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Here in Ars we were a bit surprised to find a BBC headline stating that a university-industry partnership in Japan was working on the development of wooden satellites. The plan is less crazy than it sounds: wood is an extraordinary material that is largely unappreciated due to its ubiquity. But most of the reasons for switching to lumber yield to the plan’s coverage.
To the extent that there is a plan, at least. According to the BBC and other coverage, the partnership is between Kyoto University and a company called Sumitomo Forestry. But neither the university nor the company have information about the project available on the English versions of their websites. The BBC article gets all of its quotes from Takao Doi, who is currently a professor at Kyoto University. According to Doi, the collaboration is on track to make wooden satellite flight models by 2023.
While wood may seem like a horrible fit for the harsh environment of space, the idea may seem less crazy if you think of wood in terms of its structural composition: a blend of two robust polymers, cellulose and lignin. The strength and durability of wood largely depends on the proportion of these polymers and what is also present in the mixture with them. But it is also possible to physically and chemically treat wood to further alter its properties. A version of wood was as strong as aluminum in some measures and had some interesting additional properties. And a forestry company can be expected to have extensive knowledge of how to process wood.
The question is whether wood has material properties that make it more suitable for satellites than any other alternative material. Nikkei Asia indicates that a potential advantage is that the wood is transparent to many wavelengths that satellites use to communicate, potentially eliminating the need for external antennas. If such antennas need to be deployed after a satellite reaches orbit, this could eliminate a potential source of hardware failure.
But coverage by the BBC and others focuses on space junk. This is a real problem, as the number of defunct satellites and random debris in low Earth orbit has created hazards for the functional things we’d like to keep there. Everything from scientific observatories to the International Space Station has had to be maneuvered around passing bits of garbage.
Unfortunately, making wooden satellite housings will not help with this, for many, many reasons. To begin with, much of the garbage is not ex-satellites; Often it’s the boosters and other hardware that got them orbiting in the first place. Housings are also just a fraction of the material on a satellite, leaving a lot of extra junk untouched by the change, and any wood that’s sturdy enough to function as an effective satellite housing will be extremely dangerous if it hits anything at orbital speeds.
Most of the coverage seems to feature the wooden satellites as an aid to the space debris problem due to the fact that the wood would burn when out of orbit. But this is space junk precisely because it is not exorbitant. All of our plans to manage the existing abundance of space debris involve finding a way to induce it to leave orbit. Wood won’t make any difference here.
The only point that the wood could have going for it, pointed out in part by the cover and by Doi himself, is that it will not leave much in the atmosphere if it is exorbitant and burned. Most of the rest of the hardware will vaporize into a gas of aluminum and various other metals, perhaps oxidized. Again, having a wooden casing will not remove these metals, since many of them come from the components of the satellites and the rocket that put them in place. And, at least for the foreseeable future, this material will not be present in the atmosphere at levels high enough to be significant.
Given all this, it is not entirely clear what problem the wooden satellites should solve. Still, the idea of figuring out how to process wood to work in this context is an intriguing materials science problem and could have some very practical applications. So I hope the project will go ahead regardless.
