Friends have mocked me for suggesting that space satellites and even deep-space vessels could conceivably be made from wood. That's right, ordinary wood from trees. 

Now the Japanese have gotten serious about it and are launching a satellite made of wood. 

Without going into too much detail, it turns out that the properties of hard wood make it as good as and even superior to inorganic materials for use in space. 

Author Gene Wolfe was the first I read who pointed this out. Wolfe, who was an industrial-plant engineer/designer by trade before he became a successful author, hypothesized that with existing technology, a huge, asteroid-sized vessel made from wood and equipped with light-sails (on hundreds of 1/4 mile-high masts) could conceivably achieve relativistic speeds (near the speed-of-light "C") by catching the solar wind and light from suns.

 It might require little fuel except for steering or internal needs. Also it could have tenders (smaller vessels) with similar design which could deploy from and return to the mother ship, so that it need never slow down much at all once achieving near-"C" speed.

Wood is easily worked, shaped and replaced in structures and is just as (or more) resilient to the drastic extremes of temperature of outer space as any inorganic material humans can create and it is infinitely less-costly to produce!!

One of the fascinating things about this satellite is how they did not need to use any metal screws or glue. The reason for that is the structure uses very precisely-fitted joints and pegs made only of wood. The reason they can do that is the satellite does not need to be air-tight or pressurized, so does not have to be sealed against vacuum. 

By having the entire thing made of wood (other than the electronic/electrical components), the surfaces and joints would expand/contract consistently together without separation or cracking even when temperatures vary radically.

Wolfe passed away long ago, but he would surely have been impressed and gratified to see this satellite. 

Another interesting side to the idea of wooden vessels traveling at near light-speed is that the ship would be almost invisible as it travels in space even though it's huge. 

That's because when any object approaches luminal speeds, the mass spreads out laterally. That means the ship would appear to a stationary vantage-point as something that looks like an out-of-focus smudge or comma-shaped arc against the black backdrop of space. If seen at all it would likely not be recognizable as an artificial spacecraft.

So conceivably our solar system could actually have many such vessels orbiting in it already without our awareness, because they would be virtually impossible to see, unless someone was very close and moving at similar speed, or used a powerful telescope and knew exactly where to look. It would have little or no heat-signature to give it away to infrared observation because it burns no large amount of fuel and expels no large amounts of hot exhaust. It might  look more like a comet or cloud than a ship.