Elon Musk shares Starship SN4 passed the cryogenic pressure test

by Evelyn Arevalo April 27, 2020

Elon Musk shares Starship SN4 passed the cryogenic pressure test

Featured Image Source: Elon Musk / SpaceX logo

SpaceX is in the process of developing its next-generation spacecraft-rocket duo, Starship. Designed to carry out long-duration missions to Mars with one hundred passengers aboard. Starship’s first crewed flight is already booked by a fashion entrepreneur, Yusaku Maezawa, who dreams of going to the moon. He is partially funding the spacecraft’s development. His circumlunar voyage is scheduled for 2023. That is about three years from today, SpaceX is working on a tight schedule to accomplish that ambitious timeline. Starship prototypes are actively under construction in South Texas. SpaceX is building a production line of Starships to test-out in the assembly facility at Boca Chica Beach. This week, the fourth prototype manufactured this year, known as Starship SN4, underwent a series of pressurization tests. Conducted to determine if the stainless-steel test vehicle can withstand highly pressurized propellant and high-stress conditions it would experience during flight.



On April 25, Starship SN4 passed an ambient pressure test. Last night, April 26, SpaceX teams at Boca Chica conducted a cryogenic pressure test. During the test, SN4 was filled with sub-cooled liquid nitrogen to determine if the stainless-steel structure can withstand high pressure. The test also serves to test out weld quality strength. Previous Starship test vehicles collapsed during cryogenic pressurization tests. In November 2019, SpaceX’s first fully-assembled Starship test vehicle was destroyed during testing. The company then started building another series of prototypes to speed up the craft’s development. This series will consist of building many Starships, each featuring minor changes to test-out. On February 28, Starship SN1, the first prototype built this year, exploded during a cryogenic pressure test. Nine days later, a scaled-down prototype SN2, passed the test. The company proceeded to manufacture a full-scale Starship SN3. Early April, SpaceX's Starship SN3 vehicle collapsed during a cryogenic pressure test too, due to configuration issues.

The founder and Chief Engineer at SpaceX, Elon Musk, shared Starship SN4 passed the cryogenic pressure test at SpaceX Boca Chica, "SN4 passed cryo proof!" It is the first time a large-scale prototype withstands high pressure. Musk previously said Starship needs to withstand a pressure in between ~6 and ~8.5 bar strength; A ~6 bar is needed for orbital flight and ~8.5 bar is needed for crewed flights. During last night’s pressure test, Musk shared the structure was pressurized to 4.9 bar, “4.9 bar. Kind of a softball tbh [to be honest], but that’s enough to fly!”



After many destructive pressurization tests, last night’s achievement takes the company closer to conducting the first test flight this year. Musk shared his excitement by praising his team:

“Great work by SpaceX engineering!”

Starship SN4 will conduct a low altitude test flight of 150-meters, with a single Raptor engine. Musk said the engine will undergo a static fire test soon. “Static fire with Raptor hopefully later this week," he said.



A static-fire test, is a pre-flight preparation in which the Raptor will be ignited for a few seconds, while the craft is grounded with hold-on clamps to the launch pad. It will be the first time SpaceX attempts to fly a gigantic (almost full-scale) Starship prototype.  The company has only flown a scaled-down prototype called Starhopper. Last year, Starhopper conducted a 150-meter test flight with the power of a single Raptor engine, and engineers successfully landed the craft (video below). Now, SpaceX will try to replicate the flight with the much larger Starship SN4 cylinder structure.


As Starship SN4 is undergoing preparations to conduct a debut flight, SpaceX is working on the next Starship prototype, SN5, which Musk said will feature 3 Raptor engines and a nose cone section. Future prototypes of Starship will feature aerodynamic flaps and fins to test out. "Definitely header tanks & nose cone on SN5, hopefully flaps too," he wrote, “SN4 won't get flaps, so can only do flights with engine on. Just did a reset this week on flap, actuator & static aero design. Either SN5 or SN6 will get flaps.”

The operational version of Starship will feature 6 Raptor engines - 3 designed for atmospheric flight and 3 vacuum optimized engines for space. It will require a massive rocket booster to take it out of Earth’s atmosphere, known as Super Heavy. The rocket will feature 37 Raptor engines, SpaceX says it will be “the world's most powerful launch vehicle ever developed, with the ability to carry in excess of 100 metric tonnes to Earth orbit.” 


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