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Mars Space Science

Aerial Drone To Hunt For Life On Mars 152

Posted by Soulskill
from the care-for-some-martian-venison dept.
astroengine writes "What if the Martian terrain is too rugged for a rover to traverse? How do we study surface features that are too small for an orbiter to resolve? If selected by NASA, the Aerial Regional-Scale Environment Surveyor (ARES) could soar high above the Martian landscape, getting a unique birds-eye view of the Red Planet. Its primary mission is to sniff out potential microbial-life-generating gases like methane, but it would also be an ideal reconnaissance vehicle to find future landing sites for a manned expedition. Prototypes of the rocket-powered drone have been successfully flown here on Earth, so will we see ARES on Mars any time soon?"
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Aerial Drone To Hunt For Life On Mars

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  • Re:Rocket-powered? (Score:3, Informative)

    by edumacator (910819) on Monday November 15, 2010 @04:39PM (#34235986)

    Wouldn't that make ballons better?

    The problem there is there is no clear path for it to take. It would be at the mercy of the winds, which can reach up to 100mph.

  • Re:Rocket-powered? (Score:4, Informative)

    by Lord Byron II (671689) on Monday November 15, 2010 @04:43PM (#34236034)

    Balloons work off of the differential between the inside air pressure and the outside air pressure. If the outside air pressure is low, then even if you manage to generate a vacuum inside the balloon, the differential is still small and therefore so is the lift.

  • Re:Rocket-powered? (Score:2, Informative)

    by icebike (68054) on Monday November 15, 2010 @04:57PM (#34236180)
  • Re:Rocket-powered? (Score:2, Informative)

    by Nadaka (224565) on Monday November 15, 2010 @05:01PM (#34236224)

    What? I can't tell if you are trolling or on crack. "Vacuum" inside a ballon? really?

    For all intents and purposes, given the same temperature and pressure any volume of gas has approximately the same molar density.

    Hydrogen and Helium balloons float because they have less mass per molecule than earth air (and much less per molecule than mars air), and that mass difference is enough to make up for the relatively high density of the relatively thin balloon.

  • Re:Rocket-powered? (Score:3, Informative)

    by Anonymous Coward on Monday November 15, 2010 @05:03PM (#34236238)

    Physics FAIL

    Pressures inside balloons (and anything else like water droplets for that matter) are actually higher than the ambient pressure by an amount related to the surface tension of the membrane or liquid-gas interface.

    Also, bouyancy works based on density differences, not pressure differences. You can have compress air to have as high a pressure as you want and it will still float so long as the final density is less than water's.

  • Re:Rocket-powered? (Score:3, Informative)

    by icebike (68054) on Monday November 15, 2010 @05:03PM (#34236240)

    Balloons work off of the differential between the inside air pressure and the outside air pressure. If the outside air pressure is low, then even if you manage to generate a vacuum inside the balloon, the differential is still small and therefore so is the lift.

    Balloons work on a difference in WEIGHT of the gases inside the balloon compared to the outside air that is displaced.

    It has nothing to do with pressure. Hot air balloons are not sealed, they are open at the bottom. Essentially zero pressure differential.

    See, those days you skipped out of science in the 7th grade to smoke weed in the park come back to bite you.

  • by khallow (566160) on Monday November 15, 2010 @05:07PM (#34236306)

    That depends on your definition of environment. Planting our Earth manufactured robot underneath a bunch of martian sand might have profound effects in the future, butterfly and all that.

    It obviously does have a profound affect on the future in that it expands human knowledge concerning Mars considerably. But the sort of effect you're refer to is not a genuine change, but just a slight bump to a chaotic system (which it is reasonable to assume Martian weather is). All the good and bad parts of martian weather would happen anyway with the same frequency and we still would be relatively clueless as to what weather is to come. So it doesn't change anything for us nor does it change anything for any Martian life that happens to be there. The environment is not the second to second changes in Martian weather. It's the long term stuff which remains after you filter out the short term chaotic noise.

  • Re:Rocket-powered? (Score:5, Informative)

    by Caerdwyn (829058) on Monday November 15, 2010 @05:08PM (#34236326) Journal

    Typical Mars surface air pressure varies between 6 and 10 millibars, depending upon season and land altitude. Assuming relatively low altitude flights, it's quite possible to build aircraft that can fly in that density (particularly given that Mars' surface gravity is only about 40% of Earth's). What are the constraints?

    1. Velocity. At 6 millibars, you're looking at a near-supersonic speed to stay aloft. Sure, that's not a big deal from a drag perspective when the air is that thin, but your propulsion system has to be able to maintain that. Can propellers do that? Yes. The XF88B [wikipedia.org] could maintain 0.8 Mach.

    2. Flutter. Unlike drag, which is heavily dependent upon the product of air density, velocity and drag coefficient, flutter is only really dependent upon airspeed. Think of it as a kind of resonance. As the air flows over the wing, the wing vibrates like a guitar string. Aircraft have literally shaken themselves apart when they hit a critical airspeed; this remains an issue today (example: builders of the Van's Aircraft RV10 are warned about relying upon airspeed indicators if they have a turbocharged or supercharged motor, as at the service ceiling of 18000 feet the absolute airspeed max of around 250 knots will only be shown as 160 knots on most mechanical airspeed indicators... and at 250 knots, you're int he danger zone for flutter). This can be engineered around, though at the airspeeds necessary it won't be easy.

    3. Energy. So how do you propel this thing? Unless it's going to be a short mission, chemical propellants are right out (especially given that you need to carry both the fuel AND the oxidizer, as there's no "free" oxygen to be found. Solar-electric is being discussed, and may actually be viable; the plane would probably have to "race the sunset" to stay in sunlight constantly. This is very doable, though. At the equator, Mars has a curcumference of about 13,000 miles. At that size, with a 24.5 hour day, an aircraft would have to maintain a bit over 500mph to stay in sunlight. However, as this is likely to be near the speed necessary just to stay aloft anyway, it's a nonfactor. If you're powered enough to fly, you can stay in sunlight.

    Yep. There are problems. But none of it is insurmountable. How much tax increase are you willing to endure (and convince others to endure) to accomplish this? If that number's high enough... yes. It CAN be done, with propellers and lift from wings (as opposed to vectored thrust). The challenges are the power system and overcoming flutter, but these are solvable.

  • Re:Rocket-powered? (Score:5, Informative)

    by snookums (48954) on Monday November 15, 2010 @05:34PM (#34236564)

    What the GP is getting as is that the theoretically most efficient aerostat you can build is one with a rigid shell and an evacuated interior. It's not really a balloon, per se, hence the confusion.

    Any actual balloon full of gas will always have less density differential than this, and thus generate less lift.

    In practice, the mass of extra material required to build a rigid shell generally outweighs any extra lift you could get over a hydrogen or helium balloon. Hence, you don't see evacuated aerostats outside science fiction (e.g. Diamond Age by Neal Stephenson).

  • Re:Rocket-powered? (Score:3, Informative)

    by icebike (68054) on Monday November 15, 2010 @05:40PM (#34236630)

    Read some of the article found by Google. Most of them written by professionals in the field. They seem to disagree with your assessment.

    I'm sure you've heard about balloon flights around the world. Steve Fossett RIP.

    Do the math. Less gravity compensates for less atmospheric density on mars to the degree that you would only need a balloon twice as big for the same payload as on earth.

    Doable.

  • Re:Rocket-powered? (Score:3, Informative)

    by sznupi (719324) on Monday November 15, 2010 @05:49PM (#34236708) Homepage

    "Extremely small"? Just look at payloads quoted - the drone from TFA will most likely carry less (for just an hour)

    What didn't work for past attempts was primarily the funding - something the UAV project also has big and longstanding problems with.

  • by khallow (566160) on Monday November 15, 2010 @06:29PM (#34237028)

    Though we are sterilizing landers, just to be safe (I wonder how that will look with eventual manned exploration - we can produce sterile lab animals, but...) - and tenuousness of Martian atmosphere means even a miniscule additions make a noticeable difference (like that methane mystery - which, in the end, represents an exceedingly small amounts)

    You're mixing two different definitions of "sterile". Sterile animals simply are animals which can't reproduce. They remain chock full of microbes. Sterile landers are landers that have been exposed to adverse conditions in order to kill off bacteria and other microbes on the probe. The first few long term missions to Mars may involve sterilized humans, but that's because whoever their managers are don't want the sizable risks and obligations of pregnancy and birth to interfere with the missions.

  • Re:Rocket-powered? (Score:3, Informative)

    by Caerdwyn (829058) on Monday November 15, 2010 @07:58PM (#34237734) Journal

    Can propellers do that? Yes. The XF88B could maintain 0.8 Mach.

    That's in Earth atmosphere, though. Doesn't the efficiency of propellers directly depend on the density of air?

    It does, yes. Remember though that the density of the atmosphere is much lower than surface at the altitude at which those tests were performed (100mb or less). There's no question that the props won't be of the same efficiency... it's only if they're "good enough".

    There's the additional issue of prop blade speed. While it's very hard to make a conventional prop work well at supersonic speed from the point of view of "how fast is the prop moving forwards", there is also the issue of "how fast are the prop blades moving rotationally". When you take into account the forward motion and the rotary motion, the path a blade takes through the air is a helix. And depending upon how fast the blade is rotating and how far away from the central axis you are, part of the blades may be supersonic near the tips while near the root they're subsonic, and you have a sonic transition sliding back and forth along the blade. This is nothing new; World War II era craft had this as an issue. Brute strength solved in then, exotic materials and geometry will solve it this time.

    You also can adjust the pitch of a propeller, i.e. the angle at which the blades are tilted, in response to airspeed and density. You can pitch for climb rate, or for speed, and you can do so in flight. This is extremely common even in ordinary single-engine aircraft, and is well-understood.

    In all, as long as the true airspeed of the Mars flyer is subsonic, if there's enough atmosphere for lift there will be enough atmosphere for propeller-based thrust. Propellers are just rotating wings, and they have to solve the same problem.

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