A SpaceX Falcon 9 rocket launch that was expected to happen Friday night has been pushed back to Sunday night.

The launch window will now open at 8 p.m. The rocket is expected to lift off from Cape Canaveral Air Force Station, Space Launch Complex 40.

The rocket will carry the mysterious Zuma payload, which was supposed to be launched back in November.

SpaceX said extreme weather slowed down operations, causing the delay.

Meanwhile at Kennedy Space Center, SpaceX is moving along with preparations for the maiden flight of the Falcon Heavy rocket.

CEO Elon Musk tweeted video of the rocket going vertical at historic Launch Pad 39A Thursday. Then, on Instagram, Musk said a hold-down test fire for the rocket was happening next week, with plans to launch by the end of the month.

Musk says the Falcon Heavy's thrust is equal to 18 Boeing 747 planes at full throttle.