In the high‑stakes space race between the United States and China, the decisive advantage could come down to a metal cap that few outside the industry have ever heard of: the propellant tank dome.An ellipsoidal bulkhead several metres wide but only millimetres thick, the dome must withstand extreme internal pressures, vibration and shock. The rounded, capsule-like end cap is also very difficult to mass-produce.Whichever country can make these components faster, cheaper and more reliably will...