Oh boy. We really are going beck to the dawn of time with this one. Jetpac was first released by Ultimate in the days when Ultimate was the undisputed king of Spectrum software.
The basic idea is to collect the various bits of spaceship scattered around the first screen and from then on collect enough fuel pods to achieve lift off and get to the next level. Trouble is, you must get the stuff whilst dodging hoards of aliens that bounce about wildly.
You will soon realise that there isn't actually much gameplay in this ancient shoot 'em up but even as old as Jetpac is, it still retains some of its original addictiveness.