SpaceX has destroyed Starship’s third ‘test tank’ prototype since it began building and testing the robust steel structures earlier this year.
Just like the third test tank SpaceX built was designed with on-the-job hardware originally intended to become the prototype for Starship SN2 on a large scale, the last tank was built with parts that could initially have been designed for Starship SN7. While SN7’s purpose, to test new designs and manufacturing techniques, was largely identical to its predecessors, the test tank was by far the most radical departure from previous hardware. The reason: SN7 was built entirely from a different stainless steel alloy.
Considered 304L, the steel type is still available on the shelf and only 10-20% more expensive than the 301 alloy that SpaceX has used to build all of the Starship prototypes up to SN7. The biggest change it brings to the table is improved ductility (malleability), particularly at cryogenic temperatures where Starship tanks will often stay. By reducing brittleness, 304L steel-built spaceships should be able to fail much more gracefully in developing stable leaks rather than violently unzipping. In fact, the same test tank destroyed on June 23 demonstrated that ability perfectly when it leaked during its first pressure test on June 15.
During his first liquid nitrogen cryogenic pressure test, SpaceX CEO Elon Musk revealed that the SN7 test tank managed to reach 7.6 bar (~ 110 psi) before it started to leak, technically satisfactory for Starship orbital launches with 25% industry standard security. factor. Thanks to the overall flexibility of the steel, including the new 304L alloy the SN7 was built with, SpaceX was able to simply repair the leak it identified, preparing the test tank for a second cryogenic pressure test just a week later.
The second test of the tank was almost identical to the first until the end, where its lower dome seemed to more or less unzip from the steel ring it was welded to. It remains to be seen if SN7 was able to beat its previous record during the second test, but the failure mode was quite different from that of any previous test tank, meaning that SpaceX has collected new useful data anyway. If the 304L steel tank matches or exceeds the current record for a ~ 8.5 bar (~ 125 psi) 301 tank, SpaceX will most likely build all future Starship tanks from the material.
According to Musk, another 304L test tank is already in the works and should be able to take SN7’s place shortly. At the same time, SpaceX appears to be finally ready to launch the next large-scale spacecraft prototype (SN5) to the launch pad on June 24 to start cryogenic testing, Raptor static fires, and (hopefully) flight tests.
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