WASHINGTON — SpaceX is changing its approach to separating the two stages of its Starship vehicle to increase payload performance before its next test flight, Elon Musk said on June 24.
IN an online discussion with Bloomberg journalist Ashlee Vance on Twitter, the social media company Musk owns, said that SpaceX had recently decided to switch to a “hot-staging” approach where the Starship upper stage will ignite its engines while still attached to the Super The Heavy booster.
“We made a kind of late-breaking change that’s really quite important to the way the stage separation works,” Musk said, describing the transition to hot staging. “There is a meaningful payload-to-orbit benefit with hot staging that is conservatively about a 1[ads1]0% increase.”
Hot-staging, which has been used on Russian launch vehicles for decades, involves igniting the engines on one stage while it is still attached to the lower stage. Musk said that for Starship, most of the 33 Raptor engines on the Super Heavy booster would be shut down, but a few would still fire, when the engines on the Starship upper stage ignited. Doing so, he said, avoids the loss of thrust under traditional stage separation, where the lower stage shuts off first.
Doing so requires some modifications to the Super Heavy booster. Musk said SpaceX is working on an extension to the top of the booster “that’s almost all vents” to allow the exhaust from the upper stage to escape while still attached to the booster. SpaceX will also add shielding on top of the booster to protect it from the exhaust.
“This is the riskiest thing, I think, for the next flight,” he said of the new stage separation technique.
In addition to the stage separation change, Musk said SpaceX made a “huge number” of other changes to the vehicle, “well over a thousand.” He did not go into details about the changes, but noted that the company continued work on upgrading the launch pad to avoid the damage caused by the first Starship launch on April 20, such as a “steel sandwich” flood system. “We’re actually going overkill on the steel sandwich and the concrete, so that should make the bottom of the pad in much better shape than last time.”
SpaceX has also made improvements to the Raptor engines, with Musk describing the vehicle launched in April as using a “hodgepodge” of engines built over time. Raptors on the new vehicles include changes to the hot gas manifold in the engine to reduce fuel leakage.
Those changes, he said, gave him more confidence in the success of the next launch. “I think the probability of this next flight working, and getting into orbit, is much higher than the last one. Maybe it’s 60%.” In an online conversation in late April, he estimated a “better than 50% chance” of success on the next launch.
Musk did not commit to a specific launch date. “A lot of variables here that are out of our control,” he said, an apparent reference to the Federal Aviation Administration launching the licensing process. “We think the upgrades to the launch pad, and the booster and the ship, will probably be ready in about six weeks.” Musk said in the April call that he expected to be ready to fly “in a couple of months.”
Earlier in the call, Musk declined to comment on recent rumors that SpaceX was considering spinning off its Starlink satellite broadband business and conducting an initial public offering (IPO) of shares in it. Fox Business reported on June 21 that SpaceX investors anticipated a spinout and IPO of Starlink this year so Musk could raise money for other ventures, such as Twitter.
Asked about any plans for a Starlink IPO, Musk declined to comment. “It would not be legal for me to speculate on a Starlink IPO,” he claimed. “I think it’s against regulations to talk in all kinds of detail about a future public offering.”
Musk has previously played down any talk of spinning off Starlink and making it public. He said in 2020 that he was “thinking about that zero” to focus on making the broadband service a technical and financial success.
In an internal company meeting in June 2022, Musk said he did not know when SpaceX would go public with Starlink, but estimated it would take at least three to four years.