WASHINGTON — A Crew Dragon spacecraft is headed towards the International Space Station three days after a technical problem scrubbed its first launch attempt.

A Falcon 9 lifted off from Launch Complex 39A at the Kennedy Space Center at 12:34 a.m. Eastern March 2. The rocket placed the Crew Dragon spacecraft Endeavour into orbit on the Crew-6 mission, with four people from the United States, Russia and United Arab Emirates on board.

The launch took place on the second attempt. SpaceX scrubbed the first launch attempt Feb. 27 a little more than two minutes before the scheduled 1:45 a.m. Eastern liftoff after reporting an issue with the flow of triethylaluminum triethylborane (TEA-TEB), a chemical combination used to ignite the rocket’s engines.

“At the end of the day, we couldn’t be absolutely sure that we had enough TEA-TEB, enough of this ignition fluid, bled up to the interface of the rocket to make sure that we would get that consistent, exactly timed ignition that we need across all nine engines, so we scrubbed the launch,” said Benji Reed, senior director of human spaceflight programs at SpaceX, at a post-launch briefing.

NASA announced March 1 that it approved plans for the second attempt after reviewing the TEA-TEB problem. The agency said controllers saw an “unusual data signature” regarding the flow of TEA-TEB into a catch tank that turned out to be caused by a clogged filter in a ground system. Replacing the filter and purging the lines with nitrogen gas resolved the problem.

Reed said there is a regular schedule for changing the TEA-TEB filters, but maintenance on the system may have introduced some air into the system. The mixture of air and ignition fluid caused more oxidization that clogged the filter. The system worked as designed on the second launch attempt.

There was also a minor issue with the Dragon spacecraft after it reached orbit. The spacecraft opens its nose cone shortly after going into orbit, exposing its docking port. Steve Stich, NASA commercial crew program manager, said one sensor for the hooks that hold the nose cone closed malfunctioned, although the nose cone opened as expected. “We’ll have no problems with docking.”

Reed said the faulty sensor was one of 36 limit switches, indicating the nose cone wasn’t opening even though it was. As a precaution, the system switched the hooks to backup motor windings, which opened the nose cone normally, and he said controllers will likely ignore that sensor going forward. “At this point in time, we don’t foresee any issue and we see no elevated risk to the crew for docking or, after six months, when it comes time to close that nose cone again” for the trip home, he said.

The spacecraft is scheduled to dock with ISS at 1:17 a.m. Eastern March 3. It will deliver NASA astronauts Stephen Bowen and Warren Hoburg, who serve as mission commander and pilot, respectively, of Crew-6, along with Roscosmos cosmonaut Andrey Fedyaev and Emirati astronaut Sultan Alneyadi. It is the first flight for all but Bowen, who flew on three shuttle missions between 2008 and 2011.

The four are scheduled to stay on the ISS for about six months. The four-person Crew-5 mission — NASA’s Nicole Mann and Josh Cassada, JAXA’s Koichi Wakata and Roscosmos’s Anna Kikina — will return home from the ISS on their Crew Dragon spacecraft several days after the arrival of Crew-6. That departure could be as soon as March 8 or 9, Stich said, depending on weather conditions at splashdown locations off the Florida coast.

The Crew-6 launch took place four years, almost to the hour, after the first Crew Dragon launch on the uncrewed Demo-1 mission. Crew-6 is the ninth crewed flight of the spacecraft, including six crew rotation missions, the Demo-2 test flight and Ax-1 and Inspiration4 private astronaut missions.

“It’s just a little hard to believe that we’re on our sixth crew rotation mission in just four years,” Stich said. NASA and SpaceX, he said, have gotten into a rhythm of such flights, although each is unique. “It never is easy and it’s never really routine. They’re each different. They each have their challenges.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...