SpaceX calls last-second rocket abort

US rocket company SpaceX had to halt a launch right at the moment of lift-off on Sunday.

Its Falcon 9 vehicle had ignited its engines and was all set to push away from the Cape Canaveral pad when onboard computers called the abort.

It was the third time in five days that SpaceX had attempted to launch a satellite for Luxembourg-based operator SES.

A fourth attempt is possible later this week.

But engineers will need time to assess the data to work out why the abort was triggered, and the US Air Force will also require some time to prepare the Florida range.

SpaceX CEO Elon Musk tweeted: "@SpaceX Launch aborted on low thrust alarm. Rising oxygen temps due to hold for boat and helium bubble triggered alarm."

The "boat" referred to an incident earlier the evening when the countdown had to be paused and re-set because a vessel out at sea had moved into the restricted zone under the rocket's flight path.

Tweet comment from former space station commander Chris Hadfield

SpaceX is getting back into the business of routine launches after the failure last year that saw a Falcon 9 break apart just over two and a half minutes into a mission.

The company returned to action in December with the successful deployment of a multiple satellite payload for the operator Orbcomm.

That mission also marked the historic first landing and safe recovery of an orbiting rocket stage, when the Falcon's lower section flew back to the Cape for a controlled touchdown on deployable legs.

January then saw SpaceX loft the Jason ocean altimeter mission for US and European space and meteorological agencies.

The California-based rocket company is now using an upgraded, higher thrust version of its Falcon 9.

The extra performance is achieved in part by using super-chilled liquid oxygen (LOX) as one of the two propellants (the other being kerosene).

But it has become evident in the countdowns of recent days that the new LOX comes with some additional handling challenges - in terms of how best to load the liquid into the rocket and to keep it at the right temperature.

No movement on the Cape Canaveral pad for the Falcon 9

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