Interference/Hardening Issues for Spacecraft

Recently, a discussion occurred between a number of friends about the problems associated with microwave power beaming through space, some of which we could not answer. Perhaps this list can be of some assistance.

The problem discussed was using terrestrial power stations/systems to supply
power to three or more equatorial sites with large antennas. Through those
antenna's and the associated filtering equipment, a rather clean microwave
signal can be sent up into orbit, to track various spacecraft to provide power.

The conversation rapidly focused on reusable upper stages utilizing high energy
and high thrust electrical propulsion systems, such as VaSIMR or thermal/arcjet
systems. If the tracking for ground stations could be enhanced, a rather
tightly focused microwave beam could be targeted onto a portable/reusable
rectenna onboard this reusable upper stage.

Questions are as follows

1. What is the high end of resonable energy density on the rectenna face, and
what style of rectenna would be appropriate in a high energy density
environment?

2. How serious are the problems associated with microwaves missing the rectenna
but impinging on the upper stage at full strength, and the associated question
of energy reflections and whatnot from microwaves striking a non-orthogonal
rectenna?

3. Firing a beam onto a rapidly moving target implies some energy will miss
completely on a regular basis. How hazardous is this to existing and near
future spacecraft, and what are the technologies involved in mitigating this?
The obvious answer is using a good tracking database of known operational
spacecraft, and have a gap in power beaming whenever one comes into the line of
fire, but as spacecraft numbers go up and are more free to move on their own,
the more problematic such a method becomes.

Any assistance would be much appreciated.

Asteroza