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I started getting curious about this question during my Flight Test Engineering class. My professor was talking about a part of the International Standard Atmosphere that is a similar pressure to that of Mars's surface. So I was wondering how a supersonic aircraft would perform in such a colder, emptier atmosphere. On one hand, because Mars's atmosphere is less dense than Earth's, there would be less pressure drag to slow it down, and the lower gravity could reduce the amount of lift the aircraft needs to fly. Hence, an aircraft would be able to fly faster and more efficiently than it could on Earth. But on the other hand, a lower temperature and a lower density would mean that the speed of sound is lower on Mars than it is on Earth. Thus supersonic effects, like wave drag and shockwaves, would start to form at lower speeds than they do on Earth; which could possibly negate the benefits of flying in a lower pressure environment.

So, assuming it is a rocket propelled spaceplane to neglect the effects on the propulsion system, how well would a supersonic aircraft perform when it is flying in the Martian atmosphere compared to Earth's? And how would it be possible to optimize such an aircraft for Martian supersonic flight?

Edit: I also posted this question onto r/AerospaceEngineering earlier in case anyone is interested in some of the answers there too.

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    $\begingroup$ Welcome, Mattias. Flying at supersonic speed over Mars would be fun... until it was time to land. The low air density means high stall speed. Really high. Existing Martian runways would be too short for you, so you would need to "land" by returning to orbit. $\endgroup$
    – Woody
    Jan 18 at 2:33
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    $\begingroup$ @Woody "Existing Martian runways" ... are there many? $\endgroup$ Jan 18 at 2:38
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    $\begingroup$ You may be misunderstanding stall speed @Woody. Airspeed is a measure of dynamic pressure, I think what you are trying to say is that because of the low air pressure the ground speed at which the airplane would need for approach and landing is extremely high. $\endgroup$
    – GdD
    Jan 18 at 10:20
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    $\begingroup$ @SolomonSlow, that's true for many light airplanes but by no means all of them, and I've flown both types. You certainly do not stall a jetliner or fighter onto the runway, although you do land close to stall speed. $\endgroup$
    – GdD
    Jan 18 at 19:30
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    $\begingroup$ @GdD I think aviation SE is Earth-centric, but not sure. Possibly the question would be accepted there. On the Space SE, aerodynamics is not off-topic. Afaik lift increases quadratically by the velocity in rare atmosphere. So I think, maybe a 13 times higher velocity would be needed in the 160 times more rare Martian atmosphere. The typical landing speed is some hundred km/h on the Earth, so maybe 1-2 km/s landing speed would be required on the Mars, which is unimaginable today on any land vehicle. However, plane optimized to the Mars might have a much lesser landing speed. $\endgroup$
    – peterh
    Jan 18 at 22:24

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