# Why aren't we sending quadcopters to mars?

After watching the MARS series on National Geographic I noticed that they sent one of their crew members down a chasm to check for ice. I wondered, why they did not just take a regular commercial drone with them and explore the chasm with that?

Immediately after that, I realised, we have only been sending rovers to explore Mars till now (which was confirmed here). I think this is far too inconvenient to explore Mars. I understand a rover is more useful if you want to analyse the compounds in the surface of Mars.

Drones could cover a large area in a short time (depending on sunlight). Rovers have covered 40km max on their own:

If we are actually searching for present or past life on Mars, drones would come in way easier; they can fly right over large stones, (or into) chasms and other uneveness on the surface of Mars.

In my eyes, only energy supply would be a problem; however, this is solvable by landing the drones in sunny spots... which drones can find easier.

So, what's the deal?

Update (2018-05): NASA is sending a helicopter to Mars.

• The atmosphere on Mars is really really thin - top of Mt Everest thin. How well would these drones work at 30,000 feet? – Dan Pichelman Nov 28 '16 at 20:05
• He means the air on the surface of Mars is so thin, it'd be like trying to fly a drone on Earth at 30k ft. – Hobbes Nov 28 '16 at 20:10
• Except it's more like 30km, not 30k feet. At 30k feet atmospheric pressure is about 32% of sea level. – Russell Borogove Nov 28 '16 at 20:43
• @DanPichelman Here;s a quick way to check: A rough value for surface atmospheric pressure on Mars is 1% that of Earth, though it varies due to extreme variations of surface altitude on Mars. $ln(0.01)$ is about -4.6 meaning the Earth's atmosphere reaches 1% of sea level pressure at about 4.6 times the scale height. Earth's scale height is something like 8 kilometers, so it reaches 1% at about 37 km or roughly 120,000 feet, not 30,000 feet. Compares well to tabular values of about 110,000 feet. – uhoh Nov 28 '16 at 23:28
• Obligatory link: what-if.xkcd.com/30 (I'm surprised noone posted it yet) – Federico Nov 29 '16 at 15:33

Mars has two disadvantages compared to Earth:

• it's farther form the Sun, so you get less sunlight.
• Atmospheric density on Mars is 0.011 kg/m3 (at the surface, at a temperature of 0 °C). On Earth: 1.2 kg/m3, so Mars' atmosphere has 1% of the density of Earth's. Lift is proportional to air density, so a wing will have 1% of the lift on Mars.
• Gravity is 38% that of Earth.

A consumer drone that can lift 0.5 kg (total weight of airframe and payload) on Earth, can lift 7.5 grams on Mars. This means you need a large aircraft to accomplish anything.
(thanks to a comment by Russell Borogove): A drone massing 0.5 kg carrying 0.5 kg of additional payload on Earth must produce 1.0 kg-f of lift to hover; on Mars the same drone produces about 0.01 kg-f of lift (or less) but needs 38% of 0.5 = 0.19 kg-f to get off the ground with no payload.

This also explains why it hasn't been done yet: only recently have batteries achieved the power density you need to get a drone to lift off at all on Mars. In the last 30 years, batteries have doubled in energy density, with most of that change happening in the last 10 years due to the increased popularity of mobile phones.

Until now, helicopter flight on Mars just wasn't possible because an engine and power source powerful enough to fly the aircraft would be too heavy to be lifted off the ground.
And electric power is the only feasible technology for aircraft on Mars. An internal combustion engine would need oxygen as well as fuel, and you'd have to transport them to the aircraft (too expensive), or make them in-situ (theoretically possible, but has not been demonstrated yet).

NASA is looking into adding a drone to an upcoming mission.

Individual daily flights would be limited to just 3 minutes or so due to power constraints. The helicopter would likely fly as high as 330 feet (100 m) and cover a ground track of about 2,000 feet (600 m) each day, the researchers said.

• Perhaps worth mentioning is that any worthwhile exploration would require more than just a camera - an arsenal of sample-collecting equipment and a well-equipped lab to process collected samples and observe/measure the results. The latest Mars rover was basically a mobile lab - quite the engineering feat in and of itself. To get one airborne in the thin Martian atmosphere would be far more heroic. – Anthony X Nov 29 '16 at 2:08
• @AnthonyX Combine a ground based, wheeled lab with an airborne sample collector & that problem is largely solved. Many other problems with the idea, but others have covered those.. – Andrew Thompson Nov 29 '16 at 7:40
• I think that would still serve a good purpose. I imagine the qc resting on the rover collecting solar power until it is fully charged. Then going on a flight of a few minutes to take pictures of the local area which can be used to make better decisions on which direction the rover should move the next day to maximise it's effectiveness – Darren H Nov 29 '16 at 8:37
• @Btuman the power (mass) density of RTGs is truly awful, though their energy density is pretty stellar. Flight requires a high power-to-weight ratio, for either generating thrust/lift, or more subtly, actuating controls so you don't slam into a rock. – Nick T Nov 30 '16 at 17:48
• I think this answer is complete from an engineering standpoint. Having worked at JPL, I can say definitevely that the issue is at least 50% science driven. A small bodied vehicle of any kind can't do much science other than taking pictures. Also, missions are often designed to target one feature in one area, so speedy travels aren't really vital. We have oribters for taking pictures over large areas, after all. Mars 2020 rover will travel much much further and is the first many-site rover mission we've had. Even that mission has to collect samples, something a quad can't do. – Josh Vander Hook Sep 21 '17 at 17:50

An additional issue that needs to be addressed: such a drone would need to be completely autonomous, or at least have an autonomous controller (rover?) on the Mars surface.

The drone in your example is piloted remotely, but the signal delay between Earth and Mars varies between 4 and 24 minutes (one way), depending on their relative orbital locations.

At some level, this implies the military-grade hardware you wanted to avoid.

To address some of the comments, don't forget that you don't have any GPS for guidance. Your drone needs to be able to take an entire sequence of commands, execute them with complete autonomy in harsh, uncertain conditions, and report results for further analysis. Yes, it's "just software", but that's handwaving away some pretty significant hurdles.

Military grade doesn't mean it has to be developed by the military, but that it has to be developed to a precision that goes beyond most consumer applications.

So here are some of the harsh conditions that such a device would need to deal with:

• Dust. Dust everywhere.
• Global dust storms that can last for months
• Variable winds (during dust storms these have been measured with gusts up to 94 km/h)
• Low thermal inertia - rapid heating/cooling cycles, around 100 K per daily cycle.
• Along with that, extreme cold. Different regions are obviously different, but polar temperatures can go as low as -153 C; equatorial regions can reach a balmy 20 C at summer noon, but the nightly lows can fall to -100 or more.
• No magnetic field, so high cosmic radiation. And no magnetic guidance either.
• Not sure how this goes "military-grade"; if you're just trying to do a general survey, with basic object avoidance and even the ability to go back and look for more details if so instructed, there's nothing military-grade about that. Actually analyzing those details and autonomously deciding whether something needs additional investigation is more advanced, but it's still just software. – Tin Wizard Nov 28 '16 at 22:47
• No, more like "pizza deliver-grade hardware." Military-grade hardware has several distinct capabilities and technologies beyond this. – uhoh Nov 28 '16 at 23:12
• @RedSonja GPS constellation for Mars – user Nov 29 '16 at 13:41
• @Mayou36 No dust, on Mars??? – GalacticCowboy Nov 29 '16 at 14:15
• Also, it is not your usual dust. The dusts on Mars are way finer (they are called fines for that reason). They get into everything and cover everything – njzk2 Nov 30 '16 at 14:03

To complement Hobbes' answer with a few numbers, a basic comparison of the power requirements for a lifting rotor on Earth and Mars is presented:

The approximate ratio of surface atmospheric pressures of Mars and Earth:

$$R_M/R_E = 0.0123$$

The approximate ratio of surface gravity, and therefore required thrust on Mars and Earth:

$$T_M/T_E = 0.379$$

From actuator disk theory, the power requirements of a rotor scales via the following:

$$P_M/P_E = (T_M/T_E)^{1.5} (R_E/R_M)^{0.5}$$

Therefore, the same rotorcraft on Earth would need around 2.1 times the power to lift itself on the surface of Mars.

Side note, to achieve the same power requirements, you'd need to beef up the rotors to 4.42 times the disk area.

Actuator disk theory is the most basic and idealized analysis you can put forward for this kind of problem. It neglects a whole host of effects like blade drag, compressibility, etc, which all tend to increase the power requirements even more.

Note that as with all aircraft, the more power you need, the bigger the batteries and motors you require to fly. This leads to greater required thrust to lift those bigger motors and batteries which increases power requirements. Extend this argument and you can see that the power requirements and hence the weight of the aircraft tends to snowball. Pop this on a rocket and it tends to snowball the cost of the launch and delivery system too.

Added note: another factor to take into account is Mars low sound velocity due to its low temperature, and the fact that to produce enough lift, a rotor would have to rotate at very high speeds. In such case, a great proportion of the rotor would be in a supersonic flow, and in such cases, the lift is generally entirely lost due to the aerodynamic shock. One side note: if we didn't have this phenomenon, the rotor would naturally rotate at much higher speeds for the same power than on Earth since the air resistance from Marsian athmosphere is so low.

You're looking on the wrong planet.

As others have said, Mars's atmosphere is too thin for a drone to generate sufficient lift. It's also worth pointing out that satellites can do and have done a very good job of mapping planets and moons from orbit, even being able to detect possible water using spectrographic techniques.

Venus, on the other hand, has a very thick atmosphere, and surface temperatures that are inhospitably high. Flying probes, both of the heavier than atmosphere type and the balloon / airship type have been proposed for that planet.

The trouble is, there's not that much of interest to be seen at height, so some proposed missions have decided to have a surface rover for exploration, too, with the main computers and interplanetary radio flying around in the relative cool of the upper atmosphere.

Here's an example proposal. We'll see if it becomes reality.

https://www.newscientist.com/article/dn7354-to-conquer-venus-try-a-plane-with-a-brain/

• A better planet for drones? Mercury is too hot and the atmosphere too thin, Venus is too hot and too dense to land. The temperature on Mars is OK for rovers and drones but the atmosphere too thin. There is one more of the four inner rocky planets with very good conditions for drones, but this planet is no target for space exploration. We all know this planet well, it is our Earth. The four outer planets are gas giants and drones would be destroyed long before landing on the surface of their rocky core. But do we know for sure that there is a rocky core inside? – Uwe Nov 29 '16 at 14:22
• @Uwe Titan has a nice thick atmosphere and is, of course, rather cool. Don't overlook the moons. – Samuel Nov 29 '16 at 16:56
• @Samuel: The pressure of the atmosphere of Titan is nice for drones, but the intensity of solar energy is very low. The distance of 9 to 10 AU to sun results in 1/81 to 1/100 of the radiation level in an earth orbit. Loading the battery of a drone using solar cells would require a pretty long time. But the temperature is to low for the batteries to provide enough power for a flight. The same is true for all other moons of gas giant planets, the distance to sun is to large for using solar cells. – Uwe Nov 30 '16 at 10:06

This supplemental answer may be of some interest to the use of quadcopters on other solar system bodies. The Phys.org article Researcher sets eyes on Saturn's largest moon describes the potential application of large (~2 meter) quadcopters on Saturn's moon Titan. A surface gravity of only 0.14 that of Earth and a surface pressure 1.45 that of Earth's are much more accommodating to an aircraft than those on Mars.

An artist’s rendering shows the proposed Dragonfly quadcopter landing on the surface of Saturn’s moon Titan, unfolding its rotors and lifting off again to survey the landscape and atmosphere. Credit: Steve Gribben/Johns Hopkins APL

• The energy to fly is not generated with solar cells, it is from a Radioisotope Thermoelectric Generator. But to get enough power for a flight, batteries are charged during a Titan night. Of course the duration of a flight is much shorter than the necessary time to recharge the batteries. – Uwe Feb 24 '18 at 9:16
• Is the RTG part of the copter, or on a static base station that the copter has to return to to recharge? – Steve Linton Feb 24 '18 at 17:34
• @SteveLinton dunno, so I've asked Does the Dragonfly project (quadcopters on Titan) envision attached RTG's or would they be static and revisited for charging? – uhoh Feb 21 '19 at 10:50