in space , a linear accelerator firing charged pellets can be situated at a large distance from a target at which the pellets are aimed . the accelerator can fire a graduated - speed train of pellets over a period of seconds or longer which arrive at the target simultaneously , and impart a large pulse of energy . an accelerator of modest power can thus provide a pulse in the megajoule range , sufficient to ignite fusion . it is necessary to provide course corrections to the pellets , to bring them together with very high precision as they approach the target . an ideal siting is to place the accelerator at the earth - moon l1 or l2 lagrange point , and the fusion target at a point on the surface of the moon where the pellets will strike at grazing incidence , i . e . on a great circle intersecting the lunar poles . length of the particle trajectory is over 60000 km .