Using a LFTR as power source for microwave booster

Speculation alert:  As usual, talking out my ass here.  But it is a brainstorm, which means it might or might not be a good idea.  The critical examination of it as an idea is for another time or place.

Anyway, the idea is to solve the launch problem.  Now, Kevin Parkins came up with the idea in his doctoral thesis to use a microwave beam to get a payload to orbit.

I've played around with the idea a bit on this blog.  One of these ideas was the MABB or Microwave Air Breathing Booster.   The MABB could be modified to carry some hydrogen onboard to convert it into an afterburner, like the LANTR concept, that could still get high ISP, but with much better thrust.  What this does is to decrease the mass necessary for orbit.  The more mass you save the better as 98% of the mass is fuel.  This will achieve better payload fractions.  What it will also do is decrease the size of the LFTR as less energy will be needed to get to orbit as the burning hydrogen in the afterburner will effectively double the energy produced.

Now the advantage of the LFTR is that it can be shut down to safe-mode much easier than a conventional reactor.  It can stay in safe-mode until the next launch.

The LFTR can be modular, so it can be mass-produced.  If you need a dozen or so 100 MW reactors, that could be configured into a 1.21 gigawatt power source for your microwaves ( a bit of Back to the Future lingo there), therefore you could do it potentially cheaply.

Back tracking a bit to the original idea, which was to lift an X-33 type system using a 747 or Stratolauncher:

You could lift it up to 30k feet, then release it.  The microwave beam will power it up to orbit from there.

At first, it will use atmospheric oxygen in the afterburner.  Once the altitude gets high enough, then it will shift to onboard hydrogen only.  The afterburner will shut off and it will be in fully rocket mode, except the energy will be provided by the microwave beam.

Update:

A little research shows that you could separate the oxygen from the atmosphere in the way that Skylon proposes while using the hydrogen as a pre-cooler.  This will allow hypersonic flight in air-breathing mode before switching to fully rocket mode.  That will allow the air-breathing portion to act as first stage in a staged rocket system without having to jettison the stage.