The renewed global interest in space operations has initiated a modern Space Race, resulting in an increase in the number of satellites orbiting the Earth. In particular, small satellites, characterized by limited development costs and highly optimized mission capabilities, are increasingly overpopulating Low Earth Orbit (LEO) and Very Low Earth Orbit (VLEO). This rapid and widespread phenomenon has led to a rising demand for accurate and reliable mission scenario simulations. Addressing the challenge of developing an in-house high-fidelity Orbit Propagator, this work covers the modelling and integration of the principal external disturbances which can affect satellite operations in orbit, such as the gravity and magnetic field potential, third body perturbation caused by Sun and Moon, Solar Radiation Pressure (SRP), as well as atmospheric density and drag.