One reason SpaceX isn’t attempting an orbital flight this week is Starship’s failure to complete one of its test objectives on the last launch, when the spacecraft was supposed to ignite one of its six Raptor engines for a brief burn in space. The spacecraft skipped the burn after a Raptor engine shut down prematurely during the launch sequence.

The rest of the ship’s flight went according to plan, culminating in a pinpoint splashdown in the Indian Ocean. It was the first flight of SpaceX’s Starship V3 debuting new, more powerful Raptor engines. But officials need confidence in the Raptor engine’s ability to reignite in the airless vacuum of space before proceeding to an orbital flight. In a worst-case scenario, a failed Raptor engine relight would strand Starship in orbit, leaving the enormous stainless steel vehicle to an unguided reentry that could become a risk to public safety.

The flight plan for this week’s mission includes the Raptor restart objective left unaccomplished in May. In an update posted to its website over the weekend, SpaceX did not address what caused the premature shutdown of the Raptor engine on Flight 12.

“The vehicle was able to demonstrate its engine out capability and reach its planned suborbital trajectory,” the company wrote on its website. “Several hardware and operational modifications have been made to address the interconnected causes with additional reliability improvements planned in upcoming versions of the Raptor engine.”

The other goal left incomplete on Starship’s last flight involved the splashdown of the rocket’s Super Heavy booster, or first stage, which lost control moments separating from the ship, or upper stage, a few minutes after liftoff. SpaceX intended for the booster to fly itself to a water landing in the Gulf of Mexico downrange from its launch base in South Texas.

“At stage separation on Flight 12, slight differences in engine startup on the ship caused the directional flip of the booster to be off by approximately 90 degrees,” SpaceX wrote. “The startup sequence has been modified to be more robust to timing variability and more reliably flip in the desired direction, which is done to increase overall performance.