Advanced life support systems are essential for the success of future human planetary exploration. Striving for self-sufficiency and autonomous operation, future life support systems will integrate physical and chemical processes with biological processes, resulting in hybrid systems. A program was conducted to demonstrate the synthesis of ethylene and other useful products, e.g, polyethylene and ethanol, from metabolic wastes, i.e., carbon dioxide and water, as an adjunct to the Life Support Systems (LSS) required in manned spacecraft, e.g., Space Station Freedom, and planetary bases, e.g., on the Moon and Mars. These products will be synthesized using inorganic processes based on chemical engineering principles, making use of the major components of metabolic waste, carbon, hydrogen, and oxygen.This same technology can be used on Mars by converting carbon dioxide (from the atmosphere) and water to ethylene and other useful products for the manufacture of foodstuffs for life support and plastics for the fabrication of structures and spare parts for Martian bases. In addition, this technology can be used for the production of oxygen and methane for use as propellants in local and space propulsion systems.The program was focused on two synthetic paths to produce ethylene in conversions greater than 95%, (1) direct catalytic reduction of carbon dioxide with hydrogen and (2) catalytic reforming of methane produced by the reduction of carbon dioxide with hydrogen, as shown in the following equations.Direct Conversion Indirect Conversion Useful Products on Spacecraft The benefits to be derived from the program are: (1) conversion of metabolic wastes to useful products for use on manned spacecraft and planetary bases, (2) the use of indigenous Martian resources for the production of useful products for life support, base construction, and propulsion system fueling/refueling, (3) weight savings which result from reduced on-board supply requirements; (4) production of useful products based on efficient engineering principles, i.e., mass, volume and energy, and (5) reduced resupply from Earth which enable economic exploration and colonization of space.The chemistry and chemical engineering processes which were demonstrated on the successful program for the synthesis of ethylene will be presented and discussed, e.g., (a) the direct synthesis of ethylene from carbon dioxide and (b) the indirect two-step synthesis of ethylene using water electrolysis and modified Fischer-Tropsch processes. They will be directly applicable to the development of closed life support systems for manned spacecraft, lunar and Martian bases, and, ultimately, lunar and Martian colonies, e.g., the conversion of the Martian atmosphere to methane, ethylene, ethanol, and a variety of polymers for constructions and other uses. This may be followed by other interesting syntheses, e.g., polyethylene, a plastic with many varied uses, and ethanol, a potential foodstuff and precursor to polyesters, another very useful plastic.