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(CNN)SpaceX and NASA have called off an astronaut launch to the International Space Station after an issue with the rocket's ground system was detected.
With about two minutes left on the countdown clock, the launch was called off because of a problem related to the TEA-TEB ignition fluid, which is used to ignite the SpaceX Falcon 9's rocket engines at liftoff.
The decision to wave off the launch was made "out of an abundance of caution," said Kate Tice, a SpaceX systems engineer, in commentary on Monday's webcast.
The four astronauts, who were strapped into their Crew Dragon capsule atop the rocket in the hours leading up to launch,