Starship SN4 passed ambient pressure test, SpaceX aims to conduct a cryogenic test tonight

by Evelyn Arevalo April 26, 2020

Starship SN4 passed ambient pressure test, SpaceX aims to conduct a cryogenic test tonight

Featured Image Source: @SpacePadreIsle via Twitter

SpaceX is in the initial phase of developing a Starship that will one day transport one hundred passengers to the moon and Mars. The rocket company’s grand vision is building a fleet of 1,000 Starships to send all towards the Red Planet with tons of cargo, over the course of 10 orbital synchronizations with Earth –that is a period of about 20 years to build a sustainable city on Mars by the year 2050. The founder and Chief Engineer at SpaceX, Elon Musk stated:

“A thousand ships will be needed to create a sustainable Mars city. As the planets align only once every two years. So, it will take about 20 years to transfer a million tons to Mars Base Alpha, which is hopefully enough to make it sustainable.”

Mars Base Alpha / SpaceX

Last night, SpaceX South Texas conducted an ambient pressure test of the Starship SN4 vehicle, which is the fourth prototype the company has built to test at Boca Chica Beach, TX this year. The test vehicles are made of stainless-steel; pressure testing is required to ensure the structure meets standards required for flight. Musk wrote via Twitter:

“SN4 passed ambient pressure test. Aiming for cryo [cryogenic] pressure test tonight.”

Starship SN4 is at the launch pad awaiting the next pressure test, which will be conducted with cryogenic (sub-cooled) liquid nitrogen. During cryogenic pressurization, SN4’s tank will be filled up with sub-cooled liquid nitrogen, to determine if the stainless-steel structure can withstand high pressure. The test also serves to determine the weld quality strength ahead of flight. 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.



Previous Starship prototypes did not survive the cryogenic pressure test. 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. Musk says he expects to build at least 20 Starship test vehicles this year. 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. After the test, Musk said some valves and configuration caused the issue.

Tonight, we could witness Starship SN4’s cryogenic pressure test. Local Boca Chica residents have set up cameras to live-stream the event. You can watch the live-stream 24/7 in the video below. According to the city’s announced road closures, the test could happen sometime today, April 26, between 9:00 p.m. to 6:00 a.m. Central Time (local time), with a back-up date scheduled tomorrow at the same time.



If the pressure test goes well, SN4 could be the first fully-assembled cylinder structure to take flight. The first flight would be a low-altitude test of about 150-meters. When asked when the test flight would be if tonight’s test is a success, Musk said this morning Starship will be “Physically ready in a few weeks,” but flight “Approvals may take longer.”



Musk shared he foresees the next Starship test vehicle, SN5, as more than just a steel cylinder structure, SN5 will feature a nose cone –"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.” So, the next Starship test vehicles will feature aerodynamic flaps and fins to test out in South Texas.



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