In 27 February 2013, Dennis Tito, the founder Inspirational Mars Foundation, an American non-profit organization announced their plans to produce space hardware, launch vehicles services and select a two-person married couple as crew and attempt to raise funding necessary to launch a mission to Mars in 2018.
Dennis Tito said he was going to fund the foundation with $100 million for the first years of operation.
However, later Dennis Tito indicated that the plan was impossible without significant investment from NASA and the use of NASA spacecrafts. NASA, however, was unwilling to get into a partnership with the foundation.
Finally, in by late 2015 their website became defunct but it is archived by the Internet Archive [Wikipedia]. The foundation's future plans are still unclear.
4. Boeing Affordable Mars Mission Design (2014)
On December 2, 2014, NASA's Advanced Human Exploration Systems Director Jason Crusan and Deputy Associate Administrator of Programs James Reuthner announced tentative support for the Boeing "Affordable Mars Mission Design".
This included NASA support for systems like radiation shielding, centrifugal artificial gravity, in-transit consumable resupply and a lander that can return.
Reuthner suggested that if adequate funding were forthcoming, the proposed mission would be expected in the early 2030s.
3. Mars One: One Way Trip To Mars (2012)
On May 2012, the Dutch entrepreneur Bas Lansdorp announced his plans to establish a permanent human settlement on Mars. From there was born the Mars One organization, they have proposed to land the first humans on Mars and establish a permanent human colony there by 2025. The organization consists of two entities: the non-profit Mars One Foundation and the profitable Mars One Ventures.
The Mars One Foundation, which is based on Netherlands, implements and manages the mission while the Mars One Ventures holds all the monetization rights, including broadcasting rights. They have proposed to launch a rover and a series of satellites by 2018. The rover would help to select the location of the settlement while the series of satellites named ComSats would enable near-24/7 communication between Earth and Mars.
However, unfortunately the initial plan of this mission has slipped two times, with a two-year delay each time. Therefore, these rover and satellite missions would take place only after 2026.
They have also planned to sign contracts with Elon Musk's SpaceX for using their Red Dragon spacecraft and Falcon Heavy Rocket in these missions but no such contracts have been signed until now.
2. NASA's Journey To Mars: Pioneering Next Steps In Space Exploration (2015)
On October 8, 2015, NASA published its official plan for human exploration and colonization of Mars. The Plan operates through three distinct phases leading up to fully sustained colonization. The first stage, already underway, is the "Earth Reliant" phase. This phase continues the utilization of the International Space Station until 2024. It also studies the effects of long duration space missions on the human body.
The second stage, "Proving Ground", moves into cislunar space for most of its tasks. This will happen around 2020, in this phase NASA plans to capture an asteroid, test deep space habitation facilities and validate capabilities required for human exploration of Mars.
Finally, the third phase is the transition to independence from Earth resources. The "Earth Independent" phase includes long-term missions on the lunar surface, which leverage surface habitats that only require routine maintenance and the harvesting of Martian resources for fuel, water and building materials.
NASA is still aiming for human missions to Mars in the 2030s, though Earth independence could take decades longer.
1. SpaceX Interplanetary Transport System (2016)
In September 2016, SpaceX CEO Elon Musk publicly announced a comprehensive vision to begin the colonization of Mars called Interplanetary Transport System (formerly, Mars Colonial Transporter).
This included a number of high-level design details for an ITS launch vehicle and the Interplanetary Spaceship and ITS tanker spacecraft that would provide the on-orbit pieces of the transportation technology, as well as a propellant plant to be built on Mars, at a base referred to as Mars Base Alpha.
The aspirational objective is to advance the technology and infrastructure such that the first humans to Mars could depart as early as 2024.