SpaceX To Try Another Rocket Launch Tuesday

SpaceX expects to be ready to launch the first private spacecraft bound for the International Space Station early Tuesday, after its Falcon 9 rocket came within a split-second of blasting off Saturday morning.

Technicians planned to replace a faulty engine valve Saturday night that is believed responsible for prompting the abort of the first launch attempt with a half-second remaining in the countdown, after all nine first-stage engines had ignited.

Computers detected high pressure in one engine's combustion chamber, triggering an automatic shutdown just before the planned 4:55 a.m. EDT liftoff.

Analysis of the repaired engine and the potential for similar problems on its neighboring engines will continue Sunday.

"If things look good, we will be ready to attempt to launch on Tuesday," SpaceX spokeswoman Kirstin Grantham said in a statement.

A launch Tuesday from Cape Canaveral Air Force Station's Launch Complex 40 would occur at 3:44 a.m.

Preliminary forecasts show a 60 percent chance of favorable weather conditions.

After the last-second abort, SpaceX began preparing for the possibility that engine No. 5 -- the middle one in the group of nine -- might need to be swapped out.

But inspections Saturday afternoon determined that time-consuming operation wasn't necessary.

SpaceX said the culprit was a turbopump "check valve," which permits the flow of gas or liquid in only one direction.

Hawthorne, Calif.-based SpaceX is attempting to launch its second demonstration flight under a NASA program supporting the development of new commercial vehicles to deliver cargo to the space station.

The company's unmanned Dragon capsule could become the first commercial vehicle to reach the station if it successfully completes a battery of tests of new navigation, communications and electrical systems.

SpaceX and NASA have selected potential launch dates and the instantaneous launch windows to ensure the Dragon has the maximum propellant possible to reach the station and perform all the test maneuvers.

If the demonstration mission launches Tuesday, berthing at the station would be expected Friday morning.

If all goes well, SpaceX would then turn its attention to the first of 12 station resupply missions ordered under a $1.6 billion NASA contract.

While disappointed at not launching Saturday, company officials said the aborted countdown showed rocket systems working properly to prevent a launch with engine trouble.

"This is not a failure," SpaceX President Gwynne Shotwell said at a news conference shortly after the scrub. "It would be a failure if were to have lifted off with an engine trending in this direction."