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Aerial Drone To Hunt For Life On Mars
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?"
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.
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.
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 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.
Everybody gets what the majority deserves.
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).
Be careful. People in masks cannot be trusted.