Abstract: In general terms the present invention proposes a 3D printing apparatus 100 for printing a satellite component. The 3D printing apparatus comprises a housing 102, a seal 104 arranged movably inside the housing such that the seal partitions the housing into first and second chambers 106A, 106B that are fluidically isolated from each other, and a nozzle 108 in fluid connection with the second chamber 106B. The first chamber 106A comprises a gas having a pressure P1 and the second chamber 106B comprises a printing material. When the 3D printing apparatus 100 is exposed to an external environment having a pressure P2 being less than the pressure P1 of the gas in the first chamber 106A, the gas in the first chamber 106A exerts a force on the seal 104 which in turn exerts a force on the printing material thereby extruding the printing material out of the second chamber 106B through the nozzle 108 to print the satellite component.