Balloons for controlled roving/landing on Mars

Until now, the only practical balloon systems proposed to explore the marti an atmosphere have been superpressure balloons, which fly at a constant alt itude, or short-lived helium balloons, which precariously drag a snake thro ugh;all types of surface weather, or a day/night combination of the two. Fo r the first time, two novel atmospheric balloon systems now appear quite vi able for controlled balloon landings at selected martian surface locations. These balloons could softland payload packages, such as lightweight surfac e roving vehicles. The two balloon approaches and a land rover concept are described below, along with a combination of the two approaches. Solar Hot-Air Balloons: These "Montgolfiere" balloons are named after the 1 8th-century French brothers Joseph-Michel and Jacques-Etienne Mongolfier, w ho first flew hot-air balloons. Using entirely solar heat, they are ideal f or landing at the martian poles during summer or for shorter flights at low er latitudes. Recent tests have already confirmed the ease of altitude depl oyment and filling of these solar hot-air balloons. Furthermore, actual lan dings and reascents of solar hot-air balloons have been recently demonstrat ed by JPL, using a novel, lightweight, top air vent that is radio controlle d. One particularly useful application of these balloons is their use as a parachute to soft-land packages that are up to 50% of the total entry mass, which represents a fivefold improvement over present retrorocket landing-s ystems. Variable-Emissivity Balloons: A second atmospheric balloon system uses a va riable-emissivity superpressure helium balloon that can land at night at an y martian latitude. These balloons would be gold-coated, superpressure heli um balloons during both night and day, They could land at prescribed target s by exposing a section of the upper white balloon surface to the radiant c ooling of deep space during the night. This reduces the temperature and pre ssure in the balloon to create negative buoyancy, thus causing descent, whi le replacement of the gold top cover; causes reascent. Specific areas could be targeted for landings by using atmospheric currents at various altitude s, similar to techniques used by balloonists flying over the Earth. Inflatable Roving Vehicles: JPL has recently fabricated and tested a number of roving vehicles with large inflatable balloons that act as tires. One v ersion, with 75-cm-diameter wheels, has already demonstrated the ability to make large traverses in JPL's simulated "Mars Yard." A full-scale version, with 1.5-m-diameter wheels, should be capable of climbing large rocks (les s than or equal to 0.5 m), traveling reasonably fast (approximate to 500 m/ h) and far (approximate to 10 km), and yet have very low mass (approximate to 6 kg). Low-Cost Combined Atmospheric/Surface Mission: A simple, solar hot-air ball oon would act as a parachute to land a 6-kg inflatable rover. The balloon w ould then rise to a 3-km altitude while carrying a 2-kg camera/magnetometer /communications package for the remainder of daylight hours. The entire pac kage would then soft-land at dusk. Total Mars entry mass would be about 20 kg, and the mission could be flown to Mars at very low cost (approximate to $5M total launch costs) via one of the CNES Ariane 5 GTO piggyback launche s. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.