Microsoft Corp. co-founder Paul Allen indicated he is prepared to commit $200 million or more of his wealth to build the world's largest airplane as a mobile platform for launching satellites at low cost, which he believes could transform the space industry.

Announced Tuesday, the novel, high-risk project conceived by renowned aerospace designer Burt Rutan seeks to combine engines, landing gears and other parts removed from old Boeing 747 jets with a newly created composite craft from Mr. Rutan and a powerful rocket to be built by a company run by Internet billionaire and commercial-space pioneer Elon Musk.

Dubbed Stratolaunch and funded by one of Mr. Allen's closely held entities, the venture seeks to meld decades-old airplane technology with cutting-edge booster-rocket designs in an unprecedented way to assemble a hybrid that would offer the first totally privately funded space transportation system.

The ultimate goal—which has eluded corporate and government rocket scientists for decades—is to build a reliable and flexible aircraft-based launch option capable of hurling satellites as heavy as a pickup truck into low-earth orbit.