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SpaceX has been working on the design of a huge lift vehicle that they call the Starship. As it says on the SpaceX website, “SpaceX's Starship spacecraft and Super Heavy rocket (collectively referred to as Starship) represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the Moon, Mars and beyond. Starship will be the world's most powerful launch vehicle ever developed, with the ability to carry in excess of 100 metric tons to Earth orbit. Drawing on an extensive history of launch vehicle and engine development programs, SpaceX has been rapidly iterating on the design of Starship with orbital-flight targeted for 2020.
They developed four designs into full scale prototypes referred to as Mk1, SN1, SN3 and SN4. The Mk1, SN1 and SN3 have all failed cryogenic proof testing in which the Starship is filled with liquid nitrogen to verify that its tanks can withstand flight pressure. The SN2 prototype did pass cryogenic proof testing but it was not a full version of the design. It was only a partially assembled nitrogen tank. SN4 is being prepared for cryogenic proof testing next week.
It is very important for SpaceX that the cryogenic proof testing of SN4 be successful. When it is readied for an actual launch, this will be one of the first phases of launch preparation. The problems with Nk1and SN1 involved faulty welding. The SN3 failure was attributed to a test configuration mistake that resulted in a major pressure difference between the liquid oxygen and methane tanks. In the SN3 test, the liquid oxygen tank was crushed by the full methane tank.
The SpaceX teams are aiming to test the SN4 this evening. A proof test with nitrogen at ambient atmospheric temperature was successfully performed yesterday. These test schedules are very fluid and often subjected to delays. If the SN4 passes the cryogenic proof test, then engine testing will follow in a few days.
SpaceX currently has three Raptor engines that are ready to test. The engines are not installed in the Starship until after the cryogenic proof test has been carried out because those tests use hydraulic pistons to simulate the forces that the Raptors exert during actual flight. If SpaceX can install the Raptor engines they will need to be subjected to extensive tests. These will include testing of gimbals, ignitors and fuel pre-burners. Following this testing, SpaceX will ready to run static fire single engine tests or they may go directly to static fire testing with all three engines simultaneously.
SpaceX has had problems with static fire testing on their Starhopper vehicle. They may have to make a few attempts on with the Starship SN4 to get it right. It will be the first time that a Starship has actually been filled with cryogenic methane and liquid oxygen. It is likely there will be at least minor problems with the ground support equipment that will have to be solved ahead of the static fire test. If SpaceX can successfully make it all the way to static fire testing of all three Raptor engines, they may go on to test the Starship SN4 on actual short hops.
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