WASHINGTON -- A source monitoring the launch of the X-43A research aircraft that was destroyed Saturday told SPACE.com that several pieces detached from the vehicle's Pegasus XL booster shortly before the two-vehicle combination spun out of control.

What, if any, aerodynamic forces were created by the X-43A itself, causing the out-of-control maneuvers, is still unknown.

NASA's bid to delve into hypersonic flight suffered a setback with the destruction of the X-43A on Saturday, June 2. Following its release from a B-52, the vehicle and its booster veered out of control and was ordered to self-destruct high over a Pacific Ocean test area.

Video of the drop from the B-52 and subsequent firing of the Pegasus showed that several pieces flew off the booster/X-43A combination. The malfunction occurred about five seconds after the Pegasus motor ignited. The rocket was to fire for some 90 seconds, boosting the X-43A to 95,000 feet (28,955 meters) then let it loose.

Members of a special board that will investigate the X-43A mishap are likely to be announced later this week, NASA spokesman Jim Cast told SPACE.com. Root cause of the problem is only speculation at this point, he said, with the board charged with carrying out a detailed and methodical look into the failed first flight test.

The X-43A is one of three test aircraft to be flown within NASA's $185 million Hyper-X program. A second, ready-to-fly X-43A is already at NASA's Dryden Flight Research Center in Edwards, California. All three vehicles are called X-43A and are built by MicroCraft, Inc. of Tullahoma, Tennessee.

Attention is being paid to the Pegasus itself, as the booster was modified to carry the X-43A.

The rocket-maker, Orbital Sciences Corporation (OSC) of Dulles, Virginia, had no statement about the failure on Monday, said Barron Beneski, director of corporate communications for the firm. But he distinguished the booster used for the Hyper-X program from Pegasus rockets used for space launches.

The booster used to launch the X43-A "shares some systems, technology and operational methodology, but is not a three-stage space launch vehicle for deploying satellites," Beneski told SPACE.com in an e-mail.

So the connection to Pegasus, while it must be and will be examined very closely, is more like a "cousin" vehicle than a "brother" or "sister" vehicle, he said.

In launch press material distributed before the flight, OSC said that a "derivative" of its Pegasus rocket was used for the X-43A tests. Along with elimination of the Pegasus rocket's second and third stages, a payload fairing, used normally to protect satellite payloads during launch, also was dropped.

The X-43A and its adapter were fitted atop the specially configured Pegasus first-stage solid-fuel rocket motor. A newly developed thermal protection system was put in place to protect the Pegasus composite structures against severe heating loads associated with lower-altitude hypersonic operations.

Lastly, modifications to the booster included upgrading the first-stage guidance and a repackaging of electronic gear that permits ballasting of the booster for hypersonic flight conditions, from the mach 7 up to mach 10 speeds the X-43A craft would fly.

In prelaunch interviews with X-43A aerodynamic experts, both the Pegasus and its top-loaded research aircraft were heavily instrumented. Data from both the Pegasus and the experimental aircraft should help investigators pinpoint the true cause of the in-flight failure.

"We've spent a lot of time reducing risk. It's a fairly risky experiment, but we're confident we've done all the right things and we're ready to go fly," said Walter Engelund, aerodynamics group leader for Hyper-X flight experiments, at NASA's Langley Research Center in Hampton, Virginia.

Engelund said that a significant number of aerodynamic assessments of the Pegasus/X-43-A combination were undertaken. Overall, in excess of 5,800 runs in 15 different wind tunnels were completed over the last several years.

Larry Huebner, Hyper-X scramjet propulsion research engineer at NASA Langley, said work on the X-43A was started in 1996. OSC did studies of the solid rocket propellant performance of the Pegasus, he said, with the adapter linking the booster to the X-43A called a "very significant change" to what was first planned.

Both Huebner and Engelund noted that ground testing and computer simulated "electronic wind tunnels" can provide excellent and useful data. However, the total range of environments -- and the interplay between those conditions and the flight vehicle -- can only be studied while in actual flight.

The Hyper-X Phase 1 is a NASA Aerospace Technology Enterprise program being conducted jointly by the Langley Research Center, Hampton, Virginia and the Dryden Flight Research Center, Edwards, California.