NASA/TM—2002-211467 AIAA–2002–0819 Atmospheric Flight on Venus Geoffrey A. Landis Glenn Research Center, Cleveland, Ohio Anthony Colozza Analex Corporation, Brook Park, Ohio Christopher M. LaMarre University of Illinois, Champaign, Illinois June 2002 The NASA STI Program Office . in Profile Since its founding, NASA has been dedicated to • CONFERENCE PUBLICATION. Collected the advancement of aeronautics and space papers from scientific and technical science. The NASA Scientific and Technical conferences, symposia, seminars, or other Information (STI) Program Office plays a key part meetings sponsored or cosponsored by in helping NASA maintain this important role. NASA. The NASA STI Program Office is operated by • SPECIAL PUBLICATION. Scientific, Langley Research Center, the Lead Center for technical, or historical information from NASA’s scientific and technical information. The NASA programs, projects, and missions, NASA STI Program Office provides access to the often concerned with subjects having NASA STI Database, the largest collection of substantial public interest. aeronautical and space science STI in the world. The Program Office is also NASA’s institutional • TECHNICAL TRANSLATION. English- mechanism for disseminating the results of its language translations of foreign scientific research and development activities. These results and technical material pertinent to NASA’s are published by NASA in the NASA STI Report mission. Series, which includes the following report types: Specialized services that complement the STI • TECHNICAL PUBLICATION. Reports of Program Office’s diverse offerings include completed research or a major significant creating custom thesauri, building customized phase of research that present the results of data bases, organizing and publishing research NASA programs and include extensive data results . even providing videos. or theoretical analysis. Includes compilations of significant scientific and technical data and For more information about the NASA STI information deemed to be of continuing Program Office, see the following: reference value. NASA’s counterpart of peer- reviewed formal professional papers but • Access the NASA STI Program Home Page has less stringent limitations on manuscript at http://www.sti.nasa.gov length and extent of graphic presentations. • E-mail your question via the Internet to • TECHNICAL MEMORANDUM. Scientific [email protected] and technical findings that are preliminary or of specialized interest, e.g., quick release • Fax your question to the NASA Access reports, working papers, and bibliographies Help Desk at 301–621–0134 that contain minimal annotation. Does not contain extensive analysis. • Telephone the NASA Access Help Desk at 301–621–0390 • CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored • Write to: contractors and grantees. NASA Access Help Desk NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076 NASA/TM—2002-211467 AIAA–2002–0819 Atmospheric Flight on Venus Geoffrey A. Landis Glenn Research Center, Cleveland, Ohio Anthony Colozza Analex Corporation, Brook Park, Ohio Christopher M. LaMarre University of Illinois, Champaign, Illinois Prepared for the 40th Aerospace Sciences Meeting and Exhibit sponsored by the American Institute of Aeronautics and Astronautics Reno, Nevada, January 14–17, 2002 National Aeronautics and Space Administration Glenn Research Center June 2002 Available from NASA Center for Aerospace Information National Technical Information Service 7121 Standard Drive 5285 Port Royal Road Hanover, MD 21076 Springfield, VA 22100 Available electronically at http://gltrs.grc.nasa.gov/GLTRS ATMOSPHERIC FLIGHT ON VENUS Geoffrey A. Landis* National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135 Anthony Colozza Analex Corporation Brook Park, Ohio 44142 Christopher M. LaMarre University of Illinois Department of Aeronautical Engineering Champaign, Illinois 61820 ABSTRACT the planet Venus actually absorbs less energy from the Sun than the Earth, despite its orbital position We propose a solar-powered aircraft system for 27 percent closer to the Sun. the exploration of Venus. The atmosphere of Venus provides several advantages for flying a solar- Venus is nearly the same size as the Earth, but powered aircraft. At the top of the cloud level, the utterly unlike the Earth [1,2]. Due to a runaway solar intensity is comparable to or greater than greenhouse effect, the temperature of the surface is terrestrial solar intensities. The atmospheric nearly 500 °C. pressure makes flight much easier than on planets Use of a solar-powered aircraft for exploration such as Mars. Also, the slow rotation of Venus of Venus was recently proposed by Landis [3]. The allows an airplane to be designed for flight within Venus atmosphere is a favorable environment for continuous sunlight, eliminating the need for flying powered aircraft. The atmospheric pressure energy storage for nighttime flight. These factors makes flight much easier than on planets such as make Venus a prime choice for a long-duration Mars. Solar power is abundant; at the top of the solar-powered aircraft. Fleets of solar-powered cloud level, the solar intensity is comparable to or aircraft could provide an architecture for efficient greater than terrestrial solar intensities, and the and low-cost comprehensive coverage for a variety slow rotation of Venus allows an airplane to be of scientific missions. designed for flight within continuous sunlight, eliminating the need for energy storage for nighttime flight. These factors make Venus a prime INTRODUCTION choice for a long-duration solar-powered aircraft. With the success of missions such as the Mars In 1985, the Russian Space Agency successfully Pathfinder, exploration of the planet Mars has deployed a balloon mission, VEGA, in the received a large amount of public attention, and has atmosphere of Venus [2], but airplanes have not recently been suggested as an environment for previously been developed for Venus. An aircraft, flying a powered aircraft. Venus, Earth's evil twin, with the ability to control its position in the is also an extremely interesting planet, but far less atmosphere of Venus instead of drifting with the studied. Because of a white cloud cover that reflects wind, would be a powerful tool for scientific most of the incident solar radiation back into space, exploration. * Engineer, Photovoltaics and Space Environmental Effects Branch, Associate Fellow, AIAA. NASA/TM—2002-211467 1 Figure 1 shows an artist's conception of a small The acceleration due to gravity on Venus is solar-powered airplane flying above the cloud layer 8.87 m/s2, slightly lower than that of Earth, making of Venus. Venus a slightly easier planet for powered flight. VENUS Above the clouds, solar energy is available in abundance on Venus. Venus has a solar flux of With a period of 243 days, the planet Venus has 2 2 2600 W/m , compared to Earth's 1370 W/m . the slowest rotation of any planet in the solar Figure 3 (adapted from [4], see also fig. 3 of [5]) system. This slow rotation results in a very long shows the altitude variation of the intensity of the solar day, of duration 117 (Earth) days. This means downward solar radiation (expressed as a fraction that the ground speed required for an airplane to of the solar intensity above the atmosphere) remain at the subsolar point is extremely slow, only as measured by the Venera-11 probe during 13.4 km/hr at the equator. In the Venus descent. The solar intensity is 20 to 50 percent environment, it may be possible to maintain flight of the exoatmospheric intensity (depending on within the sunlit portion of the planet continuously. wavelength) at the bottom of the cloud layer at This possibility of continuous sunlight makes 50 km and increases to nearly 95 percent of the Venus extremely attractive for a solar-powered exoatmospheric intensity at 65 km, the top of the aircraft. main cloud layer. The bottom of the cloud layer is Figure 2 shows the atmospheric pressure on clearly seen by the leveling out of solar intensity. Venus as a function of altitude above the surface The atmosphere between 50 and 75 km on [2,3]. The altitude where terrestrial aircraft operate, Venus is one of the most dynamic and interesting between sea level and 24 km, corresponds to regions of the planet. The challenge for a Venus atmospheric pressure from 1 bar to 30 millibar. On aircraft will be the fierce winds and caustic Venus, this pressure range is found from 50 to atmosphere. 75 km above the surface. At these flight altitudes, the temperature varies from 80 °C at 45 km, The winds peak at about 95 m/s at the cloud top decreasing to –10 to –35 °C at 60 km. Averaged level. In order to remain on the sunlit side of temperature, pressure, and density data on the Venus, an exploration aircraft will have to be atmosphere is given as a function of altitude in capable of sustained flight at or above the wind table 1. speed. )LJXUH &RQFHSW IRU D 9HQXV DLUSODQH GHVLJQ NASA/TM—2002-211467 2 The cloud layer extends from about 45 to 50 km A Venus aircraft must also contend with violent altitude to roughly 64 km. Clouds are composed of weather conditions. The region just above the cloud sulfuric acid, free sulfur, and trace contaminates tops experiences a phenomenon known as “super- such as HF, HCl, CO, and H2O [1,2]. There is also rotation” where the atmosphere circles the planet significant ultraviolet at the higher altitudes that can every 4 days, traveling in excess of 200 mph [1]. accelerate degradation through photochemistry. By The cloud system also may experience high vertical any measure, this is an extremely acidic and wind shear. A solar-powered aircraft will also have hazardous environment for machinery and electrical to contend with decreasing power as it descends systems. Nevertheless, materials are available that into the clouds. The combination of a caustic easily withstand the sulfuric acid environment, and atmosphere and hurricane force wind makes aircraft assuming that the design avoids exposed metal on design and control challenging.