How about a series of superguns of different sizes? You start with a small gun,
it fires a projectile that hits an object hovering in front of it. The
projectile knocks the object forward and in front of a second slightly larger
gun which fires a projectile hitting. The target goes faster and higher each
time it is hit by projectiles fired by increasingly larger superguns. The guns
are igged to fire at a precisely timed moment hitting the target as it passes
in front of it. The projectiles never have a fast enough relative velocity to
actually destroy the target, only to push it faster and higher. Eventually you
need superguns to push the target to near orbital velocities. Each supergun
only fires once for the launch of the payload. Does this sound like a good
idea?

Tom