Research Activities on Venus Atmosphere Balloon Observation Mission
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A feasibility study of the small Venus entry capsule and the scientific observation by the water-vapor balloon are described in this paper. Though Venus is the nearest planet to the Earth, it is still filled with mysteries and surprises. The atmosphere observation under the thick cloud on the venusian surface is of great scientific interests. Because a super-pressure type of the balloon can travel long time a wide area by strong winds on the Venus, it is considered to be of prime candidate for the atmosphere observations. A water-vapor super-pressure balloon is advantageous to obtain buoyancy force in the hot Venus atmosphere. At the entry to the Venus, the liquid-phase water is adhered to a number of the water-absorption films layered inside of the outer sealing film. The heat required for the water vaporization is supplied from the ambient environment during the ascending phase. Recently, IC chips, batteries, and solar arrays that function under the high-temperature environment ranging 180 to 220 ?C have been developed and been in practical use. By use of solar arrays, the electric power is supplied to the onboard instruments without any extra cooling system, which enables long-term observation. Then the target altitude is determined to be from 35 to 37 km considering the operation range of the high-temperature electronics. A small entry capsule with the 20m-long water-vapor balloon accommodated in it is separated from a 150kg small spacecraft and carries out direct entry from the interplanetary transfer orbit at the velocity of 11.5 km/s. The capsule releases the balloon at the appropriate altitude after passing through the aerodynamic heating corridor. Total weight of the capsule is about 30 kg containing balloon and observation instruments with weight of 10kg.