The human exploration of Mars presents many challenges, not least of which is the task of entry, descent, and landing. Because human-class missions are expected to have landed payload. masses on the order of 40 to 80 t, significant challenges arise beyond those of current robotic missions. This study uses parametric trade studies to provide insight into the feasibility of using Viking and Apollo heritage technologies to enable a human-class mission to Mars. The challenges encountered with human-class missions, as well as potential solutions, are highlighted through the results of parametric studies on vehicle size and mass. To populate the trade space, aerocapture, and entry-from-orbit analyses of 10 and 15-m diam aeroshells with a lift-to-drag ratio of 0.3 and 0.5 were investigated. The methodology developed to perform these trade studies represents a significant advancement in human Mars entry, descent, and landing system sizing. Numerous comparisons are made with past missions, both real and conceptual, and sources of discrepancies are discussed. Results indicate that in the limit, a crew capsule used only for entry from orbit could have an arrival mass as low as 20 t. For larger landed payloads, such as a 20-t surface power system; a vehicle with an arrival mass on the order of 80 t may be required. Finally, no feasible entry, descent, and landing systems were obtained with the capability to deliver more than approximately 25 t of landed payload to the Mars surface for arrival masses less than 100 t. This suggests that extension of traditional entry, descent, and landing technologies used for robotic exploration may be insufficient for human Mars exploration.