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Mars does have an atmosphere, but is there enough atmosphere to glide, shed speed and land if there was a runway? What would this require from the shuttle, in terms of aerodynamics?

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  • $\begingroup$ Related: Challenges to build a landing strip on Mars $\endgroup$ – Edlothiad Jul 18 '18 at 6:54
  • $\begingroup$ Elon Musk has claimed SpaceX's BFS would shed most of it's speed aerodynamically, although it would then land on it's tail. $\endgroup$ – JCRM Jul 18 '18 at 9:45
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    $\begingroup$ From wikipedia: "The highest atmospheric density on Mars is equal to that found 35 km (22 mi)[141] above Earth's surface." The U-2 had a service ceiling of 21.3 km only. Is there any airplane able to fly at 35 km height? $\endgroup$ – Uwe Jul 18 '18 at 9:53
  • $\begingroup$ A blimp would not survive an entry from orbit into the atmosphere of Mars. $\endgroup$ – Uwe Jul 18 '18 at 21:08
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    $\begingroup$ As a rule of thumb lift generally scales linearly with air density/pressure so to achieve the (terrible) glide ratio of the space shuttle on Mars the surface area of the wings would need to be around 100 times bigger while maintaining the same mass. $\endgroup$ – Dragongeek Nov 25 '18 at 1:34
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The essential problem is to build something strong enough to withstand the reentry from orbit, with a big enough wing surface compared to its mass to glide while moving slowly enough to land, and with a low enough mass to be more economical than a propulsive landing.

As @Dragongeek has said, lift is very roughly proportional to air density and wing area. Now the air density on Mars is roughly 1/50 of that on Earth (from here) and the gravity is roughly 1/3, so we need about 17 times as much wing area per kilogram of mass as the Space Shuttle for the same landing velocity. We might be able to bump up the landing velocity a bit, but the shuttle already lands pretty hard and fast.

What that tells us is that, as it comes in to land, the Mars shuttle would have to look a lot more like a glider than like a space shuttle, with huge thin wings. On the other hand, a vehicle that shape seems very very poorly adapted for reentry. Mars reentry is a bit easier than Earth because the escape velocity is lower, but even so, it's hard to imagine huge thin wings not being ripped off, or simply melting, as well as creating so much drag that the deceleration might kill the crew.

So the only way I could see this working is a variable geometry vehicle that could reenter with wings folded in some way and then extend them for the final stages of landing. The engineering and materials challenges would be formidable, but I don't see any reason why this is necessarily impossible.

Finally, though, we get back to the question of why? Folding wings for the final stages of reentry and an undercarriage to land on would add a huge amount of mass, complexity and potential for error, to do basically the same job as either parachutes or rockets.

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