ISRU, Mars, Space Program

Green Dragon


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)



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 (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 (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.

Space Program

Why “Tiw”?

“Tiw” is the old English name for the god Mars; or, at least, Tiw was the equivalent in Norse mythology of the Roman god Mars.

Why not “Ares”?

Firstly, so many programs and vehicles have been named “Ares” now, in both scientific literature and fiction, that it’s painfully unoriginal. Secondly, what most people don’t know is that Mars and Ares were not the same gods.

Mars was originally the god of agriculture and springtime, and was considered one of the most important Roman gods, second only to Jupiter. Mars eventually became equated with war because the Romans would often march to war in March, the month named for Mars, which is when spring is beginning in the northern hemisphere (the vernal equinox is around March 21). It’s much easier to march cross-country in spring when the weather is nice, than in, say, winter! Most of the festivals celebrating and worshipping Mars occurred, unsurprisingly, in March. Of course, the soldiers marching off to war then would ask the god Mars to bless and guide them, and grant them victory – and thus, over time, Mars became thought of as the Roman war god. But this is not the true nature of Mars.

Personally, I like Mars the god of springtime and agriculture more than Mars the god of war!

Ares, on the other hand, was the Greek god of war and was considered brutal and vile, and was not a well-respected or loved god. Note that Phobos and Deimos (fear and panic) were consorts of Ares – not of Mars. So, just to be clear: Mars good and popular, Ares horrible and unpopular. Not the same. (This is also why I think “Phobos” and “Deimos” are terrible names for Mars’ moons.)

Although I would prefer not to use the name “Ares” for an H2M program or vehicle, the name “Ares” will always be linked with Mars whether we like it or not. It’s the root of the prefix “areo”, which can be substituted for the prefix “geo” to create Mars-equivalent words:

Earth Mars
geology areology
geography areography
geochemistry areochemistry
geosynchronous areosynchronous
geostationery areostationery

There are numerous equivalent names for Mars in other languages. However, why not use one that we use every day – or, at least, every week?

Yes – the word “Tuesday” means “Tiw’s day”. And “Tiw” means “Mars”.

The days of the week were originally named by astrologers for the 7 known planets. “Planet” simply meant “wanderer”, and referred to any astronomical object that did not maintain a fixed position like a star. This, therefore, included the Sun and Moon.

In most cultures, the planets were personified as gods.

Planet name (English) Latin equivalent Day of week (old Latin) Norse equivalent Day of week (English)
Sun Sol Dies Solis
(Sol’s day)
(Sun’s day)
Moon Luna Dies Lunae
(Luna’s day)
(Moon’s day)
Mars Dies Martis
(Mars’ day)
Tiw Tuesday
(Tiw’s day)
Mercury Dies Mercurii
(Mercury’s day)
Woden Wednesday
(Woden’s day)
Jupiter Jove Dies Jovis
(Jove’s day)
Thor Thursday
(Thor’s day)
Venus Dies Veneris
(Venus’ day)
Freya Friday
(Freya’s day)
Saturn Dies Saturni
(Saturn’s day)
(Saturn’s day)

The god “Tiw” (also known as “Tyr” or “Tiwaz”) was associated with law and heroic glory, and known for his great wisdom and courage. These are surely great attributes to bestow on our H2M program!

As a bonus, Tiw also has a rune. It’s slightly different from the well-known alchemical symbol for Mars, but, I think you’ll agree, it’s pretty symbolic of a space program:


Space Program

The Tiw Program

The Tiw program is the name of an ambitious H2M (Humans to Mars) program loosely based on the Apollo program, which I hope to develop and explain on this blog.

See: Why “Tiw”? if you’re curious about the name.

Here’s a mistake that I think many people in the Mars community seem to be making: They look at H2M as a single mission.

The attitude is one of: “Let’s just achieve that. Let’s just get humans to Mars. That’s the main goal, let’s focus on that, and not worry about anything that comes before or after.”

This mindset is understandable. Because funds are limited, we could only ever hope to afford a single H2M mission, hence why consider others? But such an approach is unlikely to succeed.

The goal of this blog is Mars settlement, and it’s therefore mostly about what happens after we begin sending humans to Mars. It’s not just about getting some people there and coming back. That kind of goal may be appropriate for a cold-war space-race in which one alpha tribe wants to display its technical superiority to another. But it’s not appropriate for the 21st century, where we recognise that we’re all one people sharing a single biosphere, the days of nationalistic competition is over (or soon will be), and we’re beginning to realise the importance to our future of expansion into space.

We need to look beyond just sending humans to Mars. To view H2M as a single mission is short-sighted, and should not be our goal. The goal is really to make humanity multiplanetary. In that context, perhaps Apollo is not the optimal example to follow, since it was indeed about simply winning a race and not about any kind of ongoing program of lunar settlement. However, Apollo was the greatest success in space exploration history, and there’s a reason for that: it was a program and not just a mission. The Apollo program was originally planned as a series of 20 missions. The first 10 missions were designed as preparation for the Moon landing. The second 10 missions were all planned as Moon landings; except, as we all know, Apollo 13 aborted and the last 3 missions were cancelled.

It’s not only about what happens after that first H2M mission, but also what happens before. Apollo 11 was a success because of what was achieved by the earlier missions.

The Tiw program is an H2M program designed to carry us through Stage 1 of Mars settlement: human exploration. The first series of missions (Phase 1) are designed to develop the necessary capabilities and experience for the first H2M mission to be a success. The second series of missions (Phase 2) are designed to develop the necessary capabilities and experience to take us to Stage 2: permanent settlements and infrastructure.

Phase 1 of the Tiw program includes a series of exercises in Mars analog environments on Earth (including places such as the Arctic and Antarctic, Utah, Arkaroola and Atacama), Earth orbit, the Moon, and perhaps Mars orbit. Some missions will be robotic.

Phase 2 obviously focuses on Mars.