Design me a Mars drone

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.

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?

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

3. 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.}

posted about 9 years ago

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