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In this question about a Mars battle set up in 2100-ish, we decided, that the best battle devices would be drones. In that setup the whole "drone" thing was hand-waved, but I would like to know if it is doable:

  • Year: 2040-ish
  • Setup 6th mission to Mars. We want to discover more area by having drone with us. Such a drone will be guided by Mark Watney (I am bad in names :)) from Martian ground.

Questions:

  1. Is drone feasible at all? For this drone = device which is heavier than atmosphere, but uses atmosphere (either wings or rotors) to keep itself above the ground
  2. I am assuming that such device would use rotors. How big rotors do I need to keep 5 kg heavy drone above martian ground?
  3. I am assuming battery powered drone. How much energy do I need?

Limitation: Please stay at current level of technology. Basically, you can only use whatever exists now, because I have assumption that what is "cutting-edge" by today standards, it will be "sturdy enough to survive on Mars" by 2040ish

Edit: By "drone" I did imagine something using rotors: drone Image credit: Wikipedia

Generally, I would like to have something which can fly and maneuver above a relatively small (maximum 1km) area.

Please note the tag. I want you to put down some elaborate guesses. Extra points for doing so.

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  • $\begingroup$ Side note: Check out these two sites for first and last names. At least for Earthlings. $\endgroup$ – Frostfyre Aug 20 '15 at 13:09
  • $\begingroup$ please don't take the fun away for these explorers, get them each a solar powered ATV! They will have to pedal back when night falls. $\endgroup$ – user6760 Aug 20 '15 at 13:20
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    $\begingroup$ Interplanetary Cessna has a description of what flying on Mars would probably be like. Or consider the Aerial Regional-scale Environmental Survey of Mars (ARES), which is a fixed-wing (not rotary) design straight from NASA. $\endgroup$ – a CVn Aug 20 '15 at 13:30
  • $\begingroup$ in "The long Mars", Gliders are employed for travelling in the mars atmosphere. I have no clue if that is feasible, but given it was written by Sir Terry Pratchett and Stephen Baxter, i have reason to believe it should at least be nearly feasible. The basic idea is that if it goes fast enough, it creates enough lift to stay airborne. $\endgroup$ – Burki Aug 20 '15 at 14:12
  • $\begingroup$ It's been done. A flying craft was designed for a mission to fly on mars for the 100th anniversary of Kittyhawk. It wasn't funded, but there were papers written on the marsion long-endurance aircraft. $\endgroup$ – JDługosz Aug 20 '15 at 16:58
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I'm incredibly embarrassed to be chasing the bounty here, but I can't resist the challenge. Besides, drones are cool.

Okay, to start with this, we need to know just what developments have been made in this area. The major project in the rotor-powered-drones-on-Mars field is the ESA's Dropter project1, from the StarTiger initiative. The Dropter project is not meant to be directly channeled into a Martian probe, but is merely a test of technology. Its flight envelope has not been particularly pushed; in its final test (under Earth surface gravity and atmospheric pressure) the drone was used to reach a height of 17 meters before descending and lowering a rover to the ground. It was guided at first by GPS and then by visual data.

There are some difficulties associated with chucking the Dropter onto Mars and seeing what happens:

  • There is no GPS network on Mars. As noted in GPS / Iridium for human presence on Mars?, there is currently minimal demand. However, NASA's Deep Space Network solves those problems with a large network of receivers, so the positions of all autonomous craft are known. The communications delay could be an issue, though.
  • The Dropter has not been tested in conditions like those on Mars. The StarTiger team rigged up a recreating of the Martian landscape, but the atmosphere was still the atmosphere on Earth, and the surface gravity was still the surface gravity on Earth. NASA is researching conditions for aircraft on Mars, but a lot is still up in the air. Also, most designs proposed are fixed-wing aircraft, not rotorcraft, and the rotorcraft designs have been small, as noted in Young et al. (2004).

Young et al. (2004) is the most in-depth study on Martian rotorcraft that I could find. It's eleven years old, but it does cover some rather important points that I'd like to mention:

  • Range: Smaller scout drones - along the lines of your idea - are probably limited to an operational radius of 50 km. That's rather large, especially for a scout craft. It will also be perfectly fine for your specifications (1 km). Larger (manned) craft could reach distances of a couple hundred km.
  • Energy use: Rotorcraft - especially small ones - take up a lot of energy compared to traditional rovers. There are, of course, some advantages to flying, primarily being able to travel over large obstacles (e.g. mountains and canyons) at comparatively high speeds.
  • Rotor mass: Martian rotors must be lighter than terrestrial rotors - perhaps only one-tenth as massive. This severely constrains choices of materials.

Young et al. (2002), a related study, focused on the types of craft you seem to be looking at: small, light drones with scouting ability. In that study they listed some requirements and calculations for drones of this type, typically weighing 10 to 20 kilograms:

  • Two rotors, with four blades per rotor
  • Rotor radii of 1.22-1.72 meters
  • Top cruise speed of 40 meters per second
  • 50 km range

They also discuss tests that have been done2:

  • Single-rotor hover tests in a simulated Martian atmosphere
  • Coaxial rotor hover tests in a simulated Martian atmosphere
  • Tests of visual navigation techniques3

One important test that had not been done as of the publication of the paper was the choice of power, between electric motors (with regenerative power technology) vs. an Akkerman hydrazine engine. The latter is based on ideas by Akkerman (1978) (paywalled!) and mentioned in Young et al. (Date?). A good comparison for propulsion is Young et al. (2001). The Akkerman engine provides greater power, but electric motors are cleaner and have no harmful waste products. Electric motors have their issues too: fuel cells can produce contamination, and solar power isn't always easily accessible - or enough.

More investigation has been done, and specific designs have been covered (see this NASA slideshow). Here is the design given in that slideshow:

Notice the coaxial rotors, a common feature in designs for Martian rotorcraft.

So, answering your specific questions:

  1. Is drone feasible at all? For this drone = device which is heavier than atmosphere, but uses atmosphere (either wings or rotors) to keep itself above the ground

Absolutely. Most studies are optimistic but agree that it is possible.

  1. I am assuming that such device would use rotors. How big rotors do I need to keep 5 kg heavy drone above martian ground?

You can get a 10 kg drone off the ground using rotors 1.22 meters in length.

  1. I am assuming battery powered drone. How much energy do I need?

That depends on the mission capabilities and other instruments on board, but 1550 watts for a 10 kg craft should be fine, according to Young et al. (2002).


1 "Dropter" is a contraction of "dropship" and "quadcopter".
2 All tests are from during or before 2002, when this paper was published.
3 These would have been the precursors to some of the navigation used for the Dropter project.

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  • $\begingroup$ This deserves all the points. Especially for making me proud that this is partially ESA idea ;) $\endgroup$ – Pavel Janicek Aug 23 '15 at 12:14
  • $\begingroup$ @PavelJanicek Aw, thanks. :-) The ESA does seem to have beaten NASA's Skycrane idea for the Curiosity rover in terms of coolness. $\endgroup$ – HDE 226868 Aug 23 '15 at 13:13
  • $\begingroup$ FYI, the GPS problem should be somewhat solved by the target context. These drones are launched from already-established science bases on Mars that have been there long enough to get angry and start a war, so they should have plenty of time to set up at least a local positioning system. $\endgroup$ – MichaelS Aug 24 '15 at 2:09
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Wikipedias article Mars aircraft leads us to Sky-Sailor. This is a 2.5kg drone that would fly using 13.2Watts of solar power. So for a 5kg probe I would suspect between 26.4 Watts(linear growth) and 105.6 Watts(cubic growth) is reasonable guesses.

Sky Sailor has a wingspan of 3.2 meters and is a fixed wing aircraft though, so it's not cabably of hovering. It's also not intended to be capable of take-off, instead it's released from a spacescraft after athmospheric entry.

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    $\begingroup$ Wikipedia does not satisfy the requirements of the hard-science tag. $\endgroup$ – HDE 226868 Aug 22 '15 at 16:54
  • $\begingroup$ As I pointed out on another comment, Wikipedia is a very good place to start looking. One of the links on the page Taemyr linked to is dtic.mil/cgi-bin/GetTRDoc?AD=ADA480702, which is a paper on experimental rotorcraft. They don't go into the science behind how they came to their conclusions (and some of their references are "private communication"), but they suggest using a 1.5 kW motor to power a 2-rotor, 4-blade-per-rotor, coaxial setup, 10 kg rotorcraft with ~50 km range. This seems to fit your requirements better than the Sky-Sailor mentioned. $\endgroup$ – MichaelS Aug 24 '15 at 2:01
  • $\begingroup$ The Sky-Sailor (sky-sailor.ethz.ch) is a fixed wing aircraft that has a lot of cool features, but it's designed to be launched from orbit and stay airborne through it's entire mission. It doesn't have hovering capabilities, and can't take off once it's landed on the ground. As such, I don't think it really fits the concept of a Martian battle drone. On the other hand, it could be very useful as a one-way Kamikaze type drone. Launch it from a stationary aircraft-carrier type platform, and you could reach the enemy facility with much less power requirements. $\endgroup$ – MichaelS Aug 24 '15 at 2:03
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According to wiki, average pressure on Mars is 0.6 kilopascals (0.087 psi), while atmospheric pressure on Earth is 101.3 kilopascals (14.69 psi) - the pressure on Mars is 170 times lower, than on Earth. According to Roto craft altitude record, the Rotorcraft can operate on heights of 12,442 meters. The pressure on this height is 3-4 times lower than on sea level, still at least 50 times higher, than on Mars. I think Mars atmosphere is too thin to support rotor craft.

UPD: by rough estimations, the 5kg machine need to have 10m rotors. UPD1: probably you can build flying drone as big dirigible, but it is not a combat device - it is really easy to detect and shot. Sand buggy / tank with machine guns looks more realistic for me, or even the bipedal bot like in Red Faction looks more realistic bipedal bot like in Red Faction

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  • $\begingroup$ Wikipedia does not satisfy the requirements of the hard-science tag. $\endgroup$ – HDE 226868 Aug 22 '15 at 16:55
  • $\begingroup$ Wikipedia is one of the better sources of hard science you're likely to find in many cases. Following the wikipedia link, you can see (with a bit of extra legwork due to the dead link on the wiki page) that the FAI has certified Jean Boulet with the highest altitude of a 500-1000 kg helicopter without payload at 12,442 meters in 1972. (fai.org -> records -> more records -> "rotorcraft 1972" -> search). Atmospheric pressure on Earth is commonly known and easily verified at around 14.5 psi / 1 bar / etc. Mars pressure is also easily verified. nineplanets.org/mars.html puts it at ~7 mbar. $\endgroup$ – MichaelS Aug 24 '15 at 1:41
  • $\begingroup$ The place I'd worry about citations is the "by rough estimations" section. What math / website / physics model / etc. was used to come to that estimate? $\endgroup$ – MichaelS Aug 24 '15 at 1:43
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Personally, I'm not sure that drones would really be the ideal way to do battle in the hypothesized scenario. The problem with your hovercraft idea is that the hovercraft itself is fairly useless unless you're trying to annoy them to death. You could put some small guns on the hovercraft then shoot at people, but you're not going to do much once they realize you're shooting at them. They'll just wait inside until you run out of fuel. You could use the hovercraft to plant explosives, but it's going to be tricky to get the explosives somewhere useful.

It would probably be much easier to design a self-guiding missile with a fairly large explosive payload and just destroy critical sections of the enemy compound than to design and pilot drone aircraft in some kind of dogfight. A missile is a sort of drone aircraft so it could apply here. One big advantage of a missile is they move extremely quickly and would be almost impossible to defend against. Additionally, the high speeds of a missile mean you can use its kinetic energy to help penetrate enemy walls to detonate inside rather than out. http://hypertextbook.com/facts/1999/SeanManning.shtml cites missile speeds of 860 m/s and higher, but a crude missile made in a few days by some random nerds would likely have a lower velocity. Still, the low air density and gravity on Mars mean you can get very good results with lower power. Depending on resources available, it could be feasible to create multiple missiles and target every building in the enemy facility at once.

With fewer missiles (or the prospect of a long development/fabrication time per missile), you'd want to be strategic about your initial targets. The specifics would depend on the actual configuration and logistics of the enemy base, but in general the priority is preventing them from counter-attacking. Unless you have access to extremely high-yield explosives, you're not likely to kill all of them quickly. So you'd want to destroy things like their life support and let them freeze to death or suffocate rather than attacking them directly.

The scientists would have access to rocket fuel (they have to leave Mars somehow) and all kinds of chemicals that that could be used to make decent explosions. Depending on the nature of the mission, they might have premade explosives for blowing holes in the local rocks. For example, mining operations. At this point, they just need to make a missile.

As pointed out in other answers, air pressure and density are much lower on Mars than Earth, so missiles would need much larger fins for guidance, at which point they would begin to resemble airplanes rather than traditional missiles. Something like the Sky-Sailor might be a good start for this, but unless you really want to save fuel, you don't need aerodynamic lift. Given the abundance of rocket scientists, you could also forego guidance fins and use maneuvering thrusters like a spaceship.

Cameras in the missile could be used to identify and aim for a target structure, making it virtually impossible to jam the device. Alternately, it could be remotely guided, or use some type of local GPS to detonate at a target coordinate, but those methods would be easier to jam and/or hijack the missile. Still, the war likely wouldn't last long enough for either side to develop methods for hacking the opponents' missiles, so it might be fine.

One problem you'd have with explosives on Mars is the lower air density. Explosions typically work by temporarily increasing the local air pressure to extreme levels which causes damage. But a thousand-fold increase in Martian air pressure is much less of an issue than a similar increase on Earth. (This is also why explosions in the water can be much more devastating than those in air.) Unless you were able to land on the surface of a structure then detonate, concussive forces will be fairly non-lethal.

However, you can still use explosives to good effect by encasing them in something hard and dense. The explosion then rips the casing apart and showers the area with high-energy fragments which work regardless of atmospheric pressure. This is the basic premise of a fragmentation grenade.

A similar idea is the premise behind firearms and some types of mines: Put the explosive at one end of a tube, then pack ball bearings or similar in front of the explosive. Detonate right before you hit the target structure and you've got a shotgun blast. There are three advantages of this method over the previous method: First, you aren't wasting much energy tearing the casing apart. Second, you can focus the energy into a small angular area which in turn means A) you aren't wasting energy throwing fragments into the sky or ground and B) you'll do much more damage to the smaller area and be more likely to tear all the way through. Third, the force of the impact isn't going to be nearly as affected by the distance to the target (a spherical explosion means the fragments per square meter decrease inversely with the square of distance, while a shotgun blast is fairly collimated and the damage decreases in an almost linear fashion).

An even better method, although trickier to pull of, is to detonate an explosive inside the enemy facility. This way the dense air inside propagates the energy much more efficiently, and damage to critical systems will be much higher. One method is an armor-piercing explosive. This type of explosive has a very dense nose cone designed to punch a hole in the wall of the facility, allowing the rest of the missile to follow and land inside, at which point it explodes in a normal fashion. A second method would be to detonate one explosive outside, creating a breach in the wall, then following right behind with the payload explosive that flies through the hole you left and detonates. A third, more Hollywood method, would be to covertly fly or drive a vehicle through the front door, down various corridors, and then explode. The best bet for pulling this off would probably be to land the explosive inside a crate outside the building and wait for the enemy to bring the crate inside for the night (or something similar). You might also land inside an open maintenance bay or airlock, then wait until it's been pressurized to detonate, but detection would be more likely.

If you don't consider missiles to be "drones" and must use something like your picture above, all of the above can be applied to a rotorcraft with explosives. However, you're less likely to penetrate the enemy structure with momentum and would almost have to use a two-stage or covert approach to get the primary explosives inside the building. A two-stage approach would be hard though, because you'd want to detonate while internal pressure is still high, and the air venting out the initial hole would blow the rotorcraft away.

Also, the size of the rotorcraft or missile is going to depend greatly on how much explosive you need to destroy the enemy compound. 5 kg might not be enough if you're trying to destroy a 100-meter dome. Here's a YouTube video of 4.5 lbs (2 kg) C4 inside a bus: https://www.youtube.com/watch?v=0nc98hzR-tk. You certainly wouldn't want to be in that bus, but the blast force goes down exponentially with distance, and even the fairly small bus isn't completely destroyed. On the other hand, domes would be extremely expensive, and likely much smaller than 100 meters.

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