A test firing of the first motor of NASA’s planned Ares 1 crew launch vehicle will take place no earlier than Sept. 10 as NASA and its contractor, Alliant Techsystems (ATK), continue to investigate the glitch that forced the postponement of a test attempt Aug. 27, ATK said in a statement Aug. 31.

Engineers have ruled out the possibility that booster hardware or software was at fault, and the focus of the investigation has shifted to ground test hardware, ATK said. “Specific suspect circuitry and components have been identified and are being methodically investigated, utilizing a systematic, detailed fault tree approach,” the company said. “The team is assessing removal and replacement plans for potential suspect items.”

The $75 million test of the five-segment motor, based on the space shuttle’s giant solid-rocket boosters, was aborted with 20 seconds left in the countdown Aug. 27 when a power system used to point the motor’s nozzle failed. Engineers initially suspected a fuel valve in an auxiliary power unit on the booster had failed.

The test will take place at ATK’s facilities in Promontory, Utah.