Space X founder, CEO, CTO, and chief designer Elon Musk has said the SpaceX SN10 Star ship was low on thrust after latest prototype landed and promptly exploded into flames earlier this month.
The test flight for the rocket seemed all well from the start when from ascend and completed the descent back to the landing pad and just a few moments later, it burst into flames.
Musk says the engine was low on thrust due to partial helium ingestion.
“SN10 engine was low on thrust due (probably) to partial helium ingestion from fuel header tank,” he tweeted. “Impact of 10m/s crushed legs & part of skirt. Multiple fixes in work for SN11.”
The presence of helium, however, was an intentional and not by accident. After it was pointed out that the helium pressurization was added to the Star ship prototype’s CH4 header tank to avoid the same issue that a previous prototype, SN8, encountered. Musk agreed that it contributed to SN10’s explosion.
Back in November 2020, the rocket encountered an issue with pneumatic pressure, with the liquid oxygen header tank pressure increasing.
“If autogenous pressurization had been used, CH4 bubbles would most likely have reverted to liquid,” Musk agreed. “Helium in header was used to prevent ullage collapse from slosh, which happened in prior flight. My fault for approving. Sounded good at the time.”
Prototypes like SN10 are designed to help work through these sort of challenges, and SpaceX clearly is still in the midst of development. That includes identifying when intended fixes actually could be presenting more of an issue than helping with it. Asked about whether baffles would be used to prevent the slosh issue in future rockets, Musk said that they were actually present on SN10, and could’ve been part of the problem.
“There were baffles, but one may have acted like a straw to suck bubbles in from above liquid/gas level,” he explained. “Something similar happened on an early Falcon 1 flight, resulting in unexpectedly high liquid oxygen residuals at main engine cutoff.”
The Star ship SN11 prototype has already been constructed, and SpaceX is currently preparing to launch another high-altitude test.
The SN10 completed the 10km altitude ascend and we wait to see what SN11 will take on.