Flying Above Mars

I was also a big fan of science-fiction, futuristic stories of exploring the universe. I read Ray Bradbury, Robert Heinlein, Isaac Asimov, Arthur C. Clarke and Frederik Pohl, among others, and hoped that I might someday possess the imagination to emulate them.

In my own little, nonfiction world, I've written at least a dozen articles about space travel and the benefits of space technology, and I've been one of NASA's strongest boosters. Last year, I was one of the last journalists to fly the world's only motion-based Space Shuttle simulator at NASA headquarters in Houston.

Back in the early '80s when the Journalist in Space program was announced, I applied enthusiastically, knowing I had little chance against folks such as Walter Cronkite, Peter Jennings and Hugh Downs. Whatever my chances might have been, they evaporated with the explosion of Challenger in January 1986 and the death of teacher-in-space Christa McAuliffe and six other astronauts.

Even so, space exploration remained a fascinating preoccupation. Over the years, I've interviewed astronauts such as Buzz Aldrin and Frank Borman. I've also visited the Kennedy Space Center on Cape Canaveral several times and witnessed a half-dozen launches.

I was probably as enthusiastic about the recent landing of the Mars rover, Curiosity, as the JPL scientists who built the one-ton, SUV-sized vehicle. It was truly an amazing triumph, especially considering that Mars is roughly 154 million miles away. Any command from Earth requires nearly 12 minutes to cover such a distance. The descent from orbit to landing required only six minutes, so the computers aboard Curiosity had to be totally autonomous. They needed to make all their own decisions during the descent and actual touchdown.

They did it pretty well. Curiosity blazed through the Martian atmosphere at 13,000 mph then slowed to land at 1.7 mph. Now, Curiosity will begin the tasks for which it was designed, exploring Mars to answer the big question: Was there once life on the Red Planet?

In pursuit of that goal, I couldn't help wondering how difficult it might be to explore Mars by aircraft, perhaps the ideal method of examining as much of the surface as efficiently as possible.

Not too surprisingly, NASA was way ahead of me. The idea is far from new. Nearly a half-century ago, the late Wernher von Braun envisioned landings utilizing hypersonic gliders. NASA-Langley has been investigating the possibilities for several years, concentrating on a concept called ARES (Aerial Regional-Scale Environmental Surveyor), a rocket-powered system that would maneuver a mile above the planet at 400 mph until it ran out of fuel. NASA isn't sure the concept is viable, but they're continuing to investigate the possibilities for a future mission. NASA scientists would love to come up with an aircraft that could explore all the impressive geologic features on the planet, especially Valles Marineris, the 2,500-mile-long, 30,000-foot-deep canyon that makes our Grand Canyon look like a road rut.

By any method, flying on Mars is an intriguing idea, especially to one who's been operating above Earth for the last 50 years. Mars is a much smaller planet, so gravity is only about 37% of the standard one G force here on Earth. Lifting the weight of a research aircraft would be far less of a problem on Mars than it is here.

Unfortunately, that's about the only positive factor of aviating above Mars. The typical Martian atmosphere is extremely thin, about six millibars, less than one percent of Earth's protective shield. At a typical ground level (there are no seas on Mars), it's roughly the equivalent density of the Earth's sky 100,000 feet above sea level.

That means any form of aircraft might need very large lifting surfaces, and stall speeds would be extremely high, just to remain aloft. Such realities would demand an imaginative takeoff and launch mechanism, and controlled landings on the surface of Mars would be nearly impossible because of the high stall speed.

Several concepts have been considered for a Mars-capable aircraft. One was a series of small, expendable gliders, launched from orbit. These could enter the atmosphere as capsules, descend to a reasonable altitude, leave their cocoons, deploy wings and a tail and reconnoiter and photograph specific areas of interest before landing and perhaps serving as miniature science platforms after touchdown, assuming they survived the crash. There's nothing even close to a runway on Mars, as the surface is strewn with boulders and craters.

Another option might be entomopters, small machines that fly like insects. To bypass the problem of large lifting surfaces, one proposal was to design aircraft that would generate lift similar to insects on Earth. Unlike aircraft or birds, insects develop lift by the continuous creation and shedding of vortices on their wings. Such vortex formation and shedding produces very high lift coefficients, roughly five times more efficient than conventional aircraft airfoils.

This allows insects to take off, maneuver, hover and land vertically. If such techniques could be applied to a miniature Martian aerial rover, possibly by blowing air out the trailing edges of the wings, a much smaller flapping-wing aircraft, perhaps one meter in span, could take off, fly a reconnaissance mission, execute its photo mission and return to the mother ship without concern for the thinner air.

Of course, Mars' atmosphere is almost pure carbon dioxide with no oxygen, so any flying machine would need to bring along its own oxygen supply or use an alternate power source. The obvious alternatives would be solar or nuclear power. Most previous Mars ground rovers (especially the two most recent, Spirit and Opportunity) employed solar power, but were plagued with dust storms that covered the solar panels with sand and reduced charging capability to near zero.

Curiosity uses nuclear power, a radioisotope, thermoelectric, plutonium dioxide, that will be unaffected by dust storms and could provide energy for as long as 14 years. A similar system might be utilized by a Martian aircraft.

Another limiting factor on Mars might be the temperature. The average temperature on Mars is about -60 degrees C, though it may reach 20 degrees C during the day at the equator. At the poles, the temperature may drop to -120 degrees C. Such realities would demand very resilient operating systems plus a major heater to protect any form of aircraft.

Cosmic radiation also could be a problem, even for an unmanned robotic system, carrying nothing more than gas sensors, cameras and instrumentation. Shielding would be mandatory for any aircraft flying above the surface of the planet. Solar radiation could effectively fry critical systems of an aircraft flying above Mars.

Navigation above Mars would be a challenge, too. The planet has no magnetic field, so there would be no convenient way to determine north or any other direction. Without several satellites overhead, there would obviously be no GPS guidance, though a form of ADF provided by the mother ship might work. Another possible method of navigation might be a modified type of inertial guidance. Similarly, a downlink might be utilized from satellites orbiting overhead, commanding relative bearings toward a given destination.

General aviation rarely receives credit for all the missions it performs---cargo, air ambulance, firefighting, aerial survey, law enforcement, pipeline patrol, wildlife management and about a hundred other jobs. Wouldn't it be interesting if the first Martian Aerial Rover Reconnaissance vehicle turned out to be a descendant of the Skyhawk?