Welding in Space

Welding in space is characterized by unusually complex conditions. It is performed in vacuums as high as 10^-10 newton/m² (10^-12 mm Hg) under zero-gravity conditions, features a high rate of gas diffusion, and exhibits a temperature range from - 150° to + 130 °C. Because of the high vacuum and relatively high temperatures, a spontaneous diffusion welding of parts pressed tightly together sometimes occurs. In order to prevent this, various features are provided in the design of spacecraft.

Welding in space can be used to assemble large spacecraft and orbital stations, repair spacecraft equipment, and produce materials and articles with special properties that cannot be obtained on earth. Metals that can be welded under space conditions include aluminum, titanium alloys, and stainless and heat-resistant steels. Conditions in space are extremely favorable for various types of welding, including diffusion, cold, electron-beam, resistance, and solar welding. Although arc welding and plasma-arc welding show some promise, they have encountered a number of technical difficuties because of zero-gravity conditions, particularly when the work involves large weld pools. Weightlessness changes the conditions for the separation of liquid, solid, and gaseous phases, thus causing porosity in the welds and an increase of nonmetallic inclusions.

In a number of cases, the temperature gradient is sufficient to cause cracks. In order to overcome the unfavorable effects of the space environment, it is necessary to develop special welding techniques and special equipment. Such equipment must be very reliable and safe, must have low weight and power consumption, and must be simple to operate. Automatic and semiautomatic welding equipment is particularly suitable.

Welding in space was first accomplished on Oct. 16, 1969, aboard the spacecraft Soyuz 6. Cosmonauts V. N. Kubasov and G. S. Shonin used the Vulkan automatic welding equipment build at the E. O. Paton Institute of Electric Welding.