Protium

Protium is a side-view horizontal scrolling shooter where the screen
scrolls constantly from left to right as you control spacecraft blasting and
avoiding aliens over various levels. Earth have been threatened with
hyperspace by the aliens and because their base is so far away, an attack
isn’t plausible. The only solution is to activate the Galactic Shield but this
requires large amounts of Protium and there isn’t any on Earth. To get some,
Protium, a ship laden with it has to be stolen and brought back to Earth to
save the planet. The aliens attack in formations and if you touch any or are
shot then you lose one of six lives. Icons occasionally appear and when one is
touched then you receive a power-up and these are extra fire-power, extra
speed, reverse fire, laser, plasma bomb and shield. Half-way through each
level, a Mothership appears and must be destroyed to progress through the
level.