Free The Case for Mars by Robert Zubrin Page A

have been able to rac several thousand kilometers in its windborne wanderings across the Martian surface. With Russia’s economy continuing to lurch, however, it is questionable whether this mission will ever fly.
    While the Russian planetary exploration program may be dying, new players are entering the field. Europe will send its first interplanetary mission, Mars Express , to the Red Planet in 2003. An ambitious mission, Mars Express includes both a French-made orbiter and the British lander Beagle II , which will carry experiments to search the surface for life. France has also signed a bilateral agreement with the United States to team on a 2005 Mars Sample Return mission, and offered to make spare payload capacity on its new Ariane 5 launch vehicle available to support Mars “micro missions,” as well. Italy has proposed a Mars communications orbiter, while Japan has launched a radar probe, called Nozomi , which will reach Mars via a roundabout orbit in 2002.
    Among missions currently under discussion in the United States is the Mars Aerial Platform mission, or MAP, developed by myself and others at Martin Marietta. MAP is a conceptual design for a low-cost mission that would return tens of thousands of high-resolution photographs of the Martian surface, analyze and map the global circulation of the atmosphere, and examine Mars’ surface and subsurface with remote sensing techniques. At the heart of the mission is a hightech approach to a very low-tech concept—balloons.
    This is how MAP would work: A single Delta-class booster would launch the MAP payload on a direct trajectory to Mars. The payload would consist of a spacecraft carrying eight entry capsules, each capsule packed with a balloon, deployment equipment, and a gondola carrying science instruments. Ten days prior to arrival at Mars, the spacecraft, now spinning like a top, would release the capsules, casting them off in directions that would ensure their entry at widely dispersed locations. As each capsule began its descent through the atmosphere, a parachute would deploy to slow the capsule to the point where a balloon could be inflated. Each would be made of a commercially available material known as “biaxial nylon 6” that is just 12 microns thick—one third the thickness of a standard plastic trash bag. Though seemingly made of gossamer, these balloons will be surprisingly tough. The material’s manufacturing process guarantees that it harbors no pores, which means that balloons made of this nylon simply will not leak and, therefore, can be expected to remain inflated not for days, but years. Following inflation, the parachute, capsule, and inflation equipment drop away, carrying a meteorology package to a soft landing on the Martian surface. Free of extraneous equipment now, each balloon begins the first of perhaps hundreds of days of roaming the highways of Mars, the planet’s eternal winds.
    The 18-meter-diameter balloons will cruise over the surface of Mars at an altitude of 7 to 8.5 kilometers and, unlike the French balloon that had been planned for Mars 98 , will maintain these altitudes day and night. They will be able to do this, because with their new material and compact configuration (enabled by a very lightweight gondola) the balloons will be strong enough that when their gas pressure is increased by the heat of the day they can just hold it in without venting. Since they won’t vent gas by day, these “superpressure” balloons have no need to drop ballast at night, and therefore can fly almost forever at constant altitude. Current models of Mars’ atmospheric dynamics suggest that the winds will carry the balloons primarily in a west-east direction on the order of 50 to 100 kilometers per hour. At these speeds, each balloon could circumnavigate Mars every ten to twenty days and, assuming a conservative average mean time to failure of a hundred days, we can expect each balloon to circumnavigate Mars at least four times. Each