CEO Elon Musk has offered an explanation for SpaceX’s recent Starship static fire anomaly and says that an overview of the next-generation rocket development program will be delayed to account for some “notable” design changes.
Over the last several months, Musk has promised to do one of his (thus far) usual annual Starship updates, either in the form of a presentation in South Texas, an article published on SpaceX’s website, or both. Originally expected in September or October, the CEO’s tentative schedules have come and gone several times. Simultaneously, however, SpaceX has been preparing Starship serial number 8 (SN8) for a range of crucial tests and Starship program firsts, recently culminating in a successful cryogenic proof test, multiple wet dress rehearsals (WDRs), nosecone installation, the first triple-Raptor static fire test, engine tests using smaller ‘header’ tanks, and more.
Unfortunately for SN8, the most recent Raptor engine header static fire – drawing propellant from two small internal tanks mainly used for landing burns – did not go according to plan, resulting in some kind of high-temperature fire and severing Starship’s hydraulic systems. For SpaceX test controllers, that meant a total loss of control of most vehicle valves and pressurization systems, essentially putting one of Starship SN8’s header tanks through an unplanned pressure and failsafe test. In the days since, what exactly caused that unfortunate failure has been the subject of a great deal of discussion – discussion that can finally be put to rest with new information from Musk himself.
In a surprise, SpaceX had apparently decided to add a failsafe to Starship SN8’s new nose section, installing what is known as a burst disk – effectively an automatic single-use valve. Once the upper (liquid oxygen) header tank reached dangerous pressures, the force of that pressure broke the seal, allowing the rocket to vent excess pressure and avoid what would have otherwise been a potentially catastrophic explosion.
The cause of that near-miss, according to Elon Musk, was as simple as debris kicked up during the Starship SN8 Raptor engine static fire directly prior. Producing up to 200 metric tons (~450,000 lbf) of thrust and an exhaust stream traveling some 3.3 kilometers per second (2 mi/s, Mach ~10), Musk says that Raptor tore apart a special ceramic coating covering the concrete directly beneath Starship SN8. Likely accelerated to extreme velocities in milliseconds, shards of that coating reportedly “severed [an] avionics cable, causing [a] bad [Raptor engine shutdown].”
Prior to Musk’s comments, SpaceX technicians had already removed on of SN8’s three Raptors – SN32 – on November 14th and replaced it with Raptor SN42 on November 16th, effectively confirming that any damage suffered by Starship’s engine section was easily repairable. It’s unclear how exactly a single severed cable could result in a Raptor engine seemingly dripping molten metal but regardless of the cause, the fix appears to have been a quick one.
In response to the anomaly, Musk says that Starship avionics cables will ultimately be routed inside steel pipes to shield them from debris, while “water-cooled steel pipes” will be added to the launch pad to help limit the damage Raptors can cause. Perhaps as a partial result of SN8’s troubles at the launch pad, Musk says that his Starship blog post will have to wait, as SpaceX “[may be] making some notable changes” to the launch vehicle.
Prior to Starship SN8’s failed November 12th Raptor test, SpaceX was expected to attempt three consecutive static fires before clearing the rocket for an ambitious 15 km (9.5 mi) flight test. One of those static fires had already been completed on November 10th and it’s unclear if SpaceX’s SN8 test plan has remained unchanged or if the static fire counter has been effectively reset. Either way, barring more surprises, there’s still a definite possibility that Starship SN8 will be ready for its launch debut by the end of November and an even better chance that it will launch some time between now and 2021. Stay tuned for updates!