A numerical tool is developed for the design and analysis of Mars atmospheric entry trajectories. Simple latitude dependent density model is employed along with an approximate temperature model for Mars' atmosphere. Radiative heat flux and convective heat flux (with cold wall boundary condition) relations are used for the study of stagnation point heating. Approximate drag profile of Mars Pathfinder is used for most simulations. Effects of non-spherical gravity and Mars' surface elevation considerations are discussed in brief. De-orbit thrusting, direct entry, lifting entry, parachute deployment, heat shield release and terminal descent thrusting scenarios are also incorporated into the tool, and their design characteristics are studied. Advantages of lifting entry and the necessity for parachute deployment and terminal descent thrusting are discussed. Different direct entry scenarios are analyzed within feasible launch windows for a typical Mars mission.