As for the moon, a reasonable initial Mars program would be an umanned geology laboratory. An additional component, low-level flight using some type of air vehicle, can be considered. Aerobraking can be used for freight delivery
A manned mission can be considreed. The mission considered here is in the category called a "split mission". Equipment is sent to Mars via ion propulsion. The astronauts then travel to Mars via chemical propulsion, and return this way also. A 40 ton payload booster might be useful fof manned Mars, but is unnecessary otherwise. Nuclear power can be avoided.
Simulations in Some Mars Trajectory Optimization (PDF) show that a trip of 180 days out, 25 days on Mars, and 95 days return is feasible. Aerocapture is used at every target entry. This had previously been considered problematical for the Mars equipment entry; but the large object vehicle solves this problem. The manned entry is higher velocity than in previous missions (10 Km/sec for Apollo), but appears to be feasible.
A specific mission plan using the optimal trajectories is considered in the manuscript; a summary follows. The crew size is 2. The astronauts travel in 1 Earth gravity. They rendezvous with equipment in Mars orbit. One of them remains in orbit and operates a long range rover, which gathers samples. The other descends to the surface.
The equipment for the surface excursion includes a return rocket and capsule, rover, experiments, and solar power plant. Probably there should also be a crew compartment in addition to that of the return rocket, since the former needs to be as small as possible and the latter must be comfortable for the duration. It can be mounted low on the platform, with a hatch directly to the rover. The return rocket capsule must be mounted high, so a tube is probably needed. Prior to return, the astronaut is always either in the "tent" or the rover, alleviating the space suit problem. He or she descends in the crew sphere of the surface to orbit vehicle. The power plant is of the standard variety, except the reflector is unfolded; it charges batteries, including exchange batteries for the rover.
The radiation problem can be solved as follows. The transit capsules have both clean and waste water in the outer perimeter. In addition, if there is a solar storm a cabinet can be prepared, and water pumped into its boundary (to thicken the shielding layer).
Other mission architectures benefit from an integrated program. In a long stay with two short flights, the "habitat'' can be made larger, indeed into a small permanent base, by using the ion freight method to deliver as much as hundreds of tons of equipment to the Mars surface prior to the first manned flight.