SpaceX changes the spacecraft separation phase before the next launch

Elon Musk said June 24 that SpaceX is changing the approach of separating two stages of the Starship vehicle to increase payload performance before its next test flight.

in Online discussion With Bloomberg journalist Ashley Vance on Twitter, Musk’s social media company said that SpaceX recently decided to switch to a “hot staging” approach in which the Starship’s upper stage would fire its engines while still attached to a Super Heavy booster.

“We made a kind of late change that’s very important to the way phase separation works,” Musk said, describing the shift to hot staging. “There is a beneficial payload-to-orbit advantage with rapid staging that is a conservative 10% increase.”

Hot staging, which has been used on Russian launch vehicles for decades, involves igniting the engines on one stage while still attached to its lower stage. For the Starship, most of the 33 Raptor engines on the Super Heavy booster will be turned off, but a few are still running, Musk said, when the engines on the Starship’s upper stage are ignited. Doing so, he said, avoids the loss of thrust during a traditional stage separation, in which the lowest stage is closed first.

Doing so requires some modification to the Super Heavy booster. Musk said SpaceX is working along the top of the booster “which is nearly all the vents” to allow exhaust from the upper stage to escape while it’s still attached to the booster. SpaceX will also add a shield to the top of the booster to protect it from exhaust.

“This is the most dangerous thing, I think, for the next flight,” he said of the new phase separation technology.

Besides the change in class stage, Musk said SpaceX has made an “enormous number” of other changes to the vehicle, “over a thousand.” He did not go into detail about the changes, but noted that the company continues to work to upgrade the launch pad to avoid damage caused by the launch of the first spacecraft on April 20, such as the “steel sandwich” water immersion system. “We’re actually going to overdo it with the steel and concrete sandwich, so that should leave the pillow base in much better shape than last time.”

SpaceX has also been making improvements to the Raptor’s engines, with Musk describing the vehicle’s April launch as using a “hodgepodge” of engines built over time. Raptors on newer vehicles include changes to the engine’s hot gas manifold to reduce fuel leakage.

He said these changes gave him more confidence in the success of the next launch. “I think the probability that the next flight will be successful, and will reach orbit, is much higher than the previous flight. Probably as high as 60%.” In an online chat in late April, he estimated a “better than 50% chance” of success in the next launch.

Musk has not committed to a specific launch date. “There are a lot of variables here that are out of our control,” he said, an apparent reference to the FAA’s launch authorization process. “We believe, most likely, that the launch pad, booster and ship upgrades should be ready in about six weeks.” Musk said, in that April conversation, that he expects to be ready to fly “in a couple of months.”

Earlier in the conversation, Musk declined to comment on recent rumors that SpaceX was considering taking over the Starlink satellite broadband business and conducting an initial public offering (IPO) of shares in it. Fox Business reported on June 21 SpaceX investors expected a Starlink public offering and IPO to happen this year so that Musk could raise money for other projects, such as Twitter.

Musk, when asked about any plans to go public with Starlink, declined to comment. He claimed “It would not be legal for me to speculate about the Starlink IPO”. “I think it is against the regulations to speak with any kind of detail about a future public offering.”

Musk has previously downplayed any talk of the Starlink IPO and made it public. He said in 2020 that he was “thinking zero” in order to focus on making broadband service a technical and financial success.

At an internal company meeting in June 2022, Musk said he didn’t know when SpaceX would go public with Starlink, but estimated it would take at least three to four years.

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