It's premature to say how Paul Allen will go down in history, but it's safe to conclude that, at this point, he's doing a pretty good job of keeping up with his fellow flashy billionaires. His latest pursuit is earning him a lot of attention--and a few skeptics.

For the last several decades, the formula for men who have too much money is to spend it on sports teams (Allen has the Trail Blazers, the Major League Soccer Seattle Sounders and the Seattle Seahawks Football Team); homes (in France, California, Seattle, an island with homes for him and his mother in the San Juans; and Hawaii); and yachts (last year, Allen put his 313-foot Tatoosh up for sale, probably because of his purchase of his 414-foot Octopus, one of the largest yachts on the planet).

In recent years, a new way to spend your money has surfaced: space travel. Amazon's Jeff Bezos has been funding Blue Origin, Virgin's Richard Branson has Virgin Gallactic and Elon Musk, whose fortune comes from PayPal and who has spent much of it developing the Tesla, has SpaceX.

Last week, Allen unveiled his effort to keep up: Stratolaunch Systems.  In one way, Allen has bested the other Buzz Lightyear wannabees, because his plan to launch rockets is quite different--rather than sending them into orbit from the ground, Allen wants to launch a rocket from 30,000 feet in the air, by carrying it on a the largest plane ever built.