SpaceX is implementing “well over a thousand changes” to its next Starship prototype and fixing its launch pad in Boca Chica, Texas ahead of the rocket’s second orbital test this summer, said CEO Elon Musk. During a Twitter Spaces discussion on June 24 with his biographer Ashlee Vance, Musk said, with all the modifications, the chance of the second Starship flight reaching Earth’s orbit will go up to 60 percent from his previous estimate of 50 percent.
“I think the probability of this next flight getting to orbit is much higher than the last one. Maybe it’s like 60 percent,” Musk said. “It depends on how well we do at stage separation.”
SpaceX launched the first orbital Starship test on April 20, during which the rocket exploded in the sky before reaching orbital altitude. The Starship prototype used for orbital tests consists of two stages and uses a total of 39 Raptor engines: a giant booster called Super Heavy powered by 33 engines and a Starship upper stage powered by six. During the April 20 test, at least eight engines shut down shortly after liftoff or never started, according to flight video, and the upper stage failed to separate from its booster mid-air as planned.
Stage separation will be the biggest risk
The extra 10 percent chance of success will come from a new stage separation technique SpaceX will try on the second attempt, Musk said. According to Starship’s original design, the booster’s 33 engines will shut down once the rocket thrusts above the lower atmosphere. Then, the upper stage will separate itself from the booster, fire up its six engines, and climb toward orbital altitude. For its second test, SpaceX will try a different approach called “hot staging,” where the upper stage’s engines will begin firing before all booster engines shut down. The side effect, however, is an increased chance of the upper stage’s engine ignition damaging the booster’s top.
“We shut down most of the engines on the booster, leaving just a few running, and then at the same time, start the engines on the ship or upper stage,” Musk explained. “Obviously that results in kind of blasting the booster, so you’ve got to protect the top of the boost stage from getting incinerated by the upper-stage engines.”
“The super hot plasma from the upper-stage engines has got to go somewhere,” he added.
Musk said earlier this month he’s aiming for between late July and mid-August for the second Starship test, pending approval from the Federal Aviation Administration (FAA).