Monopropellant thrusters still have a role to play in orbit insertion of small satellites whenever a sizable thrust is required. A new preliminary design analysis methodology is adopted. Two monopropellant catalyst bed reactor models are employed. The first model divides the flow into liquid, liquid-vapor, and vapor regimes. Each regime is divided into pore and free stream levels. This model is basically used off line to estimate the liquid phase regime behavior. A second model, which assumes the propellant to be readily vaporized, is used to predict the performance of the vaporized regime grossly on the free stream level. The analysis is conducted for a blow-down type feed system. A case study is presented employing hydrazine as a monopropellant. The results point out a collective impact of the tank pressure on minimum system mass. The optimum tank pressure is influenced by the bed loading and blowdown ratio. The technological complexity may have a vital impact on the choice of the bed loading and blowdown ratio.