An experimental SpaceX rocket exploded at the end of a high-altitude test flight Tuesday, but heavy fog at the site left even SpaceX at least publicly uncertain about exactly what caused the explosion.

SpaceX CEO Elon Musk did confirm the explosion on Twitter, though, saying “At least the crater is in the right place!”

Looks like engine 2 had issues on ascent & didn’t reach operating chamber pressure during landing burn, but, in theory, it wasn’t needed.

Something significant happened shortly after landing burn start. Should know what it was once we can examine the bits later today.

— Elon Musk (@elonmusk) March 30, 2021

All three of SpaceX’s previous launches of prototypes for this model of rocket crash landed or exploded shortly after landing.

SpaceX engineer John Insprucker, who hosted a webcast of the test launch, said the rocket, known as SN11, had a normal ascent and that all appeared to be well before on-board cameras lost signal and the vehicle was subsumed by fog moments before landing.

Insprucker said the company will share updates on social media once SpaceX engineers are able to check out the landing site. The area surrounding the vehicle must be cleared before lift-off for safety reasons.

Insprucker said the company is not expecting to recover video footage. “Don’t wait for landing,” he advised webcast viewers.

SpaceX intends to use Starship for a variety of purposes, including shuttling paying customers between cities at breakneck speeds, potentially aiding NASA’s Moon landing efforts, and, eventually, launching cargo and human missions to Mars.

Starship is still in the early stages of development. A full-scale prototype has yet to be constructed. And SpaceX has not yet begun publicly testing Super Heavy, a gargantuan rocket booster that will be needed to propel the Starship to Earth’s orbit or beyond. The first Super Heavy booster prototype, however, was recently spotted at SpaceX’s South Texas facilities.

Musk said during a recent interview with podcast host Joe Rogan that he expects Starship will be conducting regular flights by 2023, and he hopes the vehicle will reach orbit by the end of this year. It’s not clear if SpaceX will hit that deadline. The aerospace industry is notorious for announcing projects that take far longer than first anticipated, and Musk is particularly prone to that.