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For the second time in as many days, the planned launch of a Delta IV rocket from Vandenberg Air Force Base on Thursday was postponed for 24 hours.

The launch, which is slated to be the first of 2018 from VAFB, was delayed several times on Thursday before ultimately getting called off around 4:45 p.m., nearly four hours after the launch window first opened at 1 p.m.

United Launch Alliance, which provided the rocket, reported that another attempt to launch will be made beginning at 1 p.m. Friday.

The launch had initially been planned for Wednesday, but was pushed to a day later due to high ground winds, base officials reported Wednesday.

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Thursday's delays were due to an issue with a ground system valve, according to ULA, which had also earlier reported issues with swing arms, which connect parts of the rocket to the launchpad and typically move away from the vehicle between ignition and liftoff.

The rocket is set to carry a secret payload for the National Reconnaissance Office as part of the NROL-47 mission. The weather forecast shows a 90-percent chance of favorable conditions for a Friday launch, according to ULA.

Willis Jacobson covers the city of Lompoc for Lee Central Coast Newspapers. Follow him on Twitter @WJacobsonLR.