The Crew Dragon capsule will launch aboard SpaceX's Falcon 9 rocket. | Photo by Joe Raedle / Getty Images SpaceX is getting ready to set out on its historic Polaris Dawn mission, which will send four astronauts into orbit aboard its Crew Dragon capsule. The five-day journey through the Van Allen radiation belts will include the first spacewalk done by private astronauts.If you're curious about the mission, here's what you should know about today's launch targeting currently targeting 5:23AM ET.