[pjc50]

This sounds related to "railgun launch": http://physics.stackexchange.com/questions/35139/what-is-the... and http://physics.stackexchange.com/questions/35921/could-we-ma...

The main limitations are surviving the hypersonic launch and short trip through the atmosphere, and you still need a second stage to get into a stable orbit. Your launch vehicle would basically be an upwards-travelling meteor.

Considerably more viable on the moon; lunar escape velocity is "only" 2.38km/s and there's no atmosphere. There's lots of 70s moonbase concept art depicting the use of rail launchers to return mined material to earth. Although I'm not sure it would be economically viable even if the moon were made of solid platinum.