SpaceX Falcon rocket launch halted due to thruster problem

SpaceX called off its planned flight to the International Space Station early Tuesday because of rocket trouble, another delay in the delivery of groceries and overdue Christmas presents.

The unmanned Falcon rocket was supposed to blast off before sunrise. But the countdown was halted with just over a minute remaining.SpaceX will re-attempt the launch Friday, Elon Musk, SpaceX'sbillionaire founder, tweeted.

It is scheduled for 5:09 a.m. ET.

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Friday is the next available time slot for SpaceX to launch, NASA said.

Officials said the problem was with one of the two motors needed for second-stage rocket thrust steering. A thrust vector control actuator failed to perform as expected, NASA said.SpaceX officials said one of two motors needed for rocket thrust steering of the second stage was moving when it should have been still.

If controllers had not aborted the launch, computers would have done so closer to flight time, NASA launch commentator George Diller said.

The Dragon capsule aboard the rocket contains 2,268kilogramsof supplies and experiments ordered up by NASA.

Certainly, there's a little bit of disappointment because it had fresh fruit and those types of things that we're all interested in getting.- Space station commander ButchWilmore

Space station commander Butch Wilmore said the six crew members ran out of condiments a month ago, and he's yearning for some yellow mustard to spice up the food. He and his crewmates were watching the launch countdown just before sunrise live via a video feed from Mission Control in Houston.

"Certainly, there's a little bit of disappointment because it had fresh fruit and those types of things that we're all interested in getting," Wilmore said in an interview with The Associated Press after the postponement. "But they'll get off the ground here in a couple of days and it will all be great."

Ocean pad landing attempt

While the delivery is SpaceX's primary objective, the California-based company also was to attempt an even more extraordinary feat once the Dragon is on its way: flying the booster rocket to a platform in the Atlantic.

The platform won't be anchored down and is 91 metres by 30 metres wide though wings extend its width to nearly 52 metres.

Its instability and size will make the landing difficult, and the company predicts a 50 per cent chance of success at most.

Despite the low odds of success, SpaceX says the company will be able "to gather critical data to support future landing testing." It hopes to eventually have the Falcon 9 descend on land rather than water.

Musk says recovering and reusing rockets could speed up launches and drive down costs.

A reusable rocket "is the pivotal breakthrough needed to substantially reduce the cost of space access," according to the company.

The delivery was supposed to occur before Christmas, but was delayed because of a flawed test firing of the rocket engines. The test was repeated successfully, paving the way for Tuesday's try.

NASA is using SpaceX and another private company Orbital Sciences Corp. to help keep the space station stocked. The last shipment attempt by Orbital ended in an explosion seconds after the October liftoff from Virginia. Orbital has grounded its rocket fleet until next year.

Included in the Dragon's payloadis the science project of a group of students from McGowan Park Elementary School in Kamloops, B.C. The four boys won a contest to get their experiment -- which will examine how crystals grow in the zero-gravity environment of space -- included with 17 other student projects onthe trip to the space station.The students lost their original experiments when the Orbital Sciences'Antares rocket exploded shortly after takeoff.