Future manned space exploration missions will require space suits with capabilities beyond the current state of the art. Portable Life Support Systems for these future space suits are extremely challenging, since they must maintain healthy and comfortable conditions inside the suit for long-duration missions while minimizing weight and venting no consumables. We propose an innovative system for thermal and humidity control in a space suit that is simple, rugged, lightweight, and nonventing. In Phase I we will prove the feasibility of our approach by analysis and laboratory testing of a proof-of-concept unit to identify the optimum configuration. We will produce a conceptual design for a full-size system. In Phase II we will develop fabrication methods to produce a full-size prototype, then demonstrate operation in a prototypical environment.