Feasibility of identifying natural landing strips for winged aircraft from orbit

[Robotbeat]

So I’m wondering if a combination of photogrammetry and texture matching with ground-truthed imagery from the various surface probes could identify suitable natural flat landing strips on Mars for horizontal landing aircraft. Obviously large wheels and low enough landing speeds would be needed (in spite of the low density), but perhaps some sandy or otherwise flat place could be found to meet the requirements with big enough wheels and slow enough stall speed.

Perhaps you’d still need a rover or a helicopter to ensure a safe landing site free of boulders bigger than the tires could handle, but it’d be interesting to see if any suitable spots could be found from orbit.

It might make logistics on Mars easier to have existing landing strips and ability to use wing borne aircraft without the massive range penalty of VTOL.

[freddo411]

It would be interesting to work the napkin numbers to flesh out this thesis.

The shuttle's landing speed was crazy fast, even in the Earth's atmosphere.   Mars is roughly 2 orders of magnitude less dense, although the lower gravity helps a bit.

My intuition is that the range of possible stall speeds are crazy high to supersonic  --depending on the surface to mass ratio.   Keep in mind the shuttle is already a mass optimized vehicle

I don't think high speed horizontal landing can accommodate anything but a  very long surface that is very smooth along its entire length

[whitelancer64]

The main problem with a runway on Mars is it would need to be very, very long - I would guess at least 5-10 km even for a relatively small passenger / cargo aircraft - because the air is so thin that takeoff and landing speeds must be very high (close to supersonic) to generate lift, requiring a very long distance to roll up to flight speeds / brake from flight speeds, and even small bumps at that speed would likely be diastrous. You might be able to use a slightly shorter runway at very low elevations.

Anyway, I doubt there are very many reasonably flat / smooth areas on Mars that long. On the other hand, you could probably fairly easily identify long strips that are mostly flat / smooth that a bulldozer could make more flat / smooth. We have maps of Martian elevation with sub-meter accuracy from laser altimetry.

[Robotbeat]

Why long? Just use air brakes or a parachute. For launch, use a winch, a catapult, or a rocket assist.

[Robotbeat]

I think if you get the wing loading very low, like for Helios, the landing speeds would be fairly reasonable. A high stall speed might be preferred for long distance and more rugged aircraft tho.

[Robotbeat]

At low altitudes, Mars has an atmospheric density about 2% that of the earth. And its gravity is about a factor of three lower. That means there’s a factor of 18.9 difference in lift to account for. Since lift is proportional to speed squared, you can take the square root of that to see how much faster an aircraft will have to travel on Mars than on earth to maintain level flight. About a factor of 4.34.

For a human powered aircraft, you can have flight speeds as low as 8mph. https://en.wikipedia.org/wiki/MacCready_Gossamer_Condor

So flight speed on Mars would need to be about 35mph. that’s not bad at all. So maybe we can afford not to make the airplane out of Saran Wrap.

If we said 200 mph is the maximum speed for landing on Mars, that means a similar earth design would need to be capable of flight of about 46mph. Tundra tires max out at around 120mph, so maybe we need more like a 28mph Earth minimum level flight speed for a viable Mars aircraft. Maybe the return of biplanes??

[whitelancer64]

Why long? Just use air brakes or a parachute. For launch, use a winch, a catapult, or a rocket assist.

Because it will take a while to ramp up to ~800 km/h for takeoff and to slow down from about that speed when landing.

Parachutes might be okay but then you need to pack them back up when you want to take off again. Only a few examples of aircraft that used them on a regular basis.

If you have a winch, catapult, or whatever, then it's no longer an unprepared runway. You'd have the runway smooth and graded and you might as well make it as long as you need, then you wouldn't really need anything special to assist the aircraft to take off. Or you might as well have catch wires like an aircraft carrier for landing.

But then this thread needs to be "Feasibility of building an aircraft carrier deck on the surface of Mars"

[whitelancer64]

At low altitudes, Mars has an atmospheric density about 2% that of the earth. And its gravity is about a factor of three lower. That means there’s a factor of 18.9 difference in lift to account for. Since lift is proportional to speed squared, you can take the square root of that to see how much faster an aircraft will have to travel on Mars than on earth to maintain level flight. About a factor of 4.34.

For a human powered aircraft, you can have flight speeds as low as 8mph. https://en.wikipedia.org/wiki/MacCready_Gossamer_Condor

So flight speed on Mars would need to be about 35mph. that’s not bad at all. So maybe we can afford not to make the airplane out of Saran Wrap.

If we said 200 mph is the maximum speed for landing on Mars, that means a similar earth design would need to be capable of flight of about 46mph. Tundra tires max out at around 120mph, so maybe we need more like a 28mph Earth minimum level flight speed for a viable Mars aircraft. Maybe the return of biplanes??

I was assuming you were talking about a small crew or cargo carrying aircraft, something that could do useful work, not an ultralightweight gossamer condor.

150 mph is close to the minimum landing speed for most commercial aircraft on Earth. 4.34 x 150 = 651 mph

[Barley]

Why long? Just use air brakes or a parachute. For launch, use a winch, a catapult, or a rocket assist.

Not much air.

If you to use a rocket assisted takeoff, if your rocket can push you at 1g the gravity losses for a takeoff that skims a few meters above the ground are quite small, so you don't need a "runway", just no vertical obstructions or better yet a downhill slope.

[Bob Shaw]

What about landing *uphill*?

[Jim]

Not feasible for winged landing.  Too fast.

[Twark_Main]

wing borne aircraft without the massive range penalty of VTOL

[citation needed]

[Twark_Main]

I think if you get the wing loading very low, like for Helios, the landing speeds would be fairly reasonable. A high stall speed might be preferred for long distance and more rugged aircraft tho.

Low wing loading = large wing area per payload mass = large wing mass penalty.

[Barley]

I think if you get the wing loading very low, like for Helios, the landing speeds would be fairly reasonable. A high stall speed might be preferred for long distance and more rugged aircraft tho.

Low wing loading = large wing area per payload mass = large wing mass penalty.

Or wings made of saran wrap.

[Robotbeat]

 

I think if you get the wing loading very low, like for Helios, the landing speeds would be fairly reasonable. A high stall speed might be preferred for long distance and more rugged aircraft tho.

Low wing loading = large wing area per payload mass = large wing mass penalty.

Not really. Remember the gravity is lower as well, so there are some structural advantages to Mars. Biplanes on Earth can have big wing areas with not that bad of a mass penalty even using century old construction techniques. I think the biggest penalty is wetted area drag, which is less important if the air is low density.

People act as if the only way you can make an airplane on Earth is with heavy aluminum transonic wings and a landing speed of 120mph or more like a jet. But some of the most produced airplanes in the world are utility aircraft with 30mph stall speed and lightweight wing skins over an aluminum frame (could be upgraded to carbon fiber), the Antonov An-2. Heck, some of the main reasons not to use wood and canvas for airplane construction is that they can get destroyed by moisture (or termites, etc), not a problem on Mars… https://www.planeandpilotmag.com/scroll/1-waco-ymf-5/

[JAFO]

People act as if the only way you can make an airplane on Earth is with heavy aluminum transonic wings and a landing speed of 120mph or more like a jet. But some of the most produced airplanes in the world are utility aircraft with 30mph stall speed and lightweight wing skins over an aluminum frame (could be upgraded to carbon fiber), the Antonov An-2. Heck, some of the main reasons not to use wood and canvas for airplane construction is that they can get destroyed by moisture (or termites, etc), not a problem on Mars… https://www.planeandpilotmag.com/scroll/1-waco-ymf-5/

WADR, lot of bad info in this post.

The "Ant" is a bad example to use. It's got a metal frame and fuselage skin, fabric wings/tail/control surface coverings, and a tricked out wing that added a bunch of weight to make the STOL magic work. While it theoretically has no stall speed, upper 20's/low 30s are generally used.  https://www.an2flyers.org/an2specs.html

Can't think of any modern LSA/LSX aircraft made from wood, most are made from 6061 or carbon fiber, and the fabric is actually a polyester blend called Polyfiber coated with a polyrubber blend. https://www.conaircraft.com/polyfiber

It all depends on your mission. Want to fly anytime/anywhere through (almost) anything? Call me and you can charter my 787. Need something to fly on another planet? My hat is off to and I am incredibly proud of the Ingenuity project team. https://mars.nasa.gov/people/?category=helicopter

[JayWee]

Why long? Just use air brakes or a parachute. For launch, use a winch, a catapult, or a rocket assist.

...
Parachutes might be okay but then you need to pack them back up when you want to take off again.
...

And don't forget the dust.

[chopsticks]

I wonder about an aircraft type like a powered glider with really long wings and a shallow cord. Those can fly really slowly, have tons of lift, and are very efficient aerodynamically.

I mean, it works pretty well on Duna in KSP..

[Robotbeat]

I wonder about an aircraft type like a powered glider with really long wings and a shallow cord. Those can fly really slowly, have tons of lift, and are very efficient aerodynamically.

I mean, it works pretty well on Duna in KSP..

Exactly. need to get the landing speed slow enough that you can land on natural flat areas of Mars with tundra tires.

The older 737s had kits for landing on unpaved (i.e. gravel) landing strips. The kits included a shield attached by the landing gear that keep rocks from spraying up and hitting parts of the airplane. Those planes land at like 150mph. The landing strip can handle obstacles up to 3 inches high. So it's doable in principle.

[Robotbeat]

People act as if the only way you can make an airplane on Earth is with heavy aluminum transonic wings and a landing speed of 120mph or more like a jet. But some of the most produced airplanes in the world are utility aircraft with 30mph stall speed and lightweight wing skins over an aluminum frame (could be upgraded to carbon fiber), the Antonov An-2. Heck, some of the main reasons not to use wood and canvas for airplane construction is that they can get destroyed by moisture (or termites, etc), not a problem on Mars… https://www.planeandpilotmag.com/scroll/1-waco-ymf-5/

WADR, lot of bad info in this post.

Nothing is incorrect in what I said.

The "Ant" is a bad example to use. It's got a metal frame and fuselage skin, fabric wings/tail/control surface coverings, and a tricked out wing that added a bunch of weight to make the STOL magic work. While it theoretically has no stall speed, upper 20's/low 30s are generally used.  https://www.an2flyers.org/an2specs.html

Why is it a "bad example"? You just kinda showed that it's viable. It doesn't use wood, but it does use fabric and has very low landing speed.

Can't think of any modern LSA/LSX aircraft made from wood,

There are some still in production which are. The full article from the link I posted says:
https://www.planeandpilotmag.com/news/pilot-talk/10-wooden-airplanes-you-can-buy-or-build/

As we progress well into the second century of flight, most of us take to the sky in machines of metal or advanced composites like carbon fiber and Kevlar. The science is solid and techniques well established for flying machines of these materials. But if you step away from the mainstream types most commonly decorating the ramp at your local airfield, you may well stumble across wooden airplanes that survive as antiques, warbirds and homebuilt designs, as well as a few types built more recently. There are even a few designs in current production—one featured below is a throwback to the days of old, while another is a Light Sport Aircraft utilizing a wood wing to stay below the 1,320-pound gross weight limit.

most are made from 6061 or carbon fiber, and the fabric is actually a polyester blend called Polyfiber coated with a polyrubber blend. https://www.conaircraft.com/polyfiber

It all depends on your mission. Want to fly anytime/anywhere through (almost) anything? Call me and you can charter my 787. Need something to fly on another planet? My hat is off to and I am incredibly proud of the Ingenuity project team. https://mars.nasa.gov/people/?category=helicopter

Yeah, carbon fiber and other advanced modern materials are the obvious choices, but it's worth reconsidering things that the environment of Mars may enable due to lack of moisture and rot.

[Barley]

Consider a Harrier.  Launch vertically and immediately vector for zero vertical acceleration.  If you can accelerate at 1g the cosine loss is not large.  0.38g is a big win.  Probably lighter than tires. 

[Robotbeat]

Consider a Harrier.  Launch vertically and immediately vector for zero vertical acceleration.  If you can accelerate at 1g the cosine loss is not large.  0.38g is a big win.  Probably lighter than tires.

The F-35 version that has VTOL capability loses a lot in range and payload to accomplish, and that's in Earth's much thicker atmosphere. It's possible, but VTOL (especially for an electric vehicle, as you'd likely want on Mars due to logistical simplicity) halves the range, doubles the cost (especially maintenance), halves the energy efficiency, and probably increases development cost and time by a factor of 4.

[Barley]

Consider a Harrier.  Launch vertically and immediately vector for zero vertical acceleration.  If you can accelerate at 1g the cosine loss is not large.  0.38g is a big win.  Probably lighter than tires.

The F-35 version that has VTOL capability loses a lot in range and payload to accomplish, and that's in Earth's much thicker atmosphere. It's possible, but VTOL (especially for an electric vehicle, as you'd likely want on Mars due to logistical simplicity) halves the range, doubles the cost (especially maintenance), halves the energy efficiency, and probably increases development cost and time by a factor of 4.

You have not considered what .38g means, Mars is not Earth.

Base line a 2600kg plane and a Rutherford rocket engine since it's the right size.

If you can fly at 100 m/s a Rutherford rocket could launch and land a using about 110kg of rocket, fuel and battery.   That's about 4.2% of the takeoff weight.  It's about 220 kg if stall speed is 250 m/s.

Using propulsive takeoff and landing lets you optimize everything else for cruise, you don't need a Gossamer Albatross just to take off.  You may not need flaps.   And you don't need a runway, or tires rated for 100 m/s on rough ground.
 
I'd expect flight to use chemical fuels.  There should be kilotonnes of methane and lox somewhere.  A few tonnes for flights should not strain logistics.

[Robotbeat]

You don’t need “Gossamer Albatross” without rockets, either.

[Valerij Zhilisky]

Consider a Harrier.  Launch vertically and immediately vector for zero vertical acceleration.  If you can accelerate at 1g the cosine loss is not large.  0.38g is a big win.  Probably lighter than tires.

The F-35 version that has VTOL capability loses a lot in range and payload to accomplish, and that's in Earth's much thicker atmosphere. It's possible, but VTOL (especially for an electric vehicle, as you'd likely want on Mars due to logistical simplicity) halves the range, doubles the cost (especially maintenance), halves the energy efficiency, and probably increases development cost and time by a factor of 4.

     
It is not necessary to limit ourselves to discussing the presence of natural takeoff and landing strips on Mars, and, moreover, their search from orbit. A full-fledged study of the regions of Mars will require equipment weighing tens and hundreds of tons, and either Starship from Earth or heavy ground transport will be able to deliver them. It is worth discussing all the possibilities of using aircraft in the initial reconnaissance, in-depth exploration and exploration of Mars up to the creation of the Martian Colony. In the Colony phase, for example, it doesn't make sense to limit yourself to natural runways, because it won't be a big problem to build them at this stage.
     
Therefore, I believe that it is necessary to consider different options for different stages.

First, it is worth considering the possibility of dropping several autonomous drones from a Starship that is landing. One of them can film the landing of Starship from the side, and it will be invaluable footage, both for engineers and for the general public. The other two can take up aerial photography and detailed mapping of the area over which the Starship flies during braking before landing, the third can go to survey the area of ​​the caves, and so on. These are disposable, drones that can be mass-produced, which will drastically reduce their cost. It is worth considering so that when landing, their airframe is destroyed, and the hardware unit, including the communication system, control computer, batteries, and, if possible, the cameras remain operational. It would be very useful for future colonists.
     
Here, absolutely rightly, they remembered Antonov's airplane, AN-2. After the landing of the colonists, his Martian reincarnation will be in great demand. On Mars, its landing speed will be about one hundred and fifty kilometers per hour, and the flight range will be more than a thousand kilometers. He will not be able to transport tens of tons, but it would not be difficult at all to build a strip for it a hundred to two hundred meters long in almost any place. Even if he can carry only a ton of cargo or 5-10 passengers, this will be a very serious help. And a drone based on such an aircraft can be very useful in a detailed study of Mars.
   
But I don’t believe in a heavy transport aircraft on Mars with a carrying capacity of tens or more tons. Instead, there will be Starship, which, if necessary, can be launched along a ballistic suborbital trajectory.
     

[Valerij Zhilisky]

In Russia, such a coating is usually built by soldiers, but in the world, as far as I know, there are also options for a "road in a roll." Aircraft can land on such a strip at speeds up to 200 km /h.
   

[Twark_Main]

Consider a Harrier.  Launch vertically and immediately vector for zero vertical acceleration.  If you can accelerate at 1g the cosine loss is not large.  0.38g is a big win.  Probably lighter than tires.

The F-35 version that has VTOL capability loses a lot in range and payload to accomplish, and that's in Earth's much thicker atmosphere. It's possible, but VTOL (especially for an electric vehicle, as you'd likely want on Mars due to logistical simplicity) halves the range, doubles the cost (especially maintenance), halves the energy efficiency, and probably increases development cost and time by a factor of 4.

I disagree. VTOL is easier with electric, because the drive systems have much higher specific power vs combustion engines. This lowers the mass penalty for adding VTOL capability.

If your battery has a large energy capacity it also tends to have a large power capacity, so fortunately you generally don't need to upsize your battery to enable VTOL takeoff.


VTOL landing is trickier, because pretty much all battery chemistries deliver less power at low SoC.  I did notice that Lilium, as part of iterating toward certification, has added rolling landing capabilities (extending their reserve range) that allow them to utilize more of their battery capacity in the low-SoC range.




Latest update on their certification, btw: https://lilium.com/newsroom-detail/faa-issues-g-1-for-lilium-jet

[Hobbes-22]

So I’m wondering if a combination of photogrammetry and texture matching with ground-truthed imagery from the various surface probes could identify suitable natural flat landing strips on Mars for horizontal landing aircraft.

With current Mars assets, no. HiRise has a resolution of 30 cm/px.
Fermi estimate: that means you can have terrain elevation changes of at least 30 cm that are not visible in a HiRise image, including e.g. boulders on otherwise-flat terrain. I wouldn't want to land on a field that uneven in anything less than a hovercraft.

[Robotbeat]

One option would be multispectral texture mapping and comparison. “This color surface does not have large boulders on it but is largely smooth sand based on comparison with ground truth images of similar textured images from areas around the rovers.”

I just thought of a really good option:
Another is looking for shadows cast by boulders near sunrise and sunset. 10cm tall obstacles will still cast a meter long shadow near sunrise and sunset, and that can be seen by the orbiters. Especially if you compare to noonday. Shadows will be one meter eastward at sunset, one meter westward at sunrise. That should be easily resolvable. Probably could see 7.5cm high obstacles. And by looking at the changing shades, you probably can infer a height distribution of even smaller obstacles.

3inch high obstacles is what the 737’s gravel airstrip system is rated for, and that lands at like 150mph. So with the right sort of tires and low (but not absurd) wing loading, it should be possible to find a workable landing site purely careful analysis of orbital imagery.

[Valerij Zhilisky]

One option would be multispectral texture mapping and comparison. “This color surface does not have large boulders on it but is largely smooth sand based on comparison with ground truth images of similar textured images from areas around the rovers.”

I just thought of a really good option:
Another is looking for shadows cast by boulders near sunrise and sunset. 10cm tall obstacles will still cast a meter long shadow near sunrise and sunset, and that can be seen by the orbiters. Especially if you compare to noonday. Shadows will be one meter eastward at sunset, one meter westward at sunrise. That should be easily resolvable. Probably could see 7.5cm high obstacles. And by looking at the changing shades, you probably can infer a height distribution of even smaller obstacles.

3inch high obstacles is what the 737’s gravel airstrip system is rated for, and that lands at like 150mph. So with the right sort of tires and low (but not absurd) wing loading, it should be possible to find a workable landing site purely careful analysis of orbital imagery.

     
There is no practical need for this. It is impossible to ensure landing from orbit of a heavy apparatus with a low wing load even on Earth, especially on Mars. Therefore, it is easier to search for natural landing strips not from orbit, but from a drone conducting stereo aerial photography from a low altitude.
   
What is the special meaning of searching for a runway from orbit? Are you going to land on the runway from orbit?
   
In order to provide the orbiter with a wing loading similar to the 737's (not equal to namely, similar in the Martian atmosphere and under Martian gravity) the landing speed of the orbiter should be four times greater - about 600 miles per hour. But the wing loading of the Space Shuttle was much higher.
   
But for a good landing and runway, one relief and the absence of stones is not enough. The quicksands will look just perfect from the air, but it will be difficult to take off from them. You also need sufficient bearing capacity of the soil. Mars rovers have had problems with quicksand before.
     

[Robotbeat]

You have a much looser definition of “impossible” than the one I use.

[Valerij Zhilisky]

You have a much looser definition of “impossible” than the one I use.

   
Maybe. But, rather, I've set the conditions more rigidly. First of all, the device must land from orbit, or from deep space, with a trajectory approaching the planet. Otherwise, there is no point in searching for a landing site from orbit, an inexpensive atmospheric drone will do it faster and with greater accuracy. Secondly, the device must have a large mass, at least several tens of tons. We (earthlings) already know how to carefully lower rovers weighing a little more than a ton to Mars, but the landing vehicle has a mass of about three times the mass of the rover. Third, by definition, there are no prepared runways on Mars right now....
   

[Robotbeat]

You have a much looser definition of “impossible” than the one I use.

   
Maybe. But, rather, I've set the conditions more rigidly. First of all, the device must land from orbit, or from deep space, with a trajectory approaching the planet. Otherwise, there is no point in searching for a landing site from orbit, an inexpensive atmospheric drone will do it faster and with greater accuracy. Secondly, the device must have a large mass, at least several tens of tons. We (earthlings) already know how to carefully lower rovers weighing a little more than a ton to Mars, but the landing vehicle has a mass of about three times the mass of the rover. Third, by definition, there are no prepared runways on Mars right now....
   

Um, the context of this is like a bushplane on Mars able to travel to places that haven't been visited yet. It doesn't need to do what you're describing.

[Valerij Zhilisky]

     
Um, the context of this is like a bushplane on Mars able to travel to places that haven't been visited yet. It doesn't need to do what you're describing.

     
Well, then we just don't quite understand each other. Here https://forum.nasaspaceflight.com/index.php?topic=59475.msg2520428#msg2520428 I mention the An-2 airplane. This airplane was recalled in the topic and a bit earlier. But there is no need to confirm the suitability of a landing site for it from orbit, a lightweight and inexpensive atmospheric drone, perhaps even a disposable one, can successfully do that.
   
Just read the title of the thread. It's about natural runways, and finding them exclusively from orbit. That doesn't make sense. If we have a Martian reincarnation of the AN-2 on Mars, we also have search drones that provide more detailed aerial surveys. It only makes sense to search for a place to land from orbit if we land outside the area available for drone survey. If we need to land a heavy payload there, Starship will land there, and it doesn't need a landing strip.
   

[Robotbeat]

Starship may have much the same problem actually but for different reasons.

It’s really better to land Starship on a solid pad.

[Lampyridae]

You have a much looser definition of “impossible” than the one I use.

   
Maybe. But, rather, I've set the conditions more rigidly. First of all, the device must land from orbit, or from deep space, with a trajectory approaching the planet. Otherwise, there is no point in searching for a landing site from orbit, an inexpensive atmospheric drone will do it faster and with greater accuracy. Secondly, the device must have a large mass, at least several tens of tons. We (earthlings) already know how to carefully lower rovers weighing a little more than a ton to Mars, but the landing vehicle has a mass of about three times the mass of the rover. Third, by definition, there are no prepared runways on Mars right now....
   

Um, the context of this is like a bushplane on Mars able to travel to places that haven't been visited yet. It doesn't need to do what you're describing.

So basically you want a gyrocopter? Turns out there's a paper for that:

https://www.mdpi.com/2504-446X/5/2/53

TL;DR, mass is 10kg but the power required is only 1/3 of that on Earth.

Alternatively here is a tailsitter design, mass 26kg.

https://link.springer.com/article/10.1007/s12567-022-00479-4

Attached is an old design for a manned Marsplane, cruising speed is 75m/s. From what I've read, rotor size becomes a major issue for manned copter sizes (>30% weight) but that was before the paradigm of sticking 512 rotors on a wing.

Ingenuity might seem the maximum physically possible, but aerodynamics in low Reynolds numbers and blade manufacture are two areas which seem to be advancing quite rapidly.

The Marsbees entomopter research is also quite promising with the use of flexible, energy-saving wings.

[Robotbeat]

Horizontal take off and landing.

Short take off and landing. STOL, not VTOL.

[Lampyridae]

Horizontal take off and landing.

Short take off and landing. STOL, not VTOL.

So then I think a larger version of the gyrocopter in the paper I linked could work, but there's the caveat of non-linearly increasing rotor size and mass.

They give a cruise speed of 45kph, so I think (maths not yet run) it could be feasible to have <60kph takeoff speeds for a crewed version.

If it's just 60kph then it shouldn't be hard to identify a stretch long and uncluttered enough for a bush plane kind of takeoff and landing. Windspeeds a few metres above the surface of Mars can get pretty high, so the takeoff/landing roll could be even shorter.