Space missions, early

The most practical reason for interest in the chemistry of the early actinides is their technological importance. In particular, the importance of uranium and plutonium in applications ranging from nuclear power to radiothermal generators for deep space missions. The production and use of nuclear materials in nuclear weapons from the 1940s has also driven the development of a great deal of the chemistry of these metals, from their separation and isolation to investigations of their behavior under biologically relevant conditions. 

The opportunity to employ nuclear power (power released by fissioning heavy nuclei and power released in radioactive decay) in space systems became evident as early as in the middle of the twentieth century. After the creation of atomic weapon both in the USA and in the USSR, practical studies of possible lines and patterns of atomic power sources for different space missions were initiated (Snyder 1961). 

Examples of generators are presented with power outputs ranging om micro-milliwatts to kilowatts and include an early Russian examples from the 1950 s to NASA s multihundred watt systems that provide on-board power to deep space missions. Improvements in generator performance due to advances in material figure- of- merit, thermoelement design and module configurations are reviewed. 

The very early membranes, fabricated by Gmbb and Niedrach of GE, were phenol-formaldehyde sulfonic acids produced by flic condensation of phenolsulfonic acid and formaldehyde. Unfortunately, they hydrolyzed easily and were extremely weak. These were followed by membranes wifli a partially sulfonated polystyrene backbone. Their performance was also unsatisfactory, achieving a lifetime of only 200 hours at 60 °C. The first membranes to have sufficient physical strength were D membranes, manufactured by American Machine Foundry. They were fabricated by grafting styrene-divinylbenzene into a fluorocarbon matrix, followed by sulfonation. D membranes achieved life spans of 500 hours at 60 °C and were utilized in the fuel cells as auxiliary power sources for seven Gemini space missions [14]. 

The superior ORR kinetics of the AFC meant that in the early days of fuel cell development, it was the dominant technology, with the pioneering work of Bacon [48] and the use of AFCs in the Apollo space missions. The AFC employs an aqueous KOH electrolyte, usually around a 30 wt% solution, often contained in a matrix (Figure 2.6). As with other H2/O2 fuel cells, the HOR occurs at the... 

Very early hydrocarbon-based membranes tested as electrolytes in PEMECs for Gemini space missions, such as sulfonated phenol-formaldehyde resins, sulfonated poly(styrene-divinylbenzene) copolymers, and grafted polystyrene sulfonic acid membranes, were chemically weak, and therefore PEMFCs using these membranes showed poor performance and had only lifetimes of several hundred hours (LaConti et al. 2003). Nafion , a PESA membrane, was developed in the mid-1960s by DuPont (LaConti et al. 2003). It is based on an aliphatic perfluorocarbon sulfonic acid, and exhibited excellent physical properties and oxidative stability in both wet and dry states. A PEMEC stack using Nafion 120 (250- tm thickness, equivalent weight = 1,200) achieved continuous operation for 60,000 h at 43-82°C (LaConti et al. 2003, 2006). A Nafion -based PEMFC was used for the NASA 30-day Biosatellite space mission (LaConti et al. 2003). 

LaConti et al. proposed a mechanism where oxygen molecules permeate through the membrane from the cathode side, and are reduced at the anode platinum catalyst to form (LaConti 1982 LaConti et al. 1977, 2003) in the early R D era for space missions. This mechanism for H Oj formation in a PEMFC is shown schematically in Fig. 4a. 

Fuel cells have been reliably providing electricity to spacecraft since the 1960s, including the Gemini and Apollo missions as well as the space shuttle. The leading manufacturer of fuel cells for the National Aeronautics and Space Administration (nasa), United Technologies Corporation, has sold commercial units for stationary power since the early 1990s, with more than 200 units in service. 

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