The Gas Hollow Tungsten Arc (GHTA) welding experiments on aluminum pipe were carried out in a simulated space environment using an aircraft. A vacuum chamber and welding machine for GHTA welding test were placed in the cabin of aircraft and the 10-2 G gravity environment was produced by a parabolic flight of the aircraft. The square butt welding joints with non root gap on aluminum pipe were made by orbital welding in the vacuum chamber without wire filler metal using DC or DC-pulsed power supply under the 10-2 G and 1 G gravity conditions. The welding phenomenon during the aluminum GHTA welding recorded in the high-speed video image was analyzed and also the macrostructure and mechanical properties of butt weld joints were investigated. The welding experiments under simulated space environment showed that the DC-pulsed GHTA process could make the welding joints without the weld defects such as a lack of fusion, oxide film inclusion and spattering, though throat thickness decreased by the impulsive arc pressure of pulsed current. It was also clarified that the arc discharge phenomenon and melting characteristic at the molten pool surface during the DC-pulsed GHTA welding were insensitive to the gravity condition. However, the sagging weld metal made at 1 G gravity condition increases a little than that welded under the 10-2 G gravity condition.
