Though it ended in another “rapid, unscheduled disassembly” instead of the successful landing we’d hoped for, yesterday’s test-launch of the Starship SN9 prototype was a spectacular sight and will doubtless yield valuable data and help inform the next attempts and further evolution of SpaceX’s prototypes.
Like SN8, SN9 reached its target altitude (10km this time) with smooth stability. The controlled free-fall went remarkably well, as it did for SN8, which is a very encouraging result given the importance of this means of re-entry to the design. An interesting difference vs. the SN8 test was a very visible overshoot during the rotation back to vertical, which SN9 attempted unsuccessfully to correct. An astute observer pointed out to me that SN9 had only one engine firing at the time, whereas reviewing the SN8 test flight’s landing you can see two Raptors firing during the landing attempt (until one of them started to burn out with a bright green flame, at least). This leads one to wonder whether the failure was at least partly a matter of not having sufficient thrust (and the stability of a pair of pivoting thrust sources vs. just one) to correct the overshoot past vertical once it happened. But noting that SN8 rotated to vertical more slowly without overshooting and having to correct, it also seems like maybe a gentler approach to the rotation maneuver could have avoided the problem. I therefore wonder if control software or the feedback loop of sensors that informs it could have been partly at fault. Maybe the software that controls the maneuver, adaptive as it is designed to be, has a certain degree of hard-to-avoid reliance that the engines will successfully ignite and start providing thrust on command, and is limited (both logically and physically, with only one gimbaled rocket motor firing) in its ability to cope with failure of one engine to relight. I’m very curious about what actually happened and am looking forward to SpaceX’s findings and resultant changes to the next prototypes.
Here’s SpaceX’s livestream footage from yesterday:
Here’s SN8’s test-launch and landing attempt for comparison:
And here’s an illuminating side-by-side comparison and SN9 crash analysis from Terran Space Academy: