This weekend, SpaceX’s fourth Starship prototype (SN4) achieved a major milestone by passing the crucial cryogenic load test. This consisted of the prototype’s liquid oxygen and liquid methane tanks being filled with liquid nitrogen to see how they hold up when fully-pressurized. This test was vital since the three previous prototypes suffered structural failures and were lost during this exact same procedure.
In the first test, the prototype in question (Mk.1) experienced a blowout that sent its top bulkhead flying off, followed shortly thereafter by a blowout at the bottom. This was followed by the second prototype (SN1) exploding from the rear and flying off the pad, then falling down sideways and exploding out of the top. In the third test, the SN3 prototype suffered a leak, which was followed by its fuselage collapsing.
Musk took to Twitter to share the good news, posting a gif of the successful test with the caption, “SN4 passed cryo proof!” Responding to questions, he indicated that the test reached a maximum pressure of 4.9 bar (490 kPa). That works out to about 72 pounds per square inch, or about five times the normal atmospheric pressure at sea level. As Musk admitted, this was “[k]ind of a softball” test, but it is enough to proceed with flight testing.
As always, the cryogenic loading test took place shortly after the ambient temperature pressure test, which took place on Sunday morning and went off without a hitch. This puts the Starship one step closer to orbital testing, which will validate the spacecraft for commercial launches to orbit, the Moon, and even Mars.
The next step will consist of the prototype receiving a Raptor engine (which is to be installed this week) and then conduct a static fire test to make sure it is working properly. After that, SpaceX intends to conduct the first “hop test” of the full-scale Starship prototype, which will see it flown to an altitude of 150 meters (492 feet) before touching down again.
This mirrors what was achieved using the Starship Hopper, the single-engine test vehicle that completed tethered and untethered tests by January of 2019. Originally, Musk was hoping to conduct a flight-test using the Mk.1 that would involve three Raptor engines and flying the prototype to an altitude of 20 km (~12.5 mi).
According to Musk, this is what will take place with the next prototype (SN5), development of which is currently underway already at their Boca Chica testing site in Texas. In addition, each new prototype incorporates new design elements, as the telescoping landing legs on the SN3 demonstrated. So it stands to reason that the SN5 will incorporate some changes or additional features.
Ever the one for cheek, Musk also posted a video taken from underneath the prototype’s fuselage (shown above) with the caption “Snowing in Texas.” The effect was caused by the liquid nitrogen being released from the fuselage (to control the level of pressure within) which then forms ice particles and falls to the ground like snow.
In the meantime, Musk indicated that everything for the hop test will be “[p]hysically ready in a few weeks,” but that Federal Aviation Administration (FAA) approval “may take longer.” If all goes well, orbital flight tests using the SN5 prototype could be taking place this summer, one year after the Starship Hopper finished testing.
As always, delays happen, but the developmental milestones speak for themselves! And while Musk has always been optimistic with his timelines, there is still plenty of time to get the Starship and Super Heavy prepared to make cargo and crew missions to space and to the Moon before this decade is out!