As you remember weather forced the postponement on Wednesday of what would have been the first launch of American astronauts from US soil since the space shuttle program ended in 2011.
The Falcon 9 rocket with SpaceX's Crew Dragon capsule is scheduled to liftoff at 3:22 pm Eastern Time (1922 GMT) on what is designed to be the final test flight before NASA certifies the spacecraft for regular crew flights.
The next window, which is determined by the relative position of the launch site to the space station, is Sunday at 3:00 pm (1900 GMT), and fair weather is predicted.
NASA astronauts Robert Behnken, 49, and Douglas Hurley, 53, former military test pilots who joined the US space agency in 2000, are to blast off for the ISS from historic Launch Pad 39A on a two-stage SpaceX Falcon 9 rocket. This same launch pad was used by Neil Armstrong on Apollo 11 for the historic 1969 journey to the Moon.
NASA has urged crowds to stay away from Cocoa Beach, the traditional viewing spot -- but that did not deter scores of space fans on Wednesday.
President Donald Trump, who flew in for the previous launch attempt, is expected to attend again.
The Crew Dragon mission, dubbed "Demo-2," is a defining moment for SpaceX, the company founded by Musk in 2002 with the goal of producing a lower-cost alternative to human spaceflight.
SpaceX conducted a successful test flight of Crew Dragon to the ISS in March 2019 with a sensor-laden mannequin on board named Ripley, after the character played by Sigourney Weaver in the "Alien" movies.
Two years later, NASA ordered the next step: to transport its astronauts there by adapting the Dragon capsule.
The US space agency paid more than $3 billion for SpaceX to design, build, test and operate its reusable capsule for six future space roundtrips.
The project has experienced delays, explosions, and parachute problems -- but even so, SpaceX has beaten its competitor, aerospace giant Boeing, to the punch.
Crew Dragon is scheduled to dock with the ISS about 19 hours after liftoff, for a duration that is yet to be finalized, but likely around early August.