Architecture

Dragon capsules

The current version of the SpaceX Dragon capsules, including the one that historically became the first commercial spacecraft to dock with the ISS, are designed to splash down in water, like those used in NASA’s Mercury, Gemini and Apollo programs and like NASA’s new Orion capsule.

The next generation of Dragon capsules are designed to land on solid ground. Currently in development at SpaceX, they are fitted with eight “SuperDraco” engines, which are a powerful new variation of the Draco engines used by the Dragon RCS (Reaction Control System). Like the Dracos, they use non-cryogenic propellant: monomethyl hydrazine fuel and nitrogen tetroxide oxidiser. However, they’re much more powerful, each capable of delivering about 67 kilonewtons of axial thrust, for a total of about 534kN. These engines will enable the Dragon to land propulsively on solid ground, usually back at the original launchpad, thereby saving the time and expense of water recovery and opening up the possibility for Dragon capsules to land on  the Moon, Mars and other worlds with solid surfaces. This is in alignment with SpaceX CEO Elon Musk’s stated purpose of establishing settlements on Mars.

SpaceX Dragon capsule landing on Mars
SpaceX Dragon capsule landing on Mars

DragonRider

SpaceX offer two basic configurations for the Dragon capsules: cargo and crew. The crewed version is known as a “DragonRider”, and can accommodate up to seven astronauts. These may be used for transporting crew between Earth and the ISS in the near future.

In the Blue Dragon architecture, which is designed for a crew of six, the seventh seat is removed and the volume that it (and a seventh person) would normally occupy is reserved for cargo. This may be last minute personal items from Earth, or samples from Mars. All three DragonRiders in the architecture will be modified to accommodate six people plus storage.

DragonRider capsule with 7 crew
DragonRider capsule with 7 crew
DragonRider capsule with 7 crew
DragonRider capsule with 7 crew

Red Dragon

Red Dragon” is a proposed variant of the SpaceX Dragon capsule currently being investigated by NASA as a low cost alternative for delivering payloads to Mars (Karcz et al., 2012).

Red Dragon will presumably be similarly configured with SuperDraco engines. Alternatively, they may utilise new methane-fuelled “Raptor” engines being developed at SpaceX, which would have the advantage that they could be refuelled on Mars. In addition, Red Dragon will incorporate several modifications necessary for EDL on Mars, including:

  • Removal of systems unique to LEO missions, such as berthing hardware.
  • Addition of deep space communications.
  • Modifications to SuperDraco (or Raptor) engines to suit the Martian atmosphere.
  • Reduction of heat shield thickness, since the atmosphere is far less dense.
  • Algorithms and avionics for pinpoint landing on Mars.

The gravity on Mars is lower, which reduces the acceleration of the capsule towards Mars; however, in the case of direct entry the capsule will be approaching from interplanetary space at a much higher velocity than if it were descending from orbit. Also, Mars’ atmosphere is much thinner (less than 1%) than Earth’s, so it will play less of a role in reducing spacecraft velocity during EDL. However, for the same reason, there is less heating due to atmospheric friction, and therefore less or, perhaps, different heat shield material may be used. The different conditions will affect the forces experienced by the spacecraft, which may require changes to thrusters, heat shield, avionics and other aspects.

NASA have calculated that a Red Dragon capsule will be capable of delivering payloads of up to 1.9 metric tonnes to the surface of Mars. This delivery mechanism has been receiving increasing attention from NASA, being considerably simpler and cheaper than, for example, the sky crane method used to deliver Curiosity. Not only will it be cheaper per kilogram of payload mass, but much cheaper overall.

Another clear advantage is that a landed capsule can be repurposed as a storage unit, shelter or habitat.

Once the Red Dragon technology has been proven as a reliable mechanism for delivery of cargo, this approach may be used to deliver up to seven crew members to Mars surface, simply by using a DragonRider modified in the same way.

Red Dragon represents a near term technology that can enable comparatively inexpensive and functional Mars missions. It’s a fundamental element of the Blue Dragon architecture (hence the name), being utilised for delivery of both crew and cargo to Mars surface.

The Dragon capsules are being designed to land with a high degree of accuracy. From the SpaceX website:

“SuperDraco engines will power a revolutionary launch escape system that will make Dragon the safest spacecraft in history and enable it to land propulsively on Earth or another planet with pinpoint accuracy.”

This ability to land “with pinpoint accuracy” is supported by the Dragon’s GNC (Guidance, Navigation and Control) system. Due to the lack of GPS (Global Positioning System) on Mars, high-accuracy landings must be achieved using alternate methods. However, this problem has effectively been solved. For example, ESA (European Space Agency) have been developing a system known as “LION” (Landing with Inertial and Optical Navigation) that will enable pinpoint landing on the Moon, Mars and asteroids using image recognition of major landmarks (Delaune et al., 2012). Another important development is the Fuel Optimal Large Divert Guidance (G-FOLD) algorithm (Acikmese et al., 2012), able to autonomously calculate landing trajectories in real-time. This was recently tested successfully with Masten Space System’s Xombie VTOL experimental rocket, with the vehicle making a 750 metre course correction in real time. Considering these developments it’s reasonably safe to assume that the Red Dragon will be capable of pinpoint landings on Mars by the time we begin sending them. Because the position of landed base components can be known with precision, a neat, safe and optimised layout of the base can be designed beforehand.

Red Dragon potentially represents a mechanism for delivering cargo or crew to the surface of Mars that is not only repeatable, but affordable. SpaceX currently charge $135M for a Falcon Heavy launch including the Dragon capsule. Making use of COTS and other pre-developed hardware it may be possible to develop and deliver a payload to Mars for under $250M. This is a mere one tenth of the $2.5B Curiosity rover.

Once SpaceX have developed their RLS (Reusable Launch System) for the Falcon Heavy – a goal likely to be achieved within a few years, considering the recent Grasshopper tests, and thus well before the first H2M mission – this price will come down even further.

5-metre capsules

Dragon capsules have a diameter of 3.7 metres. However, the architecture for the Mars One mission, which proposes to send 24-40 astronauts on a one-way mission to Mars, proposes to rely on a larger, 5-metre-diameter Dragon capsule for habitat modules. Although these are yet be to be built or demonstrated, their plan is to land the first two of these on Mars in 2020, which is only seven years from the time of writing.

It could perhaps be inferred that plans exist at SpaceX to have these larger Dragon capsules operational and available within seven years. This is well within the timeline of Blue Dragon. However, SpaceX and Mars One do not have a formal association so there is no real evidence of this yet, and as no information about these larger capsules is currently available, the Blue Dragon architecture does not presently include them. This may change if more information becomes available.

Ice Dragon

NASA have commenced studies of a mission to Mars based on the Red Dragon landing system, which may be flown as early as 2018. Known as “Ice Dragon” (Stoker et al., 2012), it’s being developed in collaboration with SpaceX, and will deliver a science package to Mars including a drill that will penetrate up to two metres into the permafrost to investigate environmental conditions suitable for past or extant life.

There are six objectives currently envisaged for Ice Dragon:

  1. Determine if life ever arose on Mars.
  2. Assess subsurface habitability.
  3. Establish the origin, vertical distribution and composition of ground ice.
  4. Assess potential human hazards in dust, regolith and ground ice, and cosmic radiation.
  5. Demonstrate ISRU for propellant production on Mars.
  6. Conduct human relevant EDL demonstration.
Ice Dragon showing drills. (Human figure shown for scale only)
Ice Dragon showing drills. (Human figure shown for scale only)

Besides the scientific outcomes of the mission, which will certainly be of tremendous value to human missions, one of the most important contributions of Ice Dragon will be demonstration of the EDL capabilities of the Red Dragon capsule.

References

B. Acikmese, J. Casoliva, and J. M. Carson III, “G-FOLD: A Real-Time Implementable Fuel Optimal Large Divert Guidance Algorithm for Planetary Pinpoint Landing,” Concepts and Approaches for Mars Exploration, 2012.

J. Delaune, G. Le Besnerais, M. Sanfourche, T. Voirin, C. Bourdarias, and J. Farges, “Optical Terrain Navigation for Pinpoint Landing: Image Scale and Position-Guided Landmark Matching,” Proceedings of the 35th Annual Guidance and Control Conference, 2012.

J. S. Karcz, S. M. Davis, M. J. Aftosmis, G. A. Allen, N. M. Bakhtian, A. A. Dyakonov, K. T. Edquist, B. J. Glass, A. A. Gonzales, J. L. Heldmann, L. G. Lemke, M. M. Marinova, C. P. Mckay, C. R. Stoker, P. D. Wooster, and K. A. Zarchi, “Red Dragon: Low-Cost Access to the Surface of Mars Using Commercial Capabilities,” Concepts and Approaches for Mars Exploration, 2012.

C. R. Stoker, A. Davila, S. Davis, B. Glass, A. Gonzales, J. Heldmann, J. Karcz, L. Lemke, and G. Sanders, “Ice Dragon: A Mission to Address Science and Human Exploration Objectives on Mars,” Concepts and Approaches for Mars Exploration, 2012.

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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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.
Architecture

Red Dragon

“Red Dragon” is a potential variant of the SpaceX Dragon capsule that will be able to land on Mars, currently being investigated by NASA and SpaceX.

The first series of Dragon capsules, including the one that historically became the first commercial spacecraft to dock with the ISS, were designed to splash down in water, like those used in NASA’s Mercury, Gemini and Apollo programs, and like NASA’s new Orion capsule.

The next generation of Dragon capsules, currently in development at SpaceX, are fitted with eight SuperDraco engines. These are a powerful new variation of the Draco engines used by the current Dragon RCS (Reaction Control System). Like the Dracos, they use non-cryogenic propellant (monomethyl hydrazine fuel and nitrogen tetroxide oxidiser), however, they’re much more powerful, each capable of delivering about 67 kilonewtons (15,000lbf) of axial thrust, for a total of about 534kN (120,000lbf). These engines will enable the Dragon to land on solid ground back at the launchpad, saving the time and expense of water recovery, and opening up the possibility for Dragon capsules to land on Mars. This is in alignment with SpaceX CEO Elon Musk’s stated purpose of establishing settlements on Mars.

Red Dragon will presumably be based on this or a similar engine configuration, with modifications to suit EDL on Mars. Variations may include:

  • Remove systems unique to LEO missions, such as berthing hardware.
  • Add deep space communications.
  • Modifications to SuperDraco engines to suit Martian atmosphere.
  • Reduction of heat shield mass.
  • Algorithms/avionics to enable pinpoint landing on Mars.

The gravity on Mars is lower, which reduces the acceleration of the capsule towards Mars; however, the capsule will be approaching from interplanetary space at a much higher velocity than if it were approaching from Earth orbit. Also, Mars’ atmosphere is much thinner (less than 1%) than Earth’s, so it will play less of a role in reducing spacecraft velocity during EDL. However, for the same reason, there is less heating due to atmospheric friction, and therefore less (or different) heat shield material may potentially be used. The different conditions will affect the forces experienced by the spacecraft, which may necessitate changes to thrusters, heat shield, avionics and other factors.

Red Dragon landing on Mars
Red Dragon landing on Mars

Another clear advantage is that a landed capsule can be repurposed as a storage unit, shelter or habitat.

Once the Red Dragon technology has been proven as a reliable mechanism for delivery of cargo, this approach may be used to deliver up to seven crew to Mars surface, by using a DragonRider modified in the same way.

Red Dragon represents a near term technology that can enable comparatively inexpensive and functional Mars missions. It’s an fundamental element of the Blue Dragon architecture, being utilised for both crew and cargo delivery to Mars surface.

Theoretically, Red Dragon will be able to land with a high degree of accuracy. From the SpaceX website:

SuperDraco engines will power a revolutionary launch escape system that will make Dragon the safest spacecraft in history and enable it to land propulsively on Earth or another planet with pinpoint accuracy.

This ability to land “with pinpoint accuracy” is supported by the Dragon Guidance, Navigation and Control (GNC) system. Due to the lack of GPS on Mars, alternate methods of achieving high-accuracy landings must be achieved using alternate methods; however, this problem is effectively solved. For example, Jeff Delaune at ESA has been developing a system known as “LION” (Landing with Inertial and Optical Navigation) that enables pinpoint landing on the Moon, Mars and asteroids using image recognition of major landmarks. Another impressive development is the Fuel Optimal Large Divert Guidance (G-FOLD) algorithm developed by JPL, able to autonomously calculate landing trajectories in real-time. This was recently tested with Masten Space System’s Xombie VTOL experimental rocket, very successfully, making a 750 metre course correction in real time. Considering these developments it’s safe to assume that the Red Dragon will be capable of pinpoint landings on Mars by the time we begin sending them, enabling a neat and optimised layout of the base to be designed beforehand.

It’s estimated that a payload of up to ~2 tonnes can be delivered to Mars surface via a Red Dragon. This will be a major breakthrough in the goal of human settlement of Mars.

Red Dragon potentially represents a mechanism for delivering cargo to the surface of Mars that is not only repeatable, but affordable. SpaceX currently charge $135M for a Falcon Heavy launch including the Dragon capsule. Making use of COTS and other pre-developed hardware, and simplifying missions, it may be possible to design and build a payload and send it to Mars for only $200 – $250M. Compare this with the $2.5B price tag of the Curiosity rover.

Once SpaceX have developed their RLS for the Falcon Heavy – a goal likely to be achieved within a few years, in light of the recent Grasshopper tests, and thus well before the first H2M mission – this price will come down even further.

Red SuperDragons

The architecture for the Mars One mission, which proposes to send up to 40 astronauts on a one-way mission to Mars, relies on a larger, 5-metre-diameter Dragon capsule for habitat modules. Although these are yet be to be built or demonstrated, their plan is to land the first two of these on Mars in 2020 – only 7 years from the time of writing.

Mars One settlement
Mars One settlement

Therefore, it can be inferred that a plan exists to have operational “SuperDragons” available within 7 years. This is well within the timeline of Blue Dragon.

Mars One is also planning to build a model settlement in a Mars analog environment in order to commence crew training in 2015, so it may even be possible that we will see what the SuperDragon capsules look like within 2 years or less.

At present the Blue Dragon architecture does not incorporate SuperDragon capsules. However, this may change as more information about them becomes available.

 

Ice Dragon

NASA have commenced studies of a mission to Mars based on the Red Dragon landing system, which may be flown as early as 2018. Known as “Ice Dragon”, it’s being developed in collaboration with SpaceX, and will deliver a science package to Mars including a drill that will penetrate up to two metres into the permafrost to investigate environmental conditions suitable for past or extant life.

There are 6 objectives currently envisaged for Ice Dragon[xx]:

  1. Determine if life ever arose on Mars.
  2. Assess subsurface habitability.
  3. Establish the origin, vertical distribution and composition of ground ice.
  4. Assess potential human hazards in dust, regolith and ground ice, and cosmic radiation.
  5. Demonstrate ISRU for propellant production on Mars.
  6. Conduct human relevant EDL demonstration.

Aside from the scientific outcomes of the mission, perhaps the most important contribution of Ice Dragon will be the demonstration of the EDL capabilities of the Red Dragon capsule.

Architecture

Microgravity, Artificial Gravity and Blue Dragon

One of the most hotly debated topics related to sending humans to Mars is the health effects of prolonged exposure to microgravity and how these might be mitigated.

Prolonged exposure to microgravity (a.k.a. “zero gravity”) has several serious effects on the human body:

  1. Without the need to support the weight of the body, the musculoskeletal system atrophies and weakens. Bone and muscle mass tend to decrease at a significant rate. Bone mass can decrease at 1-1.5% per month.
  2. Under normal gravitational forces blood pressure is highest at the feet and legs, and lowest in the head. In microgravity, however, blood pressure is distributed evenly along the body length. The sustained, higher blood pressure in the head can affect brain function and vision.
  3. Without the need to pump blood around the body against the force of gravity, the heart does not need to work as hard and can therefore also atrophy and weaken.

The longer a person spends in microgravity the more serious these effects become, and the longer it takes to recover after they return to Earth.

H2M (Humans to Mars) and microgravity

A trip to Mars based on a long-stay, or conjunction-class, mission profile using normal chemical propulsion involves approximately a year in space – approximately 6 months outbound and about the same return. A short-stay mission requires around 20 months total in space. This is a significant amount of time to spend in a microgravity environment.

Only two people, both Russians, have spent more than one year in space: Valeri Polyakov’s 438 days in 1994-5, and Sergei Avdeyev’s 380 days in 1998-9. Therefore, we only have a small amount of data about such long-term exposure to microgravity, and much of this data is more than a decade old. Although a variety of techniques for mitigating the adverse effects of microgravity have been developed during the past decade, we have minimal data about spending a year or more in microgravity with access to these.

In addition to a year in space, the crew must also spend 1.5 years on the surface of Mars, which is also a reduced gravity environment (0.38g). Living on Mars surface will reduce the load on the body by 62% and is therefore expected to have effects proportionally similar to microgravity.

The primary concern is that the crew will return to Earth after 2.5 years in reduced gravity environments, be unable to fully recover, and have to spend the rest of their lives in wheelchairs. Apart from the fact that we wouldn’t wish this on our beloved interplanetary explorers and heroes of humanity, such an outcome would hardly add to the glory of space exploration, and may become a deterrent to future human exploration.

An almost equally important concern is that the crew will spend approximately 6 months in microgravity during the outbound trip, arrive at Mars surface, and be unable to do any useful work – thus invalidating the mission.

The problem of microgravity in an H2M mission is hardly a minor one. In conjunction with the similar concerns about health effects of radiation in interplanetary space, it’s considered by many one of the top reasons why not to send humans to Mars.

H2M and artificial gravity

Because of these concerns, some H2M mission designers include AG (Artificial Gravity) in their architecture. The simplest way that we know of to create a feeling of gravity is through the use of centrifugal force, which we can produce by spinning either part or all of the spacecraft. Unfortunately centrifugal force is not a perfect substitute for actual gravity. From DRA5:

“Adverse physiological changes due to reduced gravity may be prevented by exposure to some level of artificial gravity, but the specific level of gravity and the minimum effective duration of the exposure that is necessary to prevent deconditioning are not yet known. Although artificial gravity should reduce or eliminate the worst deconditioning effects of living in zero gravity, rotating environments frequently cause undesirable side effects, including disorientation, nausea, fatigue, and disturbances in mood and sleep patterns. If artificial gravity is to be employed, significant research must be done to determine appropriate rotation rates and durations for any artificial gravity countermeasures. The decision on whether artificial gravity must be employed to adequately support crews on their transits to and from Mars, as well as the decision on the necessary gravity level and rotation rate, has significant implications for vehicle design and operations.”

So in a sense, trading microgravity for artificial gravity is really just trading one set of health problems for another, albeit less serious. The severity of the negative effects of centrifugal force can be mitigated by increasing the radius or decreasing the rate of rotation. A spinning cylinder such as that shown in the movie Mission to Mars may seem fun, but with such a small radius these effects would be quite noticeable.

The problem is that implementing AG in an early-stage H2M mission adds considerable complexity, mass and cost, and these are exactly the kind of things we want to minimise as much as possible. It’s a classic trade-off, and hence the debate. The question is whether AG will produce a better result than a regimen of PT (Physical Training), food and drugs.

AG in Mars Direct

In Mars Direct:

“Artificial gravity is provided to the crew on the way out to Mars by tethering off the burnt out Ares upper stage and spinning up at 1 rpm.”

A spacehab connected to a counterweight by a tether, spinning around a common centre of gravity to create AG.
A spacehab connected to a counterweight by a tether, spinning to create AG.

In this way a comparatively large radius of rotation of about 340m can be created, which would seem to address the side-effects of centrifugal force. However, consider what this idea means for the architecture:

  • The hab is designed for a gravity environment: AG in space and Mars-g on Mars. That means it will have a floor, ceiling and walls, with cupboards, screens, controls, etc. mainly on the walls. The result is a less compact and heavier spacecraft (or one with fewer fixtures/features).
  • Although designed for a gravity environment, after launch the hab will be in microgravity until the AG is set up. In addition, if the AG system fails and the tether must be dropped for any reason, the hab should continue to Mars in a microgravity mode, despite not being designed for that.
  • There is a risk the counterweight could crash into the hab, and it may not be possible to prevent this even by dropping the tether.
  • The mass of the cable must also be launched (more mass, more fuel, more cost).
  • Communications with Earth are more difficult with a spinning spacecraft, as it’s more difficult to keep antennas pointed in the right direction without sacrificing signal strength. Communications with Mars are already up to one million times more difficult than with the Moon, since Mars is up to 1000 times as far away (signal strength decreases with the square of the distance).
  • With a spinning spacecraft it’s more difficult for navigation sensors to track the position of Earth, the Moon and stars.
  • Collecting solar energy with solar panels is more difficult and possibly less efficient, as they should ideally be always directly facing the Sun.
  • The hab and the counterweight both require an RCS (Reaction Control System), which must work in tandem in order to produce a stable spin around a common centre of gravity, or for any course manoeuvres.
  • Additional fuel is required for RCS on both the hab and the upper stage.
  • Additional fuel is required to send not just the hab, but also the upper stage, on TMI (Trans Mars Injection).
  • Course corrections and other manoeuvres are more difficult, as both the spacecraft and counterweight must be pushed in the same direction at the same time, without overstressing and breaking the tether, or causing it to stretch and rebound, or causing it to become slack. Plus, the dynamics of the spinning masses must also be accounted for.
  • As the assembly approaches Mars it must be spun down and the tether dropped before aerocapture. However, this will leave the spacecraft on a trajectory that is difficult to predict in advance with precision, making it more difficult to calculate the required burn to place the spacecraft on an aerocapture trajectory. It may have to be re-calculated in real time, which is risky. Yet for aerocapture to work, the hab must hit the atmosphere at exactly the right angle and altitude. EDL (Entry, Descent and Landing) is already a very technically challenging and dangerous process, especially in a hab – this additional factor makes it even more dangerous.
  • Once the assembly must be spun down, the interior of the hab will return to a weightless environment, despite not being designed for that.
  • If the tether breaks for some reason (e.g. micrometeoroid) the hab and counterweight will fly off in different directions. The hab must carry additional fuel to make a course correction if this happens. In addition, the ground crew must be prepared to track and communicate with the spacecraft (which may be on an unknown trajectory) and assist with on-the-fly calculations to determine course correction manoeuvres. Otherwise it will mean LOC (Loss Of Crew).

Many of these items will also apply to other AG solutions. Several could be addressed by using a rigid telescopic truss instead of a tether, but that would have a high mass and therefore be an even more expensive solution. There’s got to be a better way! The rest of Mars Direct is comparatively much simpler.

Note that Mars Direct does not use AG for the return trip, but only the outbound portion of the mission. Therefore the crew still must spend about 6 months in microgravity.

AG in DRA5

DRA5 doesn’t commit to using AG for a long-stay architecture. It only states that AG should be used if a short-stay mission class is selected, due to the longer time (~600 days) spent in space.

Microgravity in Blue Dragon

AG is not used in Blue Dragon. The crew will travel through space for about 8-12 months in microgravity. There are several reasons for this decision.

Cost

One of the main obstacles to sending humans to Mars (other than concerns about microgravity health effects) is cost. The cost of a Mars mission is driven by two main factors:

  • The amount of mass to launch and send to Mars, which determines fuel requirements, rocket sizes, number of launches, and size/mass of major components.
  • The complexity of the architecture and hardware, which drives cost of development time, including engineering, manufacturing and human resources.

As the above review of the AG solution presented in Mars Direct shows, using a tether and centrifugal force to produce AG requires greater mass in several ways:

  • Mass of the tether.
  • Mass of additional fuel for RCS.
  • A spacecraft designed for a gravity environment must be bigger/heavier, or have less features, than one designed for microgravity.
  • The spacecraft must be more complex (see below), which will also make it heavier.

It increases complexity in numerous ways:

  • Navigation systems.
  • Solar panels.
  • Communications.
  • RCS.
  • Major manoeuvres: TMI and MOI (Mars Orbit Insertion)
  • Tether design and operation.
  • EDL.

It’s difficult (at least, for me) to quantify exactly what the additional cost would be to implement an AG solution like the one proposed in Mars Direct. However, what we can assume is that Blue Dragon will likely cost billions of dollars in hardware and development costs. While AG will surely be a feature of future missions once launch costs decrease and launch vehicle capabilities increase further, omitting it from at least the first few will greatly reduce costs without greatly increasing risk.

Risk

Although you could say that AG reduces the risk that the crew might reach Mars or Earth in less than tip-top physical condition, the Mars Direct solution adds other risks, such as:

  • Hab crashing into counterweight.
  • Tether breakage.
  • More complex course manoeuvres could send the spacecraft in the wrong direction.
  • Harder to track and communicate with spacecraft.
  • More risky/complex EDL.

More risk means more failure points, potential emergency situations, abort modes, development costs, and training.

The risks associated with microgravity health effects, however, are comparatively well-known and easy to address.

Additional reasons

  1. The AG solution described in Mars Direct is only valid for the outbound trip anyway, so it’s not a complete solution. Maybe they’ll get to Mars well-adapted to Mars gravity, but on return to Earth they will be in almost the same condition as if no AG was provided at all.
  2. The Mars Direct AG solution only produces Mars-level gravity. This is still a reduced-gravity environment and therefore the crew will still experience some degree (perhaps ~62%) of the usual effects of microgravity. You could say that overall, this idea only goes about 19% (38% * 50%) towards addressing the microgravity problem.
  3. By this stage we have many human-years of experience with microgravity thanks to the International Space Station, Mir, and other space stations and missions before that. Similarly, we have experience with many astronauts and cosmonauts fully recovering from their time in microgravity. Commander Chris Hadfield returned a few days ago from the ISS after 5 months in microgravity, and is experiencing dizziness and weakness. However, he is in good humour, giving interviews, and reports feeling better “by the hour”.
  4. By constructing Abeona (our MTV) on orbit rather than sending a hab on TMI from a single launch, Abeona‘s cruise stage can be provided with additional fuel to reduce the total time spent in space to less than one year and perhaps even less than 10 months.
  5. NASA and JAXA successfully demonstrated in 2011 that osteoporosis drugs can be used to mitigate bone density loss. Without the drug Fosomax, the average bone density loss was 7% in the femur and 5% in the hip; with the drug, the loss in the femur was only 1%, and hip bone density actually increased by 3%.
  6. If the crew travel to and from Mars in the same vehicle and in the same gravity environment, the return trip will be much more comfortable, because they’ll already be used to Abeona and will have made it homely. Personal solutions and routines for dealing with microgravity will already have been developed during the outbound trip.
  7. On arrival at Mars, it’s estimated that it will only take 1-2 weeks at the most for the crew to adapt from microgravity to Mars gravity. Since they have 18 months on the surface, this is only 2.5% of the total time on Mars and quite acceptable. The most important thing is to design the architecture so that the crew will not be required to do any strenuous work during the first few weeks. This is exactly what we’ve done with Blue Dragon, in which the hab is landed 26 months earlier, powered up, checked out and inflated.
  8. Considering the current state of medical research, especially in nanotechnology, prosthetics and replacement organs, the exponential pace of technological development, and the hero status of the first Mars astronauts, it’s safe to say that in 20-30 years, in the very unlikely event that that do arrive back at Earth in a really messy, unrecoverable state of health, there will be a multitude of techniques to restore them to full health, strength and mobility.

Conclusion

The conclusion is hopefully clear: attempting to implement an AG solution for an early stage H2M mission simply isn’t worth it.

Benefits of travelling to Mars in microgravity:

  • More compact and/or full-featured MTV (Mars Transfer Vehicle).
  • Cheaper.
  • Safer.
  • Simpler.
  • Microgravity is fun.

There are, of course, other ways to create AG, for example, using a spinning cylinder, or by separating the MTV and a counterweight with a fixed steel truss; however, these each come with their own similar set of drawbacks. The most important are cost and complexity. For the first few human missions, we’ll be just fine without AG.

Exercise

While not a complete solution to the effects of microgravity, the most important strategy is daily exercise.

Resistance training

As a qualified personal trainer and lifelong fitness and bodybuilding enthusiast, I’m fortunate to have some specialised knowledge about resistance training, also known as strength training. The simple fact is that the human body responds to loading. If you unload it – for example, by spending time in microgravity – the body will adapt by losing muscle and bone mass, as this isn’t needed to carry the weight of the body. If you load the body – for example by lifting weights several times per week – the body will adapt by increasing muscle and bone mass.

Although there’s a vast body of knowledge around fitness and bodybuilding, once you trim away all the cruft there are really only a few basic principles:

  • The body responds to loading. This is a function of two things:
    • The amount of weight it’s loaded with. The more weight the body is loaded with, the more it will be forced to grow stronger.
    • The amount of time it’s loaded (also called “TUT” or “time under tension”). The more time the body spends loaded, the more it will be forced to adapt.
  • Nutrition is a critical factor, especially protein. Protein should be the primary macronutrient in the diet, as it provides the building blocks (amino acids) to synthesise new muscle tissue for growth and repair. A balance of other nutrients is also essential: complex carbohydrates for energy and recovery, minerals for muscle function, essential fatty acids (EFA’s), vitamins, and lots of water.

Someone can get started in bodybuilding knowing just two things: lift weights, eat protein.

Strength training involves performing a range of exercises to train all the muscles in the body. But is there an exercise that simulates loading due to gravity? Yes, and this exercise is well-known to bodybuilders as being the number one exercise for loading and therefore building almost the entire body: squats. Squats are called the king of exercises because they load the entire load-bearing kinetic chain of the body – the same muscles used in standing, walking, jumping and running. Squats load the body in almost the same way as normal gravity (vertically downwards), but with a greater load. They will surely be revealed as the number one exercise for reversing the deconditioning effects of microgravity.

The intention for Blue Dragon is for the crew to spend 1-2 hours per day doing strength training. Not only squats, because that would be a bit boring and would lead to over-training, but all the so-called “Big 5” exercises: squats, deadlifts, chest press, shoulder press, and chin-ups.

Spending only 5% of each day with the body partially loaded may not seem like enough to offset the effects of microgravity, unless the body is loaded with a larger force than normal Earth gravity. This is, of course, what we do in the gym in order to stimulate muscle growth. By loading the body with heavy weights during training, it becomes stimulated to increase muscle mass. We can use the same principle in space.

Usually when we talk about resistance or strength training, the goal is muscle growth and fat loss. But one of the major problems with microgravity is loss of bone density. Strength training will help with this, too. Research shows that resistance training produces noticeable increases in bone density, and is therefore sometimes recommended for women suffering from osteoporosis. Actually many other conditions have been shown to benefit from strength training, including cardiovascular disease, diabetes, and high blood pressure.

But how can we lift weights in microgravity? Resistance doesn’t have to come from lifting lumps of iron against gravity. There’s plenty of commercial gym equipment based on hydraulics, which will work perfectly well in a microgravity environment.

Yoga

There’s something else we can do in microgravity to stay fit: yoga. Yoga is well-known to have a huge range of benefits for the entire body. Can we do yoga in microgravity? Yes, as long as we have space. Also, yoga positions that emphasise balance won’t apply in microgravity. But flexibility, breathing, clearing the lymphatic system (detoxing), releasing stress stored in the spine and muscles, and the many other benefits of yoga can be gained.

Cardio

Because it’s easier to push blood around the body without gravity, the heart doesn’t have to work as hard. This can cause a decrease in heart mass. But this can be mitigated by regular cardiovascular activity. The heart must be exercised like any other muscle, but it’s exercised differently, using cardiovascular exercise instead of resistance training. The heart rate must be elevated. Although this is achieved for intermittent periods with strength training, cardiovascular exercise serves to sustain an elevated heart rate for longer periods.

EHA (Extra Habitat Activity) on Mars

While on Mars for 1.5 years, the crew will be engaged in considerable additional exercise in the form of regular, perhaps daily, EHA. This will frequently last several hours, perhaps all day in some cases, and during this time they’ll be wearing a MSS (Mars Surface Suit) also known as a marssuit.

The marssuits will probably weigh about 50kg. The spacesuits used by the Apollo astronauts weighed about 100kg, but in the lunar gravity, which is only about 1/6 of Earth’s, they felt like only about 17kg. This is almost what a full traveller’s backpack weighs, and perhaps half what a soldier’s backpack weighs. It’s hard to imagine spending hours walking around and doing hard-core science and exploration on Mars while carrying more than around 20kg, which is why one of the goals for H2M is a marssuit design of 50kg or less. A 50kg marssuit will feel like 19kg on Mars.

The average human weighs 62kg. With a marssuit on, an astronaut on Mars will weigh about 110kg – but they’ll feel like they weigh a total of about 42kg. Thus, they’ll be carrying about 2/3 their normal weight instead of only about 1/3. Going on EHA will be an important part of the necessary physical conditioning to mitigate bone and muscle atrophy. And let’s be honest: if you have a choice between going EHA on Mars and doing squats in the hab, which would you choose?

Blue Dragon daily program

The health and fitness program for the Blue Dragon crew will be something like this:

  • PT 6 days, rest 1 day.
  • Morning exercise: yoga or cardio (alternating days).
  • Afternoon exercise: resistance training or EHA.
  • Appropriate osteoporosis drugs and supplements (e.g. calcium) to mitigate bone loss.
  • A high protein diet to minimise muscle loss and support muscle growth and repair.
  • Plenty of minerals, especially calcium and magnesium.
  • Plenty of water, and a healthy balanced diet.
  • Sufficient sleep.