This was the second cryogenic pressure test to failure with the SN7 test tank, the previous of which took place about a week ago (June 15th, 2020). The purpose was to test a new type of stainless steel (Steel 304L) and a new manufacturing technique SpaceX has been trying out. By testing this steel to failure with their test tank, they intend to find out if it is a better fit for the final Starship design than the 300 series they’ve been using until now.
Much like the test that happened on June 15th, the second pressure test took place in the morning after ambient testing was completed the night before. After popping a leak in the upper dome, the tank exploded, releasing liquid nitrogen and ice particles also across the facility. The test tank was then repaired and resealed so it could undergo a second round of ambient and pressure testing last night and this morning.
This latest test was captured by the many live streams that monitor the Boca Chica testing facility twenty-four hours a day, which includes NASA Spaceflight’s own Mary Pointer (aka. @BocaChicaGal). The live stream event also featured a panel NASA Spaceflight members, including Chris Bergin (@Chris B), Jack Beyer (@thejackbeyer), Das Valdez (@KSpaceAcademy), and Michael Baylor (@nextspaceflight).
Things began in earnest about an hour later with the test tank releasing liquid nitrogen from its top, which slowly intensified. Almost three hours and after live coverage began (2h53m24s), the panel noticed an unusual amount of liquid nitrogen venting from the test tank following by nitrogen ice falling off the tank walls. Speculation began that the tank had sprung a leak, as with the previous test.At 11:37 am, almost three hours after the live stream event began (2h59m21s), Mary can be heard saying “and there it goes!” The tank burst from the bottom, hopped about ten meters (33 ft) into the air, and then collapsed on its side. The entire facility was covered in heavy clouds of icy nitrogen particles, which began cascading outwards from the site.
Chris tweeted news of the explosion shortly thereafter via NASA Spaceflight’s official Twitter feed, showing a fourteen-second clip of the explosion with the caption: “RIP SN7 Test Tank. Thanks for the data!” A little while later, the panel confirmed that the test tank had traveled vertically as a result of the explosion, prompting the cheeky observation: “10 meter hop. Hopper: Nice try, Junior!”
This, of course, is a reference to the Starship Hopper (aka. Starhopper) vehicle, which completed hop testing last summer. These tests, where a single Raptor engine was integrated into a scaled-down prototype, concluded with the Starhopper successfully flying to an altitude of 150 m (500 ft), moving laterally, and then making a soft landing on another pad.
Like the repeated tests using SN hull prototypes, the purpose here is to test the technology and manufacturing methods that will go into the creation of the Starship and Super Heavy launch system. This rapid-prototyping iterative approach allows SpaceX to rigorously check all the different elements of the flight system before flight tests beings.
Once they are confident that an SN can pass muster, SpaceX hopes to conduct a 150 m (500 ft) hop testing with a single-engine prototype. Once that is complete, the company will proceed with a 20 km (12 mi) hop test – as well as a supersonic reentry and controlled landing – using a three-engine prototype.
Alongside the development of the Super Heavy booster, this will be the last step before a full-scale orbital flight using six Raptor engines takes place, followed by the finalizing of the Starship‘s design and the start of commercial production.
Further Reading: Twitter