SpaceX appears to have successfully fired up its fourth full-scale Starship prototype for the third time, although the Raptor engine test ended with the aft end of the ship catching fire and burning for quite some time.
Around May 7th, hours after Starship SN4 completed its second wet dress rehearsal and Raptor static fire in ~24 hours, SpaceX removed the SN18 Raptor engine it had used to support those tests, transporting it back to storage facilities a mile down the road. Three days later, SpaceX sent Raptor SN20 down the same same road and installed it on Starship SN4 – a swap made for unknown reasons.
Regardless, that swap meant that SpaceX would need to perform at least one more static fire test to prove that Starship and its new Raptor engine were getting along before the company could proceed to hop test preparations. After several days of at least 4 aborted Starship static fire attempts, SpaceX has finally managed to fuel Starship SN4 and ignite Raptor engine SN20 – but not before a new challenge cropped up.
Just shy of 1:01 pm CDT (18:01 UTC), Starship SN4 appeared to successfully fire up Raptor SN20 for at least several seconds, serving as an in-situ acceptance test for the advanced rocket engine. Like the Merlin 1D engines that power Falcon 9 boosters, Raptors are built in Hawthorne, California, shipped to McGregor, Texas for standalone acceptance testing, installed on their assigned rocket, and static fired one more time before SpaceX deems them ready for launch.
This static fire thus served to verify that Starship SN4 and Raptor SN20 were both still in good health after a busy week of numerous tests and several weeks or months in storage, respectively. If fully successful, it would likely clear Starship SN4 to attempt what would be the inaugural flight of a full-scale Starship prototype, potentially ready to occur as early as May 21st (pending an FAA license, of course). Unfortunately, when Raptor SN20 ignited, it appeared to shake or overpressurize one or several plumbing lines, catching what must have been a methane vent or drain line on fire.
While the rocket itself is likely totally fine, much like its Starhopper predecessor suffered even worse fires during its summer 2019 test campaign, the dark smoke that appeared shortly after the secondary fire started is not a great sign. As methane and oxygen burn quite cleanly, that smoke likely means that the fire(s) got to some of the extensive wiring covering Starship and connecting to its test stand and ground controllers. If damaged, all of that wiring will need to be replaced, while the leaky methane pipe that burned for a solid 15 minutes will also need to be fixed.
As such, it’s likely that Starship SN4 will need to wait at least several more days – and may even need to complete a fourth static fire test – before SpaceX can clear it for an inaugural 150m (~500 ft) hop test.