When you select your level press UP, LEFT, DOWN, RIGHT, UP, RIGHT, UP, DOWN, LEFT, UP, L1 + R1, L2 + R2.
Hidden Mission 1A
Finish mission 1 in less than 5 minutes and 2 seconds with higher accuracy than 40%.
Hidden Mission 4A
Finish mission 4 in less than 6 minutes and and 44 seconds with accuracy higher than 40%.
Secret Mission 5A
Crush half of the energy plough and use your tractor beam to destroy the second half when on mission 5.
Hidden Mission 5B
Look for the info unit in the middle of the two asteroids, near the crushed shuttle when in mission and you have to get it with the tractor beam to pick it up.