Although NASA would prefer round trips for astronauts, in a recent interview Buzz Aldrin, he suggested that the fist crews to land on Mars should stay there until a colony of about 100 people is settled. From an investment standpoint this makes a good deal of sense, since round trips would only delay the development of a settlement and increase the cost. Some agree with Aldrin and some have other approaches.

The Dutch-led "Mars One" Project has announced plans to establish the first human Mars colony by 2025. This mission calls for initially sending a crew of four on a one-way traverse to the Red Planet. Once there, they would spend the rest of their lives building the first permanent settlement. One of the key assumptions is that the entire mission can be built with existing technologies.

However, MIT researchers have developed a detailed analysis tool that has assessed the feasibility of the proposed Mars One mission, and has concluded that new technologies will be needed. Technology challenges were identified in several areas, including locally grown crops and water extraction from Mars' soil.

Logistical issues were also discovered in the area of spare-parts resupply. Researchers determined that, as the colony grows, spare parts would quickly dominate future deliveries to Mars, possibly requiring up to 62% of payloads from Earth.

Even the initial crew transfer requirements were studied and found to be overly optimistic. The Mars One plan calls for six Falcon Heavy vehicles to provide initial supplies before the astronauts' arrival. The MIT assessment determined that the number might be closer to 15 Heavy vehicles. In summary, it appears the Mars One plan may be a bit too optimistic.

In 2013, the first tourist-astronaut, Dennis Tito, announced the founding of the Inspiration Mars Foundation with the objective of launching a crewed spacecraft that would flyby Mars and safely return to Earth. He claimed such a mission could commence as early as 2018 and would revitalize interest in science, technology, engineering and mathematics (STEM) education. Mission details were presented in a 2013 IEEE research paper. In that year, the Foundation announced plans to procure space hardware, buy launch vehicle services and select a married couple to be the crew.

Tito hopes this concept will excite the public to provide much of the needed funding. He intends to fund the foundation with up to $100 million for its first two of years of operation. However, Tito indicated they would need a significant investment from the Government, including a NASA-supplied spacecraft.

The planned mission would have a duration of 501 days and include a free-return trajectory. Such a mission would require the smallest possible amount of propellants in order to get to Mars and back to Earth. As it turns out, Earth and Mars will align in 2018 such that the total trip time will be only 501 days.

The mission will take the two-person crew to within about 160 km of Mars and return them to Earth safely. The mission's first target launch date is January 5, 2018, but it could be later. Quick, free-return orbit opportunities occur twice every 15 years. After 2018, the next opportunity will occur in 2031.

Tito's "Plan B" alternative involves a mission beginning in 2021, but would be 88 days longer in duration. It would require a double fly-by, one of Venus and one of Mars. The required trajectory would take the couple to within 800 km of Venus and use the planet's gravitational pull to speed onward travel to Mars.

However, Tito prefers "Plan A" which offers a lower-risk, 2018 mission and requires fewer critical propulsive maneuvers. Furthermore, the 2018 launch opportunity coincides with the 11-year solar minimum, providing the lowest solar radiation exposure.

Several other organizations have indicated an interest in human excursions to Mars, but the financial and technical challenges are indeed huge. Mars One and Tito certainly offer interesting ideas and do present concepts that might increase public awareness and enthusiasm. Stay tuned for further developments in the coming years.