SpaceX Says Countdown Abort Demonstrates Falcon 9 Reliability

No word yet on exactly what triggered the countdown cutoff two seconds before a planned 3.5-second test-firing Tuesday of the SpaceX Falcon 9 rocket at Cape Canaveral Air Force Station.

And no word yet on when the California-based company might make another attempt to ignite the nine Merlin 1C engines that will power the rocket's first stage during an inaugural flight now scheduled for launch no earlier than April 12.

But SpaceX officials say the countdown cutoff shows the systems required to execute a pad abort worked as designed, demonstrating a key reliability feature of the Falcon 9:

Once the rocket's engine start-up sequence begins, the Falcon 9 is held down on the pad and not released for flight until all propulsion and vehicle systems are confirmed to be operating normally, or within predefined ranges. The system will automatically abort if any problems are detected, and that's exactly what happened Tuesday.

The Falcon 9 engine start-up sequence is called "Spin Start" at SpaceX. High pressure helium from a storage tank at the pad is used to spin up the turbopump assemblies in the Merlin engines to about 50 percent of operating speeds. The spinning turbopumps force liquid oxygen and kerosene into the combustion chamber, where they are ignited. The hot gas from the combustion of the propellants bring the turbopumps up to full operating speed.

At T-Minus 2 seconds during Tuesday's countdown, a still unspecified problem was detected during the engine start-up and the Falcon 9 automatically aborted before engine ignition. Pre-valves were closed to isolate the engines from propellant tanks and purge residual propellants.

The orange flames seen at the base of the rocket resulted from the burn off of residual liquid oxygen and RP-1, a highly refined kerosene. The engines did not ignite and there was no engine fire.

SpaceX officials note than an "off-nominal condition" doesn't exactly mean there was a serious problem. Rather, it is indicative of some sensor reading that was outside predefined limits. The automatic abort enables engineers to sort out the situation before committing a Falcon 9 to launch, thus preventing any potential failure in flight.

SpaceX has experienced aborts on Falcon 1 missions at Kwajalein Atoll and then recycled the countdown on the same day. However, since the attempt Tuesday was a first with the Falcon 9, launch managers decided it would be prudent to scrub for the day and get a good look at the rocket and data from the countdown cutoff before proceeding with another try.

SpaceX said engineers were to inspect the rocket at Launch Complex 40 Tuesday night and then hold a data review on Wednesday. The next attempt is expected later this week or sometime next week.