Facility where humans could live on Mars
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. Alternatively, the habitat might be placed underground, which helps solve some problems but creates 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 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 growth variants therefore, is envisioned as having the payload capacity and qualities needed for human Mars missions, utilizing 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 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. An example of how engineering demands and operational goals can interact, is a reduced-pressure greenhouse area. This would reduce the structural demands of maintaining air pressure, but require the relevant plants to survive at that lower pressure. Taken to an extreme, the question remains just how a low a pressure could a plant 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:
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 non-growing food supply eating out of 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 the 2010s aboard the International Space Station.
Another issue is waste management. On Skylab all waste was put in a big tank; on Apollo and the Space Shuttle urine could be vented out 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 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:
Context.
A Mars habitat is often conceived as part of an ensemble of Mars base and infrastructure technologies. Some examples include Mars EVA suits, Mars rover, 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; however, they are hard to separate from each other. 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 CO2 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 CO2 to the Mars atmosphere, once that process is completed another one can be used, and the one that was used can take a break.
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.
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 fluctuation outside. There can be large temperature swings on Mars, for example at the equator it may reach 70 degrees F (20 degrees C) in the daytime but then go down to minus 100 degrees F (−73 C) at night.
Examples of Mars surface temperatures:
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 (i.e.: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 must 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 may 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 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 (GRC) and Solar Particle Events (SPE's) 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 as well.
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 in 2010.
On some of the first crewed missions, three types of medications that were taken into orbit; the antiemetic trimethobenzamide; the painkiller pethidine; the stimulant dextroamphetamine. By the time of ISS, space crew-persons had almost 200 medications available, with separate pill cabinets for Russians and Americans. One of the many concerns for crewed Mars missions is what pills to bring and how the astronauts would respond to them in different conditions.
In 1999, NASA's Johnson Space Center published "Medical Aspects of Exploration Missions" as part of the Decadal Survey. On a small mission it might be possible to have one be a medical doctor and another be a paramedic, out of a crew of perhaps 4–6 people, however on a larger mission with 20 people there could also be a nurse and options like minor surgery might be possible. Two major categories for space would be emergency medical care and then more advanced care, dealing with a wide range concerns due to space-travel. For very small crews its difficult to treat a wide range issues with advanced care, whereas with a team with an overall size of 12–20 on Mars there could be multiple doctors and nurses, in addition to EMT-level certifications. While not at the level of a typical Earth hospital this would transition medical are beyond basic options typical of very small crew sizes (2–3) where the accepted risk is higher.
With a modest number of Mars inhabitants and medical crew, robot-assisted surgery could be considered. A crew member would operate the robot with help via telecommunications from Earth. Two examples of medical-care situations that have been mentioned in regard to people on Mars is how to deal with a broken leg and an appendicitis. One concern is to stop what would otherwise be a minor injury from becoming