The Thermodiver project aims to develop a reusable space tug using Air-Breathing Electric Propulsion (ABEP), which collects atmospheric particles from the upper atmosphere to enable in-situ refuelling and extended mission durations. This propulsion method supports a range of missions, including satellite servicing, orbital transfers, and reducing orbital congestion from space debris. A key part of the design process was the use of ARISS (Air-breathing Refuelling Iterative System Solver), a solver developed by the team that encompasses the initial design, sizing, budgeting, and performance assessment of the air-breathing spacecraft. ARISS integrates various simulation tools: Direct Simulation Monte Carlo (DSMC) for intake and aerodynamic performance, the General Mission Analysis Tool (GMAT) for mission planning, and Finite Element Methods (FEM) for thermal and structural analysis. The project produced a detailed 6.2-meter-long, 800 kg spacecraft design with a parabolic intake for efficiency and the bus shielded in its wake. Capable of de-orbiting satellites such as Proba-V and refuelling within five months for continued missions, the system is being further refined in the final stages of development. Ultimately, the Thermodiver offers a sustainable solution to orbital congestion and a versatile platform for affordable in-space transportation and future interplanetary exploration.