SpaceX Analyzes Explosion During Rocket Booster Test

“Yeah, actually not good. Team is assessing damage,” Mr. Musk, chief executive of Space Exploration Technologies Corp., the formal name for SpaceX, said in a tweet Monday in response to that video.

Later, Mr. Musk said he visited the site himself and that the base of the booster seemed OK. The company shut down the pad where the test was taking place for safety reasons, he added.

SpaceX didn’t immediately respond to a request for comment.

SpaceX has been pushing to prepare for a first orbital test flight of Starship from its site in Texas, recently winning regulatory approval to conduct such a mission. The Starship rocket system consists of a spacecraft also called Starship that would be blasted toward orbit on top of a massive Super Heavy booster.

Challenges during spacecraft testing aren’t uncommon, as teams of engineers and other staff work to prepare vehicles for flights into orbit. It wasn’t immediately clear what Monday’s explosion would mean for the company’s plans to blast Starship into space.

About a month ago, SpaceX said in a tweet that the company was “one step closer” to such a mission, after the Federal Aviation Administration gave the company the green light to pursue such operations, provided it met a number of conditions.

Mr. Musk said in another tweet Monday that cryogenic fuel, a type of propellant that is kept at very cold temperatures, creates an added challenge, “as it evaporates to create fuel-air explosion risk” when oxygen is partially present in the atmosphere, like on Earth. He also indicated the problem that arose was tied to a particular test of the booster’s engines.

During a presentation about Starship in February, Mr. Musk said SpaceX had made progress on Starship’s engines, called Raptors, adding power to a new version of them while reducing costs. Recently, the company tweeted out a photo of what it said were 33 Raptor engines clustered together at the bottom of a booster.

Yesterday’s event doesn’t fall under the FAA’s purview ensuring that space launches and re-entries are conducted safely, an agency spokesman said. However, the FAA is in close contact with SpaceX as the company looks into the fire, he added.

In addition to working on Starship, SpaceX has been busy with other launches, most of which have been to loft its own Starlink satellites into orbits relatively near Earth using the company’s workhorse Falcon 9 rockets, according to FAA data.

Write to Micah Maidenberg at micah.maidenberg@wsj.com