Turbulent space weather has forced Orbital Sciences to postpone the launch of its unmanned Cygnus spacecraft on a supply mission the International Space Station.
The company said it is now aiming for Thursday to launch its cargo ship atop an Antares rocket, carrying 1260 kilograms of gear including science experiments, supplies and hardware.
The delay was due to what NASA described as "the first significant" solar flare of the year, causing increased levels of space radiation that might have damaged the spacecraft's electronics.
The US space agency said the potent X-class solar flare erupted on January 7.
Solar flares are bursts of magnetic energy that originate on the Sun, unleashing radiation that can briefly disrupt radio signals and GPS and satellite communications.
"Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground," NASA said.
Orbital said in a statement on Wednesday the delay was "due to an unusually high level of space radiation".
The levels "exceeded by a considerable margin the constraints imposed on the mission to ensure the rocket's electronic systems are not impacted by a harsh radiation environment".
The liftoff time from Wallops Island, Virginia, will now be at 1.10pm on Thursday (0510 AEDT on Friday), allowing the cargo ship to reach the ISS by January 12.
Orbital's attempt was previously delayed in December due to a cooling system breakdown at the ISS, which required American astronauts to make two spacewalks in order to replace an ammonia cooling pump.
When the launch goes ahead, it will mark the company's first regularly contracted mission and its second trip to the orbiting outpost, coming on the heels of a successful demonstration launch in September.
