Architecture, ISRU, Mars

In Situ Air Production (ISAP)

The primary constituents of the Martian atmosphere are carbon dioxide (CO2), nitrogen (N2) and argon (Ar), whereas Earth’s are mainly N2, oxygen (O2) and Ar. Therefore, all the elements required to make breathable, Earth-like air are available in Martian air.

A Mars habitat may include inflatable extensions to significantly increase habitat volume beyond the size of the initial spacecraft. If the Hab is landed along with the MAV during a pre-deployment phase, it will be remotely activated from Earth, initiating the ISAP system, and causing the inflatable extensions to inflate. If the Hab is sent one launch window earlier than the crew, we will have about 20 months to inflate the Hab and test its other systems before the crew leave Earth. In order to inflate the extensions it will be preferable to make the necessary air using ISRU technology rather than bring air from Earth, which would require tanks of compressed O2 and N2.

The mass of the proposed ISAP system is likely to be less than the mass of full O2 and N2 tanks.  More importantly, having the capability to manufacture breathable air from local resources will be a useful advantage for the mission, providing increased safety and reducing limitations on the mission. Locally manufactured air can compensate for air losses due to leaks, airlock cycling, atmosphere scrubbing, refilling of O2 and N2 tanks in pressurised vehicles and marssuits, punctures if they occur, and other potential causes.

The DRA proposes separating N2 and potentially also Ar from the Martian atmosphere for use as a buffer gas. However, it is actually much cheaper and easier to use the gas that remains after CO2 and dust is removed from Martian air, as this is mostly N2 and Ar, both of which are perfectly acceptable buffer gases. The Martian atmosphere may also contain undesirable toxic gases such as ozone (O3), carbon monoxide (CO), and nitric oxide (NO), that exceed safe limits (as specified in JSC 20584: Spacecraft Maximum Allowable Concentrations for Airborne Contaminants). However, these can be relatively easily scrubbed out using ordinary COTS catalytic converters, and this process is far simpler and energetically cheaper than trying to separate out pure N2 from the air. (Note that NO is not actually toxic, but when combined with O2 it rapidly oxidises to form NO2, which is.)

Flowchart for In Situ Air Production system for Mars habitat
Flowchart for In Situ Air Production system for Mars habitat (click to enlarge)

Step 1: Mars atmosphere is drawn into the ISAP system through a dust filter.

Step 2: Water is removed from the gas mix via zeolite adsorption. The captured water is stored in the Hab’s water tank and used to replace recycling losses, and for O2 production.

Step 3: Water is separated into H2 and O2 via electrolysis. The O2 is stored for habitat atmosphere.

Step 4: Microchannel adsorption or cryogenic separation (CO2 freezing) is used to separate CO2 (about 96%) from the gas mix.

Step 5: The CO2 is reacted with H2 via the reverse water gas shift (RWGS) reaction:

CO2 + H2 → CO + H2O

The H2O produced is returned to the water tank. The CO may be stored for use in fuel cells, or it may simply be vented.

The gas mix that remains after CO2 is removed is mostly N2 and Ar, with trace amounts of various gases, which may include neon (Ne), krypton (Kr), xenon (Xe), O3, CO, NO, methane (CH4), hydrogen peroxide (H2O2), and sulphur dioxide (SO2).

Step 6: This gas mixture is first passed through an ozone scrubber, which reduces the O3 to O2.

Step 7: The resultant gas mixture is then passed through an ordinary automobile 3-way catalytic converter, which converts any CO and NO into CO2 and N2.

Step 8: The result is a safe buffer gas comprised mostly of N2 and Ar, with small amounts of O2 and CO2, and traces of Ne, Xe and Kr. This mixture can be combined with additional O2 to provide breathing gas for  the Hab. The CO2 level in this gas mixture is slightly higher than the proposed upper limit for the habitat atmosphere, but this excess will be removed by the ECLSS.

The DRA describes several methods for making O2 from CO2, including:

  • SOCE (Solid Oxide CO2 Electrolysis)
  • Sabatier reaction
  • RWGS reaction

SOCE requires considerable energy, whereas the other two options require H2. Fortunately, H2 is available because the Hab will contain H2O for the crew, which makes SOCE’s less appealing than the other two alternatives.

RWGS, which produces CO and H2O, is preferred over the Sabatier reaction, which produces CH4 and H2O, because in RWGS all the H2 is converted to H2O, which is a valuable resource in its own right, and from which H2 can be easily recovered via electrolysis. Using the Sabatier reaction would either consume H2, or the H2 would have to be recovered from the CH4. In theory CH4 could be used in a fuel cell to provide additional energy to the Hab. Combustion of the CH4 would produce H2O, which could be captured. However, it remains to be seen if fuel cells will be relevant for the Hab, and this process would add a layer of complexity and inefficiency to H2 recovery. Choosing RWGS eliminates the need for any method to recover H2 from methane. An effective method for separating H2O from the gas stream existing the RWGS chamber is to adsorb it with zeolite 3A, as in step 2.

The DRA specifies that H2 be brought from Earth in order to make water for the crew; however, in the Blue Dragon architecture H2O is obtained from the atmosphere, and potentially also from the ground. Research into extraction of H2O from the Martian atmosphere (Grover et al, 1998; Williams et al, 1995) has shown how 3.3kg of H2O per day (enough to replace losses through life support regenerative processes) could potentially be obtained from the Martian atmosphere using adsorption into zeolite 3A. This idea has been incorporated into the ISAP process above, indicating that H2O necessary for the RWGS reaction need not necessarily come from the Hab’s supplies. The amount of H2O obtainable from the atmosphere may be small, but this doesn’t matter because predeploying the Hab allows plenty of time to collect the necessary H2O and make the air, and the H2 is recycled anyway.

More research needs to be done into this system. We need to investigate efficient gas separation techniques, the rate at which air can be manufactured, the unit’s mass, volume and energy requirements, and how it integrates with the ECLSS.

Architecture, Mars

Atmosphere design for the surface of Mars

The Hab

The advantages of a normal Earthian atmosphere apply equally well to the Hab as they do to the ISS and other spacecraft. However, there are several compelling reasons for a reduced atmospheric pressure for the Hab:

  • Lower Hab mass.
  • Less air to be manufactured, which therefore reduces the mass and energy requirements of the ISAP system.
  • Potential for a zero prebreathe protocol for EHA/EVA.

The higher the atmospheric pressure of the Hab, the stronger and therefore heavier it will need to be. This is contrary to our requirement of reducing the mass of the Hab as much as possible because of the significant challenge of landing such a heavy object on Mars.

Atmospheres in early spacecraft had low total pressure, low oxygen pressure, or both. However, not all of these atmospheres would be suitable for an 1.5 year stay on Mars. Research conducted in recent years has more clearly defined the limits for artificial atmospheres suitable for extended exposure.

The minimum partial pressure of oxygen required to support human physiology is considered to be 16kPa. However, for long-duration space missions, a minimum partial pressure of oxygen of 18kPa is recommended  (Duffield, 2003). This is based on a previous study about planetary surface habitats (Campbell, 1991), which reviewed 33 different considerations related to atmospheric pressure and composition.

From a physiological perspective, an O2 pressure of 18kPa is perfectly safe. This is equivalent to about 1370m altitude (approximately the altitude of Kathmandu, Nepal), which does not even qualify as “high altitude” in mountain medicine (1500 – 3500m). Acclimatisation to reduced O2 pressure at altitude is characterised by an increase in pulse and breathing rate. Most people can ascend to 2400m (where O2 pressure is about 16kPa) without difficulty, however, altitude sickness may occur above this level. Astronauts can be conditioned for an O2 pressure of 18kPa by training in a hypobaric chamber, or at a moderate altitude (e.g. Black Mesa, US). In a microgravity environment there would already be increased strain on the cardiovascular system , and it would be preferable not to cause any further strain; however, the habitat is in a gravity environment on the surface of Mars, and although this is still a reduced gravity environment compared with Earth, the increased load on the heart will be mitigated.

The next design question is how much buffer gas to include. A pure oxygen atmosphere introduces an unacceptably high risk of fire, such as the one that occurred in the Apollo 1 Command Module. The upper limit of oxygen concentration with regard to fire safety has not clearly defined, but 30% is considered a reasonable upper limit (Campbell, 1991). This gives us a total atmospheric pressure of 60kPa, about 60% of Earth.

Buffer gas refers to the component of the atmosphere comprised of metabolically inert gases, which usually means nitrogen (N2), plus the noble gases helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe). The buffer gas portion of the atmosphere of Earth is almost entirely N2 (99%), with about 1% Ar and trace amounts of He, Ne and Kr. As described in the section on In Situ Air Production, because we’re making buffer gas in an economical way by simply using the Martian atmosphere with dust, CO2 and contaminants removed, our buffer gas on Mars will be about half-half N2 and Ar, possibly with trace amounts of Ne, Kr and Xe.

Nominal atmospheric concentrations of CO2 and H2O must also be determined. According to JSC 20584 (Spacecraft Maximum Allowable Concentrations for Airborne Contaminants), the maximum CO2 concentration is 0.7%. A CO2 concentration of 1% can cause drowsiness, with more serious symptoms occurring at higher concentrations. A typical concentration in normal spacecraft operations is 0.5%, which is a reasonable design goal. This gives us a CO2 partial pressure of about 0.3kPa.

With regard to water vapour, NASA specifies a RH (Relative Humidity) of 30-70%, i.e. an average of about 50%. Our target temperature is 295K (about 72°F or 22°C, which is optimal for human comfort and productivity), and the saturated water vapour pressure at this temperature and pressure is about 2.6kPa. Our average water vapour partial pressure will be 50% of this, or about 1.3kPa.

Any other gases present in the atmosphere should be present in trace amounts only.

Proposed design for Mars habitat atmosphere.

Gas Partial pressure (kPa)
Oxygen (O2) 18.0
Carbon dioxide (CO2) 0.3
Water vapour (H2O) 1.3
Buffer gas (N2/Ar) 40.4
Total 60.0

This atmosphere will produce differences in sound quality that the crew will be required to adapt to. The higher density of Ar compared with N2 will have the effect of lowering audio frequencies, including astronaut voices. Sound will also not be as loud or travel as far due to the reduced atmospheric pressure.

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ISRU, Mars

In Situ Food Production (ISFP)

Growing food on Mars is an exercise in efficiency. The facilities will not (at least initially) be available to grow every kind of fruit, vegetable, grain, nut and herb that we are used to. We may only be able to grow small amounts of a small number of crops. For a while there may be restrictions on the number of available ingredients and therefore the meal choices. The challenge is to find which crops deliver the most nutrition for the amount of volume, mass and energy required to produce them.

Top of this list would surely be spinach. Tomatoes, mushrooms, cabbages, garlic, kale, carrots would perhaps also make the list. What is the best way to grow each of these?
There are 3 primary mechanisms proposed for producing food on Mars:

  • In soil
  • Hydroponics
  • Aeroponics

Experiments are already underway to grow food in Martian soil simulant. Because all the chemical elements necessary for life are available in Martian soil, it should be possible to grow plants in it; however, it will be necessary to analyse the crops thus produced, in order to determine if they have healthful levels of vitamins and minerals. They will not necessarily have the exact same nutrient profile as their counterparts on Earth, because of the availability of those elements in the soil.

Some chemical processing of the soil may be necessary to prepare it for plant growth; for example, it may be too acidic or salty. Therefore the addition of a specially prepared fertiliser may be necessary. It may be beneficial to introduce worms to the soil and feed them with food scraps, so they can process the dirt grains and organic material together to make fertile soil. Of course, for this to happen we would initially need food scraps, which would have to come from somewhere, so this would not be an option for the first crops.

In any case, the first crops are more likely to be grown using hydroponics or aeroponics. These are similar setups in that the plants are grown in a dirt-free environment, fed with nutrient-rich water. In the case of hydroponics, the water flows through pipes in which sit the roots of the plants, so they can access the nutrients in the water. In the case of aeroponics, the plants are suspended, with their roots exposed to the air; nutrient-rich water is provided to the roots as a mist.

The primary advantage of aeroponics over hydroponics is that the water requirement is minimal, which will be important for a Mars base where water may be scarce in the early years. The disadvantage, however, is that the mist greatly increases the relative humidity of the greenhouse atmosphere. Relative humidity of controlled environments like spacecraft atmospheres should not exceed 70% (according to NASA guidelines), as this can interfere with electronics or cause build-up of mould. This could be addressed by separating the greenhouse environment from the main habitat environment by a gate.

A double-gate, whereby a person transitioning from the habitat to the greenhouse would open one gate, step through, close that gate behind them, open a second gate, step through and close that one behind them, may be an effective method of containing humidity in the greenhouse. However, this level of control is probably unnecessary, and a single gate will work fine if people don’t leave it open. The small amount of water vapour that would travel across from the greenhouse to the habitat would be easily soaked up by the habitat’s ECLSS.

One way to mitigate the migration of water vapour from the greenhouse into the habitat would be to place intake fans near the gate, which draw air form the region around the gate into the THC (Thermal and Humidity Control) subsystem of the habitat’s ECLSS, which will remove any surplus water vapour from the atmosphere.
Aeroponics may therefore be the preferred choice. The questions remain:

  • What crops would be good to commence experimentation with? (e.g. spinach and tomatoes)
  • What nutrients are added to the water provided to the system, if any?
  • What mass and volume of equipment is required to produce what mass, volume and nutrient value of food?

Another downside of aeroponics is that in some cases the crops will not grow as large as they would in a hydroponic system or if they were grown in soil. This is usually due to lack of available nutrients in the provided water. When using water enriched with sufficient nutrients, and with the proper equipment, aeroponic crops can grow to full size.

Therefore, if we are to experiment with an aeroponic system on Mars, it will be important to take with us a supply of nutrients optimised for aeroponic crop production.

Aquaponics combines hydroponics with fish-farming, and is another approach to food production that has been suggested for Mars. The fish can be fed food scraps, possibly supplemented with special food; the water in which the fish swim becomes nutrient-rich due to the metabolic outputs of the fish, and is then provided to the plants via the hydroponic system.

The main problem with aquaponics is the amount of water required, which is naturally much higher than for the other proposed methods. It is far more likely that Martians will be vegetarians, which is perfectly safe and healthy; many millions of people on Earth live healthfully on plants only. Producing food from plants is considerably more efficient in terms of energy and water, which will be crucial on Mars. In fact, it’s also crucial on Earth, but humanity is still learning this. Some scientists predict that by 2050 everyone (or perhaps the majority of people) on Earth will be vegetarian due to expansion of the population. In any case, if aquaponics is implemented on Mars it will probably not be for a few years, when water and energy production are much higher.

 

Mars, Video

Me presenting Blue Dragon at the Australian Space Science Conference, 1 October 2013

“Blue Dragon” is a humans-to-Mars mission architecture based on the NASA Design Reference Architecture, with various improvements to improve safety and reduce cost. It leverages COTS hardware likely to be available within the next decade, is designed as the seed of a settlement rather than a “flags and footprints” program, and is specifically intended as an international mission.

ISRU, Mars, Space Program

Green Dragon

Introduction

Green Dragon is a mission concept to send integrated ISRU packages to function as resource factories to support human Mars missions. It builds on the accomplishments of NASA’s Ice Dragon mission, while functioning as an important precursor to the Humans-to-Mars mission architecture, Blue Dragon. The intention is to test and iteratively improve both ISRU and EDL systems.

The mission is named “Green Dragon” as, like Ice Dragon, it is based on the Red Dragon EDL system. It’s “green” because it demonstrates technologies and provides resources crucial to life support, and to match the pattern of red, green, blue commonly associated with Mars.

The initial Green Dragon program will land 1-3 Dragon capsules on Mars containing integrated ISRU hardware capable of manufacturing several products that will be of great value in exploration and settlement, namely LOX/LCH4 bipropellant, water and breathable air, from local Martian resources.

It will also serve as an opportunity to test and refine the Red Dragon EDL system in preparation for using it to land crew and cargo on Mars in the Blue Dragon mission. Our goal for landing humans on Mars is to maintain g-forces below an acceptable threshold for human health, and to land with a reasonably high degree of accuracy. Green Dragon will ideally serve to bringing the ISRU and EDL systems needed by Blue Dragon up to TRL-9.

Apollos 11-17 succeeded largely because the preceding missions in the program tested and proved each element of the target mission, i.e. the human landing. This approach of a program of precursor missions is not normally described in conjunction with H2M architectures, presumably because the large cost of sending stuff to Mars has typically resulted in very conservative programs. However, if the Red Dragon technology can be shown to reliably deliver a 1-2 tonne package to Mars surface for under $200M per launch-plus-capsule, a program of precursor missions that build the necessary confidence in a human landing will be affordable. Green Dragon would represent a key subset of those missions.

Entry, Descent and Landing

The Ice Dragon mission will inevitably stimulate ideas for improving the Red Dragon EDL system, and it will be important for the success of the Blue Dragon mission that we take the opportunity to implement these improvements and refine Red Dragon further. The more capsules we’ve landed on Mars before we attempt the landing of humans, the greater confidence we will have that the landing will succeed.

One of the EDL factors necessary to improve is a reduction in the deceleration forces experienced by the capsules. The first mission to land a Dragon capsule on Mars may involve deceleration forces that would be excessive for a human crew. While this is acceptable for a cargo capsule, the Green Dragon series of missions will aim to reduce deceleration forces to below about 10 g’s, and ideally lower, in preparation for safe landing of humans.

Another factor related to EDL that Green Dragon would seek to improve is the accuracy of landing. Green Dragon missions will make use of image recognition software, as well as signals from spacecraft, to land on preselected coordinates as accurately as possible. Having proven that Red Dragon capsules can be landed on a dime will make it possible to design a layout of the Blue Dragon base with much greater precision, thus improving safety and probability of success. For example, the DragonRider that delivers the crew to Mars surface can be landed exactly the desired distance from the Hab, which is to say, not so close that debris thrown up by the landing could damage the Hab’s inflatable modules or instruments (or any other part), yet not so far away that it would be unreasonably difficult or time-consuming for the crew to reach the Hab after landing.

The more Dragon capsules we land on Mars before sending humans, the more confidence we will have in the technology before using a DragonRider to land a crew on the surface of Mars. We need to know exactly how the capsule behaves during EDL to Mars, how it interacts with the Martian atmosphere and surface (especially dust), how to land one with precision, and where the strengths and weaknesses are in this approach. This knowledge can only be obtained definitively with practice.

By the time we land a crew on Mars in a DragonRider, we will ideally have landed a minimum of four uncrewed Red Dragons:

  • 1 for Ice Dragon
  • 1-3 for Green Dragon
  • 2+ pre-deployed cargo capsules for Blue Dragon

In Situ Resource Utilisation

The Green Dragon mission, or series of missions, is designed to test, demonstrate and develop the ISRU technologies necessary for successful execution of the Blue Dragon architecture. Previous architectures have been reasonably conservative in terms of inclusion of ISRU due to the low TRL of the concepts. Blue Dragon pushes the boundaries of what has previously been considered in terms of ISRU to support a humans to Mars mission, and, being mission critical elements, it’s essential to prove that they will work.

Green Dragon will allow us the opportunity to test a variety of ISRU experiments on Mars, including the manufacture of LOX/LCH4 bipropellant, water and breathable air from local Martian resources.

In particular, the demonstrated ability to obtain abundant water on Mars is considered crucial to exploration and settlement. This capability will reduce the cost and increase the likelihood of success of all future H2M missions by a significant margin, as neither water nor hydrogen will need to be brought from Earth.

A design goal of Blue Dragon is to not take any surplus hydrogen, water, oxygen or nitrogen to the surface of Mars. As all these things are available locally and can be obtained directly from Mars, and since utilising local resources significantly reduces mission cost, there’s no sense carrying them all the way from Earth; that is, if the necessary hardware can be developed to successfully and reliably obtain them, which it certainly can.

Proposals for ISRU tech for Mars have traditionally been very simple and conservative. Considering the success of MER’s, Phoenix and MSL – all very complex robots – this cautiousness is probably unfounded. Although the ISRU experiments encapsulated by Green Dragon are more complex than basic ISPP, they are also much less complex than any of these missions that have already been successful. Furthermore, the whole Green Dragon program should, in theory, cost less than MSL.

Green Dragon contains a set of three integrated ISRU experiments:

  1. ISPP – In Situ Propellant Production: Making LOX/LCH4 bipropellant.
  2. ISWP – In Situ Water Production: Extracting water from the ground.
  3. ISAP – In Situ Air Production: Producing breathable air.

This will include the following subsystems:

  • Storage tanks for water, LOX, LCH4 and buffer gas
  • Small, self-contained nuclear fission reactor, or solar panels
  • Electrolysis unit
  • Catalytic converter
  • Ozone scrubber
  • Heating unit
  • Refrigeration unit
  • Compression unit

The following colour codes are used for tanks:

Blue tank Red tank Yellow tank Green tank
Water LCH4 LOX Buffer gas
(mainly N2/Ar)

The following schematic illustrates the flow of materials through the system. The masses are calculated based on Mars Direct ERV propellant requirements, but can be scaled to suit the capacity of the Green Dragon (small or large version).

Integrated IISRU schematic
Integrated IISRU schematic (click to embiggen)

 

ISPP

The concept of ISPP (In Situ Propellant Production), whereby LOX/LCH4 (Liquid Oxygen/Liquid Methane) bipropellant is produced by reacting carbon dioxide obtained from the Martian atmosphere with hydrogen brought from Earth, was most famously described by Robert Zubrin and David Baker as part of the Mars Direct mission architecture in 1990 [1]. They also constructed a small plant to prove that the technique was viable.

Our goal is to use hydrogen manufactured via electrolysis of locally collected water, rather than bringing it from Earth as in the original ISPP concept.

The process is as follows:

Step 1: Carbon dioxide is obtained from the Martian atmosphere by filtering out dust, removing water via zeolite adsorption, and freezing the CO2 out of the remaining gas mix, enabling it to be separated from the remaining gases. The small amount of water captured by zeolite adsorption may be cycled into step 3.

Step 2: The AWESOM rover traverses back and forth across a patch of ground, microwaving the regolith below and collecting released water. When the rover’s tank is full, it returns to the MAV to deliver its payload of water, then returns to work. This step requires some form of LPS (Local Positioning System) so the rover knows which ground it has covered.

Step 3: Water is separated into hydrogen and oxygen gas via electrolysis:

2 H2O(l)  →  2 H2(g) + O2(g)

The oxygen is stored cryogenically as LOX.

Step 4: Methane is produced by reacting carbon dioxide (CO2) obtained from the Martian atmosphere with hydrogen (H2) produced in step 3, via the Sabatier reaction:

CO2(g) + 4 H2(g)  →  CH4(g) + 2 H2O(v)

The Sabatier reaction occurs at high temperatures, optimally around 600K. The methane is liquified to LCH4 and stored in the red tank. The water produced by the Sabatier reaction is stored in the blue tank, where it may be used to make more hydrogen.

Combining the reactions in step 3 and 4, the overall result is:

CO2(g) + 2 H2O(g)  →  CH4(g) + 2 O2(g)

66 tonnes of carbon dioxide combined with 54 tonnes of water (a total of 120 tonnes) will produce 24 tonnes of methane and 96 tonnes of oxygen. This gives us a surplus of 12 tonnes of oxygen that may be used for air. As the Martian atmosphere is about 95% CO2, we need to process about 70 tonnes of it to obtain 66 tonnes of CO2, which therefore results in about 4 tonnes of buffer gas.

ISWP

ISWP (In Situ Water Production) via extraction of water from the Martian ground is well understood to be a crucial enabling technology for human settlement of Mars, and would similarly be a boon for preliminary exploration. The robotic technology required to achieve this is likely to be simpler than that we have already deployed to Mars in the form of Spirit, Opportunity and Curiosity, and is therefore well within our capability.

The advantage of not having to bring hydrogen from Earth is of such value that developing a system for obtaining water on Mars is one of the most important outcomes of Green Dragon. Not only will we save the mass of the hydrogen needed for ISPP, but also the water required by the crew during the 1.5-year surface mission. This capability will greatly reduce the launched mass, landed mass, cost and complexity of any H2M mission.

Producing LOX/LCH4 propellant using hydrogen obtained from Martian atmospheric water vapour, instead of hydrogen brought from Earth, has only been discussed theoretically and not demonstrated. One goal of Green Dragon is to demonstrate that.

Water collected by the ISWP experiment will be collected in a tank. This will be connected to the electrolysis unit so that any amount can be converted to H2 and O2 as required. H2 will not be stored, but will be fed directly into the ISPP unit. In this way we avoid the need to store hydrogen gas, and thereby losing any through leakage.

Note also that water is also produced by the Sabatier reaction used in the ISPP experiment. This water will simply be captured and collected in the same tank, thus recycling the hydrogen.

ISAP

ISAP (In Situ Air Production) will be an important aspect of Blue Dragon. The Martian atmosphere contains plenty of nitrogen and oxygen, which is readily accessible, and considering the benefits of minimising launched mass there is no justification for bringing air from Earth. Of course, the Hab, MAV and rover may be launched full of air, but we need more than that.

Because we intend to utilise inflatable modules to expand the Hab volume, our primary requirement for air is to inflate these modules. Also, if the rover or MAV becomes depressurised for any reason, they will need to be re-pressurised.

Air pressure within the Hab may be lost due to:

  • Airlock cycling (a daily occurrence during the surface mission).
  • Leakage.
  • Recycling/scrubbing.
  • Punctures or tears.

Oxygen is easily produced via electrolysis of water, as described above. Every kilogram of hydrogen manufactured from water for ISPP will produce eight kilograms of oxygen that may be used for air.

Earthian air is approximately 78% nitrogen, 21% oxygen, 1% argon, plus traces of other gases. Oxygen is needed by animals; nitrogen is needed by plants and certain microbes, and acts as a buffer gas. Argon is non-reactive and safe to breath as long as there’s sufficient O2 in the mix. Ideally in our habitats we will want a full 1 atmosphere of pressure, as on the ISS, because then we can use COTS equipment which is much cheaper. However, the buffer gas does not necessarily need to be comprised of the same ratio of nitrogen and argon as on Earth.

The ISPP process separates carbon dioxide from the remainder of the Martian air using fractional distillation, which means cooling the gas to below the boiling point of carbon dioxide, thus causing it to become liquid, in which state it can be easily separated from the remaining gases.

There are at least 12 gases present in the Martian atmosphere. As part of the ISPP process, dust and water will be removed from the atmosphere first, then carbon dioxide is separated from the remainder. This produces a residual gas mix with the following approximate composition, which is about 98% safe to breathe.

Gas Fraction Notes
N2 60% Preferred buffer gas.
Ar 35% Safe.
O2 3% Safe.
CO 1.8% Toxic.
NO 2200ppm When combined with oxygen this will oxidise to NO2, which is toxic.
Ne 55ppm Safe.
Kr 7ppm Safe.
Xe 2ppm Safe.
O3 0.7ppm Toxic.
CH4 0.2ppm Safe.

Creating an exact match for Earthian air by separating out the nitrogen and argon would be energetically costly due to the low boiling point of these gases (77K and 87K respectively). However, the above gas mix can be made breathable by the removal of toxic elements, highlighted above in green. Fortunately, this is a PSP (Previously Solved Problem).

Scrubbing CO and NO

A standard automobile catalytic converter (~$200 – $500) can be used to scrub CO and NO from the gas mixture.

Automobile catalytic converter
Automobile catalytic converter (click to embiggen)

The reduction catalyst (platinum and rhodium) in the catalytic converter converts NO into N2 and O2:

2NO → N2 + O2

The oxidation catalyst (platinum and palladium) in the catalytic converter converts CO into CO2:

2CO + O2 → 2CO2

It will also oxidise the tiny amount of methane:

CH4 + 2O2 → CO2 + 2H2O

One issue to address is that COTS catalytic converters operate at high temperatures, whereas the ambient temperature on Mars is comparatively very low. The nuclear power plant can provide ample electricity to heat the converter as required. We can simply position the catalytic converter somewhere near the Sabatier reactor, which operates at around 600K.

Scrubbing ozone

Ozone is relatively easily eliminated using a COTS ozone scrubber (or “ozone destruct unit”) (~$1200). Ozone scrubbers work best with dry gas, therefore, since the catalytic converter will produce a small amount of water in the process of oxidising the methane, it’s preferable to pass the gas through the ozone scrubber before the catalytic converter.

Ozone destruct unit
Ozone destruct unit (click to embiggen)

Breathing gas

A breathing gas comprised of 20% oxygen plus 80% of the resultant buffer gas mixture (which has a little O2) will contain about 48.3% nitrogen, 28.6% argon, 21.7% oxygen, 1.4% carbon dioxide, and traces of neon, krypton, xenon and water vapour.

This is a very good breathing gas mixture except that it’s a little high in CO2, and would cause drowsiness. This can be easily removed by the air recycler in the ECLSS (Environment Control and Life Support System). In other words, once the air has been manufactured in this way, it is first treated in the same way as stale air coming from the Hab and pumped through the air recycler to scrub out the excess CO2. In fact, it may even be better to incorporate the ozone scrubber and catalytic converter in the ECLSS rather than the ISAP unit, and simply treat all buffer gas as stale/dirty air.

At one atmosphere of pressure, this breathing gas is sufficiently similar to Earth-normal that no difference would be noticeable except perhaps a reduction in audio frequencies (including astronaut voices) due to the high percentage of argon.

However, it is not a firm requirement that the habitat air pressure be one atmosphere, although that would be ideal in some respects (the internal atmospheric pressure of ISS is one atmosphere, which simplifies design of other components). Green Dragon produces about three times as much surplus O2 as buffer gas, therefore we may opt for a lower concentration of buffer gas (say, 20-50% instead of the usual 80%), which would probably be acceptable.

With a source of oxygen plus a suitable buffer gas mix available, we can plug these into the Hab to maintain an optimised internal atmosphere. Whenever the partial pressure of O2 fraction drops below a certain threshold, additional O2 is pumped in; similarly, if the buffer gas partial pressure drops too low, more buffer gas will be automatically pumped in. This is how the ECLSS functions on the ISS.

Larger Green Dragons

The Mars One mission plans to land both cargo and crew on Mars using an upgraded Dragon capsule with a 5 metre diameter. At the time of writing this capsule has not yet been developed, although SpaceX has indicated that it will be developed within the next few years in order to be ready for the first Mars One cargo mission in January 2016. This larger Dragon will be capable of delivering a payload upwards of 2.5 tonnes to Mars surface.

For at least the first Green Dragon mission, the smaller capsule with the 3.66m diameter and the approximately 1-2 tonne payload will be adequate. However, when these larger capsules become available, larger Green Dragons based on these could be sent as resource factories to support Blue Dragon, Mars One, or other missions or bases. The primary advantage of the larger capsules will be the capacity to store greater volumes of their products.

The suggested approach therefore is to use the smaller capsules to develop and refine the design of a self-contained resource factory, then use the larger capsules to support missions.

Mars

Introduction

The 21st century will forever be remembered as the one during which humanity became multiplanetary.

We stand at the brink of a new era in human evolution. Some would say we’re standing at a precipice. We face unprecedented global challenges while simultaneously merging into a true global culture and commencing expansion into space. Perhaps that’s the way the universe works; maybe huge challenges often or always coincide with huge opportunities. Maybe that’s the nature of planetary transformation; maybe it’s the way it has to happen. Regardless, space settlement will assuredly have overwhelmingly positive effects for our species, and will provide us with all the necessary resources to overcome any of our current global challenges, whether environmental, economic or social.

Elon Musk, CEO of SpaceX, said that human expansion into space and becoming a multiplanetary species is an evolutionary leap so great and significant that it can be compared with life crawling out of the oceans. The stated purpose of SpaceX is to be a key player in that event, and put thousands, if not millions, of humans on Mars.

But it’s not just SpaceX taking steps towards Mars. We’re seeing a general surge of interest in Mars at this time, spurred on by the recent announcements of two serious human missions. The first, Mars One, proposes to send as many as 40 astronauts on a one-way mission to the surface of Mars, where they’ll spend the rest of their lives as the subjects of a reality TV show. The second mission, Inspiration Mars, is a Mars flyby that will carry two people, most likely a married couple, to within just 100 kilometres of Mars. After more than 60 years of space agencies planning to send humans to Mars but not actually doing it, for the first time in history, entrepreneurs are taking matters into their own hands and making things happen.

But why Mars? Why not the Moon, or Venus, or Mercury? Why not just build cities in Earth orbit? Why all this hoop-la about Mars?

Mars has a feature set that makes it a stand-out champion in terms of potential settlement targets. It has an abundance of all the resources necessary to support life and technological civilisation. There’s plenty of water, carbon and metals, and energy is available from solar, wind, areothermal and nuclear sources. The length of the solar day on Mars is just 40 minutes longer than Earth’s, suggesting that humans and other Earthian species could adapt to the Martian environment with comparative ease. Mars’ axial tilt is also very nearly the same as Earth’s, giving it a familiar seasonal cycle. Another advantage, often overlooked, is that Mars is the only planet in the Solar System other than Earth with a transparent atmosphere. This gives you the advantages of an atmosphere – an easily accessible resource, effective heat distribution, aerobreaking/aerocapture – plus you can see the surface of the planet from space, and vice versa. Mars is colder than Earth, but not excessively so (it’s comparable with Antarctica), and it’s right next door. Almost everyone in the space community agrees: Mars is the target. It is the new “New World”. Even most “loonies” (lunaphiles, or Moon-lovers) agree that Mars is the next logical step beyond the Moon.

Mars will be the first planet that humans live on other than their home world, Earth.

Ideas and plans for sending humans to Mars have been proposed for many years now; at least since Das Marsprojekt was published by the great rocket engineer Wernher von Braun in 1948. As our knowledge of Mars has grown, so has our ability to believe in a future where humans live there. The more we learn about Mars and the better our technology becomes, the closer Mars becomes. And we are getting close. Those entrepreneurs who openly state their intentions to put humans on Mars are being taken seriously because most people can now see that the necessary technology, people and other resources are all available to make this dream true. It’s possible, and is happening now.

Robots vs. Humans

Many people believe that it’s preferable to send robots to Mars instead of humans because it’s cheaper and doesn’t jeopardise human lives. However, if settlement is our aim – and it should be – we must send people. In fact, even if exploration and science are our only goals, we can still achieve much more with humans.

In recent years we’ve witnessed a number of tremendous successes with robotic exploration of Mars. This effort has moved us significantly forward in our scientific understanding of Mars, how sensors and actuators function on Mars, and how to land stuff on Mars. The Mars Exploration Rovers Spirit and Opportunity have been a fascinating triumph: with an initial planned mission duration of just 90 sols (a “sol” is a Martian day, about 24 hours and 40 minutes), Spirit lasted about seven years and Opportunity is still going strong and making discoveries after 10. The landing of the Curiosity rover in 2012 was also a spectacular achievement in terms of engineering, being the largest mass (900kg) ever soft-landed on Mars.

Although much can and has been achieved with robots, humans on Mars will achieve much more. Although robots may not require air, water and food, humans offer greater cognition, dexterity, flexibility, adaptability, creativity, independence and efficiency; at least for now. The robots we’ve sent to Mars are in fact semi-autonomous, remote-controlled machines, directed by people on Earth. Astronauts on the surface of Mars will be guided by experts on Earth, but they’ll also have the freedom to indulge their own curiosity, pursue individual interests, and organise their own time and activities to a large degree.

Whether humans or robots go to Mars, the goal is for humans to gain knowledge and experience of Mars. Robots are simply a tool to achieve this, and are therefore effectively the “middle-man”. But the middle-man can be removed in order to get a better result. With humans on Mars, the experience of Mars can be obtained more directly and much more efficiently.

Robotic exploration proceeds extremely slowly and cautiously, partly because of the time delay in communications, but partly because these machines cost millions or billions of dollars to develop and send to Mars, and are therefore designed to move very slowly to ensure their survival. Every action must be considered and approved by a team on Earth before being sent to the robot. Every instruction takes between four and 20 minutes to reach Mars, and every photo and piece of data collected takes at least the same amount of time to be sent back to Earth. These machines have limited cognitive and physical abilities; if one becomes stuck in soft soil, such as what happened to Spirit, sometimes nothing can be done to get them out.

Humans will also move cautiously on Mars, but they can still move a lot faster while being careful. They can do many more things, both cognitively and physically, they don’t have to wait for instructions from Earth for every little decision, they can react in real time to unexpected events or discoveries, and if they get stuck in soft soil (for example) they can figure out a solution themselves or one of their crewmates can help them. A group of co-operating humans is functionally equivalent to a group of networked bipedal dexterous robots with strong AI. Perhaps in 20 to 40 years we can send machines to be that; or, we can just send people now.

Humans on Mars will not only deliver new information about Mars, but also the experience of Mars. They’ll be able to communicate with people on Earth in a way that robots simply cannot; they’ll be able to share emotions and sensory experiences that robots can’t have. This empathy will engage humanity with the Martian adventure and bring Mars within the sphere of our collective experience. The gates of human imagination and ingenuity will open, stimulating a flood of new ideas, missions, projects, experiments, businesses and plans, leading us directly into our dream of becoming multiplanetary.

Robots will always be part of our life on Mars. But we must send people, to more rapidly increase our knowledge of Mars, to bring Mars within the human sphere, and to commence a process of settlement.

Mars

Energy on Mars, Part 2

Solar

In the short term, solar energy is the simplest way to obtain energy on Mars, which is why we use solar panels on rovers such as Pathfinder, Spirit and Opportunity.

An MER (Mars Exploration Rover) showing solar panels
An MER (Mars Exploration Rover) showing solar panels

Because Mars is farther from the Sun it receives less incident solar energy per square metre. It’s also smaller than Earth, with about half the radius, which means it also receives less total solar energy.

Mars has a fairly elliptical orbit, which means the distance between Mars and the Sun varies considerably, between about 207 and 249Gm (gigametres, or millions of kilometres). Therefore the intensity of solar energy reaching Mars varies as much as 20% during a Martian year. Earth’s orbit is much more circular, and we don’t see as much variation in solar intensity. The distance between Earth and the Sun varies between about 147 and 152Gm.

We can calculate a ballpark comparison between the amount of solar energy reaching Mars and Earth using average distances:

Average distance between Sun and Earth = 150Gm

Average distance between Sun and Mars = 228Gm

The intensity of solar energy decreases with the square of the distance, because it’s spread out over area. Therefore:

Solar energy at Earth: Ee = k/de2

Solar energy at Earth: Em = k/dm2

where k is some constant of proportionality.

To compare: Em/Ee = de2/dm2 = 1502/2282 = 0.43 = 43%

This calculation suggests that the amount of solar energy per square metre on Mars is only about 43% of that on Earth. In reality, there’s very little cloud cover on Mars and the atmosphere is much thinner than Earth’s, which tends to boost that figure. On the other hand, there’s also a lot of suspended dust in the Martian atmosphere, which tends to reduce it. Overall, the intensity of incident solar energy is about half Earth’s.

This lower level of solar energy on Mars is not as serious a problem as it might first seem. Solar energy is currently experiencing a revolution on Earth – the technology is rapidly advancing, and the price is also rapidly decreasing. The solar energy technology currently being developed now will be available by the time we’re sending humans to Mars. We’ll be significantly better at collecting solar energy in the time frame of human settlement of Mars.

The primary downside of solar energy on a planetary surface is that it’s intermittent (that is, unless the planet is tidally locked to a star). Solar energy can only be collected from a point on the surface of the planet when the Sun is visible from that point; in other words, during the day time. However, methods for storing solar energy are also advancing rapidly.

Strip of solar panels at the Mars One base
Strip of solar panels at the Mars One base

Wind

It’s well-known that Mars is windy. In fact, it’s this windiness that kept the Mars Exploration Rovers, Spirit and Opportunity, rolling for as long as they did, because the wind kept blowing dust off the solar panels. Hopefully the same thing will happen to solar panels at a Mars base, thereby reducing the time and energy required for maintenance.

Wind energy has also experienced a revolution on Earth in recent years, with great improvements in turbine technology and efficiency, and considerable reductions in price, to the point where wind has achieved grid parity or better in many regions. Wind is now one of the most important energy sources in north-west Europe and Scandinavia.

Even though Mars is windy, leveraging wind energy on Mars as a major power source may be difficult. This is because the air pressure is very low, less than 1% of Earth’s, which means that even if the wind is moving fast the amount of force it can generate is very small. Therefore it would not be able to force high turbine speeds or generate much electricity. Nonetheless, Mars’ low gravity could help out here, enabling construction of very tall wind turbines with long blades, which will be able to effectively harness Martian wind.

Another factor is that the air on Mars is full of very fine, suspended dust, which could get into turbine bearings and cause them to wear down. This problem is likely to be solvable with good engineering design, but that may not happen until we have a permanent human presence on Mars.

A large desert wind farm, similar to what we could build on Mars.
A large desert wind farm, similar to what we could build on Mars.

Areothermal

It has not yet been established conclusively whether or not Mars contains hyperthermal zones (“hot spots”) in the shallow crust that could be utilised for energy. On Earth we refer to this as geothermal energy, however, the word “geothermal” becomes “areothermal” on Mars because we replace the prefix “geo”, which refers to Earth, with the prefix “areo”, which refers to Mars. (Other examples: geology/areology, geography/areography, geosynchronous/areosynchronous, etc.)

On Earth, geothermal energy holds great promise as being the only form of sustainable energy considered capable of providing baseline power. Solar and wind energy are intermittent, and therefore require an energy storage solution such as rechargeable batteries. However, these are generally expensive, inefficient, and not very environmentally friendly.

A reliable source of areothermal energy on Mars will be of exceptional value, possibly superior to all other energy options currently under consideration. Areothermal energy provides a continuous abundant supply of energy, like fission, but without the risk and waste issues. It does not require storage solutions like solar or wind, does not to be launched into space like SSP (Space Solar Power), and can also be used directly for settlement heating or as a source of hot water. If it’s eventually shown that areothermal energy is only available in a few places, these places may well be settled first. Settlements close to both an areothermal energy source and significant water and/or mineral resources will be at a significant advantage.

Basic geothermal power plant
Basic geothermal power plant

One of the challenges associated with geothermal energy is efficiently distributing electricity, as geothermal power plants are often geographically distant from users, and distributing electricity through copper wires introduces losses proportional to distance (compare with traditional coal-fired power stations, which can be located close to, or in, cities). However, as with solar and wind, significant advancements have been made in recent years in geothermal technology, and it’s now possible to access geothermal energy in more places. This increases the amount of geothermal energy is available for use, while also reducing distances between sources and consumers.

The prevailing view is that Mars has cooled to the point where it’s effectively areologically inactive. However, research by the planetary engineering expert Martin Fogg (see: The Utility of Geothermal Energy on Mars, 1996) shows that regions of Mars with very low crater counts, which have been recently resurfaced by magmatism, may be indicative of regions of above-average heat flow on Mars and may therefore potentially offer sources of areothermal energy. According to his research, regions with the highest probability of offering areothermal energy are almost completely contained in one large area of Mars:

In fact they are almost exclusively located in the planet’s northwest quadrant, from longitude 220° in Elysium eastward to longitude 20° in Acidalia Plantia and north of 15°S and south of 50°N. Such is the clustering of such outcrops in adjacent geographic areas that one can surmise the existence of a distinct province of recent anomalous heat flow on Mars, including Elysium, Amazonis Planitia, Arcadia Planitia and Tharsis.

The challenge for Mars, of course, is that accessing geothermal energy requires deep drilling, a capability we will probably not have on Mars until we have permanent settlements and some sort of industrial base.

Such are the advantages of areothermal energy, if it is shown to be practical for Mars, and if this area is particularly rich in this resource, it may be settled earlier than other regions of Mars. As Fogg writes:

Some of the first permanent Martian communities could spring up around such geothermal oases. By the latter half of the next century, the spa towns of Mars might even be known for offering the best of high life on the high frontier.

Fission

It seems very likely that at least some early-stage H2M missions will make use of nuclear fission energy. Almost all Mars mission architectures specify the need for a small nuclear reactor to power the ISSP (In Situ Propellant Production) equipment in an ERV (Earth Return Vehicle) or MAV (Mars Ascent Vehicle), and to provide power and heat to the hab. Modern nuclear reactors are able to produce energy for decades without maintenance, and can provide an abundant supply of energy. Unlike solar, nuclear energy is not subject to diurnal variations and is not affected by dust or weather.

In the past, I have been very opposed to the use of nuclear energy on Mars as well as Earth. My concern was that a Chernobyl-like steam explosion combined with a planet-wide dust storm or even normal Martian winds, would distribute radioactive dust across the whole planet. As you can imagine, this would be disastrous for present and future settlements over almost the entire planet and would significantly compromise scientific studies of Mars, in particular the search for extant life, and could also seriously hamper settlement efforts. I felt that if we allowed even just one nuclear reactor on Mars, it would set a precedent that would lead to hundreds or thousands. Without sufficient qualified people or an industrial infrastructure, it would simply be a matter of time before an accident occurred. In addition, we would be creating a nuclear waste problem. Nuclear waste is hard to manage and dispose of on Earth. On Mars, waste management would be even more difficult, and we may risk ruining the Martian environment before human settlement even gets into full swing.

However, I’ve since learned that this opposition was born of ignorance, that not all nuclear energy is the same, and that appropriate use of nuclear energy is an enabling factor that makes H2M far more possible. The described problems may be characteristic of Generation I and II nuclear reactors (almost all reactors currently in use are Gen II), however, in terms of development we are now up to Generation IV, which encompasses a variety of reactor types that are considerably safer, cheaper and better.  The one particular type that I believe holds the most promise for both Earth and Mars is the LFTR (Liquid Fluoride Thorium Reactor), which is fuelled with thorium.

LFTR’s offer significant advantages over current uranium reactors:

  • Thorium is a much more common element than uranium, and is abundant on Earth, the Moon and Mars. It’s therefore cheaper.
  • LFTR’s can also be made smaller, which is useful for space applications as we want to keep the mass of hardware as low as possible.
  • LFTR’s can’t melt down. In a Gen II reactor water is used as a coolant, so if the reactor is damaged and water cannot be supplied, they can overheat catastrophically and melt down. However, if power is lost to a LFTR, the liquid fluoride salt drains away and the reaction stops.
  • Gen II uranium reactors must operate at very high pressures, up to 700 atmospheres. However, LFTR’s operate at normal pressures, so there’s no possibility of a Chernobyl-like steam explosion.
  • LFTR’s produce very little waste, because they burn almost all of their fuel. In fact, they can even use existing nuclear waste as fuel. That’s right – those pesky stockpiles of nuclear “waste” on Earth could become fuel for the next generation of nuclear reactors. Thus we have a massive, easily accessible energy source, plus the nuclear waste problem becomes solved. Obviously this feature is more important on Earth than it will be on Mars.

LFTR’s are not the only type of nuclear technology currently being developed that holds significant promise. Another is the TWR (Travelling Wave Reactor), which can be completely sealed and operate for perhaps half a century or more without maintenance. However, it seems that LFTR’s offer the most promise, especially for Mars. Both of these reactors are still in development, and not likely to be deployed on Earth for another 2 decades. However, that may well line up with our settlement plans.

Some type of small, self-contained reactors will almost certainly be used on Mars from the beginning. As to what specific reactor type this will be, that remains to be seen. But Mars has plenty of nuclear fuel, and nuclear fission technology is becoming much better.