How about this? Remember the film when worlds collide?. Basically they used a rocket propelled sled down a ramp to assist in the initial launch phase then the sled fell away & rockets continued. Lets update the idea. Same sled/ramp idea, but, using maglev & rail gun technology to accelerate the launch vehicle electrically to supersonic speeds whereupon air breathing ram/rocket engines could take the vehicle to the upper atmosphere before converting to pure rocket power for the final acceleration into orbit or beyond. Thereafter some form of electrically produced ion drive could be used for extended periods to travel away from Earth. Ram jets only become effective after the speed of sound, but are light/simple & work at hypersonic speeds. The initial launch phase & acceleration use most of a current spacecraft`s fuel/mass. Electricity is relatively easy to produce & renewable. An unmanned rocket assisted satellite could be fired into space by a suitable rail gun (if the accelleration was carefully controlled & the rail gun long enough, could even launch manned rocket assisted capsule/craft). Any boffins out there who know how much of the shuttles total mass is used in the initial acceleration to mach 3?, & then how much more mass is wasted carrying liquid oxygen through an oxygen rich atmosphere?. I still hate rocket engines though, surely by now we should have something better?.