Oh good, it's "carbon free"...
...which I guess is the standard by which we now morally judge any industrial or recreational activity. (But then again, by that standard so was the Space Shuttle, for the most part, as its engines were fueled by hydrogen) Never mind the infrastructure required to launch and retrieve the vehicle, or the massive use of non-renewable Helium.
Not that I wish to be so critical of this venture. Actually, I think it looks pretty cool. But if you're going to throw the "carbon footprint" argument in as a justification, then that's the framework you have to be willing to be criticised under.
Also, achieving "zero-g" is not a function of altitude, but velocity. Once must acquire either a 9.8m/sec vertical deceleration, orbital (horizontal) velocity (dependent upon altitude) or some combination thereof.
