NASA astronauts Mike Hopkins, Shannon Walker, Victor Glover and Japan's Soichi Noguchi are on their way to the International Space Station. Why it matters: The crewed launch marks the second time SpaceX has launched people to orbit for NASA and the mission is expected to be the first of many regular flights like this to the space station.Details: The Falcon 9 carrying the four crewmembers took flight at 7:27 p.m. ET and the Crew Dragon capsule is expected to dock with the space station Monday night.During their flight to the station, Hopkins, Walker, Glover and Noguchi are planning on testing out what kind of choreography is needed to make sure that everyone is comfortable during their trip to the station. When astronauts Bob Behnken and Doug Hurley flew on the Crew Dragon for SpaceX's first crewed flight, there was plenty of room in the capsule because only two of them were flying, this time around, space will be at a premium.The four crewmembers will stay onboard the space station for about six months before heading back home.Of note: NASA tweeted late Sunday that engineers encountered an issue with heaters used to keep thruster propellant lines at a regular temperature. The agency added in an update early Monday that these had been re-enabled and were now "functioning properly with no issues."Between the lines: All four of the astronauts were in quarantine ahead of launch to ensure they did not catch COVID-19 or another infection before heading up to the station.The big picture: The Crew Dragon is the first American-made spacecraft able to bring astronauts to orbit since the end of the space shuttle program in 2011. Until this summer's crewed SpaceX launch, NASA was solely reliant on Russia's Soyuz spacecraft to bring their people to and from the space station. Boeing is also working to develop its own crewed capsule, called the Starliner, that is expected to fly its first crewed mission in the next year or so. This article has been updated with details on the propellant heaters issue.