The roughly eight-hour flight to the station will be SpaceX's first operational mission, as opposed to a test, after NASA officials this week signed off on Crew Dragon's design, ending a almost 10-year development phase for SpaceX under the agency's public-private crew program.
Boeing's first crewed test mission with its Starliner capsule is planned for late next year.
The Crew-1 spaceflyers - NASA astronauts Victor Glover, Mike Hopkins and Shannon Walker and Japan's Soichi Noguchi - will stay on board the space station for a six-month mission, and have already begun their final preparations before liftoff.
The SpaceX flights are far less expensive - NASA spent over $85 million per seat on the Soyuz, but it's about $55 million per seat on the Crew Dragon.
NASA astronauts Shannon Walker, Victor Glover and Mike Hopkins, and JAXA astronaut Soichi Noguchi pose for a picture with Junichi Sakai, manager of the International Space Station Program for JAXA, NASA administrators Jim Bridenstine and Jim Morhard, and Kennedy Space Center director Bob Cabana, after speaking with members of the media following their arrival at the Launch and Landing Facility at NASA's Kennedy Space Center, on November 8, 2020. You can watch via embedded video stream below. The space agency is looking to save big by no longer having to buy seats on Russian Soyuz capsules for USA astronauts.
The astronauts, named Crew-1, took the walk through Kennedy Space Center as did Ben Behnken (right) and Dough Hurley (left) in May when they prepared for "Launch America" that brought space flight back to U.S. soil.
Standing on the launch pad at Launch Complex 39A at the agency's Kennedy Space Center in Florida, the rocket's nine Merlin first-stage engines were fired for 7 seconds for this critical but routine test.
More crew members means NASA and its worldwide partners can better utilize the ISS. If that attempt is scrapped, a backup launch would be set for 7:27 p.m. on Sunday with docking 27 hours later due to orbital mechanics.
'The next era in human spaceflight' © NASA NASA astronauts Bob Behnken and Doug Hurley.
Dubbed "Crew-1", Sunday's launch is how officials picture the future partnership of NASA and SpaceX to look in the years to come.
Norm Knight, a deputy manager at NASA, said the guidelines are rigid for restricting access to astronauts before flight in order to keep them safe and healthy.
"It felt like we were inside of an animal", Behnken said of the 17,500-mph dive.
NASA contracted SpaceX and Boeing in 2014 to develop competing space capsules aimed at replacing its shuttle program that ended in 2011 and weaning off dependence on Russian rockets to send US astronauts to space.
NASA Administrator Jim Bridenstine hailed Demo-2 as evidence of the Commercial Crew Program's success.
Dave Mosher and Morgan McFall-Johnsen contributed reporting.