An "oscillating roll" and possibly a resulting overreaction of the rocket's steering system are the most likely cause for the failure of Boeing's first Delta 3.

"It is pretty clear the failure is related to our control system," said Clarence Quan, Boeing investigation leader.

The guidance computer seems to have overcompensated for the roll for unknown reasons, sending commands to steer the Delta 3's main engine, control jets and three of its nine solid rocket boosters. That heavy manoeuvring soon caused the steering system to run out of hydraulic fluid.

From that point onwards, the inevitable happened: the rocket swung 35 degrees to the right and was ripped apart by aerodynamic forces, which in turn triggered its automatic destruct system. In addition, U.S. Air Force range safety officers sent destruct signals to the rocket seconds after the explosion.

There were some doubts whether all those destruct mechanisms did really work. A large object was observed exploding into an bright orange mushroom cloud. Investigators said it was actually the satellite Galaxy X, particularly its onboard propellants, that produced the fireworks.

• Delta 3 (1998-05-05)
• Boeing mishaps report
  

Launch failures chronology