A Mars habitat is a hypothetical place where humans could live on Mars. Mars habitats would have to contend with surface conditions that include almost no oxygen in the air, extreme cold, low pressure, and high radiation. Such a habitat might be placed underground, which would help to solve some problems but create new difficulties.
One challenge is the extreme cost of transporting building materials to the Martian surface, which by the 2010s was estimated to be about US$2 million per brick. While the gravity on Mars is lower than that on Earth, there are stronger solar radiation and temperature cycles, and high internal forces needed for pressurized habitats to contain air.
To contend with these constraints, architects have worked to understand the right balance between in-situ materials and construction, and ex-situ to Mars. For example, one idea is to use the locally available regolith to shield against radiation exposure, and another idea is to use transparent ice to allow non-harmful light to enter the habitat. Mars habitat design can also involve the study of local conditions, including pressures, temperatures, and local materials, especially water.
Overview
Significant challenges for Mars habitats are maintaining an artificial environment and shielding from intense solar radiation. Humans require a pressurized environment at all times and protection from the toxic Martian atmosphere. Connecting habitats is useful, as moving between separate structures requires a pressure suit or perhaps a pressurized Mars rover. One of the largest issues lies in simply getting to Mars, which means escaping Earth's atmosphere, sustaining the journey to Mars, and finally landing on the surface of Mars. One helpful aspect is the Mars atmosphere, which allows for aerobraking, meaning less need for using propellant to slow a craft for safe landing. However, the amount of energy required to transfer material to the surface of Mars is an additional task beyond simply getting into orbit.
During the late 1960s, the United States produced the Saturn V rocket, which was capable of launching enough mass into orbit required for a single-launch trip holding a crew of three to the surface of the Moon and back again. This feat required a number of specially designed pieces of hardware and the development of a technique known as the Lunar Orbit Rendezvous. The Lunar Orbit Rendezvous was a plan to coordinate the descent and ascent vehicles for a rendezvous in Lunar orbit. Referring to Mars, a similar technique would require a Mars Excursion Module, which combines a crewed descent-ascent vehicle and short stay surface habitat. Later plans have separated the descent-ascent vehicle and surface habitat, which further developed into separate descent, surface stay, and ascent vehicles using a new design architecture. In 2010, the Space Launch System, or future variants thereof, is envisioned as having the payload capacity and qualities needed for human Mars missions, using the Orion capsule.
One of the challenges for Mars habitats is maintaining the climate, especially the right temperature in the right places. Electronic devices and lights generate heat that rises in the air, even as there are extreme temperature fluctuations outside.
One idea for a Mars habitat is to use a Martian cave or lava tube, and an inflatable air-lock was proposed by the Caves of Mars Project for making use of such a structure. The idea of living in lava tubes has been suggested for their potential to provide increased protection from radiation, temperature fluctuation, Martian sunlight, etc. An advantage of living underground is that it avoids the need to create a radiation shield above ground. Another idea is to use robots to construct the base in advance of human's arrival.
The use of living plants or other living biologicals to aid in the air and food supply if desired can have major impact on the design. Using a reduced-pressure greenhouse could reduce the structural demands of maintaining air pressure, but require the relevant plants to survive at that lower pressure. It is questioned how low of pressure a plant could survive in and still be useful.
A Mars habitat may need to focus on keeping a certain type of plant alive, for example, as part of supporting its inhabitants. NASA's Caves of Mars study suggested the following food and food production characteristics:
Rapid growth survival in low light wide pH range high nutrition minimal waste
The study noted two plants, duckweed (Lemna minor) and water fern (Azolla filiculoides), as particularly suitable, and they grow on the surface of water. The Mars habitat would have to support the conditions of these food sources, possibly incorporating elements from greenhouse design or farming.
Historically, space missions tend to have a set amount of rations like Skylab, replenished with resupply from Earth. Using plants to affect the atmosphere and even enhance food supply was experimented with in the 2010s aboard the International Space Station.
Another issue is waste management. On Skylab all waste was put in a tank; on Apollo and the Space Shuttle, urine could be vented into space or pushed away in bags to re-enter Earth's atmosphere.
Considerations for maintaining the environment in a closed system included, removal of carbon dioxide, maintaining air pressure, supply of oxygen, temperature and humidity, and stopping fires. Another issue with a closed system is keeping it free from contamination from emissions from different materials, dust, or smoke. One concern on Mars is the effect of the fine dust of the Martian soil working its way into the living quarters or devices. The dust is very fine and accumulates on solar panels, amongst other surfaces.
Relevant technologies
Some possible areas of needed technology or expertise are: 3D Printing Mars atmospheric entry Caves of Mars Project Mars Excursion Module Aerospace engineering Space capsule Plants in space
Context A Mars habitat is often conceived as part of an ensemble of Mars base and infrastructure technologies. Some examples include Mars extra vehicular activity (EVA) suits, Mars rovers (both pressurized and not pressurized), aircraft, landers, storage tanks, communication structures, mining, and Mars-movers (e.g. Earth-moving equipment).
A Mars habitat might exist in the context of a human expedition, outpost, or colony on Mars.
Air
In creating a habitat for people, some considerations are maintaining the right air temperature, the right air pressure, and the composition of that atmosphere.
While it is possible for humans to breathe pure oxygen, a pure oxygen atmosphere was implicated in the Apollo 1 fire. As such, Mars habitats may have a need for additional gases. One possibility is to take nitrogen and argon from the atmosphere of Mars. As a result, a Mars habitat may use 40% argon, 40% nitrogen, and 20% oxygen. See also Argox, for the argon breathing gas mixture used in scuba diving
A concept to scrub from the breathing air is to use re-usable amine bead carbon dioxide scrubbers. While one carbon dioxide scrubber filters the astronaut's air, the other can vent scrubbed to the Mars atmosphere.
One unique structural force that Mars habitats must contend with if pressurized to Earth's atmosphere, is the force of air on the inside walls. This has been estimated at over for a pressurized habitat on the surface of Mars, which is radically increased compared to Earth structures. A closer comparison can be made to crewed high-altitude aircraft, which must withstand forces of when at altitude.
At about 150 thousand feet of altitude (28 miles (45 km)) on Earth, the atmospheric pressure starts to be equivalent to the surface of Mars.
+ Atmospheric pressure comparison Location Pressure Olympus Mons summit Mars average Hellas Planitia bottom Armstrong limit Mount Everest summit Earth sea level Surface of Venus
Temperature One of the challenges for a Mars habitat is for it to maintain suitable temperatures in the right places in a habitat. Things like electronics and lights generate heat that rises in the air, even as there are extreme temperature fluctuations outside. There can be large temperature swings on Mars, for example at the equator it may reach 70°F (20°C) in the daytime but then go to minus 100°F (−73°C) at night.
Examples of Mars surface temperatures: Average −80°F (−60°C). Polar locations in winter −195°F (−125°C). Equator in summer daytime High 70°F (20°C).
Temporary vs permanent habitation
A short term stay on the surface of Mars does not require a habitat to have a large volume or complete shielding from radiation. The situation would be similar to the International Space Station, where individuals receive an unusually high amount of radiation for a short duration and then leave. A small and light habitat can be transported to Mars and used immediately.
Long term permanent habitats require much more volume to house things such as a greenhouse and thick shielding to minimize the annual dose of radiation received. This type of habitat is too large and heavy to be sent to Mars, and likely would be constructed making use of some local resources. Possibilities include covering structures with ice or soil, excavating subterranean spaces or sealing the ends of an existing lava tube.
A larger settlement may be able to have a larger medical staff, increasing the ability to deal with health issues and emergencies. Whereas a small expedition of 4–6 people may only be able to have 1 medical doctor, an outpost of 20 might be able to have more than one and nurses, in addition to those with emergency or paramedic training. A full settlement may be able to achieve the same level of care as a contemporary Earth hospital.
Medical
One problem for medical care on Mars missions, is the difficulty in returning to Earth for advanced care, and providing adequate emergency care with a small crew size. A crew of six might have only one crew member trained to the level of emergency medical technician and one physician, but for a mission that would last years. In addition, consultations with Earth would be hampered by a 7- to 40-minute time lag. Medical risks include exposure to radiation and reduced gravity, and one deadly risk is a Solar Particle Event that can generate a lethal dose of radiation over the course of several hours or days if the astronauts do not have enough shielding. Materials testing has recently been done to explore spacesuits and "storm shelters" for protection from Galactic Cosmic Radiation and Solar Particle Events during launch, transit, and habitation upon Mars. Medical preparedness also requires that the effect of radiation on stored pharmaceuticals and medical technology would have to be taken into account.
One of the medical supplies that may be needed is intravenous fluid, which is mostly water but contains other things so it can be added directly to the blood stream. If it can be created on the spot from existing water then it could spare the weight of hauling earth-produced units, whose weight is mostly water. A prototype for this capability was tested on the International Space Station (ISS) in 2010.
On some of the first crewed missions, three types of medications should be taken into orbit; the antiemetic trimethobenzamide; the painkiller pethidine; and the stimulant dextroamphetamine. By the time of ISS, the crew had almost 200 medications available, with separate pill cabinets for Russians and Americans. One of the many concerns for crewed Mars missions is what medicine to bring and how the astronauts would respond to them in different conditions.