The objective of this study is to develop a conceptual design framework for a liquid-propellant space launch vehicle at the early stages of design. In this framework, key mission parameters including mass, geometry, flight trajectory, propulsion performance, and aerodynamic conditions are optimized. To this end, a mass–energetic approach is adopted, which models the relationship between mission energy and system mass. For solving the continuous multi-objective optimization problem, the Teaching–Learning-Based Optimization (TLBO) algorithm is employed. Owing to its parameter-free nature, TLBO demonstrates efficient convergence behavior and robust solution stability. The results show that, using this design framework, a launch vehicle capable of delivering a 440 kg payload into a 300 km circular orbit is obtained with a total liftoff mass of 69,205 kg and a total length of 22.3 m. Comparison with reference methods reveals that the proposed model, while accounting for subsystem-level details, provides greater precision and flexibility in determining design parameters. The practical implication of this approach lies in its applicability during the preliminary design phase of space missions, contributing to reduced costs and improved design reliability. The main novelty of this work lies in integrating the TLBO algorithm with the mass–energetic design approach for conceptual space system design a combination that has received limited attention in previous research.