have only been observed laying short duration mines.

Cluster-Ship
Slow but dangerous as it comprises four Single Ships. They are moderately armed.

Single-Ship
The most effective of enemy resources, it is fast and well armed.

Enemy Base
The base can not be destroyed and it has defensive missiles. Completion of the base means the planet is lost.

Power Station
Part of the planetary power grid they are critical to planetary defense. The stations are susceptible to the Drains.

Power Tube
Part of the planetary power grid. The RAS is able to exchange energy with the Power Tube. Energy captured from a Drain can be returned. The RAS can use this energy in place of a nuke bomb.

They come in waves with no end to the attacks once they begin. Your mission is delay and attrition until reinforcements arrive.
If not you cannot hold the planet you must leave them nothing of value behind.
Good Luck and Best Speed.