SpaceX changed the stage separation procedure for Starship before its next attempt at an orbital test flight. It is switching to a “hot-staging” procedure that has the upper stage firing its engines before it separates from the Super Heavy first stage booster.
Elon Musk says the change will improve payload performance. He discussed the change with Bloomberg journalist Ashlee Vance in a Twitter Spaces event.
“There’s a meaningful payload-to-orbit advantage with hot-staging that is conservatively about a 10% increase,” he told Vance. However, he acknowledged the risks involved and said SpaceX was working on a ventilation system to allow the exhaust from the upper stage engines to escape. It will add additional shielding to the top of the booster to protect it from the hot exhaust.
Musk also said that SpaceX had made “well over a thousand” other changes to Starship, likely using data from the first, abortive attempt at an orbital test flight. It is also working on additional protection for the launchpad to help avoid a repeat the damage caused during launch. Most of the protection involves what he called a “steel sandwich” water deluge system.
The changes seemed to improve the odds of a better performance during the next test launch.
“I think the probability this next flight working, getting to orbit, is much higher than the last one. Maybe it’s like 60%,” Musk said. For the previous orbital test, Musk promised only that it wouldn’t be boring.
Russian launch vehicles also use hot-staging. On the Starship/Super Heavy stack, most of the 33 Raptor engines on the Super Heavy stage will already be turned off when the upper stage engines are ignited. A few lower stage engines will still be ignited, which saves the loss of thrust associated with having all the first stage engines off when the upper stage separates.
During the first attempt at an orbital test for Starship, some of the first stage booster rockets failed to fire. The upper stage also had difficulty separating from the lower stage. It ended with the stack suffering a rapid unscheduled disassembly two minutes into the flight. Despite the loss, Elon Musk seemed to remain optimistic about the chance of a quick turnaround — at least in public.
Details of what might have occurred behind the scenes have been scanty; however, there has been some reshuffling of Starship management even before the abortive test flight occurred. SpaceX President Gwynn Shotwell and a VP named Mark Juncosa took overall charge of Starship as its new overseers in November 2022. In May 2023, SpaceX hired former NASA Commercial Crew Program manager Kathy Lueders as Starship’s general manager.
SpaceX and Elon Musk may have also become frustrated with delays in the FAA approval process for the orbital test flight, which had originally been scheduled for Summer 2021. However, the time it took has not stopped environmental groups from alleging that the FAA was too hasty in its approval. They say the rapid unscheduled disassembly caused debris to rain down on a beach and in a local park and caused a fire in the park.
Musk seemed to hesitate to give an exact date for the next test launch, saying it depended on “A lot of variables here that are outside of our control.” One of these variables is probably the FAA approval process. However, he seemed confident in SpaceX’s ability to get work done: “We think, probably, the launch pad upgrades, and the booster and ship, are ready in about six weeks.”