ROLLA, Mo. Motivated by the notion that the Mars landscape may prove easier to navigate by air than with ground-based rovers, NASA is backing a research project to build toy-sized flying robots, modeled on the entomology of insects, that can hover like helicopters. Patented as "entomopters," the robots are on the drawing board of University of Missouri professor Kakkattukuzhy Isaac.
"We are looking mainly at the dragonfly, the hummingbird and the fruit fly, but we are not trying to mimic one particular insect," said Isaac, who is assisted on the project by graduate student Pavan Shivaram. "Instead we are identifying the principles that enable insects to create such high lift, which is still not completely understood. That is our main task."
NASA is sponsoring a large team of diverse researchers on the project, titled "Planetary Exploration Using Biomimetics." Isaac's part is the wing design and aerodynamic analysis to ensure that sufficient lift will be provided. Researchers at Georgia Tech Research Institute are concentrating on propulsion, as are colleagues at the University of Cambridge (England) and the Ohio Aerospace Institute.
"We are investigating building flying robots modeled on insects because insects create a higher amount of lift than conventional aircraft, enabling them to fly at low speeds," Isaac said. "General-aviation fixed-wing aircraft cannot fly below about 80 miles per hour on Earth, but our application calls for robotic aircraft that can fly in hover mode, standing still above interesting areas while taking pictures." Eventually, the researchers hope to enable the flying robots to land, pick up samples and return them to a central collection point.
Exploring the Martian landscape presents formidable problems for land-based rovers, but flying robots also face significant challenges there. Mars' gravity is only 37 percent of Earth's, thereby making payloads appear lighter; but the thinner atmosphere makes helicopters unfeasible, and fixed-wing aircraft, despite the weight advantage, would have to cruise at more than 250 mph just to stay aloft. Such high speeds would make the "dwell time" over a landscape feature exceedingly short, and taking off and landing at such high speeds would be extremely dangerous on the rugged terrain of Mars.
Thus the entomopter was conceived to maximize lift by rapidly flapping its wings to increase the dwell time over interesting features. It would land, take samples and communicate its findings, then return to its launch point for refueling, downloading and transferring samples.
"From an aerodynamic point of view, the frequency of flapping is very important, because it appears that at very high frequencies of motion there are vortexes created under the wing that enhance lift. That is why we are studying insects with a high frequency of flapping," said Isaac.
"We want to understand the underlying theory that enables insects to create so much more lift than conventional aircraft and apply that to the entomopter," he said. "Even if we could completely understand the motion of a particular insect, we may not be able to completely duplicate that insect's characteristics of motion, because the [process] is extremely complicated. It depends on what they are doing; for instance, when they are hovering they use a certain type of motion, but when they are in forward flight they change the way they move their wings."
The second biggest problem with the Martian atmosphere is that its lack of oxygen knocks internal-combustion engines out of the running as potential mechanisms for propulsion. The team is considering electric motors, powered by solar cells, but the alternative currently in highest favor is a chemically powered engine that creates its own compressed "air" to power the vehicle as well as an electrical generator for communications equipment. The exhaust gases from the power generator could also be directed out through the wing's tips to enhance lift, Isaac said.
"We are currently favoring an artificial muscle that derives its power from a chemical reaction and that acts like a muscle in a human body," Isaac said. "By contracting and expanding this muscle we can make the robot flap its wings."
The chemical fuel version makes use of an artificial "reciprocating" muscle actuator that has been demonstrated by researcher Robert Michelson at Georgia Tech to be capable of flapping the wings of a robotic insect at about 70 cycles per second. Georgia Tech has demonstrated prototypes of the chemical muscle actuator but so far has only built small, 50-gram prototypes that carry a payload of only 10 grams.
"Since we need to put cameras and communications equipment aboard the entomopter, we cannot make them as small as insects but will probably need to [specify] a wing span of about 5 feet and a length of about 2 1/2 feet," said Isaac. The chemical fuel may have to be carried from Earth to Mars, or there may be a way of making the fuel from resources available on Mars, according to Isaac.
NASA aims for 2003
The project is now in its second phase, with phase three slated to prove the feasibility of a full-sized prototype during 2003. NASA scientists hope to have the entomopter ready for a Mars landing by the end of the decade.
While the space agency is the principal sponsor of the entomopter project, the military is pursuing parallel research, sponsored by the Defense Advanced Research Project Agency, into "micro air vehicles."
"The military may be able to adapt our technology to create flying robots that could hover so that they could investigate hard-to-reach place like those caves in Afghanistan and similar places," Isaac said. Other practical uses for the entomopter could be to enter hazardous zones like "hot spots" inside nuclear power plants or other contaminated areas.
An audio recording of reporter R. Colin Johnson's full interview with Kakkattukuzhy Isaac can be found online at AmpCast.com/RColinJohnson.