Tim Furniss/LONDON
Boeing hopes to complete the investigation into the failure of the guidance system on the first launch of its Delta III booster by the end of the month. The booster was launched on 26 August from Cape Canaveral, Florida, and broke apart at about T+72s.
"The control system recognised and tried to correct a slow oscillating roll which developed during the first minute of the flight, but the system contributed to the situation and in the end expended the hydraulic fluid used to gimbal the thrust vector controls and those of the solid-rocket boosters," Boeing said on 5 September.
The Delta III control system consists of an on-board computer which controls the main engine, two vernier engines and three of the booster's nine solid-rocket boosters with thrust vector assemblies.
The company had said earlier that the roll was unexpected and that the control system "overcompensated" and was eventually "overwhelmed" by the situation it had caused.
The oscillation had smoothed itself out at this point, but with the thrust vector control system no longer operating and the thrust vector assemblies in a fixed position, eventually the booster pitched 35¼, breaking apart under the extreme aerodynamic forces and triggering the self-destruct system.
Meanwhile, the US Air Force says that the loss of the final Lockheed Martin Titan IVA during its launch from Cape Canaveral on 12 August was caused by a sudden momentary battery power outage in the guidance system.
At T+39.4s, the electrical power for the guidance system was lost for a fraction of a second, which resulted in the loss of the system's horizon acquisition data.
As the power was restored almost immediately, the guidance system computer sent an attitude-correcting command that resulted in the booster pitching down and breaking up at T+41.3s, triggering the auto-destruct system.
Source: Flight International