Before dawn on January 10th, SpaceX technicians and engineers intentionally blew up a miniature Starship tank in order to test recently-upgraded manufacturing and assembly methods, likely to be used to build the first Starships bound for flight tests and orbit.
SpaceX CEO Elon Musk quickly weighed in on Twitter later the same day, revealing some crucial details about the Starship tank test and effectively confirming that it was a success. While somewhat unintuitive, this is the second time SpaceX has intentionally destroyed largely completed Starship hardware in order to determine the limits of the company’s current methods of production and assembly.
Most notably, on November 20th, SpaceX is believed to have intentionally overpressurized the Starship Mk1 prototype in a very similar – albeit larger-scale – test, destroying the vehicle and sending its top tank dome flying hundreds of feet into the air. It’s generally believed that SpaceX (or perhaps even just Musk) decided that Starship Mk1 was not fit to fly, leading the company to switch gears and deem the prototype a “manufacturing pathfinder” rather than the first Starship to fly – which Musk had explicitly stated just a few months prior.
Dome to barrel weld made it to 7.1 bar, which is pretty good as ~6 bar is needed for orbital flight. With more precise parts & better welding conditions, we should reach ~8.5 bar, which is the 1.4 factor of safety needed for crewed flight.— Buff Mage (@elonmusk) January 10, 2020
Instead, Starship Mk1 suffered irreparable damage during its pressurization test and was rapidly scrapped in the weeks following, although several segments were thankfully salvaged – perhaps for use on future prototypes. Along those lines, it can arguably be said that the results from the mini Starship tank’s Jan. 10 pop test have paved the way for SpaceX to build the first truly flightworthy Starship prototypes – potentially all the way up to the first spaceworthy vehicles.
Hours after the test, Musk revealed that the Starship test tank failed almost exactly where and how SpaceX expected it would, bursting when the weld joining the upper dome and tank wall failed. Critically, the tank reached a maximum sustained pressure of 7.1 bar (103 psi), some 18% over the operating pressure (6 bar/87 psi) Musk says Starship prototypes will need to be declared fully capable of orbital test flights. In other words, given the tank’s size, it survived an incredible ~20,000 metric tons (45 million lbf) of force spread out over its surface area, equivalent to about 20% the weight of an entire US Navy aircraft carrier.
Musk also revealed that SpaceX will require Starships to survive a minimum of 140% of that operating pressure before the company will allow the spacecraft to launch humans.
Some have less than generously taken to smugly noting that several modern spaceflight and engineering standards require that launch vehicle tankage be rated to survive no less than 125% of their operating pressure, while this test tank would be rated for less than 118% under identical conditions. However, this ignores several significant points of interest. First and foremost, the Starship test tank intentionally destroyed on January 10th was assembled from almost nothing – going from first weld to a completed pressurization test – in less than three weeks (20 days).
Second, all visible welding and assembly work was performed outside in the South Texas elements with only a minor degree of protection from the coastal winds and environment. Although some obvious tweaks were made to the specific methods used to assembly the prototype tank, it also appears that most of the welding was done by hand. For the most part, in other words, the methods used to build this improved test article were largely unchanged compared to Starship Mk1, which is believed to have failed around 3-5 bar (40-75 psi).
Additionally, it appears that almost all aspects of this test tank have smaller structural margins, meaning that the tank walls and domes are likely using steel stock that is substantially thinner than what was used on Starship Mk1. Nevertheless, thanks to the addition of continuous (single-weld) steel rings, a tweaked dome layout, and slightly refined welding, this test tank has performed anywhere from 20% to 200+% better than Starship Mk1 – again, all while coming together from scratch in a period of less than three weeks.
As Musk notes, with relatively minor improvements to welding conditions and the manufacturing precision of Starship rings and domes, SpaceX can likely ensure that Starships (and thus Super Heavy boosters) will be able to survive pressures greater than 8.5 bar (125 psi), thus guaranteeing a safety margin of at least 40%. Even a minor improvement of ~6% would give vehicles a safety margin of 125%, enough – in the eyes of engineering standards committees – to reasonably certify Starships for orbital test flights.
All things considered, it’s safe to assume that SpaceX is going to begin building and assembling Starship SN01 (formerly Mk3) hardware almost immediately. Given that this test tank took just 20 days to assemble, it’s safe to say that the upgraded prototype’s tank section could be completed in just a handful of weeks. Stay tuned for progress reports.
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