SpaceX’s Falcon 9 rocket is grounded again after the vehicle’s second stage did not come down in the expected area of the ocean, following an otherwise successful mission that delivered a Dragon capsule and its crew to orbit.

“We will resume launching once we better understand root cause,” the company said in a statement posted to X. 

The Crew-9 mission, which carried NASA astronaut Nick Hague and Russian cosmonaut Aleksandr Gorbunov to orbit, launched on Saturday. (Two seats were left empty to ensure the two Boeing Starliner astronauts could return on the capsule in February.) Hague and Gorbunov arrived safely at the International Space Station early Sunday evening. 

While the most important part of the mission was carried out without a hitch, the issue that occurred during the second stage’s deorbit burn marks the third time in three months that the Falcon 9 has experienced an anomaly. The deorbit burn is a precisely targeted firing of the stage’s single Merlin Vacuum engine to ensure any debris from reentry lands in a specific zone in the ocean. 

The other two issues appeared in July and August. In the first instance on July 11, a liquid oxygen leak sprung up in the insulation surrounding the second stage’s engine during a routine Starlink launch, which led to the loss of the 20 satellites on board. Later, on August 28, the booster came down hot in its attempt to land on a SpaceX landing drone ship and was destroyed on impact. 

These have not grounded the Falcon 9 for long; after the issue with the liquid oxygen leak in July, SpaceX resumed flying the rocket after just two weeks. SpaceX said it had identified the cause of the leak — a cracked line connected to the pressure sensor — and took a number of steps to ensure the issue didn’t recur. The landing anomaly in August led to no pause in missions at all as the U.S. Federal Aviation Administration allowed the company to continue with launches while the investigation was underway. 

This most recent issue could delay some critical upcoming missions, notably the European Space Agency’s Hera mission to study asteroids on October 7 and NASA’s Europa clipper mission to the Jupiter moon of the same name on October 10. Both missions have tight launch windows that close by the end of the month. A Falcon 9 mission scheduled to launch 20 internet satellites for Eutelsat OneWeb scheduled for last night was also delayed.