So, you want to build a CubeSat?
I had this thought, why not build a small rifled tube with an explosive charge and bullet like projectile.The projectile has a rocket motor too.Get the cannon as high as possible with a balloon.At the limit, the cannon fires the projectile at high velocity. The rocket motor ignites giving the extra velocity.Do you think it could reach escape velocity?IANARS (I am not a rocket scientist)