The main idea behind WISA Woodsat is to test how plywood behaves not only in space, but also when building a satellite.
In general, the materials used in spacecraft have to be lightweight, impact resistant, electrically conductive, non-magnetic and they have to heat up and cool down easily.
Most of the materials are compromises with some better properties and some less desired ones. Plywood is not an exception.
What is wood?
Wood consists of wood fibres, vessels and parenchyma ("filler" tissue). Fibres are the main component, accounting in birch wood on average for 65 % of mass. The high content and density of wood fibres make the birch wood a strong and lightweight material.
The main chemical components of wood are natural biopolymers (cellulose, polysaccharides and lignin), proteins and starch. These are mostly composed of carbon (50% by weight) and oxygen (42% ) with some hydrogen, nitrogen and other elements like calcium, potassium, sodium, magnesium, iron, and manganese).
Cellulose is a crystalline polymer derived simply from glucose. The polysaccharides are sugars. And lignin is a natural polymer consisting of very large repeating molecules related to synthetic plastics.
While raw wood is not suitable for the primary structures of the satellites, plywood is totally different. Plywood supports temperature changes well and is lightweight and strong. It not only resists chocks but also damp vibrations.
Just like the carbon fibre materials are made by layering and laminating carbon sheets, the plywood used in WISA Woodsat is made from laminations of birch veneer. It is the strongest and dimensionally most stable plywood suitable for many special uses from skateboards to aircraft.
UPM Plywood’s Sami Uuksulainen explains in this video how plywood is made and where it is used.
The wood materials like plywood are very hydrophilic. This was the biggest concern with the space use of the wood, but as in space there is no water, the problem exists only here on Earth while manufacturing the parts. The plywood panels are therefore extensively dried in heat and vacuum and kept in vacuum packing always when not being machined.
Finally they are protected by ALD or lacquer.
In space the biggest concerns of using wood are the electric and thermal conductivity. A thin layer of aluminium oxide helps with the electric conductivity and thermal conductivity issue is (hopefully) solved by using quite thick panels.
The plywood used in WISA Woodsat is basically the same UPM WISA-birch plywood that everyone can buy at the stores. UPM Plywood’s R & D laboratory manager Minna Lindroos shows on this video how and why the quality is constantly monitored.