One-Way Human Settlement Projects
Instead of bringing a crew to Mars and get them back after several months with a huge effort it is much cheaper to perform a Manned One-way Mission with the same technilogical and scientific results. The crew stays on Mars without any planned return concept. There are several possible aims:
Short Trip with Planned Death
The crew is brought to Mars with a certain amount of supplies (food, oxygen, etc.) that lasts, let's say, a year. When they run out of supplies they die and the mission is over. There are plenty of volunteers for such a mission, for it is a great honour to be the first on Mars.
Foundation of an Earth-supported Colony
The crew is brought to Mars with a certain amount of supplies (food, oxygen, etc.) that lasts, let's say, a year. Early before they run out of supplies they receive replenishment from earth. A constant logistic maintains the colony indefinitely.
Foundation of an Autonomous Colony
The crew is brought to Mars not before basic habitats, supplies and equipment for a long term stay has deposited on Mars' surface. The equipment is technologically sufficient to allow the crew to grow their own food, build new habitats etc.