SpaceX abruptly aborted the second attempted launch of its upgraded Starship rocket system on Thursday, just moments after the booster ignited at the company’s complex in South Texas.

CEO Elon Musk said on his social media platform X that “[s]ome of the engines didn’t start, triggering an automatic launch abort” and that the company will replace two of them. SpaceX won’t try to launch Starship again until next week, he wrote.

SpaceX was hoping to launch its first third-generation Starlink satellites into space — although they are supposed to burn up around 20 minutes after deployment, as Starship has not yet demonstrated the ability to reach Earth orbit.

This is also SpaceX’s first Starship test launch attempt since it went public on June 12 in the largest IPO in history. The company raised more than $85 billion in the transaction and briefly touched the valuations of Amazon and Microsoft, though its stock has steadily fallen over the intervening month.

On Thursday, SpaceX’s stock price closed below its IPO price of $135. Its stock sank more than 4% in after-hours trading after the aborted launch.

SpaceX was trying to return to flight just a few weeks after the first-ever launch of Starship V3 in May. That mission was a mixed bag.

Getting off the launchpad with the first version of a newly upgraded rocket was a big step forward, and the company was able to deploy a number of Starlink simulators into space. But the Super Heavy booster stage suffered a failure before it could attempt a simulated landing in the Gulf of Mexico, leading to an FAA-ordered review of what went wrong. (The FAA cleared the company to fly Starship again earlier this week after identifying a number of causes and fixes for the booster failure.)

Starship’s upper stage also lost an engine on its way to deploying the Starlink simulators during the May mission. The upper stage was able to perform its own simulated landing over the water without a hitch.

SpaceX was hoping to take another step forward Thursday by launching the V3 Starlink satellites. The upgraded Starship and Starlink are key to SpaceX’s incredibly ambitious plans to prove that the concept of “orbital data centers” is both technologically and economically viable. Starlink is also the largest revenue generator and the only profitable portion of SpaceX’s business.

Thursday’s launch attempt looked to be chugging along just fine, with only a brief hold in the countdown at T-minus one minute before the scheduled launch attempt. That hold cleared quickly, and the countdown resumed.

As the countdown expired, the launchpad’s water deluge system fired up, and the booster stage visibly began firing its engines — only for everything to suddenly shut down. Graphics on SpaceX’s broadcast appeared to show that four of the company’s new Raptor engines did not fire upon ignition.

SpaceX now has to take all the propellant out of both the Super Heavy booster and the upper stage, before determining exactly what went wrong on Thursday.

This story has been updated with new information from Elon Musk.