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.

Architecture

The Mars Ascent Vehicle

The MAV will be an SSTO (Single Stage To Orbit) VTOL (Vertical Take-Off and Landing) vehicle with powerful LCH4/LOX engines, capable of pinpoint landing on Mars, refuelling from local Martian resources, and carrying up six astronauts to Mars orbit for transfer to the MTV. Ideally it will also be capable of then returning to Mars surface.

The MAV has two main sections:

  1. The lower portion is the ascent/descent stage, which includes:
    • the engines
    • fuel tanks (LCH4 and LOX)
    • a sophisticated GNC system
    • solar panels
    • ISPP plant (electrolysis unit and Sabatier reactor)
    • a water-mining robot called AWESOM (Autonomous Water Extraction from Surface Of Mars)
  2. The upper portion is a DragonRider (Pern-2) with trunk containing additional solar panels.
Mars Ascent Vehicle concept
Mars Ascent Vehicle concept

Engines

The MAV’s engines will need to be LCH4/LOX (liquid methane/liquid oxygen), in order that they can be refuelled from local Martian resources (see below). Several types of engines that burn methane fuel have been developed, however, SpaceX are currently developing a new LCH4/LOX engine called “Raptor” that is likely to be the preferred choice.

Based on SpaceX’s record, the Raptor design will presumably be more modern and advanced than existing methane fuelled rocket engines. It will also have a high degree of interoperability with other SpaceX hardware used in the mission, such as the Dragon. Furthermore, since SpaceX will already be involved, using more hardware from the same company should, in theory, reduce costs, if for no other reasons that a fewer number of engineers need to be paid, since engineers who understand the Dragon and Falcon are also probably the same people who understand the Raptor engine.

The engines must be powerful enough to carry the MAV from Mars orbit to surface, and back. In theory, if the MAV is capable of refuelling itself at Mars Surface, it should be able to do this repeatably (thus making it a SSTO VTOL RLS).

ISPP

The MAV will have an integrated ISPP plant comprised of:

  • water mining robot (AWESOM)
  • electrolysis unit
  • Sabatier reactor
  • cryogenic propellant storage

The ISPP process currently envisaged for the MAV closely parallels that described in the Mars Direct architecture (1990). In Mars Direct, hydrogen (which represents the lightest fraction of the propellant yet also the hardest to obtain from local Martian resources) is carried from Earth, and reacted with CO2 obtained from the Martian atmosphere in order to produce methane (CH4) and oxygen (O2), which are liquified and stored cryogenically. Additional oxygen is obtained from carbon dioxide via the reverse water gas shift reaction, which produces water (H2O) that is then electrolysed to hydrogen (H2) and oxygen (O2).

The primary difference in Blue Dragon is that hydrogen is not carried from Earth, but is obtained by mining water from the surrounding regolith, and electrolysing it into hydrogen and oxygen. Every kilogram of Martian regolith is estimated to contain up to 40g of water (Slosberg), and 80% of this can be liberated from the top [x]cm of regolith using microwave radiation.

The optimal stoichiometric ratio for LOX/LCH4 bipropellant is 7:2. Mars Direct specifies a fuel requirement of 24 tonnes of CH4. Taking that as a nominal value (for now), the amount of LOX required is therefore 84 tonnes.

The process is as follows:

Step 1: Carbon dioxide is obtained from the Martian atmosphere by filtering out dust, removing water via zeolite adsorption, compressing the remaining gas mix to 700 kPa, and allowing it to equilibrate to ambient Martian temperatures (about 210K). The CO2 will condense, enabling it to be separated from the remaining gases.

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)

Step 4: Oxygen produced in step 3 is stored cryogenically as LOX.

Step 5: 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. Water produced by the reaction is cycled back into the electrolysis unit to produce more hydrogen and oxygen.

Combining the reactions in step 3 and 5, 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 to supplement air supplies for the Hab or the Rover.

Obtaining 66 tonnes of carbon dioxide requires processing about 70 tonnes of Martian atmosphere. The density of the atmosphere at the surface of Mars is about 0.02 kg/m3, which means 3.5 million cubic metres of atmosphere

If our goal is for the MAV to be fully fuelled within 20 months (the time difference between the arrival of the MAV at Mars and the departure of the crew from Earth), that means processing about 117kg (5830 m3) of atmosphere per day, or 80 grams (4 m3) minute. It remains to be seen how achievable this is. However, there is 44 months between the arrival and departure of the MAV, therefore, a slower processing rate may still be acceptable, although the goal of ensuring that the MAV is fully fuelled before the crew leaves Earth would not be met.

ISWP

The ability to make use of Martian water is fundamental to the Blue Dragon architecture; therefore, it’s preferable to locate Marsopolis in a region where the water content is reasonably high, while still aiming for lower latitudes in order to simplify landing and to maximise solar power.

The diagram below shows the lower limit of water concentration across Mars.

Water on Mars
Water on Mars

The proposed location for Marsopolis (discussed in the Location section) is in Arcadia Planitia, a region to the north-west of Olypmus Mons. The water content at the landing site should be at least 10% by mass, and the presence of grooves and ridges in the region are indicative of ground ice in the near surface. Furthermore, Arcadia Planitia is extremely flat, which will support autonomous water mining by a mobile robot.

If we estimate that the average water concentration of the regolith is 10% by mass [ref], and that 80% can be extracted from the top decimetre of regolith by microwave radiation [ref], 675 tonnes of regolith will need to be processed.

675 tonnes of regolith = 67.5 tonnes water + 607.5 tonnes dry soil

67.5 tonnes of water * 80% captured = 54 tonnes

The density of dry Martian soil is about 1.4 g/cm3 = 1400 kg/m3 [ref]. If the regolith is 10% water, its density will be about:

10% * 1000 kg/m3 + 90% * 1400 kg/m3 = 1360 kg/m3

The volume of regolith to process is therefore:

675,000 kg / 1360 kg/m3 = 496 m3

Assuming we can only extract water from the top decimetre of regolith by microwave radiation, the area that must be covered by the rover is about:

496 m3 / 0.1 m = 4960 m2

If the AWESOM rover has a 1 metre wide catchment, it must therefore traverse a 100 metre long strip about 50 times (or cover a square about 70 metres on a side).

Specifying the same 20 month time constraint, AWESOM must collect 90 kg of water per day, which requires covering about 8.3 m2 of terrain per day on average. This seems like it should be easy. It will be preferable to collect the water as rapidly as possible, for peace of mind, and also because H2 is needed before CH4 can be produced. The design goal will be to build the robot to be capable of carrying up to 100 kg of water; it should therefore return to the MAV to unload at least once per day.

It may be that a single AWESOM is capable of collecting enough water for the MAV as well as for the Hab; although, considering the importance of water, having two at the site will still be preferable. Note that there’s no reason why the AWESOM must be delivered to Mars inside the MAV. It could be delivered separately in one of the cargo modules, and drive itself over to the MAV.

It’s true there there would be a benefit if the MAV and AWESOM were an integrated package (i.e. the AWESOM robot is carried inside the MAV), because then the MAV could refuel anywhere on Mars; it would simply land and deploy its AWESOM to collect more water. However, for our early MAV designs it will be preferable to reduce mass as much as possible.

It may even be preferable to keep all ISRU hardware separate, in, for example, a Green Dragon capsule, and transfer propellant to the MAV via hoses. There are several benefits to doing this, such as a more efficient integrated ISRU design, and reduction in the landed mass of both the MAV and Hab. However, connecting up hoses may be difficult to do autonomously, and it will be better if the MAV is fully fuelled before the crew leaves Earth.

Keeping water in a liquid form within the rover will require heat, perhaps more than can be reliably produced from solar cells. An RTG (Radioisotope Thermoelectric Generator), like the one used in Curiosity, will provide both heat and electrical energy.

Power system

One of the primary challenges associated with the MAV is the power system.

Nuclear

In Mars Direct, once the MAV (a.k.a. ERV) lands on Mars, a small robotic truck emerges with an nuclear reactor. The truck carries the reactor some way off, trailing electrical cable connecting it to the MAV in order to provide power to the ISPP plant.

The reason why it must be distanced from the MAV is because the reactor will be unshielded and the MAV is designed to carry people. Shielding is typically very heavy and would add a lot of mass to the MAV’s payload, making it much harder to land on Mars. If an unshielded reactor is operated inside or near the MAV, it would irradiate the vehicle, making it unsafe for carrying people. Therefore, it must be moved a safe distance away where radiation from the reactor will not reach the vehicle.

There are some issues with this design. If the reactor is unshielded, even if it’s moved some distance away from the MAV (and the Hab and other parts of the base), it will create a zone around it into which the astronauts must not venture. Perhaps the MAV will not be affected by radiation from the reactor, but the natural environment surrounding the reactor will. We should treat Mars a little more responsibly than this. What if the reactor is parked near something of scientific interest? What if the reactor needs attention – for example, the cable becomes loose?

If the reactor is shielded, it achieves two things. It means it does not need to be relocated from the MAV, thus eliminating the mass of the robotic truck and partially offsetting the mass of the shielding. It would also allow for the reactor to be kept contained within the MAV, enabling it relocate itself to almost anywhere on Mars and refuel (as long as there is sufficient water in the surrounding regolith). This would be an extremely useful capability, but not essential for the first H2M mission.

One of the advantages of using a nuclear reactor, in the Mars Direct design, is that it represents a reliable source of abundant energy that can be used to convert the hydrogen into methane as quickly as possible, in order to minimise boil-off and ensure that ample fuel will be manufactured.

Solar

However, if we commit to using local water as a hydrogen source, there will be no boil-off, and less reason for to manufacture all the propellant as quickly as possible. Considering this, as well as the difficulties associated with using a nuclear reactor to power the ISPP process, it will be better to use solar panels.

Solar panels represent a fluctuating energy source that will vary with the diurnal cycle, seasonal cycle, and atmospheric dust levels. As a rule of thumb, daytime solar energy on Mars is about half that of Earth. However, we have about 20 months between when the MAV arrives at Mars and when the crew leaves Earth at the subsequent launch opportunity, which should be plenty of time to make the necessary propellant if we wish to ensure that the MAV is fully fuelled before the crew leave Earth. Actually, there is about 44 months between when MAV’s arrival and departure, which should certainly be ample if that much time is needed.

The Dragon’s trunk contains solar panels, which can be used to provide some of the power necessary for ISPP, and the MAV’s ascent stage may include additional panels as required.

By choosing solar panels over a reactor for ISPP power, we eliminate the mass of the reactor, shielding, the robotic truck to relocate it, and the electrical cable that would connect the reactor to the MAV. We eliminate the risk of an unshielded reactor irradiating the MAV, or the surrounding terrain, or the crew.

If the AWESOM can be carried inside the MAV, using solar panels for power also provides for relocating and refuelling, because the solar panels can be folded up inside the vehicle before launch.

Are solar panels a reliable energy source on Mars? The Mars Exploration Rovers Spirit and Opportunity were powered by solar energy. Spirit was active for 6 years, and Opportunity has been going for 9.

Differences from Mars Direct ERV

  1. This is a much lighter vehicle. It does not include the mass of:
    1. 6 tonnes of hydrogen brought from Earth
    2. Nuclear reactor
    3. Light robotic truck for relocating reactor
    4. Electrical cable to connect MAV to reactor
  2. Instead, it includes:
    1. AWESOM water-mining robot (although this could be delivered separately)
    2. Solar panels
  3. No need for reverse water gas shift reactions or dissociation of CO2 to produce additional O2, as ample is obtained from water electrolysis.