WASHINGTON — SpaceX is changing the approach to separating the two stages of its Starship vehicle to increase payload performance ahead of its next test flight, Elon Musk said June 24.
In an online discussion with Bloomberg reporter Ashlee Vance on Twitter, the Musk-owned social media company, he said SpaceX had recently decided to move to a “hot staging” approach where the Starship’s upper stage would ignite its engines while still attached to the Super Heavy booster.
“We made a kind of last-minute change that is really, really important to how stage separation works,” Musk said, describing the move to hot staging. “There is a significant payload-to-orbit advantage with hot staging which is a conservative increase of about 10 percent.”
Hot staging, which has been used on Russian launch vehicles for decades, involves firing the engines on one stage while remaining attached to its lower stage. Musk said that for Starship, most of the Super Heavy booster’s 33 Raptor engines would be turned off, but a few would continue to run, when the Starship’s upper stage engines were turned on. This, he said, avoids the loss of thrust when separating traditional stages, where the lower stage stops first.
This requires some modifications to the Super Heavy booster. Musk said SpaceX is working on an upward extension of the booster “it’s almost all vents” to allow the upper stage exhaust to escape while still attached to the booster. SpaceX will also add shielding to the top of the booster to protect it from the exhaust.
“It’s the riskiest thing, I think, for the next flight,” he said of the new stage separation technique.
Besides the stage separation change, Musk said SpaceX has made a “considerable number” of other modifications to the vehicle, “well over a thousand.” He did not go into details of the changes, but noted that the company was continuing work to upgrade the launch pad to avoid damage from Starship’s first launch on April 20, such as a water deluge “steel sandwich”. “We’re actually going to overdo it on the steel and concrete sandwich, so that should leave the cushion base in much better shape than last time.”
SpaceX has also made improvements to Raptor engines, with Musk describing the vehicle’s launch in April as using a “hodgepodge” of engines built over time. New vehicle Raptors include modifications to the hot gas manifold in the engine to reduce fuel leakage.
These changes, he said, gave him more confidence in the success of the upcoming launch. “I think the probability of this next flight working, getting into orbit, is much higher than the last one. Maybe it’s like 60 percent.” In an online conversation at the end of April, he estimated a “more than 50% chance” of success in the next launch.
Musk has not committed to a specific launch date. “A lot of variables here that are beyond our control,” he said, an apparent reference to the Federal Aviation Administration’s launch licensing process. “We believe, probably, that the launch pad upgrades, as well as the booster and the ship, will be ready in about six weeks.” Musk, in that April chat, said he expected to be ready to fly “in a few months.”
Earlier in the conversation, Musk declined to comment on recent rumors that SpaceX is planning to expand its Starlink satellite broadband business and conduct an initial public offering (IPO) of stock. Fox Business announced on June 21 that SpaceX investors were planning a Starlink spinoff and IPO this year so Musk could raise money for other companies, like Twitter.
Musk, when asked about any Starlink IPO plans, declined to comment. “It would not be legal for me to speculate on a Starlink IPO,” he claimed. “I think it’s against the rules to talk about any kind of details about a future public offering.”
Musk has previously played down any discussion of Starlink’s creation and publication. He said in 2020 that he was “thinking this zero” in order to focus on the technical and financial success of the broadband service.
During an internal company meeting in June 2022, Musk said he didn’t know when SpaceX would take Starlink public, but estimated it would take at least three to four years.