SpaceX’s Falcon rocket fleet was grounded for the third time in three months after a second stage problem occurred Saturday following the successful launch of a two-crew Dragon capsule to the International Space Station. The suspension of flights comes as the company prepares to launch two solar system exploration missions in October with tight launch windows.

SpaceX said the Falcon 9 second stage that launched NASA’s Crew 9 mission failed to launch less than 30 minutes after Dragon Freedom was released into a planned 117 by 128 mile (189 by 206 km) orbit could carry out correct ignition of their Merlin vacuum engine.

Engine ignition is intended to prevent the rocket body from becoming space debris by propelling the stage into the atmosphere for a destructive re-entry. All debris should fall harmlessly into the sea in an area previously identified in warnings for sailors and airmen.

“The Falcon 9 second stage was disposed of at sea as planned, but experienced an unscheduled deorbit burn,” SpaceX said in a social media post shortly after midnight EDT on Sunday. “As a result, the second stage landed safely in the sea, but outside the target area.”

The mishap is likely to trigger an investigation by the Federal Aviation Administration (FAA), which oversees the company’s launch licenses. SpaceX is currently battling with the FAA over fines related to Falcon 9 activities at Kennedy Space Center and delays in approval for the fifth test flight of its Starship vehicle from Starbase in Texas.

Spaceflight Now has reached out to the FAA for comment but has not yet received a response because the FAA’s offices were closed over the weekend.

Debris from the rocket stage should have fallen into a section of the Pacific Ocean starting east of New Zealand, but likely fell further into the depths but still south of the equator, according to Jonathan McDowell, an astrophysicist and tracker of space launches and satellites.

“The most likely failure mode that still results in reentry is mild underburn,” he said in a post on X, formerly known as Twitter. “So you’re assuming the entry is more advanced… but not too far.”

McDowell told Spaceflight Now he estimates the deorbit burn occurred around 1:55 p.m. EDT (1755 UTC) as the spacecraft passed over Yemen. If everything had gone according to plan, re-entry would have occurred about 35 minutes later.

Here is the ground trace showing the planned re-entry area in the bottom left. My analysis suggests that a deviation from the nominal orbit that still ends with a stage re-entry will hit the orange line somewhere between the end of the white rectangle and the equator pic.twitter.com/NgG2ZL3SIe

— Jonathan McDowell (@planet4589) September 29, 2024

SpaceX was scheduled to launch 20 satellites for OneWeb from its West Coast launch pad at Vandenberg Space Force Base late Sunday evening local time, but that mission was put on hold, as was a Starlink delivery mission from Cape Canaveral originally scheduled for Wednesday.

“We will resume launch once we better understand the root cause (of the problem),” SpaceX said in its statement.

This will be the third grounding of the Falcon 9 fleet in three months. A problem in the upper stage led to the loss of 20 Starlink satellites on July 11th. Flights resumed 15 days later after the company determined the cause of a liquid oxygen leak and found a quick solution. A shorter suspension of just three days occurred when a Falcon 9 first stage crash-landed on the deck of SpaceX’s drone ship after an otherwise successful launch on August 28. The company has not disclosed the cause of this mishap.

The landing of the Falcon fleet will be of particular concern to NASA and the European Space Agency (ESA), as missions to explore the solar system were scheduled to launch just days apart in early October.

On October 7, a Falcon 9 is scheduled to launch from Cape Canaveral with ESA’s Hera mission to study the binary asteroid system Didymos, which was hit by the DART mission in September 2022. The launch window runs until October 27th.

Then on October 10, a Falcon Heavy, using the same second stage as the Falcon 9, is scheduled to launch NASA’s Europa Clipper on a mission to explore one of Jupiter’s most fascinating moons. The $5 billion mission will require the Falcon Heavy’s full power, plus two burns of the rocket’s second stage.

The spacecraft will launch from the rocket at a speed of about 25,000 mph (40,200 km per hour), the highest speed ever achieved by a Falcon upper stage. The launch window for Europa Clipper ends on October 30th.