Waste Utilization for Propulsion on Manned Space Missions

The accumulation of waste products aboard spacecraft during manned missions of long duration still is an unsolved problem. Even if life support systems with regeneration of water (from urine and condensates) and oxygen are installed, waste accumulates at such a fast rate that within a short time storage space problems are encountered. Also, additional weight is required to provide a means of processing the waste material.

To date, spacecraft designers have considered life support systems and rocket propulsion systems as independent subsystems of a manned spacecraft. The Integrated Waste Management/Rocket Propulsion System concept developed by Rocket Research Corp. under NASA Contract NAS 1–6750, has demonstrated that human waste products can form a useful propellant ingredient and provide propulsion, as well as be an effective means of removing and sterilizing spacecraft waste. The propellant investigated is formed primarily from raw feces, a metal powder, and a water soluble oxidizer. As only the metal and the oxidizer must be carried along from earth, the waste material is considered “free” aboard the spacecraft. Therefore, the effective I_sp is higher than that of most storable bipropellants. In addition to feces, carbon from the carbon dioxide reduction system, used charcoal filters, evaporator wicks, and food wrappers may be included as propellant ingredients. The addition of the soluble oxidizer fluidizes the feces so that they may easily be pumped. Samples of feces generated during a 4 man, 60 day space chamber simulation experiment performed by McDonnell Douglas have been obtained, analyzed, and incorporated into propellant formulations. Some of the properties of feces obtained from the experiment were found to be significantly different from feces samples obtained under normal diet and living conditions, however, this appears to be no barrier to its use as a propellant ingredient.

Tests of bacteriological activity have also been performed to demonstrate the effective sterilization of waste products by combustion in a monopropellant rocket engine. A mission analysis has been performed for earth orbital and interplanetary missions.

The Waste Management/Rocket Propulsion System appears capable of satisfying many propulsion requirements; for example, orbit change maneuvers, aerodynamic drag makeup, midcourse correction, terminal braking, and auxiliary and emergency propulsion.