The University of New Mexico Brayton Rotating Unit-3 (UNM-BRU-3), designed for 40 g=mole He-Xe working fluid, is optimized for shaft speed of 45 kr pm, turbine and compressor inlet temperatures of 1149 and 400 K, and thermal power input of 157 kW th. At these conditions, the electrical power and thermal efficiency are 54:2 kW e and 34.5%, the compressor exit pressure is 1.044 MP a, the He-Xe flow rate is 1:54 kg=s, and the corresponding specific mass is 0:98 kg=kW e. Investigated are the effects of decreasing the turbine inlet temperature to 900 K and the thermal power input to 40 kW th and varying the shaft speed from 30 to 55 krpm. At 900 K turbine inlet temperature, thermal power input of 157 kW th, and shaft rotation speed of 45 krpm, the UNM-BRU-3 has a thermal efficiency of 22.8% and generates 34:2 kW e at a compressor exit pressure of 1.3 MP a and He-Xe flow rate of 2:07 kg/s;but the specific mass of the unit increases to ∼1:55 kg=kW e. The unit performance at 900 K is attractive for early deployment of space reactor and solar dynamics power systems with stainless steel structure, thus minimizing development cost and enhancing operation reliability and life. The low specific mass of UNM-BRU-3 will reduce the total mass and launch cost of these systems. © 2009 by M. S. El-Genk.