SpaceX is taking another stab at launching an observatory into deep space and landing the booster that carries it up.
The unmanned Falcon 9 rocket is set to blast off at 1905 GMT from Cape Canaveral, Florida. It's the company's second attempt to launch the Deep Space Climate Observatory for NASA, the National Oceanic and Atmospheric Administration and Air Force.
Last-minute radar trouble halted Sunday's countdown. SpaceX skipped Monday because of rain.
NASA says former Vice President Al Gore is returning for the launch. It was his idea in 1998 that led to this observatory.
The spacecraft will fly to a point 1.6 million kilometers from Earth to monitor solar outbursts.
In a ground-breaking experiment, SpaceX will fly its leftover booster to an ocean platform. Last month's test failed.
