What If We Tried to Fly On Alien Worlds?

Could we fly on far-away worlds, or will it forever be a tantalizing fantasy? Randall Munroe of xkcd tackled the practicalities of flight on the 32 largest stars, planets and moons of our solar system as part of his What if? series.

Top image: Excerpt of the visual summary of flying on different bodies within the solar system. Credit: Randall Munroe


Munroe's new What If?: Serious Scientific Answers to Absurd Hypothetical Questions book came out on September 2nd, so it seems like a good time to revisit one of my favourite posts from the series archives: What would happen if we tried to fly an airplane on another world?

Munroe uses a Cessna 172 as his intraplanetary craft, an extremely popular small single-engine craft. After positing that the Cessna would need to run off an electric engine to get around the whole, "Combustion engines require oxygen to operate" problem, he jumps straight into the analysis. Anywhere without an atmosphere is immediately excluded, leaving only nine bodies to analyse. While the rest are amusing ("The Sun: This works about as well as you'd imagine."), Mars and Titan are the most interesting candidates.

X-Plane flight simulator on Mars, before topography update. Image credit: Austin Meyer


With just a third of Earth's gravity and 1% of its atmosphere, Mars is close enough to Earth that it can actually be modelled in the X-Plane flight simulator. Munroe describes the community as "hardcore aeronautics enthusiast who uses capslock a lot when talking about planes," and that's entirely accurate. Back in late February, 2004, Austin Meyer excitedly announced that he rigged up a full Mars flight simulator with decreased gravity, a smaller radius, and a thin atmosphere. That seems like it'd make flying easier, but inertia stays the same as it was on Earth. Consequently, planes need to go at Mach 1 during takeoff, keep going absurdly fast when getting around, utterly fail to turn. In the words of Meyer:

All airplanes on Mars are AIRBORNE TITANICS: Ripping blissfully along, unaware of their impending doom due to their inability to TURN against their tremendous inertia.


It all gets a lot more complicated when trying to figure out how to shed all that velocity and come in for a landing. Immersing in the failures of parachutes to drag in thin atmosphere, the futility of brakes at such magnificent speeds, and the inadequacy of reverse thrust, it becomes a lot more clear why NASA adopts seemingly-ridiculous tactics like massive inflatable saucers or intricate skyhooks when trying to land on the red planet.


As for Titan, it's a moon ideal for flying! The gravity is lower while the atmosphere is thicker, making flying downright easy. The result is that not only could a Cessna fly, but there's also a good chance a human could fly simply by flapping a pair of strapped-on wings. The only downside? Titan's cooler than liquid nitrogen, chilly enough that the Huygens probe only lasted for a brief moment. Yet as Munroe stirringly concludes, that's a problem we could overcome:


But I've never seen the Icarus story as a lesson about the limitations of humans. I see it as a lesson about the limitations of wax as an adhesive. The cold of Titan is just an engineering problem


I am absolutely down with testing out his calculations with a future space mission, and am prepared to get started on testing low-temperature adhesives just as soon as I get funding approved.

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