The Japan Aerospace Exploration Agency (JAXA) is developing polymer-electrolyte fuel cell (PEFC) systems that can operate under isolated low-gravity and closed environments. Subsystems and operating methods such as the closed gas operation subsystem, the working gases counterflow method, and a dehydrator using wicking material were developed to simplify assembly of the fuel cell system. We combined these subsystems with the 1 kW-class fuel cell stack and simulated the operations of a spacecraft in Earth orbit. The system performed stably for 1100 h under various operational conditions. (c) 2006 Elsevier B.V. All rights reserved.