An emerging approach to spacecraft construction that replaces metal alloys with wood, offering potential benefits in cost, pollution and performance.
Wood has several advantages over metal alloys as a satellite material. Radio signals pass through it unperturbed, so communications equipment need not be specially deployed once in orbit—protecting it from space debris and reducing drag. Wood absorbs vibrations (a plus for sensitive instruments), insulates better than metal (reducing heating-coil use), and is cheaper than spacecraft alloys.
Regulators are tightening "design for demise" rules intended to stop chunks of falling spacecraft reaching the ground. Satellites weighing more than about 300kg usually need special guidance systems for controlled re-entry. Incorporating wood, which burns up in the atmosphere, might permit spacecraft weighing up to a tonne to re-enter uncontrolled, saving that cost.
Using wood also reduces the amount of metal vaporising on re-entry. In 2023 some 290 tonnes of space junk fell into the atmosphere; a study that year found a tenth of stratospheric sulphuric-acid particles sampled contained such metal. One forecast suggests that by 2035, more than 2,800 tonnes of space junk a year will fall from orbit. A build-up of metals at altitude might trigger chemical reactions that destroy ozone.
The vacuum of space can suck out moisture and organic compounds, weakening wood—though experiments suggest not enough to matter. A protective coat of aluminium oxide may help. Swapping metal for wood also introduces soot on re-entry; what might emerge from a reaction between soot and vaporised electronics remains unknown.
LignoSat was launched from the International Space Station on December 9th 2024, built by Kyoto University in Japan from magnolia. Its temperature oscillated from -100 to +100°C as it passed in and out of Earth's shadow, and it was bombarded by solar-wind radiation, but its wooden panels held firm for 116 days until atmospheric re-entry. Its communications failed at launch. LignoSat2, intended for launch in 2028 into a 400km orbit, will test whether enclosed communications equipment and reduced drag extend flight time—Doi Takao, a former astronaut and team member, reckons a 50% extension.
WISA Woodsat is a test vehicle designed with help from Huld, a Finnish firm, using birch plywood (routinely cooled to -163°C when insulating liquefied-natural-gas tanks). It is planned for launch in 2026.
"Necessity is the mother of invention" is a silly proverb. "Necessity is the mother of futile dodges" is much nearer the truth.