The unpiloted X-43A made a 10-second powered flight and then went through some twists and turns during a six-minute glide before it was allowed to plunge into the ocean.
"Everything worked according to plan. It's been wonderful," NASA spokeswoman Leslie Williams said. "I actually thought it was the most beautiful thing I've ever seen. We've been waiting a few years."
It wasn't immediately clear what speed the X-43A achieved after it was boosted to about 3,500 mph by a rocket, Williams said.
But engineers were ecstatic even without the details.
"This is all about learning whether this thing really works," Williams said.
The first X-43A flight ended in failure June 2, 2001, after the modified Pegasus rocket used to accelerate the plane veered off course and was detonated. An investigation board found preflight analyses failed to predict how the rocket would perform, leaving its control system unable to maintain stable flight.
The National Aeronautics and Space Administration built the needle-nosed jet under a $250 million program to develop and test an exotic type of engine called a supersonic-combustion ramjet, or scramjet.
In theory, the air-breathing engine could propel an airplane to speeds of Mach 7 or faster, enabling around-the-world flights that would take several hours. The Department of Defense also is working on the technology, which it's eyeing for use in bombers that could reach targets anywhere on the globe with deadly immediacy.
The 2,800-pound X-043A was mounted on a Pegasus rocket booster and mounted under the right wing of a B-52 bomber, which took off from Edwards Air Force Base in the high desert.
A minute before 2 p.m. local time, the craft was dropped from 40,000 feet. A few seconds later, the rocket flared, sending the jet skyward on a streak of flame and light. At about 100,000 feet, the rocket was dropped away.
The scramjet took over, using up about two pounds of gaseous hydrogen fuel before it glided and then plunged into the Pacific Ocean about 400 miles off the California.
Applause rang out in the control center at Dryden Flight Research Center at Edwards.
Technological hurdles mean it will be decades before such a plane enters service. And NASA's role in developing the technology remains in doubt, as the agency recently cut funding for more advanced versions of the X-43A.
Engineers have pursued scramjet technology because it could allow rocket-speed travel but with considerable savings in weight. That could allow smaller jet planes to fly farther or carry larger payloads than can conventional rockets.
Rockets must carry their own oxygen to combust the fuel they carry aboard; scramjets can scoop it out of the atmosphere.
In scramjets, oxygen from the atmosphere is rammed into the combustion chamber where it mixes with fuel and spontaneously ignites. To work, the engine must be traveling at about five times the speed of sound - requiring an initial boost that only a rocket can provide.
A third X-43A could fly as early as the fall.
CBS News Reporter Peter King says failure on Saturday would have jeopardized funding for testing an additional vehicle this fall, because President Bush's space initiative is diverting money to the Moon-Mars effort.