A SpaceX Super Heavy booster was rocked by a substantial explosion and subjected to multiple fires at the launch pad during the rocket’s latest round of testing.
As of 9 pm CDT, July 11th, the fate of the upgraded Super Heavy – known as Booster 7 or B7 – remains unclear and won’t be settled until all pad fires are under control and the rocket itself has been drained of all cryogenic propellant and potentially flammable gas. It’s unclear if or when that will happen, and there is an ever-present possibility that the situation will rapidly worsen as long as the pad continues to burn and Booster 7 remains partially loaded with propellant.
The incident began around 4:20 pm CDT, when Super Heavy Booster 7 (or its launch mount) unintentionally ignited a cloud of flammable gas produced during flow test involving most or all of its 33 Raptor engines. In the past, SpaceX has performed “spin prime” tests with Raptors installed on Starship prototypes, flowing high-pressure methane and oxygen gas through the engines’ turbines to get them up to operating speeds and pressures. This test ended differently.
When that apparent cloud of well-mixed methane and oxygen gas was accidentally ignited, it functioned like a small fuel-air bomb, rapidly combusting to produce a violent explosion and shockwave. After the initial explosion, the fire expanded to burn as much of the resulting gas as possible, producing a fireball some 80-90 meters (~260-300 ft) tall. CEO Elon Musk – apparently not directly participating in the test – initially stated that the fire observed was planned, implying that it was more or less nominal. Virtually everyone with any experience observing Starship testing felt otherwise, however.
To preserve the safety of the few local residents still living at Boca Chica Village, SpaceX is required to issue printed safety warnings well in advance of most Starship tests that could result in a shockwave capable of shatter glass and injuring locals. SpaceX has never intentionally performed such a test without distributing those warnings and did not distribute a warning before July 11th, all but guaranteeing that no ignition was planned. A few hours later, Musk deleted his original tweet and posted a different one, confirming that the explosion was “actually not good” and that SpaceX is “assessing the damage.”
For the most part, Booster 7 and the Starbase Orbital Launch Site (OLS) exceeded most viewers’ expectations of their sturdiness, exhibiting very little off-nominal behavior after being subjected to a unexpected explosion, shockwave, and fire. Immediately after the event, B7 appeared to safely depressurize its propellant tanks and appeared to leave its vents open, reducing the chances of the booster destroying itself if SpaceX were to lose control. SpaceX also appeared to intentionally avoid using the orbital launch mount’s (OLM) umbilical mechanism to remove propellant from the Super Heavy’s tanks, perhaps concerned that the shockwave might have weakened its connection to B7.
Starship SN4 demonstrates one possible outcome of attempting to use a leaky pad umbilical to detank.
About an hour after the explosion, Booster 7 appeared to dump most of the cryogenic liquid stored in its fuel (methane) tank out of a new vent located on its aft end, effectively producing a flood that spread around the adjacent pad. It’s unclear if that liquid was nitrogen or oxygen but either way, the emergency propellant dump appeared to cause a second fire about 100 feet (~30m) from the booster and launch mount. That fire proceeded to burn intermittently for the next two hours, all the while posing a clear and present danger to the rest of the pad and booster if it were to spread in the wrong direction or breach the wrong underground pipe. Instead, SpaceX got lucky and the fire eventually self-extinguished.
Something is on fire at the Starbase launch complex after today's engine testing: pic.twitter.com/8ZAHubHCL7
— Starship Gazer (@StarshipGazer) July 11, 2022
As of 8:30 pm CDT, Booster 7’s venting activity has dropped significantly, increasing the odds that it will survive the day, but its fate will remain uncertain until its tanks are completely emptied and SpaceX employees are seen approaching the pad. In a worst-case scenario, Super Heavy’s engine section and 33 Raptor engines could have been seriously damaged, while the subsequent pad fire(s) could have also significantly damaged crucial pad systems, requiring weeks of repairs. More optimistically, given that SpaceX appears to have gotten lucky enough to avoid a total loss of vehicle, Booster 7 may be fine after some inspections and minor repairs. The pad damage could also be limited to a single isolated, non-critical piece of equipment catching fire and burning to a crisp
Regardless, SpaceX will need to figure out what exactly caused the explosion and make absolutely sure that that failure mode does not occur again. In the meantime, the company recently finished stacking Super Heavy Booster 8, and Starship S24 – installed on a nearby suborbital test stand – is ready to begin its own static fire test campaign in the near future.
Keyword: SpaceX Starship booster test triggers explosion, pad fire