Falcon 9 scrub
A SpaceX Falcon 9 stands on the pad at Cape Canaveral, Florida, after a launch attempt Feb. 28 was aborted because of an issue with the vehicle's first stage engines. Credit: SpaceX webcast

WASHINGTON — The third time was not the charm for SpaceX, as it aborted the launch of the SES-9 communications satellite Feb. 28 at the last second because of an engine problem.

SpaceX aborted the launch when computers detected a problem during the startup of the first stage’s nine engines at 7:21 p.m. Eastern. The webcast of the launch showed the engines igniting and, within a second, shutting down when the computer triggered the abort.

SpaceX officials on the webcast did not know the reason for the abort, but company chief executive Elon Musk tweeted that a “low thrust alarm” triggered the abort. “Rising oxygen temps due to hold and helium bubble triggered alarm,” he said. SpaceX has not announced a new launch date.

The launch had been scheduled for 6:47 p.m. Eastern, but the countdown was stopped about 90 seconds before liftoff when a boat entered a “keep-out” zone around the launch range. That delay likely caused the rocket’s “supercooled” liquid oxygen propellant to warm up as SpaceX waited for the range to clear.

SpaceX postponed the previous two launch attempts, also because of issues linked to the rocket’s liquid oxygen propellant. The company postponed the first attempt on Feb. 24 more than a half-hour before the launch window opened, saying it decided “out of an abundance of caution” to delay the launch to allow the rocket’s liquid oxygen propellant to cool at much as possible.

SpaceX scrubbed a second launch attempt Feb. 25 1 minute and 41 seconds before liftoff. The company said at the time that launch controllers monitoring the transfer of liquid oxygen decided to stop the launch at that point because of issues with the final load of propellant.

The upgraded version of the Falcon 9 uses liquid oxygen cooled to near its freezing point, which increases its density. That is one of several changes SpaceX made to the Falcon 9 to increase the vehicle’s performance and thus its payload capacity. Those changes made it possible for the Falcon 9 to launch SES-9, which weighs about 5,300 kilograms at launch.

The launch would be the second this year for SpaceX, after the Jan. 17 launch of the Jason-3 ocean science satellite on an older Falcon 9 v1.1 from Vandenberg Air Force Base in California. SpaceX President Gwynne Shotwell said Feb. 3 that after the SES-9 launch, the company planned to launch “every two to three weeks” to handle a backlog of commercial and NASA missions.

After this mission, the next Falcon 9 launch, a Dragon cargo mission to the International Space Station, is tentatively scheduled for early April, also from Cape Canaveral.

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...