Spider fab and the MAB

There was a series here that involved a concept that I called the MAB.  It is an acronym for Microwave Airbreathing Booster.  The concept was to use atmospheric air as a reaction mass and microwave energy to heat up the reaction mass and use that for thrust.

How can that be used with a spider fab?

The spider fab can build a 1 gigawatt solar panel complex that would beam the energy down to a rectenna on the surface.  That's the concept for supplying energy on the ground.  What if you wanted to use it for launching spacecraft instead?  How would you do that?

Well, if the rectenna isn't too big and too heavy, I was thinking that it could go along for the ride!

That rates a speculation alert.  Big time.

Okay.  It sounds pretty far out, but here's the idea.

Just lift the entire rectenna that is attached to a device that heats up the air and expels it as thrust.  This would lift the craft all the way up to where the air is too thin and then release it.  At that point, a more conventional type rocket would light up and take the craft to orbit.

I know it would have tremendous amount of drag.  Just keep the speed down low in the lower atmosphere.  Wait until you are really high to start accelerating hard.  Perhaps you could take it all the way up to GEO!  But, practically speaking, how about to the Kármán line ?

If you were to take it all the way up, you would need to take along some reaction mass.  But why do that?  Just do it like a spacecraft stage.  Discard it, but instead of letting it be destroyed, just reverse the process and gently land it so that it can be used again.

For that part of the ascent that was air breathing, it would be infinite ISP.  On that part of the ascent that was not air breathing, the ISP could rival a good nuclear thermal engine.  Come to think of it, you should probably use a nuclear thermal engine and just take off from the Kármán line.  It would have to accelerate in a vacuum, but it wouldn't have to lift very much since it is already pretty high up there.