I actually have a reason to doubt this scheme
It takes a 767-ton Ariane V to place 80 tons into orbit. The Ariane V is a two-stage rocket, with additional solid boosters for extra oomph.
A two-rocketplane deal with comparable performance would mean a transport vehicle capable of getting an 80-ton mass into orbit, with a piggyback vehicle tasked with getting the whole thing off the ground and up to where the transport can get going.
Fine. The only reusable space vehicle in existence at this time is the Shuttle. The Shuttle can get 22 tons into orbit (on the back of a rocket, of course). It has a mass of about 100 tons. The rocket needed to put the Shuttle into orbit has a total mass (fuel included) of about 2000 tons.
So forget the 80 tons, on a rocketplane deal I seriously doubt we'd be able to get 2000 tons flying in the first place. The Shuttle has already been mounted (empty) on the back of a 747, so transporting 100 tons is possible.
Therefor, it would seem that we could make a launcher vehicle to get a Shuttle-type craft up to where it can "take off" for space.
The launcher vehicle would need to carry a payload of 120 tons to very high altitude (at least 20km probably). Then, the new transporter would have to be able to boost itself up to orbital altitude - another 270km.
As of now, the rocket that carries the Shuttle into space drops it off once the momentum is sufficient to throw it up to its orbital altitude - a maximum of 400km - just enough to reach the ISS. In other words, the Shuttle itself is entirely incapable of ascending 270km on its own. Which means the transport vehicle will have to be seriously more powerful than the Shuttle is - and that will certainly have a negative impact on payload capacities - or the launcher vehicle will have to be able to carry the whole shebang way higher than 20km - preferably to an altitude of 100 or even 150km.
In this scenario, we need a transport vehicle powerful enough to climb at least 250km while carrying 20 tons of payload. We also need a launcher vehicle capable of climbing to 150km whilst carrying the transport vehicle, its payload and the fuel for all that. On top of that, the launcher vehicle will need jet engines to get up to 20km, statoreactors for up to 100, and pure rocketery for anything above that. Three types of engines, then.
I fail to see how anything can get off the ground with all those requirements. The largest, most massive plane ever built is reportedly the Antonov-255, and it weighs in at 600 tons. I doubt it can go higher than 20km though.