Earlier scheduled for February 17, SpaceX delayed the launch, saying more time was needed for final checks of the Falcon 9 rocket's upgraded payload fairing, Space.com reported late on Sunday.
"Team at Vandenberg is taking additional time to perform final checkouts of upgraded fairing," SpaceX representatives tweeted.
The Falcon 9's launch is scheduled from Vandenberg Air Force Base in California.
"Payload and vehicle remain healthy. Due to mission requirements, now targeting February 21 launch of PAZ," SpaceX added.
The Falcon 9 rocket will send SpaceX's first Starlink broadband satellites and the Paz radar-imaging satellite for Spain into orbit. The starlink satellite aims to provide low-cost Internet access on a global scale.
SpaceX is expected to launch two prototype satellites, called Microsat-2a and Microsat-2b, as part of its Starlink broadband satellite constellation.
SpaceX has kept mum about many of the details relating to Starlink, but the company's business plan calls for putting thousands of communication satellites in orbit, with limited service starting by 2020, media reported.
The primary payload on Falcon 9 rocket is the 3,000-pound Paz.
According to a report at Nasaspaceflight.com, the Paz satellite - named after the Spanish word for "peace" - will be launched into a 514 km circular orbit.
It was built by Airbus for the Spanish company hisdeSAT, and will be used for military and civilian purposes.
SpaceX successfully launched Falcon Heavy rocket into space on February 6.