Image Source: Elon Musk
The Chief Engineer and founder of SpaceX, Elon Musk, shared a photograph today of a stainless-steel Starship propellant dome tank that they have been manufacturing and testing at the South Texas SpaceX facility located in Boca Chica Beach, Brownsville, Texas. Since the last week of December, teams have been working quick to build the crafts inner structure, they are currently working on the assembly first flight version design of Starship called SN1. First they are manufacturing parts to test them before incorporating them to the final flight-ready prototype of the craft. Last week on January 21, Musk shared that SpaceX teams and suppliers are rapidly building Starship, he said:
"Yeah, we just finished two more propellant domes. SpaceX team & supporting suppliers are doing amazing work ramping Starship production."
Yeah, we just finished two more propellant domes. SpaceX team & supporting suppliers are doing amazing work ramping Starship production.— Elon Musk (@elonmusk) January 22, 2020
Starship will be powered by cryogenic methane and liquid oxygen, the tank domes are part of craft's internal structure where it holds propellant. The tanks should be strong enough to hold highly pressurized propellant, also make the craft strong enough to endure extreme forces during flight. This month, on January 10, SpaceX conducted a test on a dome tank, during the test they intentionally pressurized the bulk head dome until it exploded. The test was preformed to ensure the assembly of all the dome tank welds and design structure were strong enough for Starship SN1 flight design. Musk shared some details about the test results that day, "Dome to barrel weld made it to 7.1 bar, which is pretty good as ~6 bar is needed for orbital flight. With more precise parts & better welding conditions, we should reach ~8.5 bar, which is the 1.4 factor of safety needed for crewed flight."
Starship 9m test tank made 7.5 bar at room temp! Small leak at a weld doubler. Will be repaired & retested at cryo. pic.twitter.com/Bz3lrwkYRU— Elon Musk (@elonmusk) January 27, 2020
"Starship 9m test tank made 7.5 bar at room temp! Small leak at a weld doubler. Will be repaired & retested at cryo."
They will improve the welding to ensure there is no leaks during next test that will now involve testing with highly pressurized cryogenic (cold) propellants and see how much the structure can endure. He added that with cold temperatures the material strength doubles, but that the "weld strength is the only real question mark." So, the next test aims to determine if the welding technique on the dome structure will endure.
Parent material strength roughly doubles, so weld strength is the only real question mark— Elon Musk (@elonmusk) January 28, 2020
Musk previously explained that "A given tank pressure is needed to feed the engine turbopumps & pressure-stabilize/relieve compression load on the cylinder walls. Everything is compressible, but liquid compression at these pressures is not significant. However, the tanks do expand under pressure, creating a bit more volume. Keeping propellant super cold has a big effect on density of ~10% in case of CH4 (methane)."