One of the richest men in the world is going to build the biggest airplane ever.

And then he is going to use it to launch rockets.

Paul G. Allen, the billionaire co-founder of Microsoft, said Tuesday that he was entering the rocket business with a concept seldom used until now: a plane that can take off the conventional way and then, at 30,000 feet, launch a rocket to orbit, carrying with it satellites, supplies and — eventually — people. The first rocket launching could be as soon as 2016.

“You have a certain number of dreams in your life that you want to fulfill,” said Mr. Allen, an avid philanthropist who has also financed efforts like a radio telescope listening for alien transmissions, “and this is a dream that I’m very excited about.”

The airplane that his new company, Stratolaunch Systems, plans to build will be larger and heavier than the Spruce Goose, Howard Hughes’s record-setting flying boat that flew, just once, in 1947. With wings that will stretch 385 feet — longer than a football field — it will dwarf the double-decker Airbus A380, which is the biggest commercial passenger plane flown today. It will take off from a runway, fly to a normal cruising altitude and then drop off a rocket, eliminating the need for costly launching pads.