The sustained return of humans to the moon, and the subsequent crewed exploration of Mars, will require the capability for in-flight mass reduction via the disposal of crew waste. The current method (used aboard the International Space Station) is to package waste into plastic bags wrapped in duct tape, store them in waste stowage bags, and then transport them to a logistics resupply module for later deorbiting and re-entry burn up. However, this practice is not viable for the more stringent logistical margins required of Lunar and Martian missions, and could violate accepted planetary protection standards. A previous study indicated that an efficient approach is to convert the waste into ventable gases (i.e., CO2, CO, CH4, etc.), the so-called Trash-to-Gas (TtG) model (as opposed to conversion into a reusable supply gas). TtG conversion could be accomplished via combustion, or a thermal degradation process (i.e., steam reforming, pyrolysis, etc.). An ideal TtG system would be light-weight, consume little power, minimize crew operation time, and provide repeatable and reliable maximized waste conversion. The study described here compares several TtG systems that have been built and tested using thermal processes that include: incineration/gasification, steam reforming, combustion, torrefaction, microwave pyrolysis, plasma pyrolysis, and plasma gasification. From experimental results, each system was evaluated for performance within the context of a spacecraft system-level theoretical framework to assess factors such as total mass reduction, mass of residual solids, and generation of water. Along with other key performance parameters (such as system mass and volume, energy consumption, heat production, etc.), these results were developed into an equivalent system mass (ESM) whereby various performance aspects were evaluated in a comparable manner. The ESM results were then compared to the baseline method (of simply storing waste) to determine mission break-even points, and thus select technologies for further development.