Why Wind Won't Topple a Mars Dome
A dome on Mars is not held up by its frame. It is held taut by the air inside it, the way a balloon is. That is why the wind is almost never the danger. In the world of ICARUS, the Russian settlement of Vostok grows its fresh food under such a dome, and a starred note in the Mítosz exhibition explains the same physics. This post goes a little deeper.
Martian wind is fast but weak
Dust storms on Mars can look terrifying. According to NASA, the strongest winds reach about 60 miles per hour, roughly 100 km/h. But the Martian atmosphere is only about one percent as dense as Earth's, and the push of the wind depends on the density of the air as much as on its speed. At 100 km/h, Martian wind presses on a wall with about 7 pascals. On Earth, a light breeze of around 12 km/h does the same. The storms are still a serious problem, as the notorious Martian dust storms show: they block the Sun and coat everything in dust. They just cannot blow a dome over.
The real force comes from inside
People need air they can breathe, at a pressure their bodies can live with. If the air inside a dome is kept near sea level pressure on Earth, about 101 kilopascals, it pushes outward on every square metre of the shell with a force of roughly ten tonnes. Outside, almost nothing pushes back. That inside pressure is more than ten thousand times larger than the push of the strongest storm.
So a Mars dome behaves like a balloon. Its shell is stretched in tension, and the main engineering problem is the opposite of the one on Earth: not keeping the structure from falling down, but keeping it from lifting off. The edges have to be anchored to the ground or held down by weight. This is one reason why building a human settlement on Mars is first a pressure problem, and only then a weather problem.
Panels, seals and the frame
In the world of ICARUS, the shell of a dome is made of fused quartz panels held in a metal frame. Quartz glass lets light through for the plants and copes well with heat. The weak points are elsewhere: in the seals between the panels and in the frame that holds them.
Mars is hard on joints. Temperatures swing widely between day and night, and glass and metal do not expand at the same rate, so every day the seals are worked back and forth. Martian dust is fine enough to get into every gap. The same is true for every door and hatch on the planet, as Breathe Carefully explains about airlocks.
Failure builds quietly
A pressurised structure rarely fails in one dramatic blow. A seal slowly loses its elasticity. A small leak grows. A bolt tires after thousands of pressure changes. Because the load is shared across the frame, a rib that gives way passes its share to the ribs next to it. That is why, on Mars, regular inspection and a close watch on the pressure gauge matter more than any wind sensor.
The dome of Vostok
Nearly a hundred people live in Vostok, in patched-up modules around the greenhouse dome that gives them their fresh food. The first chapter of the novel, When the Sky Turned Red, begins there as a great storm approaches. What happens to the dome, the book tells. You can also visit Vostok in the Mítosz exhibition, where Luna, one of the Twin Robots, guides you across Mars.
Source
The Fact and Fiction of Martian Dust Storms, NASA, 2015.
Comments