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Space travel is undoubtedly the biggest adventure in the history of mankind. Satellites, space flights and space stations head ever deeper into the endless expanse of the universe – all the while braving conditions that are unlike anything found on Earth.
Right from the beginning of their journey, spacecraft and satellites are subject to enormous strain. The initial acceleration can reach up to 4G, meaning that each part must withstand four times its own weight. The vibrations of the engines are also transmitted to the entire structure, which can cause damage. Once outside the Earth’s atmosphere, spacecraft enter a vacuum in which no air or pressure is present. Temperatures cannot be measured using conventional methods, but they can fluctuate by up to several hundred °C.
In addition, there is always a risk of collision with other objects. Meteorites and an increasing amount of space debris from destroyed or discarded satellites and exploded rocket stages can all be found in the Earth’s orbit. These objects travel at such high speeds that even a collision with the smallest pieces can have serious consequences.
All of these challenges are the reason that organisations such as NASA and ESA, or private space travel companies such as SpaceX, have extremely high manufacturing quality requirements. This applies in particular to welding technology, which has a decisive role to play in space travel.
Special materials for special welding challenges
One thing is clear: only very special materials can be used for the difficult journey into space. Materials such as titanium, stainless steel, ceramics, and above all, aluminium and its alloys, have proved to be particularly suitable. Just as in lightweight automotive construction, aluminium impresses with its low weight, high specific strength, corrosion resistance and low thermal expansion coefficient. However, welding of this material is more difficult than welding conventional materials such as steels, most notably because of aluminium’s low melting point and its significantly higher thermal conductivity.
The right welding process for space travel
For a long time, tungsten inert gas (TIG)/gas metal arc welding (GMAW) was the only welding process that could reliably meet the high demands of space travel. It is still successfully used in countless applications today. The TIG welding process creates particularly smooth, level, and non-porous weld seams that can withstand dynamic forces, making it a particularly good choice for root passes – and the process offers many other weld quality advantages.
Other specialised welding processes are now being used for an increasing number of tasks in space travel. Plasma and friction stir welding are particularly widespread and both are well-suited to creating aluminium joints with high weld-seam quality, which is the basic requirement for structurally stable spacecraft.
Welding can even be done in space now, and this is made possible by portable laser welding torches that do not need a protective gas shield or a vacuum. This is particularly important when working inside spacecraft. However, the compact devices are only used for urgent repairs that are absolutely necessary.
Finally, back on Earth, ever simpler and more reliable welding results of excellent quality can continue to be achieved.
This article is the first in Fronius’ new series: Ultimate Welding Challenges, which takes a look at welding in extreme and unusual conditions.