A Light-Weight Inflatable Hypersonic Drab Device for Venus Entry

The author has studied inflatable drag devices (ballute = balloon + parachute) for deceleration in the atmosphere of Venus, for both direct aerocapture and for entry from circular orbit. The studies indicate that ballutes made of thin materials capable of temperatures of about 500 C allow an entry system mass that is , for both aerocapture and entry, less than with the conventional entry body. For aerocapture the exit conditions are controlled by measuring the velocity loss and releasing the ballute when the desired exit conditions are indicated. A development program is necessary to explore the ballute shapes and changes in flight and to mitigate possible instabilities. To design an entry vehicle using a ballute the designer takes the vacuum orbiter or the lander as it is on the surface, chooses one surface to attach the ballute, and places an MLI blanket on the other end. PRIOR BALLUTE STUDIES Ballutes seem to have been invented in the forties and fifies to reduce the ground impact speed of empty sounding rockets or rocket casings. The investigators probably discovered that the mass of a ballute, inflated at high altitude, to slow a returning high altitude sounding rocket was less than the mass of a necessarily stronger parachute system that would open at low Mach number and high pressure. In the late sixties studies and wind tunnel tests were performed (1,2) by Goodyear and NASA Langley with a view to using ballutes to assist deceleration of the Viking landers at Mars, but these ballutes were deployed after peak deceleration and heating, thus having limited potential to change the entry trajectory. A mushroom shape was found to be more stable than a sphere. In 1976 the authors of Ref. 3 proposed to use a ballute inflated prior to entry into Venus. They proposed a ballute of mass over 300 kg and computed the ablation during entry, and evaluated some candidate materials. In the mid eighties studies of ballute materials were done at Langley, but again the concept was to deploy ballutes after peak entry deceleration and heating. In recent years NASA Ames has studied drag modulation of vehicles equipped with inflatable components (Ref. 4). RECENT STUDIES In the past five years the author has studied the use of ballutes for aerocapture and entry at several planets, including a Mars orbiter and a Pluto lander, both reported in Ref. 5. Other applications not yet reported are ballutes at Neptune, Saturn, Jupiter, Titan and Earth. The present report describes ballutes applied to aerocapture at Venus of a sample return vehicle at direct entry, and to subsequent entry from a circular orbit after a plane change at a high apoapsis and aerobraking. (Ref. 6). * A. D. McRonald is a Member of the Technical Staff at the Jet Propulsion Laboratory of the California Institute of Technology. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract of the National Aeronautics and Space Administration.