Top Image Credit: LabPadre w/ Maria Pointer
SpaceX just cannot catch a break! Last night, during the same cryogenic proof test that killed the previous two prototypes, SpaceX’s SN3 prototype experienced a structural failure. On-site video footage provided by famed NASASpaceFlight member BocaChicaGal shows the SN3 experiencing what appears to be a leak, followed by the fuselage collapsing.
The cryogenic proof test consists of the vehicle’s fuel tanks being filled to capacity with nitrogen (and sometimes oxygen) that is cooled to cryogenic temperatures. This test is carried out after an ambient pressure test, where the vehicle is filled with gas at room temperature to see if it can handle the kinds of pressure conditions it will experience during flight.
The test began late on Thursday (April 2nd) and continued into the morning until the SN3 suffered a rupture during what appeared to be the end of the test. This comes a little over a month after the second prototype (SN1) exploded on the Boca Chica facility’s launch pad on the evening of Feb. 28th, 2020, during a similar cryogenic proof test.
During that test, the liquid oxygen tanks blew out the bulkhead, which sent the vehicle’s fuselage to collapse inward and jump several meters into the air. The wrecked prototype then fell to the landing pad on its side, followed shortly thereafter by the methane tanks exploding out of the top bulkhead and flying 150 to 300 meters (500 – 1000 ft) from the pad.
The previous failure (also experienced during the cryogenic proof test) happened on November 20th, 2019. At this time, the Mk. 1 prototype suffered a failure that caused its top bulkhead to explode (and the nose cone to be hurled beyond the facility) followed by a secondary explosion from the bottom bulkhead.
In response to both incidents, Musk responded by saying that these types of failures are expected during load tests and would provide information vital to the construction of future prototypes. In fact, the design of the SN3 (Serial incorporated lessons learned from these two previous vehicles and took advantage of improved manufacturing techniques, where each ring consisted of a single welded piece of steel.
Another notable feature on the SN3 was the new, internally mounted deployable leg design, which was visible in photos shared by Musk via Twitter on March 30th. These legs were included to accommodate the short hop test flights that the SN3 would have conducted. Musk noted at the time that the legs would be longer with the SN4 and subsequent prototypes since they would be making higher flights.
Responding to this latest setback, Musks tweeted, “We will see what data review says in the morning, but this may have been a test configuration mistake.” This was posted to his official Twitter account in the early morning hours of April. 3rd. About ten hours prior, he related how the SN3 passed its ambient temperature pressure test the night before and that they were proceeding to the cryogenic test.
Four hours after that, he tweeted, “Some valves leaked at cryo temp. Fixing & will retest soon.” These tests took place just a week after the SN3 underwent final assembly and was delivered to the test facility in Boca Chica, events that were shared by Musk and LabPadre via Twitter. LabPadre was also on hand to witness the rupture experienced by SN3 and captured it on video (shown below).
At the time, it was clear that Musk intended to move ahead with testing as quickly as possible. Had things gone as planned and the SN3 passed the cryogenic proof test, Musk and his teams of engineers at Boca Chica would have proceeded with a static fire test, followed by a hop test that would see the prototype fly to an altitude of 150 m (500 ft), the same height achieved by the Starship Hopper.
These were originally scheduled to take place between April 1st and April 3rd (static fire test) and April 6 to April 8 for the flight test. However, those timelines were contingent on the successful completion of the cryogenic proof test. As he did after the previous failures, Musk has stated that rather than attempt to salvage the wrecked prototype, his company will be proceeding with the construction of the next vehicle (SN4).
This prototype has already begun construction at Boca Chica and was visible during the ambient temperature pressure test on Thursday, April 2nd. It is unclear right now when it will be assembled and put through its paces, but it seems likely at this point that the 150-m flight tests SpaceX hoped to make with SN3 will now be performed by SN4.
Of course, we should remind ourselves that test likes these happen for a reason. In short, they ensure that failure does not take place during a crucial point – like a crewed mission! In the meantime, onwards and upwards for the Starship and SpaceX!
Further Reading: NASA SpaceFlight