Mars habitat

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 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.

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 2,000 pounds per square foot (9,800 kg/m²) 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 1,100 to 1,400 pounds per square foot (5,400 to 6,800 kg/m²) 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 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.

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 person 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 of medical attention needs 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, it is difficult to treat a wide range of issues with advanced care, whereas with a team of overall size12–20 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 care 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 could 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 life-threatening due to restrictions on the amount of medical equipment, training, and the time-delay in communication with Earth. The time delay for a one way message ranges from 4 to 24 minutes. A response to a message takes that time, the delay processing the message and creating a reply, plus the time for that message to travel to Mars (another 4 to 24 minutes).

Examples of acute medical emergency scenarios for Mars missions:

• Wounds, lacerations, and burns
• Exposure to a toxin
• Acute allergic reactions (anaphylaxis)
• Acute radiation sickness
• Dental
• Eye (Ophthalmologic)
• Psychiatric

An example of spaceflight related health emergency was the inert gas asphyxiation with nitrogen gas aboard Space Shuttle Columbia in 1981, when it was undergoing preparations for its launch In that case, a routine purge with nitrogen to decrease risk of fire lead to 5 medical emergencies and 2 deaths. Another infamous space related accident is the Apollo 1 incident, when a pure oxygen atmosphere ignited in the interior of space capsule during tests on the ground, three died. A 1997 study of about 280 space travelers between 1988 and 1995, found that only 3 did not have some sort of medical issue on their spaceflight. A medical risk for a Mars surface mission is how the astronauts will handle operations on the surface after several months in zero gravity. On Earth, astronauts are usually carted from the spacecraft and take a long time to recover.

Library

One idea for a Mars missions is a library sent to the surface of that planet. The Phoenix lander, which landed on the North polar surface of Mars in 2008, included a DVD library that was heralded as the first library on Mars. The Phoenix library DVD would be taken by future explorers who could access the content on the disk. The disk, both a memorial to the past and a message to the future, took 15 years to produce. The content on the disk includes Visions of Mars. One idea for exploration is knowledge arks for space, a sort of back-up of knowledge in case something happens to Earth.

The Biosphere 2 closed-loop biosphere test included a library with the living quarters. The library was positioned at the top of a tower, and known as Library tower.

Meteor impacts

Another consideration for Mars habitats is the need to potentially deal with a meteor impact. Because the atmosphere is thinner than Earth, more meteors make it to the surface. A meteor might puncture the surface of the habitat and thereby cause a loss of pressure and/or damage systems.

In the 2010s, it was determined that something struck the surface of Mars, creating a spattering pattern of larger and smaller craters between 2008 and 2014. In this case the atmosphere only partially disintegrated the meteor before it struck the surface.

Radiation

Radiation exposure is a concern for astronauts on the surface, as Mars lacks a strong magnetic field, and atmosphere is too thin to stop as much radiation as Earth. It has been estimated that sixteen feet (5 meters) of Mars regolith stops the same amount of radiation as Earth's atmosphere.

Power

For a 500-day crewed Mars mission, NASA has studied using solar power and nuclear power for its base, as well as power storage systems (e.g. batteries). Some of the challenges for solar power include a reduction in solar intensity (because Mars is farther from the sun), dust accumulation, periodic dust storms, and storing power for night-time use. Global Mars dust storms cause lower temperatures and reduce sunlight reaching the surface. Two ideas for overcoming this are to use an additional array deployed during a dust storm and to use some nuclear power to provide base-line power that is not affected by the storms.

NASA has studied nuclear-power fission systems in the 2010s for Mars surface missions. One design planned an output of 40 kilowatts. Nuclear power fission is independent of sunlight reaching the surface of Mars, which can be affected by dust storms.

Another idea for power is to beam the power to the surface from a solar power satellite to a rectifying antenna (rectenna) receiver. 245 GHz, laser, in-situ rectenna construction, and 5.8 GHz designs have been studied. One idea is to combine this technology with Solar Electric Propulsion to achieve a lower mass than surface solar power. The advantage of this approach to power is that the rectennas should be immune to dust and weather changes, and with the right orbit, a solar power Mars satellite could beam power continuously to the surface.

Technology to clean dust off the solar panels was considered for Mars Exploration Rover's development. In the 21st century, ways have been proposed for cleaning off solar panels on the surface of Mars. The effects of Martian surface dust on solar cells was studied in the 1990s by the Materials Adherence Experiment on Mars Pathfinder.