Difficulties with mass driver technology

In most of the lunar resource utilisation projects that I have heard about, a
mass driver is used to deliver material to L2. Each payload must rendezvous with
a mass catcher in L2. It must do this with exceptional accuracy. If the payload
misses the catcher by 1 metre, it has missed. Unless our lunar mass driver is
super accurate, we must find a way of guiding the inert payloads into the mass
catcher. How can this be done without a complex guidance system in each payload? T. A. Heppenheimer came up with what he called "achromatic trajectories". These werepaths where small variations in launch speed result in small variations in trajectory, but the payloads still passing through the exact same point at L-2. It was also proposed that the payloads be electrostatically charged so that, after leaving the mouth of the launcher, one could arrange for the payloads to pass through down-range course-correcting structures which used electrostatic deflection plates to make minute adjustments in trajectory: http://www.ssi.org/assets/images/astronaut_at_lunar_mass_driver.jpg Also, I'm thinking the mass-catcher was envisioned as having an opening many 10's of meters across. Getting the payloads to hit the catcher was not considered one of the more difficult things to do in the overall system.
Regards,