Extended surface missions to Venus are a major exploration need, but are very challenging since sensitive payloads must be protected from the high atmospheric temperatures at the planet's surface. A heat pump is the only cooling system capable of providing temperature control for an extended period of time; however the large temperature differential between a typical electronics payload (50-100°C) and the outside environment (460°C) strictly limits the theoretical (Carnot) efficiency. Surface missions to Venus are extremely difficult due to the harsh environment. Surface temperatures can exceed 460°C (860°F), the ambient pressure is 93 times that of Earth, and the atmosphere itself is corrosive. In particular, the high temperatures quickly cause overheating and thermal failure of electronics and other equipment. As such, previous surface missions have been very short in duration, lasting mere hours. There is considerable interest in conducting a longer surface mission to the planet with a duration of one year or more. Heat pumps can be used for cooling in the Venus atmosphere and have been proposed for such a mission, but because of the extreme conditions, the laws of thermodynamics dictate that such a device would be extremely inefficient. For example, if a refrigerating heat pump is used to keep a payload at 50°C against the 460°C outside temperature, the maximum (Carnot) coefficient of performance for a perfect device is less than 0.8, meaning each Joule of electrical energy expended removes less than 0.8 Joules of heat. A real system would attain only a fraction of this maximum performance, removing far less than 0.8 Joules of heat per Joule of electrical energy. For comparison, the Carnot limit for a refrigerator on Earth might be ten times as high, with real devices achieving up to half the theoretical performance limit. Better performance might be achieved through chemical means. The atmosphere of Venus is composed primarily of carbon dioxide. Carbon dioxide is commonly produced through combustion of carbon-containing compounds, a process which releases thermal energy and heats the surroundings. However, this process can also be reversed: carbon dioxide can be broken apart and reformed into carbon compounds and oxygen. The reaction is endothermic, absorbing energy from the surroundings to give a cooling effect. The reformed products of such a process would be quickly carried away by the surface winds, buildup of exhaust gas.More »
Ultimately, we envision spacecraft, enabled with this revolutionary technology to be powered by aiming down at the earth, rather than up at the sun. This novel modality offers to radically reduce energy storage capacity need (for nighttime use) and eliminate the need for onboard solar tracking and pointing systems, drastically reducing spacecraft power system size, weight and complexity.More »
|Organizations Performing Work
|Marshall Space Flight Center (MSFC)
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