P-MASS, the Plant-Module for Autonomous Space Support, is designed to support and provide life support for a variety of plants, algae and bacteria in low earth orbit during the maiden flight of COMET-1. The first launch is scheduled for early 1993. With a nominal mission duration of 30 days in microgravity, P-MASS will bridge the gap between the shorter duration experiments possible onboard the NSTS Space Shuttle (approximately 14 days) and the future Space Station Freedom for space biology applications. Environmental data and video images are collected, stored onboard and downlinked daily. In addition, the payload and all specimens will be returned for ground analysis with the recovery system (reentry capsule).P-MASS is designed within a payload envelope of 0.28 x 0.22 x 0.32 m (19.71) and a mass of approximately 20 kg. A total of 115 Watt electric power is available continuously for the Plant-Module (60 W lighting, 40 Watt cooling, 15 W housekeeping). Quartz halogen bulbs, or alternatively a hybrid light emitting diode lighting system (ultrabright red LED) provide 40 W/m2 photosynthetically active radiation (PAR) for the 0.06 m2 growth area. In addition to higher plants, photosynthetic and nonphotosynthetic micro-organisms as well as plant cultivare/tissue cultures are supported.An active, solid state cooler allows the interdependent control of humidity and temperature, at the same time maintaining soil moisture by passive liquid management. Carbon dioxide and oxygen concentrations are monitored and adjusted physically or biologically. Ground tests have verified the design concept. Plant growth experiments and life support performance tests are presently being conducted. These performance data will be used together with ground controls for on-orbit performance analysis. P-MASS, though simple and reliable in design, can provide valuable information and experience in gravitational and space biology with applications directed for future life support systems.