SpaceX’s third full-scale Starship prototype has followed a little too closely in the footsteps of its predecessors, suffering a catastrophic failure during its first cryogenic test.
On April 2nd, SpaceX successfully put Starship SN3 through an ambient temperature pressure, allowing the ship to take its first breaths and ensuring that no leaks were present in its massive propellant tanks. Just a handful of hours later, Starship SN3 began its first attempted cryogenic proof test. Neutral liquid nitrogen was loaded into the ship’s liquid oxygen (LOX) tank for a brief period before SpaceX aborted the test due to frozen valves in the ground support equipment (GSE) tasked with feeding the rocket — confirmed by CEO Elon Musk around 7:30 pm PDT.
Around six hours after the first attempt, SpaceX presumably managed to alleviate GSE valve issues and began Starship SN3’s second attempted cryogenic proof test around 11pm local (04:00 UTC). While things started out somewhat normally, they did not end well for the rocket prototype.
For unknown reasons, SpaceX began the second cryo test attempt by only loading Starship’s upper (LOX) tank with supercool liquid nitrogen. Given that Starship is constructed out of stainless steel sheets only slightly thicker than two US quarters, the lower (methane) tank would have almost certainly had to be pressurized, too, likely relying on gaseous (ambient temperature) nitrogen. Already, for a rocket built out of near-continuous metal, that temperature differential could pose a major problem.
Still, for the better part of three hours, things seemed to go exactly as planned, with the rocket venting dozens of times and the upper tank visibly developing a coating of frost as it began to freeze the water vapor right out of the humid Texas air. Alas, around 2:07am local (07:07 UTC), things took a turn for the worse. The unfilled methane tank below the now-LN2-laden LOX tank appeared to crumple, beginning at a small dent that appeared over the course of the test. Gravity took over a few seconds later, further crumpling the methane tank and causing the top-heavy rocket to tip over and the LOX tank to burst.
While admittedly from the armchair, not a lot of this particular failure makes sense. If the bottom methane tank were significantly pressurized with gaseous nitrogen, a rapid loss of structural integrity would have likely been a far more violent ordeal as the gas attempted to escape. Instead, the failure was – relative to the possibilities – extremely gradual. In fact, it almost appeared as if the bottom methane tank was either never actually pressurized or not pressurized nearly enough to withstand the weight of several hundred tons of liquid nitrogen. Given SpaceX’s expertise and familiarity with rocketry, that option thankfully seems vanishingly unlikely.
All other possible explanations are at least as hard to parse, leaving it up to SpaceX or CEO Elon Musk to clarify what transpired if they choose to do so.
On a more positive note, SpaceX has continued to churn out steel rings and bulkheads and assemble them into sections of Starship SN4 – the rocket’s next full-scale prototype – for the last two or so weeks. If Starship SN1, SN2, and SN3 are anything to go by, the fourth full-scale Starship prototype could be ready to head to the pad for testing just a handful of weeks from now, picking up where Starship SN3 left off. Thankfully, the latter rocket’s April 3rd failure appears to have been relatively benign as far as pad hardware goes, likely requiring minimal repair work to be ready for its next test campaign.
While unfortunate, it’s critical to remember that this is all part of SpaceX’s approach to developing new and unprecedented technologies. Be it Falcon 1, Falcon 9 booster recovery, or Falcon 9 fairing recovery, all groundbreaking SpaceX efforts have begun with several consecutive failures before the first successes – and the first streaks of consecutive successes. Given Musk’s September 2019 claim that SpaceX is putting just ~5% of its resources into Starship, prototypes like Mk1, SN1, and SN3 are being fabricated for pennies on the dollar.
As a schedule setback, SpaceX is building ships so quickly that any single prototype failure shouldn’t cause more than a handful of weeks of delays, and the goal is to produce an entire Starship every week by the end of 2020. For now, SpaceX will hopefully learn from each failure during developmental testing and roll those lessons learned into each future prototype.
