Human mission to Mars
The idea of sending humans to Mars has been the subject of aerospace engineering and scientific studies since the late 1940s as part of the broader exploration of Mars. Long-term proposals have included sending settlers and terraforming the planet. Currently, only robotic landers, rovers and a helicopter have been on Mars. The farthest humans have been beyond Earth is the Moon, under the U.S. National Aeronautics and Space Administration Apollo program which ended in 1972.
Conceptual proposals for missions that would involve human spaceflight started in the early 1950s, with planned missions typically expected to take place between 10 and 30 years after they were drafted. The list of crewed Mars mission plans shows the proposals put forth by multiple organizations and space agencies in this field of space exploration. These plans have varied—from scientific expeditions, in which a small group would visit Mars for a period of a few weeks or more, to a continuous presence. Some have also considered exploring the Martian moons Phobos and Deimos. By 2020, virtual visits to Mars, using haptic technology, had also been proposed.
Meanwhile, uncrewed exploration of Mars has been a goal of national space programs for decades, and was first achieved in 1965 with the Mariner 4 flyby. Human missions to Mars have been part of science fiction since the 1880s, and more broadly, in fiction, Mars is a frequent target of exploration and settlement in books, graphic novels, and films. The concept of a Martian as something living on Mars is part of the fiction. Proposals for human missions to Mars have come from agencies such as NASA, CNSA, the European Space Agency, Boeing, SpaceX, and space advocacy groups such as the Mars Society and The Planetary Society.
Travel to Mars
The energy needed for transfer between planetary orbits, or delta-v, is lowest at intervals fixed by the synodic period. For Earth–Mars trips, the period is every 26 months, so missions are typically planned to coincide with one of these launch periods. Due to the eccentricity of Mars's orbit, the energy needed in the low-energy periods varies on roughly a 15-year cycle with the easiest periods needing only half the energy of the peaks. In the 20th century, a minimum existed in the 1969 and 1971 launch periods and another low in 1986 and 1988, then the cycle repeated. The last low-energy launch period occurred in 2023.Several types of mission plans have been proposed, including opposition class and conjunction class, or the Crocco flyby. The lowest energy transfer to Mars is a Hohmann transfer orbit, a conjunction class mission which would involve a roughly 9-month travel time from Earth to Mars, about at Mars to wait for the transfer window to Earth, and a travel time of about 9 months to return to Earth. This would be a 34-month trip.
Shorter Mars mission plans have round-trip flight times of 400 to 450 days, or under 15 months for an opposition-class expedition, but would require significantly higher energy. A fast Mars mission of round trip could be possible with on-orbit staging. In 2014, ballistic capture was proposed, which may reduce fuel cost and provide more flexible launch windows compared to the Hohmann.In the Crocco grand tour, a crewed spacecraft would get a flyby of Mars and Venus in under a year in space. Some flyby mission architectures can also be extended to include a style of Mars landing with a flyby excursion lander spacecraft. Proposed by R. Titus in 1966, it involved a short-stay lander-ascent vehicle that would separate from a "parent" Earth-Mars transfer craft prior to its flyby of Mars. The Ascent-Descent lander would arrive sooner and either go into orbit around Mars or land, and, depending on the design, offer perhaps 10–30 days before it needed to launch itself back to the main transfer vehicle.
In the 1980s, it was suggested that aerobraking at Mars could reduce the mass required for a human Mars mission lifting off from Earth by as much as half. As a result, Mars missions have designed interplanetary spacecraft and landers capable of aerobraking.
Landing on Mars
A number of uncrewed spacecraft have landed on the surface of Mars, while some, such as Beagle2 and the Schiaparelli EDM, have failed what is considered a difficult landing. Among the successes:- Mars 3 – 1971
- Viking 1 and Viking 2 – 1976
- Mars Pathfinder and its Sojourner rover – 1997
- Spirit and Opportunity rovers – 2004
- Phoenix lander – 2008
- Curiosity rover – 2012
- InSight lander – 2018
- Tianwen-1 lander and Zhurong rover – 2021
- Perseverance rover and Ingenuity helicopter – 2021
Orbital capture
Survey work
Conducting a safe landing requires knowledge of the properties of the atmosphere, first observed by Mariner 4, and a survey of the planet to identify suitable landing sites. Major global surveys were conducted by Mariner 9, ''Viking 1, and two orbiters, which supported the Viking landers. Later orbiters, such as Mars Global Surveyor, 2001 Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter'', have mapped Mars in higher resolution with improved instruments. These later surveys have identified the probable locations of water, a critical resource.Funding
Sending humans to Mars will be expensive. In 2010, one estimate was roughly US$500 billion, but the actual costs will likely be more. Starting in the late 1950s, the early phase of space exploration was conducted as a space race by lone nations, as much to make a political statement as to study the Solar System. This proved to be unsustainable, and the current climate is one of international cooperation, with large projects such as the International Space Station and the proposed Lunar Gateway being built and launched by multiple countries.Critics argue that the immense cost outweighs the immediate benefits of establishing a human presence on Mars and that funds could be better redirected toward other programs, such as robotic exploration. Proponents of human space exploration contend that the symbolism of establishing a presence in space may garner public interest to join the cause and spark global cooperation. There are also claims that a long-term investment in space travel is necessary for humanity's survival.
One factor to reduce the cost of sending humans to Mars may be space tourism. Growth in that business and technological developments would bring economies of scale and thus a lower cost of human spaceflight. A similar concept can be examined in the history of personal computers: when computers were used only for scientific research, with minor use in big industry, they were big, rare, heavy, and costly. When the potential market increased, and they started to become common in businesses and later in homes, the computing power of home devices skyrocketed, and prices plummeted.
Medical
Several key physical challenges exist for human missions to Mars:- Health threat from cosmic rays and other ionizing radiation. In May 2013, NASA scientists reported that a possible mission to Mars may involve great radiation risk based on energetic particle radiation measured by the radiation assessment detector on the Mars Science Laboratory while traveling from the Earth to Mars in 2011–2012. The calculated radiation dose was 0.66 sieverts round-trip. The agency's career radiation limit for astronauts is 1 sievert. In mid-September 2017, NASA reported temporarily doubled radiation levels on the surface of Mars, with an aurora 25 times brighter than any observed earlier, due to a massive unexpected solar storm.
- Loss of kidney function. On 11 June 2024, researchers at the University College of London's Department of Renal Medicine reported that "Serious health risks emerge the longer a person is exposed to."
- Adverse health effects of prolonged weightlessness, including bone mineral density loss and eyesight impairment. In November 2019, researchers reported that astronauts experienced serious blood flow and clotting problems while on board the International Space Station, based on a six-month study of 11 healthy astronauts. The results may influence long-term spaceflight, including a mission to the planet Mars, according to the researchers.
- Psychological and sociological effects of spaceflight involving long isolation from Earth and the lack of community due to lack of a real-time connection with Earth.
- Social effects of several humans living under cramped conditions for more than one Earth year.
- Lack of medical facilities.
- Potential failure of propulsion or life-support equipment.
Planetary protection
Robotic spacecraft that travel to Mars require sterilization. The allowable limit is 300,000 spores on the exterior of general craft, with stricter requirements for spacecraft bound for "special regions" containing water. Otherwise there is a risk of contaminating not only the life-detection experiments but possibly the planet itself.Sterilizing human missions to this level is impossible, as humans are typically host to a hundred trillion microorganisms of thousands of species of the human microbiota, and these cannot be removed. Containment seems the only option, but it is a major challenge in the event of a hard landing. There have been several planetary workshops on this issue, yet there are no final guidelines for a way forward. Human explorers would also be vulnerable to back contamination to Earth if they become carriers of microorganisms.