By the time Mr. Musk was 30, he had amassed $300 million and was pondering his future.

His first thoughts were of philanthropy -- and of space. He came up with the idea of "Mars Oasis," an effort to send a small greenhouse to Mars to gather scientific information and create excitement about space travel -- or so Mr. Musk thought. His idea was quickly derailed by the extraordinary cost of getting to space, but that led him to wonder why technology had not brought down the cost of space exploration or led to more of it. And that led him to found SpaceX in 2002.

Every day since then, Mr. Musk has driven to a gritty industrial zone, where he puts in long days at SpaceX. Still, he allows himself a few perks of the newly rich: a big house in Los Angeles, a $1 million McLaren F1 sports car, and a Dassault Falcon 900 business jet, which he sometimes uses to ferry his staff to the Marshall Islands.

In some ways, SpaceX is a throwback to his dot-com days. Many of the 160 employees, including former engineers from Boeing and other aerospace companies, are on a first-name basis with him. One building houses a Ping-Pong table; another has a Segway. All employees -- who call themselves "SpaceExers" -- have received stock options that could make them millionaires someday. In one spot, a blue tarp covers a small piece of a rocket that Mr. Musk casually described as a "top secret" project and joked about putting a sign on it saying so. Indeed, it was a part for a launching scheduled by the Pentagon, which already has $100 million of SpaceX business lined up. He has another $100 million in launchings from the government of Malaysia, the Swedish Space Corporation and several American companies, including Bigelow Aerospace, which is planning to build a private space station.

TheFalcon 1 flight this week is for the Air Force and the Defense Advanced Research Projects Agency, the Pentagon's research and development arm. "DARPA is excited about the launch," said Steven Walker, the DARPA manager for the Falcon program. "A successful launch demonstration will change the way we do space launch in this country."

WHAT sets SpaceX apart from other rocket makers is that the boldness of its ambition is matched by the modesty of its design. To meet his goal of a cheap and reliable rocket, Mr. Musk is producing a basic design, with fewer opportunities for systems to fail -- even if it means some technical compromises with performance. "SpaceX is optimizing for simplicity rather than performance, and that's what sets it apart from the others," said Jeffrey Foust, an analyst at the Futron Corporation, an aerospace consulting firm. "When you have a limited number of things that could fail, you can increase a rocket's reliability."

Where most other rockets have multiple stages and multiple engines, the Falcon will have just two stages, each with one engine. Most of SpaceX's stages are designed to be reusable. Although fishing small used rockets out of a vast ocean can be difficult, Mr. Musk says that it is cheaper than building a new one every time.

"Throwing away multimillion-dollar rocket stages every flight," he said, "makes no more sense than chucking away a 747 after every flight."