4 October 2004—This morning, for the second time in five days, a privately built spaceship punched a hole in the sky over Southern California. Supporters hope the flight has also broken through metaphorical barriers to wider human access to space. The flight of SpaceShipOne completed the required twice-in-two-weeks space shot to earn the US $10 million Ansari X Prize. It also won 51-year-old test pilot Brian Binnie the second pair of astronaut wings ever earned without government assistance.

In its ascent this morning, the space plane incised a vertical white smoke trail across the blue desert sky, as straight as if a ruler had been laid across the celestial sphere. It soon faded, but the permanent message of this short-lived skywriting was unambiguous—commercial human spaceflight is now a reality.

As measured by tracking radars at the nearby Edwards Air Force Base, SpaceShipOne—powered by an experimental motor that burns a combination of rubber and nitrous oxide—reached an altitude of 111 911 meters. Along the way, it also surpassed the previous world altitude record (108 000 meters) for horizontally launched space planes, set by an X-15 on 22 August 1963.

The project cost its backer, Microsoft cofounder Paul G. Allen's Mojave Aerospace Ventures, more than twice the prize amount to complete. So it did not earn a profit. But already would-be moneymakers have stepped forward with serious plans to commercialize future missions. By charging high but not unprecedented fees for "extreme sports" vacations and by leasing vehicles for research missions now conducted by expensive sounding rockets, corporate teams from the United States, Canada, Russia, and elsewhere envision profitable operations within five years. British airline mogul Richard Branson, for one, announced last week that he would license the technology behind SpaceShipOne for a space tourism venture to be called Virgin Galactic.

But if there were dollar signs in the eyes of some of today's observers at the Mojave, Calif., airfield that is the home of the SpaceShipOne project, there was also sweat on their brows. Nobody expected flight to be easy, but control problems on two previous flights had raised anxieties that perhaps the project had pushed the envelope just a tad too far. A flight on 29 September had gone into a rapid roll toward the end of its rocket burn.

"It was really heart-stopping for those of us who had seen launchings," admitted X Prize official Erik Lindbergh, whose grandfather Charles had won the Orteig Prize in 1927 for a solo trans-Atlantic crossing. "We really feared the worst," he continued, at least until pilot Mike Melvill had reconfigured his craft for reentry.

In the days that followed, project director Burt Rutan and his team conferred with Melvill and examined the spaceship and the flight telemetry. They already knew that the vehicle was only marginally stable in roll—spinning around its thrust axis—and subject to disturbing wind forces or even slight pilot miscues. And although Melvill made light of that rapid roll with typical test pilot bravado, there was more to it than mere "pilot error" or an unlucky gust of crosswind.

"We went back to the drawing board," Rutan admitted at today's post-flight press conference. He turned his aerodynamics experts loose on the telemetry from the 29 September flight, and "they ferreted out the truth of the vehicle by looking at the data."

As a result, he continued, "we reprogrammed the [rudder] sequence during climb out, and at burnout" the craft was completely stable. As he coasted in free fall, pilot Binnie used the gas-thruster orientation system only to turn the ship to get better views out the windows.

Today's flight was the conclusion of the opening phase of private human spaceflight that began eight years ago with the announcement of the X Prize project. Founder Peter Diamandis conceived of the idea as a means to focus attention on privately funded space transportation. More than two dozen contenders registered for the project, and among them were several serious teams with credible projects.

Burt Rutan's company, Scaled Composites LLC, in Mojave, Calif., had long been the favorite, based on the company's two-decade track record of innovative aerospace engineering. After commercial success with a home-built airplane design, the company constructed a series of record-breaking experimental aircraft, including one that allowed Rutan's older brother Dick and his co-pilot to fly around the world fifteen years ago without refueling. In all, Rutan's firm has built more than 40 types of aircraft, with no crashes and no casualties.

SpaceShipOne was unveiled a year and half ago, and began a series of drop tests and then powered tests that saw the first private flight through Mach 1 just in time to mark the 100th anniversary of heavier-than-air flight last December.

Higher and higher flights occurred earlier this year, culminating in the 21 June mission that broke the required 100-kilometer mark that serves as the legal edge of space. That flight did not carry the requisite weight to simulate two additional passengers, as specified in the X Prize rules. Rutan, determined not to rush into the two flights in two weeks required by the prize, scheduled a lengthy period for his team to study the aerodynamics of the vehicle.

Up-down "space hops" like today's have now retread the paths followed by X-15 rocket planes and the first Mercury-Redstone NASA launches in 1961. However dramatic they may be, they still remain substantially simpler than actual orbital flight—perhaps by a factor of a hundred, in terms of energy and complexity. But today's engineering triumph is also a symbolic success for promoters of far more ambitious projects.