booster fuel prevalves. The low-pressure booster fuel ducting was found to have collapsed from a sudden loss of fuel flow, but had not ruptured. The investigation concluded that the fuel prevalves had only opened partially and the propellant flow was enough to push them shut, starving the booster engines of RP-1 and causing a LOX-rich shutdown. Engine start had proceeded normally and all booster systems functioned properly until the valve closed. Booster shutdown occurred at T+1.7 seconds and the vehicle impacted on the pad at T+2.8 seconds. Bench testing confirmed that there were several possible ways that the valve would only open partially, although the exact reason was not determined. This failure mode had never occurred in the 240 Atlas launches prior to AC-5 despite always having been possible. Until a more permanent solution could be found, a temporary fix was made for Atlas-Agena vehicles by equipping the valve with a manual lock that would be enabled during the pre-launch countdown. A manual E-series sustainer prevalve was also installed as a precautionary measure in addition, an unrelated system malfunction in AC-5 was discovered when an examination of telemetry data found that a power failure had occurred in the guidance computer. As a temporary fix for Atlas-Centaur AC-6, 7, and 8, several unused components were removed from the computer in order to reduce system complexity and failure points. Investigation The failure of AC-5 resulted in another Congressional investigation, again headed by Rep. Joseph Karth, who argued that US$600 million of taxpayer money had been spent on Centaur so far with little to show for it and that Convair was taking advantage of being the sole supplier of the Atlas-Centaur vehicle. The committee proposed that NASA consider alternate choices for the planetary probe program, such as Titan IIIC, or outsource the manufacture of Centaur to other contractors. However, NASA representatives argued that this was impossible as no other aerospace company had the experience or technical capability to manufacture the Centaur's balloon tanks. Later flights The pad LC-36B was hastily brought online, with an entirely successful AC-6 (vehicle 151D) launched on 11 August 1965 at 14:31:04 GMT. Although Centaur appeared flight-ready, the Surveyor program was delayed. Vehicles AC-7 and AC-10 were designated for the first Surveyor missions, with AC-8 to carry out one more test, which took place on 8 April 1966 at 01:00:02 GMT with a payload of 771 kg Surveyor mass