Because we’re sending three missions to a single location in order to establish the first permanent human settlement on Mars, it’s especially important that the location choice be a good one. The intention in this section is not to identify one specific optimal location for the IMRS, which would require a more involved analysis, but to highlight the salient characteristics such a location would have, and to outline a general approach to analysis.
There are several drivers in selecting an optimal location, which must be balanced:
- Availability of key resources. This includes sunlight, heat and water and (secondarily) areothermal energy. Atmospheric resources such as carbon, oxygen, nitrogen and atmospheric water are not location-dependent. Other location-dependent resources that will become more important in the future include wind energy, certain minerals and metals, caves and lava tubes, tourist attractions, and infrastructure.
- Terrain characteristics. For safety in landing, and ease and safety of surface mobility both in marssuits and surface vehicles, we require a location that is reasonably flat, level, and not overly dusty. Low dust is indicated by high thermal inertia, which will also be advantageous for reducing energy storage requirements. In addition, we desire loose regolith to pile on the Hab for radiation and thermal protection.
- Scientific interest. Naturally the best location will be close to sites that can help to answer scientific questions about Mars. Most importantly, has Mars ever hosted, or does it currently host, life as we know it? Other questions relate to the presence of liquid water, Mars’ geologic history, etc.
Previous Mars missions and the DRA have primarily favoured scientifically interesting locations, in line with their intent to continue exploiting the scientific goldmine that is Mars. However, the goal for Blue Dragon and the IMRS is to establish a permanent human presence on Mars as a base from where further and extensive scientific exploration of Mars can occur more cheaply and conveniently. With this in mind (and the general principle that all of Mars is scientifically interesting, especially to humans on the ground), selecting a site of maximum scientific value is considered less important than selecting a site with maximum potential for supporting habitation.
Our preference for a power system based on solar energy (discussed later) is our strongest driver for location selection. Generally speaking, as on Earth, the availability of sunlight reduces with increased latitude. However, due to the eccentricity of Mars’ orbit northern latitudes receive more solar energy than southern, which is fortuitous as there are other reasons for favouring the northern hemisphere. It has been shown that the latitude of 31° north has the highest minimum solar incidence for a single sol over a Martian year (Cooper et al., 2010). Because the minimum solar energy a site receives in a single sol determines the maximum required mass of the energy storage subsystem, this is a good reason for locating the base near this latitude. The ideal location might be within approximately 5-10° of this optimal latitude, as long as it also satisfies other conditions.
In addition, we must not select a location deep in a crater or chasm, as this would increase the amount of time the PV cells are in shadow each day. Rather, we must choose a location out in the open that receives as much sunlight as possible each day. This is harmonious with our need to land somewhere flat.
One of the primary energy requirements of a habitat on Mars is thermal control. The surface temperature on Mars varies between 130K and 308K, with an average of about 218K; temperatures that are, on average, comparable with Antarctica.
The desired temperature inside the Hab, however, is a comfortable 295K (22°C) ± ~5K. Therefore the ECLSS must maintain the interior temperature of the Hab around 80K warmer than the external environment, on average. This is a significant temperature gradient, and one that must be maintained all day, every day, throughout the entire 1.5-year surface stay.
The amount of energy necessary for heating is mitigated to some extent due to warming of the Hab’s atmosphere by human metabolism and operation of electrical and electronic equipment. During warmer days the Hab will need cooling. Further analysis is required to determine the actual energy requirements for thermal control, however, the warmer the location, the lower they will be.
The amount of thermal energy available from the natural environment is partly a function of solar incidence. As we’re already selecting for high solar incidence, this automatically selects for warmth as well.
Thermal inertia of the terrain is also important, as a higher thermal inertia will keep the base warmer for longer after nightfall, reducing energy storage needs. Selecting for higher thermal inertia means choosing a less dusty site. This is somewhat harmonious with our terrain requirements, as a less dusty site is preferable for surface mobility.
For a long surface stay mission architecture (~540 days), the crew is be on Mars for approximately three-quarters of a Martian year (687 days), or three out of four seasons.
Mars seasons are aligned with the eccentricity of its orbit. At perihelion it’s winter in the north and summer in the south. At aphelion it’s summer in the north and winter in the south. The southern hemisphere therefore experiences a more extreme climate, with hotter summers and colder winters than the north.
When Alpha Crew departs for Mars in 2031, it will be close to perihelion, which is the reason we choose that particular year to travel. The distance to Mars will be at its minimum in the approximately 16-year cycle of perihelic oppositions. Therefore, it will be winter in the northern hemisphere at time of launch. The crew will arrive approximately at the end of the northern winter and spend the next three seasons on Mars, and leave at approximately the beginning of the next northern winter. Alpha Crew will therefore miss the northern winter, which is optimal for light and heat. This is fortunate, as there are several other reasons to locate the base in the north.
Bravo and Charlie Crews, however, will be at the IMRS during northern winter. The intention is to increase power production at the base by at least 100kW with each mission, thus compensating for degradation of PV cells, developing increasing energy security at the base, and ensuring ample power for surviving suboptimal conditions such as winter and dust storms. Because Alpha Crew will have the least infrastructure and experience, the intention is to make their mission as safe as possible.
Choosing an especially flat area (low surface roughness) is important for:
- Safe landings.
- Mobility in marssuits and surface vehicles.
The Blue Dragon architecture requires safely landing the MAV, Hab, and at least two cargo capsules in approximately the same location. However, note that they will not be directly adjacent to each other, because landing any item will kick up a lost of dust and debris; therefore, each item must be landed some distance, perhaps about 100-1000 metres, from the others.
The Rover must be able to negotiate the terrain between these elements, and the surrounding area. In addition, the AWESOM (Autonomous Water Extraction from the Surface Of Mars) robot must be able to traverse the ground around the MAV.
As this is our first landing on Mars with a human crew, we must minimise the probability of landing on a large boulder or a slope, so the flatter and smoother the better. Fortunately this corresponds with our desire to find a location near a potential source of areothermal energy, because it’s the locations that have most recently been covered in lava (and therefore have few craters) that are most likely to still be areologically active.
The downside of choosing an especially flat area is that there may not be much of areological interest in the vicinity, which means more exploration will have to be performed using the Rover rather than simply in marssuits. However, safety is a priority. The goal will be to locate the base within, at most, a few hours drive away from areologically interesting regions.
The flattest region of Mars is Vastitas Borealis, the vast low-lying northern region that may have once been the floor of a huge ocean (known as “Oceanus Borealis”).
The following map shows surface roughness, with smooth areas appearing dark and rough areas appearing light. Regions of low surface roughness between 26-36N are highlighted. Note that the region west of Olympus Mons is one of the smoothest on Mars:
The Martian atmosphere is warmest at lower elevations, as the atmosphere is thicker and functions as a thermal blanket.
Vastitas Borealis is at a much lower altitude than the southern highlands, which again leads us to favour this region. The following map shows the topography of Mars, based on data returned by the MOLA (Mars Orbiting Laser Altimeter). Low elevation regions between 26°N and 36°N are highlighted:
Because Martian air is warmer at lower elevations, some researchers have proposed Hellas Basin as a good location for a base. However, this choice would not exploit other advantages of the northern hemisphere, it is not very flat, and it’s a dust trap. Hellas Basin is one of the regions from where dust storms frequently erupt.
Thermal inertia refers to the ability of the terrain to retain heat. Small particles, such as dust, have low thermal inertia, i.e. they lose heat rapidly. Boulders and exposed bedrock have high thermal inertia, i.e. they retain heat longer. (This is why people use polished concrete indoors, as a thermal mass to reduce heating costs.) Thermal inertia at the location is important for several reasons:
- A very low thermal inertia implies thick dust, which could impede mobility in marssuits and surface vehicles. Dust is also less useful for piling around and on the Hab for thermal and radiation protection.
- A high thermal inertia is advantageous as the ground will serve to keep the base warmer after sunset, reducing energy requirements.
- A very high thermal inertia would imply large boulders or large regions of exposed bedrock.
- A medium thermal inertia implies loose regolith, which we desire for piling around and on the Hab, both for insulation to maintain habitat temperature after nightfall, and for radiation protection.
In other words, when it comes to thermal inertia, it’s a case of not too low and not too high.
The following map shows thermal inertia, with areas of intermediate thermal inertia between 26°N and 36°N highlighted:
One of the key goals of Blue Dragon is to make use of locally obtained water, in order to avoid transporting hydrogen from Earth.
The amount of water that could reasonably be obtained from the air would not provide enough hydrogen for ISPP. Therefore, we must look to ground-based sources. Fortunately there’s plenty of water on Mars. The following map shows, circled, the wettest areas between 26°N and 36°N:
The ground on Mars is above 20-30% water beyond ~60° north and south, which is attractive. However, at these latitudes the solar incidence is somewhat low. if we seek to remain close to 31°N, we may select a location around 35-45°N as a compromise. The wettest locations in this zone may contain as much as 10% H2O, which would be a useful quantity.
Areothermal energy may be available in some areas on Mars, most likely in regions that have been the most recently areologically active (i.e. the Upper Amazonian epoch). Although not a requirement for the first three missions, it is scientifically interesting and will be important to future settlements. If the IMRS is expanded into a larger-scale settlement, being close to areothermal energy will be a huge advantage.
A reliable source of areothermal energy on Mars will be of exceptional value, potentially superior to all other energy options currently under consideration. Areothermal energy could provide a continuous abundant supply of energy, without the environmental issues of fission or the need for energy storage subsystems as for solar or wind, and can be used directly for settlement heating, water supply, and electricity generation. If it is shown that areothermal energy is only available in a few places on Mars, these places may well be settled first, or may be more successful.
Areothermal energy combined with large ice deposits, such as we see in Arcadia ad Amazonis Planitias, could be indicative of liquid aquifers. Not only would this be a tremendously valuable resource for a settlement, but also a potential home for extant Martian life.
Regions on Mars that have been recently areologically active (Fogg, 1996) include:
- Cerberus Plains
- Hecates Tholus
- Medusae Fossae Formation
- Northwestern Tharsis
- Valles Marineris
The northern hemisphere of Mars is strongly preferred for a variety of reasons:
- More water, in the form of both ground ice and atmospheric water vapour.
- A higher minimum solar incidence.
- Less extreme climate.
- Lower elevation.
- Flatter, smoother terrain.
- Higher probability of areothermal energy sources and underground aquifers.
- More mineral ores, which are often formed by liquid water.
- More thorium, which may be important for LFTR’s (Liquid Fluoride Thorium Reactor).
Because solar energy is preferred (see Power Systems), the first base should be located close to the optimal latitude of 31°N in order to minimise the mass of the power system. However, by going a little further north more water can be accessed. Somewhere in Vastitas Borealis will be suitable, as this region is low, flat and reasonably smooth. The goal will be to find a location in this region that is not too dusty, and has loose regolith.
A higher-capacity energy storage subsystem would effectively eliminate the motivation to remain close to 31°N, which would therefore open up a wider range of options. However, there are a couple of good candidate locations near this latitude that should perhaps be investigated more closely:
Northern Amazonis Planitia, around 35°N 145°W
This may be the sweet spot in this region just northwest of Tharsis. There’s abundant water at relatively low latitudes, with good solar incidence, and it’s low and flat. This is one of the smoothest regions of Mars, and one of the most recently areologically active at only 100 million years old, making it likely to have areothermal energy. Arcadia Planitia is just to the north, which shows signs of near-surface ground water. From Wikipedia:
In a lot of the low areas of Arcadia, one finds grooves and sub-parallel ridges. These indicate movement of near surface materials and are similar to features on earth where near surface materials flow together very slowly as helped by the freezing and thawing of water located between ground layers. This supports the proposition of ground ice in the near surface of Mars in this area. This area represents an area of interest for scientists to investigate further.
Areothermal energy in combination with underground ice could be indicative of aquifers, which would be tremendously valuable resource both materially and scientifically, as they may potentially harbour extant life. This location is close to Olympus Mons, one of the most famous and impressive features in the Solar System, which is both scientifically and aesthetically interesting. The thermal inertia is a bit low, which may make this region overly dusty; however, less dusty sites may be discovered on closer inspection.
Utopia Planitia, just north of Hecates Tholus, around ~40-45°N 150°E
This area may in fact be slightly superior due to a moderate level of thermal inertia. It’s flat and smooth and has about 7-10% H2O, good solar incidence, and low elevation. The area is areologically very young and considered a candidate for areothermal energy. It’s also within striking distance of Phlegra Montes, where radar probing has indicated large volumes of water ice below the surface.