It may all have happened a long time ago in a galaxy far, far away, but there’s a secret weapon in every Star Wars film that’s found almost everywhere humans live on Earth. It explains how the scrappy Rebel Alliance were able to defeat the mighty Galactic Empire, with all its high-tech weaponry, vast space armada and the Death Star.
Even with the help of Jedis, The Force, ewoks and a wookiee, Luke Skywalker and the rebels skirted annihilation on many occasions. We believe that their ultimate victory owed less to their mystic powers and allies, and instead to something more down-to-earth.
In several key moments throughout the series, the survival of the rebels depends on their ability to escape the Empire’s clutches by retreating to, and defending, fortified bases. These are spread out on remote planets throughout the galaxy, in often hostile environments, from snowbound Hoth to desiccated Crait.
It’s time to finally give the Rebel Alliance’s engineering corps the credit it deserves. The fate of the galaxy was decided not by light sabres — but by concrete.
The Snows of Hoth
At the start of “The Empire Strikes Back,” things are looking grim. The Empire have cornered the remnants of the Rebel Alliance on the ice planet, Hoth. Fortunately, General Leia and co. are able to defend Echo Base long enough for their allies to evacuate. The base is built into subterranean caves, but concrete is still needed for the roofs and floors of the spacecraft hangars, and the defensive laser cannon emplacements.
But how could they make all that concrete when temperatures on Hoth are consistently below 0°C? Concrete doesn’t set by drying out, but by a hydration reaction, which consumes water. If the water in the concrete mix is frozen solid, it can’t take part in the hydration reaction, and so the concrete can’t develop its strength.
So how did the Rebel engineers get around this? A cheat solution for small structures is simply to make the concrete in a place it’s not freezing, and then bring it in. This is known as “pre-cast” concrete. Engineers are currently using this to upgrade the Rothera research station in Antarctica[1] — the most similar place to Hoth there is on Earth.
But shipping all that concrete through space isn’t practical. Engineers on Earth have a better solution — they use special rapid-hardening cement that contains calcium aluminates. This reduces how long the “danger zone” lasts, during which the cement must be protected from freezing. This quick-hardening ability allowed the French Army to build gun emplacements quickly[2] in World War I, and could have helped fortify rebel defences on Hoth.
The salt lakes of Crait
In 2017’s “The Last Jedi,” the rebels were almost wiped out again by the pursuing Imperial fleet. They take shelter on the barren planet of Crait, covered by flat, dried up salt...