The Taurus rocket flies successfully during first stage, but suffers control system problem during initial moments of second stage burn. Photos: Spaceflight Now/Range video

A stuck steering mechanism on the Orbital Sciences Taurus rocket is being blamed for the September launch failure that resulted in the loss of two satellite cargoes, the company's president said Wednesday.

Following blastoff on September 21 from Vandenberg Air Force Base in California, the Taurus flew normally for the first 83 seconds or so as the first stage fired. But as the second stage lit, the vehicle went out of control for several moments before righting itself and continuing on.

The investigation into the mishap, which is expected to conclude in the near future, discovered the actuator device in the rocket's second stage steering system didn't move as the solid-fueled motor ignited.

"Our failure review board is wrapping up their assessment, and the problem seems to focus on the stage two thrust vector control actuator," J.R. Thompson, Orbital's president and chief operating officer, reported during an investor conference call Wednesday.

"The actuator drive shaft appeared to bind up, or seize, for approximately five seconds right at second stage ignition. The vehicle veered off course for this relatively short period of time, but because of the performance loss and we could not make it up, orbit was not achieved. OrbView-4 and our QuikTOMS spacecraft that was aboard as well were both lost."

Although the Taurus was able to regain control and get pointed in the right direction again, the momentum lost during the incident meant the vehicle was unable to achieve the proper altitude and velocity to reach a safe orbit around Earth.

The Orbital-built OrbView-4 commercial Earth-imaging satellite and NASA QuikTOMS ozone monitoring spacecraft were deployed from the rocket's fourth stage only to crash back to Earth over the Indian Ocean where they were destroyed.

"There is no further use planned of this actuator," Thompson continued. "We had planned to change out (the actuator design), and we anticipate no collateral impact to our other launches."

Thompson did not say if it was known why the actuator seized up for those five seconds.

The failure was the first for the Taurus, which had previously flown five consecutive successful missions from 1994 through 2000. Orbital currently has just one future launch booked on Taurus -- a mission in 2003 to loft the Taiwanese ROCSAT-2 satellite.

Meanwhile, the NASA-led investigation into the June launch failure of the X-43A hypersonic test craft using a modified Orbital Pegasus booster continues. The board has repeatedly said that the mishap was likely caused by more than one factor and the focus is now on the vehicle control system and aerodynamics.

The vehicle veered out of control and gyrated wildly, in similar appearance to the Taurus, moments after it was air-launched from a B-52 aircraft. The rocket's control aerosurfaces broke off and safety personnel had to blow up the vehicle.

The X-43 inquiry has kept the Pegasus launch of NASA's HESSI solar flare research satellite grounded. The latest target date for HESSI's long-awaited ride to orbit is now no earlier than December 22.