SpaceX launch nixed at last second for engine glitch

— -- SpaceX technicians around noon today plan to begin inspecting a rocket engine that scrubbed an early morning launch attempt due to excessive pressure in its combustion chamber.

All nine of the Falcon 9 rocket's first-stage Merlin engines ignited at 4:55 a.m., but a computer quickly shut them down after detecting the high pressure in engine No. 5, a half-second before the countdown clock hit zero.

"The software did what it was supposed to do," said Gwynne Shotwell, SpaceX president.

Shotwell said the problem was not caused by a sensor or software but by a technical glitch that potentially could require the engine to be swapped out.

All nine engines must be working properly for the rocket to lift off successfully.

Pending further analysis of the cause behind the engine problem, SpaceX tentatively is tentatively planning a second launch attempt at 3:44 a.m. Tuesday.

A backup opportunity may be requested for 3:22 a.m. Wednesday.

Shotwell said the engine showed no problem during an April 30 test-fire.

A similar problem with the same engine aborted the Falcon 9's maiden launch attempt in 2010. But engineers were able to resolve the issue and launch later in the window.

This demonstration launch to the International Space Station has near-instantaneous windows that leave no room for error.

Shotwell said the high-chamber pressure likely was caused by heating that resulted from a low fuel level in the engine's combustion chamber.

If an engine swap is necessary, the replacement would come from the rocket next in line to launch, which is already at Cape Canaveral.

Shotwell said that operation takes at least two days. It was not immediately clear if SpaceX could be ready to launch by Tuesday if that work is necessary.

The company is expected to issue a statement after determining the root cause of the engine problem.