SpaceX’s Falcon 9 rocket suffered an upper-stage engine failure yesterday after lifting off from Vandenberg Space Force Base, a setback on a mission without astronauts on board that will likely delay upcoming human spaceflight launches while the company investigates what went wrong.

The problem occurred during the launch of a batch of Starlink satellites, used to beam the internet to ground stations and cellphones. The company said that since the “second stage engine did not complete its second burn” the satellites “were deployed into a lower than intended orbit.”

SpaceX CEO Elon Musk wrote on X that the engine failed “for reasons currently unknown. Team is reviewing data tonight to understand root cause.”

In a statement, the Federal Aviation Administration said it would require an investigation that is “designed to further enhance public safety, determine the root cause of the event, and identify corrective actions to avoid it from happening again. The FAA will be involved in every step of the investigation process and must approve SpaceX’s final report, including any corrective actions.”