Evaluation of Life Support System (LSS) mass has to take into account not only mass of components and stock of expendable substances but also the mass of power supply and heat rejection systems. The productivity of biological regeneration processes grows with power supply but at high level of power supply the efficiency of these processes is decreased. On the other hand increasing of power supply causes growing of energetic and hit rejection system mass. So, optimization problem on optimal intensity of regeneration processes appears. It is shown that the value of power supplied providing minimal total mass of LSS does not depend on the level of closure and mission duration.