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The private spaceflight SpaceX will launch its Dragon cargo ship to the International Space Station and the flight will be webcast by Nasa.

The launch of the SpaceX Falcon 9 rocket and Dragon spacecraft will go ahead despite a backup computer failure on the ISS that will force Nasa to perform a spacewalk repair.

The cargo ship liftoff will take place at 9.58pm BST (4:58 pm EDT) tonight (Monday) from Florida's Cape Canaveral Air Force Station. It will be the third official supply delivery mission for Nasa.

The SpaceX Falcon 9 rocket will launch from Cape Canaveral Air Force Station in FloridaSpaceX

SpaceX's Dragon will deliver nearly 2,268kg of food, equipment and other vital supplies for the station's crew.

It will alos be an opportunity to advance the technology needed to recover and reuse Falcon rocket parts.

Engineers have fitted landing legs to the vehicle's first stage, the segment that gets the rocket off the ground.

Normally, this stage is discarded at 80km above sea level, almost three minutes into flight. SpaceX scientists want to be able to recover these stages in good working order so they can be used again.

Michael Suffredini, a station program manager, said the decision to move forward with the SpaceX launch followed an in-depth analysis of the failure of a back-up computer.

The computer controls the station's solar arrays and rail car robotic arm.

The system's primary computer was working properly, he said. Engineers had devised workarounds that would safeguard the station's power and robotic systems in case of anothe failure.

Suffredini said: "We're just trying to fly as soon as we safely can, which is what we believe we're doing with this plan."

The Dragon launch has been delayed since March because of damage to a ground-based tracking radar used by the Air Force Station.