Microsoft Corp. co-founder Paul Allen is prepared to commit $200 million or more 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.

Dubbed Stratolaunch, 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. The concept envisions a behemoth mother ship with twin, narrow fuselages, featuring six Boeing Co. 747 engines attached to a record 385-foot wingspan, plus a smaller rocket pod nestled underneath. It is expected to weigh roughly 1.2 million pounds.

“Stratolaunch Systems will bring airport-like operations to the launch of commercial and government payloads and, eventually, human missions,” the company said in a statement. “Plans call for a first flight within five years. The air-launch-to-orbit system will mean lower costs, greater safety, and more flexibility and responsiveness than is possible today with ground-based systems. Stratolaunch’s quick turnaround between launches will enable new orbital missions as well as break the logjam of missions queued up for launch facilities and a chance at space.”