Tethered-Solar Power Satellite (Tethered-SPS) consists of power generation/transmission panels suspended by tether wires. The most important feature of the Tethered-SPS is that it is constructed by perfectly equivalent power generation/transmission units. Each unit panel, 100 m × 95 m, is suspended by four 5 km-tether wires deployed from a bus unit. The weight and output power of the unit SPS are 42.5 MT and 2.1 MW, respectively. The engineering studies have been conducted to design the power generation/ transmission panel and to show how to deploy the panel. In addition to the engineering research, two major environmental issues, the effect of hyper-velocity impact of the debris or meteoroids and the interaction of the solar cell array with the ambient plasma, have been studied. The engineering studies have shown that the power generation/transmission panel is technically feasible using the near-term technologies. The environmental studies have shown preliminary guidelines to design the power generation/transmission panel.