The near-Earth orbit debris population will continue to increase due to ongoing space activities, on-orbit explosions, and accidental collisions among artificial objects in space. To better limit the growth of debris population, Active Debris Removals have been proposed as effective and potential mitigation methods. In Japan, an active debris removal using electro-dynamic tether to reduce large space debris in the low-earth orbit is considered. However, tether satellite system must solve two matters in order to execute the mission successfully. First, a tether strands is thin but long enough to have a large area so that it is vulnerable to small particles. This paper suggests a double tether system and provides a mathematical approach to estimate the survival probability of a double tether system and then apply the approach to evaluate the mission success rate. Second, the tether is also long enough to be a hazard to other operational spacecraft. This paper also provides a simulation of tether satellite's impact probability to the other spacecraft and aims to propose the measurement for mission success.