Air Transportation on Mars - Gravity's affect on Air travel on Mars

Deimos · 2002-12-29 12:36:38

Just a heads up, I am not a professional scientist(as I doubt most posting here are). So bear with me...

Id just like to start some discussion on the possibilities of using air transportation vehicles somewhat similar to what we use on Earth on Mars.. Now ofcourse it would be quite expensive and impractical to transport them there. But that set aside, how would Mars's lower gravity then Earth affect the possibility of air travel as we know it on Mars..

Ideas..?

Echus_Chasma · 2002-12-29 15:50:11

Well cos of the lower gravity, it means you could have heavier planes, but I don't know how the low air pressure would effect them though.

The low amount of gas in the atmosphere, I think, would mean things like jets or areo-props could'nt work very well. Thats why Dirigibles and blimps and stuff would be better.

soph · 2002-12-29 16:40:34

it means you would have to have the jets propel themselves, rather than be carried by air, like rockets do.

RobS · 2003-01-03 02:57:01

The thinner air makes airplanes less useful, but not impossible. Lift is a function of the density of the air, not its pressure. The pressure at "Martian sea level" is 0.7% of Earth's atmosphere, but the density is 0.7/0.38 = 1.8% that of Earth. Thus to lift the same weight, Martian wings have to have 55 times as much area. However, with lower gravity, an object weighs 0.38 as much, so the wing surface ends up being 55.5 x 0.38 = 21 times bigger.

This apparent disadvantage, however, presents one advantage: the large surface area can be used as a solar collector, and the airplane can run off of solar electricity instead of an engine burning something. A solar powered aircraft named "Helios" has actually been flown at 100,000 feet on the Earth, an altitude where the air is of similar thinness. You can find information about it on Google. The wings were the length of a 747's, but their mass was less than 4 kg per square meter, which was basically the mass of the solar panels. Helios eventually will be able to store power for nighttime flying using fuel cells and fly independently for weeks at a time. Its total mass is 600 kg and its cargo is 300 kg, if I remember right. Helios has 14 propellors along its wing, too; it can probably fly on half of them, so the plane is able to fly for months at a time without maintenance. They are being developed to test technology for Mars, but they have a practical application; they can serve as a cell phone tower in the sky, floating for half a year at a time above the weather, able to be moved quickly to a disaster site to bolster communications there.

I suspect Helios-like aircraft will be the ideal early transport for crew and cargo. They can't go very fast; it would take 3 or 4 days to travel half way around Mars. But two crew in a very light-weight capsule could handle that. The cargo transportation would be limited to a half tonne at a time, but the vehicles could make repeat trips easily and inexpensively. They would need very wide, smooth landing strips, but takeoff and landing speeds apparently are very low (which would allow the use of airbags in case of a crash). They would also be ideal for closeup photographic reconnaisance of the surface, able to take photographs with resolutions of a few centimeters, the sort of resolution you need to plan a manned expedition crossing the terrain.

-- RobS

soph · 2003-01-03 14:34:36

rob, if a plane developed its own thrust, like a nuclear spaceplane theoretically would, then air density should not be a problem, correct?

RobertDyck · 2003-01-04 03:11:36

RobS

Lift is a function of the density of the air, not its pressure.

Density is directly calculated from pressure. For example, one mole of carbon dioxide gas is 22.256 litres at 0?C and 1 atmosphere pressure. The term mole is a number of molecules = 6.02*10^23. One mole of carbon dioxide masses 44.0098 grams. The ideal gas law states that PV=nRT, where P is pressure, V is volume, n is the number of moles, T is temperature, and R is a constant. R=0.0821 litre atm / K mol. Here atm is the contraction for pressure in atmospheres, K is the temperature in Kelvin, mol is the contraction for mole. This means the density of carbon dioxide at 0.7% atm pressure and 0?C will be 0.007 * 44.0098 / 22.256 = 0.01384 grams/litre. The bottom line is you factored gravity in twice. Using your numbers that means Martian wings do have to be 55 times as much area.

soph

if a plane developed its own thrust ... then air density should not be a problem

If a plane is supported by wings, then wing area is calculated by air density, speed of flight, and weight of the aircraft. Thrust will increase speed, but it won't help with lift unless you are building a helicopter or other form of vertical thrust craft.

Deimos · 2003-01-04 11:44:14

Thankyou for answering my questions... Very interesting idea with the Helios Helicopter.. Although it would present a problem with bringing something like that to Mars, as It's size would be a problem

neutrino · 2003-01-05 20:02:07

One problem in using solar cells on Mars Verses Earth is you have 1/2 the solar radiation hitting the solar cells on Mars then you do on Earth. Don?t forget the amount of dust in the Martian atmosphere will effect the amount of light falling on the planet. Your best solar cells can get only 30 percent efficiency. So you would have to scale it up to 2 times the surface area of what you would use in low Earth orbit. If you can increase the efficiency to 50 or 76 percent, the maximum allowed theoretically, by using the full electromagnetic spectrum of light hitting the solar cells, then you would have a powerful tool that you could use on solar powered flight on Mars. This also can be used to drive VASMIR, Ion engines etc. A research group at Berkley has just claimed to do that.

"A team led by Wladek Walukiewicz, working with researchers at Cornell University, and Ritsumeikan University, Japan, has discovered that, contrary to earlier reports, the band gaps of the In1-xGaxN ternary alloy system extend over a very wide energy range (0.7 eV to 3.4 eV) and thus provide a near-perfect match to the solar energy spectrum. This creates the opportunity to design and fabricate new multijunction solar cells that will have greatly improved efficiencies, possibly reaching the theoretically predicted ultimate efficiencies."

Here is the link.
solar cell discovery

soph · 2003-01-05 20:22:07

Neutrino->i thought that using certain solar panels, scattered light is just as efficient as direct light? thats according to zubrins book (case for mars maybe...or both...)

neutrino · 2003-01-05 20:53:38

Solar concentrators can concentrate light to a solar cell. The last I have read on them is they have limitation of 4 suns. The solar cell has a problem overheating if you go above that. Now if you are concentrating 4 times the light onto a solar cell but only using a small amount of the electromagnetic spectrum then the maximum up to this date you can count on is 30 percent efficiency. This is the amount of sunlight hitting a solar cell from a solar concentrator. Maybe this is what Dr Zubrin is alluding to. Most of the other light is wasted and scattered back out into space or transferred into heat energy. According to this new discovery they can increase the efficiency to 50 percent to even the maximum of 76 percent. If this proves to be affordable it will help transform the way we live on this planet and the way we travel and live within our inner solar system.

RobS · 2003-01-09 19:21:36

Thank you, Robert, for the correction about wing size.

Regarding the Helios, it uses solar cells that are 22% efficient on top and 11% efficient on the bottom. The wing is transparent and thus can pick up reflected light from underneath; very clever. Anything sent to Mars in 20 years time would certainly be at least 33% efficient, partially making up for the lower level of insolation there. If the new breakthroughs have matured by then, 50% efficiency may be possible. If the Helios were meant to be used by astronauts, you'd probably fly up five or six-meter wing sections and bolt them together on the surface.

-- RobS

dicktice · 2003-01-11 12:32:09

I'm kind of surprised that hovercraft and/or low altitude air-jet "surface" levitated transporters aren't being suggested, using the Martian air via multi-stage compressors, however powered. Lightweight structures and broad-bodied fuselages, I would think, could make this a good engineering approach....

orionblade · 2003-01-17 16:10:19

hey, anyone ever think of using a bicycle on mars? What about pegasus, some guy pedaled accross the english channel in a pedal powered plane. seeing as how there's less gravity, one wouldn't have to pedal quite so hard to get up, and drag would be reduced with the lower density, even with a larger wing. In any case, you could use a bicycle to charge up some batteries, and supplement the solar panels on an aircraft.

someone made mention of high speed transport on mars. This would NOT be less efficient. Higher speeds don't require more energy, they just require the same energy levels for more time, assuming you have some sort of transmission. I can get 40 miles per gallon in my '95 tracker, but I have a five speed. I can go upwards of 100 miles per hour. My friend has an RSX, with roughly the same power to weight ratio, but he can only max out at 25 mpg, and can go 120 miles per hour or better. with regenerative braking, big wheels, and an efficient engine, you should be able to gear it up to go as fast as you want, given terrain conditions and the abilities of the suspension system.

I think that's it for now, except with a helicopter, you don't need a bigger rotor. Not really, anyhow. Since the atmosphere is so much thinner, the local speed of sound is vastly higher. You can thereby spin an airfoil up much faster than on earth. Higher tip speeds equal higher lift, with a properly designed airfoil. Therefore you can pack a standard helicopter with the proper gearing (again with gearing...) to attain a higher tip speed. This would enable roughly equal lifting capability, with perhaps a 10 or 20 percent loss in total lift, but since you have a 60 percent loss in effective vehicle weight, you more than offset the loss. sure you might want a bigger rotor, but i don't see the problem with folding it up? Anyhow, take care, and keep the ideas rolling in.
Rion Motley

dickbill · 2003-01-18 15:30:21

Hi,

If surface area has to be 55 times bigger on Mars, then Mars gliders won't be usuable. But what about multi wing design. You remember the first world war fighters aircraft. They had 2 or sometimes 3 superimposed wing. I think the Red Baron had a three wings fighter, the smaller wing being the lowest. The very first aircraft, in the 1905 years, had even 4 wings. Maybe that design would do better than a glider with a span of 60 meters, very difficult to control during flight and with a very low manoeuvrability.

Echus_Chasma · 2003-01-18 22:44:40

Hehe, I can imagine people flying around Mars in Fokker Triplanes.

RobS · 2003-01-19 23:56:35

Regarding the speed of sound on Mars, I have heard that air density is not important to the speed of sound, but temperature is; colder air has a slower speed of sound. As a result, I read somewhere that the speed of sound on Mars is a bit LOWER than on Earth.

But maybe the air is so thin, it doesn't matter much. I don't know.

My guess is that the air is so thin, helicopters won't work very well. Probably hovercraft as well. Hovercraft would generate an incredible dust problem as well.

I love the idea of biplanes, triplanes, etc. But if the plane needs solar power, you want a big, single wing. If you have a silane/carbon dioxide power source or power cells, then multiple wings would be the way to go.

-- RobS

orionblade · 2003-01-22 00:16:48

I tend to think that if a plane could fly on mars, a helicopter could fly as well. The whole dirigible idea is probbably the best, since you could have a big clear envelope lined on the bottom with flexible solar cells, and hover/lift doesn't require any power, and neither does propulsion if you use one of those drag chutes that someone mentinoed as far as the rover propulsion goes. I'm not sure how it would work exactly, but if you can tack a sailboat, i'm sure you can tack a dirigible against the wind. As far as affixing a sail, that may be the hardest part, so parachutes might suffice. anyhow, hang in there guys, and keep the ideas flying...

Rion

dickbill · 2003-02-09 08:04:35

Hi all,

one of my hobby is to design Mars related 3d pictures, posted at
http://www.renderosity.com/gallery.ez?B … t=dickbill

so, I have a Mars shuttle with delta wings. I want it to glide and land on a martian aifield llike any good shuttle should. The wing's surface in space, enough for aerobracking is too small for gliding, what do you suggest to increase the wing surface:

1) simple adaptative wings, but I don't see how a 22 increase in surface can be achieved by this technique. The shuttle wing span would need a huge, destabiling, increased.

2) biplan then triplan wings, included in the main wing structure, deploy when the speed allows.

3) what about a hang glider wing included in the shuttle piggybacked and deployed at low speed. With a light kevlar carbon structure, such a hang glider could be big enough to provide enough lift for the shuttle to fly.

4) I have the same kind of question for a nuclear powered jet martian aircraft (U2 like). A very light nuclear reactor would heat compressed martian air. So it's nuclear reactor propulsed. does it make sense ?
what else alternatively given that solar doesn't not provide enough power for this kind of aircraft.

thanks for your comments, I don't want to waste time to design 3d objects which don't make at least a little bit of sense.

Euler · 2003-02-09 16:15:34

Helicopters are less efficient then planes, and I think it would be very difficult to get one that works on Mars. On Earth, some planes cane fly in the thin air above 100000 ft, while there aren't many helicopters that can go above 20000 ft.

Unfortunately, a wind-powered dirigible cannot "tack" into the wind. Sails are only capable of providing thrust in the downwind direction or to the side. A sailboat can use sideways thrust to propel it into the wind because the bottom of the boat is shaped so that it will not drift sideways. Dirigibles have no contact with any surface besides the air, so they cannot go against the wind without large engines.

For the Mars shuttle, have you considered deploying a large wing-shaped parachute? A parachute would probably be easier to engineer then the other options, and it should provide a lot more stability.

dickbill · 2003-02-09 18:28:15

For the Mars shuttle, have you considered deploying a large wing-shaped parachute? A parachute would probably be easier to engineer then the other options, and it should provide a lot more stability.

absolutely Euler, the hang glider, a wing like parachute. I think it would be an efficient and simple solution.
A retractable tri-plan could be another possibility maybe. Very compact, strong airframe, but I don't know if aeronautic enginneers ever considered this option. For example, what happen if the triplans from each wing don't deploy exactly at the same moment, the whole aircarft would be destabilized because of the sudden increase of lift from one side and might crash. It seems risky.
Maybe I should try render in 3d boths design to be more clear...

orionblade · 2003-04-04 10:45:52

ah yes, i forgot that a sailboat can tack because the otherwise reverse thrust from the oncoming wind is able to be turned into propulsion because of the force exerted on the keel. I'm sure, however, that there is a way to achieve something similar so that a dirigible can at least go cross-wind, or at a slight upwind angle. On earth of course, there is so much air through which the craft must navigate, that the drag would easily overcome the thrust of any engine the craft could carry, to the point where it might as well be an airplane or helicopter. On mars however, i am not sure this is the case, though the cross sectional area of the craft would be immense compared to one on earth, since to achieve equal buoyancy one needs greater volume. This might wind up giving you roughly the same drag force with the higher wind speeds and lower density of the martian atmosphere. It's still worth checking out, since a dirigible could be anchored during high wind and simply released once the wind died down. It is a highly valuable option if properly executed, since an aircraft may well be heavier if not larger than a semirigid blimp/diridgible type craft. Deflated, it should be able to fit into a container not much bigger than two 55 gallon drums, not counting any crew compartment or engine, yet it should be able to 1-2 tons. An aircraft would more likely weigh upwards of 75% the weight of its cargo.

well i'm utterly exhausted and it's only noon... not exactly up for an hour and a half drive to Richmond this afternoon, but what are friends for... UGH!

take it easy guys, and keep the ideas coming

dickbill · 2003-09-04 16:18:08

Here atm is the contraction for pressure in atmospheres, K is the temperature in Kelvin, mol is the contraction for mole. This means the density of carbon dioxide at 0.7% atm pressure and 0?C will be 0.007 * 44.0098 / 22.256 = 0.01384 grams/litre. The bottom line is you factored gravity in twice. Using your numbers that means Martian wings do have to be 55 times as much area.

Euler, RobS, Robert or anybody, can you clarify ? how much exactly a wing needs to be bigger on Mars ?

My understanding: using the martian air pressure at 0.7% the earth pressure, gives a 142 times bigger wing area needed. But I understand the argument to include the lower gravity and then 142*0.38=54 times the surface that would be needed on Earth.
Fifty four times ! my glider (see the MArs picture thread) is completely unreallistic. I think I will follow Euler's advice: the Wing Parachute. This is the solution: I can imagine a glider, wings retracted, taking off vertically, on the power of a methane oxygen rocket, then, once in altitude, the rocket shut off and a wing parachute of huge proportion would deploy.
I also want the glider to be able to take off on its own from any point of Mars.
Also, if the rocket runs on Methane/oxygen, produced in situ by a Sabatier reactor aboard the glider, what forbids the glider to produce its own carburant IN Flight ? (say the energy comes from solar panels or a small nuclear reactor)

Second question: since a wing surface depends of its geometry, and we want to increase the wing surface without using a wing of unpractical proportion, what happens if the wing is actually POROUS, consisting of small holes inside the wing which actually increase its surface 54 times or more. Is it aerodynamically feasible ?

Third question, sorry to repeat this one. What about a tri or even quadruplan, this in order to increase the total lifting surface. The triplan Fokker quoted previously (remember the Red Baron) had relatively small wings span, same for the quadriplans. Is there a reason why multiplans cannot have big wing-span, as requested for a glider ? Are they aerodynamically unstable ?

dickbill · 2003-09-10 11:32:16

(3) Even more nteresting: The Wright Brothers' airplane configuration could turn out to be the ideal one initially for Mars, including biplane wing warping (in place of weightier, less efficient ailerons), high canard elevator and aft rudder, as well as landing skids and a weighted catapult takeoff. (Thinks: Drop a weight of Mars rocks off one of those high cliffs to see how high you go!)
(4) That so much attention is being given to the Wrights' original designs this Centennial Year of their first powered flight is intriguing, because their configuration has since been recognized as a dead-end, insofar as modern aviation is concerned--being (like the Appollo) optimum for an initial single objective. But on Mars we'll be back at "square one" at first, so might not the Brothers-Wright fly again, there, at least in spirit. . . ?

Thanks for the comment Dicktice,

I have actually completely reshaped my glider. I checked in the web for porous wing and find basically nothing, so I fell in the same conclusion as yours: back to the basics, the "Wright brothers"

OK, my glider is a kind of triplan, it has a very long canard, a very very long wingspan shifted upward to avoid turbulences from the canard and a tail horizontal surface which could give some lift (for that I was inspired from the WWII bipoutre Lightning ). It still includes a small methane oxygen rocket aboard with a small tank.
You don't see very well the glider because it is from behind but I'll post later on the landing on O. Mons, you'll see better.

http://www.renderosity.com/viewed.....New=Yes

Shaun Barrett · 2003-09-12 08:15:21

I've been thinking about Dickbill's problem. No, not the 'eye and the pyramid' paranoia problem, the other problem ... with the winged re-entry vehicle!
I don't think it's quite as bad as it looks.

The density of martian air is certainly a problem and I've run through the calculations again using figures very similar to those put forward by Robert. I've rounded a few of them off to save wear and tear on my brain!
We were always taught you could get away with 22.4 litres as the volume of an ideal gas at Standard Temperature and Pressure (STP). Since I'm only making relative comparisons, absolute accuracy isn't that important.

If we assume the martian atmosphere is all CO2, then the molecular mass of martian air is about 44 grams per mole (a mole of anything being the Avogadro constant or 6.022 x 10^23). With the atmosphere being about 0.7% of Earth's, the density of martian air is 0.007 x 44/22.4 grams per litre, or 0.01375 g/l.
But the important thing is to compare this with the density of air here on Earth which is roughly 4/5ths nitrogen ( molecular mass 28) and 1/5th oxygen (molecular mass 32). This mix of gases gives us a rough molecular mass for terrestrial air of 28.8. The density is therefore 28.8/22.4 or 1.2857 g/l.
If we divide one figure by the other, we get a comparative density of one atmosphere compared to the other. i.e 1.2857/0.01375 which equals about 93.5.
In other words terrestrial air is about 93.5 times denser than martian air. At first glance, since air density is one of the factors involved in aerodynamic lift, this seems to indicate that you would need 93.5 times as much wing area on your martian aircraft as on your home-based one. Of course we can then use the lower martian gravity, 0.38g, to help reduce this terrible ratio, 93.5 x 0.38 giving us a new ratio of about 35.5x.

So, having taken air density and aircraft weight into consideration, are we left with the necessity to make our wings 35.5x the area in order to fly on Mars? Maybe not.
For a start, we've been comparing atmospheric density on datum for Mars and at sea-level for Earth. But our jets still fly perfectly well at the altitude of Mt. Everest, without having to increase their wing area, and air density at that level is about 1/3rd of its sea-level density! (And they can fly more than 2 kilometres higher than that, of course.)
An added blessing of the lesser martian gravity is that the martian atmosphere is 'taller' than ours. In other words, it doesn't lose density nearly as quickly with altitude. So at a height of, say, one or two thousand metres above datum, the martian air is still almost as dense as at datum. Very useful!
So now our wing area ratio can be revised down to 35.5 x 0.333, which equals about 11.8x.

But is increasing the wing area by 11.5x the only way to make Dickbill's vehicle fly? No, it isn't.
The profile of the wings can also be changed.
As you probably know, most of the lift provided by an airplane wing is due to the convex curve on the top surface. (The Venturi Effect) The more convex (or bulbous) the upper surface, the more lift. Of course, this also results in more drag, so we limit the convexity of upper wing surfaces here on Earth in order to fly faster. But, on Mars, the atmospheric drag is very low in the thin air, so much more curved upper surfaces will be possible without having to sacrifice speed.
The same may be true of the 'angle of attack' of the wing, the angle the lower surface makes with the oncoming air flow. Here on Earth, it has been found that up to an angle of about 15 degrees, lift rises steadily. But drag also rises, and quickly, when the angle of attack passes 12 degrees. Again, the lesser drag in thin martian air may allow us to use a greater angle of attack than we can use here, thus allowing greater lift again.
The other big factor is air speed; if you double the speed, your aerofoil's lift quadruples! Thus, with generally higher cruising and landing speeds, and longer runways (! ), a very large increase in lifting performance can be achieved.

Overall then, if we take all the factors into account, we may be able to reduce Dickbill's required wing area down to not much more than that needed by a terrestrial vehicle!

A relatively simple mechanical means of changing the angle and profile of your wings, Dickbill, may be all you'll need to achieve the performance you're looking for.
I hope this is useful

dickbill · 2003-09-12 08:46:48

doesn't lose density nearly as quickly with altitude. So at a height of, say, one or two thousand metres above datum, the martian air is still almost as dense as at datum. Very useful!
So now our wing area ratio can be revised down to 35.5 x 0.333, which equals about 11.8x.

Brilliant demonstration Shaun !
You make me confident that flight is possible on Mars as a usefull way of transportation.
Several remarks:

I am talking about a robust way of transportation here. This is very different of a demonstration concept, such as a NASA glider, limited in mass and which only purpose is scientific.

You mention the datum, indeed the martian atmospheric pressure (and maybe density) sometimes undergoes significant changes, not related to the altitude (as you say, this is a beneficial effect of the low gravity) but related to the seasons, the ambiant temperature, the polar cap defrosting etc. So, maybe that flying on Mars involves bigger air pressure difference than on earth. Flight has to be secure and to take into account these variations, the lift has to be above the minimum, well above, to make it safe. So the surface area has to be bigger than just necessary, for security reasons.

What could be the effect of the dust in the atmosphere ? I've read that the dust is as small as cigarette smoke. Maybe it provides additional lift or drag ?

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