by Paul Gilster | Jun 28, 2016 | Uncategorized |
With manned missions to Mars in our thinking, both in government space agencies and the commercial sector, the challenge of providing adequate life support emerges as a key factor. We’re talking about a mission lasting about two years, as opposed to the relatively swift Apollo missions to the Moon (about two weeks). Discussing the matter in a new essay, Brian McConnell extends that to 800 days — after all, we need a margin in reserve.
Figure 5 kilograms per day per person for water, oxygen and food, assuming a crew of six. What you wind up with is 24,000 kilograms just for consumables. In terms of mass, we’re in the range of the International Space Station because of our need to keep these astronauts alive. McConnell, a software/electrical engineer based in San Francisco, has been working with Alex Tolley on the question of how we could turn most of these consumables into propellant. The idea is to deploy electric engines that use reclaimed water and waste gases to do the job.
With a nod to the transportation technologies that opened the American West, McConnell and Tolley have dubbed the idea a ‘Spacecoach.’ Centauri Dreams readers will remember Tolley’s Spaceward Ho! and McConnell’s A Stagecoach to the Stars, and the duo have also produced a book on the matter for Springer called A Design for a Reusable Water-Based Spacecraft Known as the Spacecoach. The new essay is a welcome addition to the literature on what appears to be a practical concept.
What fascinates me about the Spacecoach is that it enables us to begin building a space infrastructure that can extend past Mars to include the main asteroid belt. Using electric propulsion driven by a solar photovoltaic array, it achieves higher exhaust velocity than chemical rockets by a factor or ten, pulling much greater delta v from the same amount of propellant. Use water as propellant and you reduce the mass of the system by what McConnell estimates to be a factor of between 10 and 20. Huge reductions in cost follow.
Water as propellant? McConnell comments:
Electric propulsion is not a new technology, and has been used on many unmanned spacecraft. The idea is to use an external power source, typically a solar photovoltaic array, to drive an engine that uses an electrical or magnetic field to heat and accelerate a gas stream to great speed (tens of kilometers per second). Because these engines can achieve much higher exhaust velocity than chemical rockets, 10x or better, they can achieve greater change of velocity (delta v) using the same amount of propellant. This means they can venture to more ambitious destinations, carry more payload, or a combination of both. It also turns out these engines can also use a wide range of materials for propellant, including water.
Image: Rendering of the “kite” design pattern for a Spacecoach, with a person shown to the right for scale. This is but one possible configuration, but McConnell notes that the pattern minimizes the materials required even as it provides a sizeable habitable area. Credit: Rudiger Klaen.
We can imagine such ships as interplanetary vessels that never enter an atmosphere. They’re also completely reusable, allowing costs to be amortized, and their habitable areas are large inflatable structures that can be assembled in space. Thus we travel within a modular spacecraft using external landers and whatever other modules are required by the mission at hand. They’re also, compared to today’s chemical rocket payloads, a good deal safer:
The use of water and waste gases as propellant, besides reducing the mass of the system by a factor of ten or more, has enormous safety implications. 90% oxygen by mass, water can be used to generate oxygen via electrolysis, a simple process. By weight, it is comparable to lead as a radiation shielding material, so simply by placing water reservoirs around crew rest areas, the ship can reduce the crew’s radiation exposure several fold over the course of a mission. It is an excellent heat sink and can be used to regulate the temperature of the ship environment. The abundance of water also allows the life support system to be based on a one-pass or open loop design. Open loop systems will be much more reliable and basically maintenance free compared to a closed loop system such as what is used on the ISS. The abundance of water will also make the ships much more comfortable on a long journey.
Having just watched “To the Ends of the Earth,” a superb BBC story about a ship making a passage from Britain to Australia in the age of sail, the word ‘comfortable’ catches my eye. A Spacecoach is a large craft with huge solar arrays and the capability of being spun to generate artificial gravity, thus alleviating another major health hazard. Conditions are more Earth-like, and the abundance of water makes for what would otherwise seem absurd scenarios. Imagine taking a shower on a flight to Mars! The Spacecoach’s water management makes it possible.
McConnell believes that much of the mission architecture can be validated on Earth without the need to build a full-scale spacecraft, with the major emphasis on tuning up the electric propulsion technology that drives the concept. Using water, carbon dioxide and waste gases to test the engines can be the subject of an engineering competition, after which the engines could be tested in small satellites. Ultimately, manned Spacecoaches could be tested in cislunar space before their eventual deployment deeper into the Solar System.
Image: An artist’s concept of two Bigelow BA 330 inflatable modules configured into a space station. Modules like these could provide habitable areas for a Spacecoach. Credit: Bigelow Aerospace (http://www.bigelowaerospace.com).
McConnell calls the Spacecoach the basis of a ‘real world Starfleet,’ and adds this:
These ships will not be destination specific. They will be able to travel to destinations throughout the inner solar system, including cislunar space, Venus, Mars and with a large enough solar photovoltaic sail, to the Asteroid Belt and the dwarf planets Ceres and Vesta. They’ll be more like the Clipper ships of the past than the throwaway rocket + capsule design pattern we’ve all grown up with, and their component technologies can be upgraded with each outbound flight.
So if you haven’t acquainted yourself with McConnell and Tolley’s earlier work on the Spacecoach in these pages, have a look at Traveling to Mars? Just Add Water!, which recaps the basics of the design and outlines surface exploration strategies from orbiting Spacecoaches by telepresence. The key, though, is to mitigate the propellant issue by making consumables into propellant. Get that right and much else will follow, including the prospect of reliable, safe interplanetary transport of the kind needed to build a truly space-going civilization.
And after that? I’ve always believed that after sending instrumented interstellar probes, we’ll expand into regions outside our Solar System slowly, building space habitats as we go, mining local objects for needed materials. A functioning, space-going civilization builds out that infrastructure from within. It’s the ‘slow boat to Centauri’ scenario — our machines, enabled by artificial intelligence, get there first — but it’s a deep future that includes a human presence around other stars. When I see something as evidently practical as the Spacecoach, I get a renewed jolt of confidence that we at least know how to begin such a journey.
by Paul Gilster | Apr 29, 2016 | Missions |
If you’re planning to make it to the International Space Development Conference in San Juan, Puerto Rico next month, be advised that Brian McConnell will be there with thoughts on a subject we’ve discussed in several earlier posts: A ‘spacecoach’ that uses water as a propellant and offers a practical way to move large payloads (and crews) around the Solar System. Based in San Francisco, Brian is a technology entrepreneur who doubles as a software/electrical engineer. In the essay below, he looks at the spacecoach in relation to the Breakthrough Starshot initiative, where synergies come into play that may benefit both concepts.
by Brian McConnell
The spacecoach is a design pattern for a reusable solar electric spacecraft, previously featured on Centauri Dreams here and developed in A Design for a Reusable Water-Based Spacecraft Known as the Spacecoach (Springer Verlag), which I wrote with Alex Tolley. It primarily uses water as its propellant. This design has numerous benefits, chief among them the ability to turn consumables, ordinarily deadweight, into working mass.
The recent announcement of the Breakthrough Starshot project, which aims to use beamed power to drive ultra lightweight lightsail probes on interstellar trajectories, is of note. This same infrastructure could be used to augment the capabilities and range of spacecoaches (or any solar electric spacecraft), while providing a near-term use for beamed power infrastructure as it is developed and scaled up.
The spacecoach design pattern combines a medium sized solar array (sized to generate between 500 kilowatts and 2 megawatts of peak power at 1AU) with electric propulsion units that use water as propellant (and possibly also waste streams such as carbon dioxide, ammonia, etc). We found that, even when constrained to these power levels, they could fly approximately Hohmann trajectories to and from destinations in the inner solar system. Because consumables are converted into propellant, this reduces mass budgets by an order of magnitude, and effectively eliminates the need for an external interplanetary stage, all while greatly simplifying the logistics of supporting a sizeable crew for long duration missions (more consumables = more propellant).
The primary constraint for space coaches, especially if you want to travel to the outer solar system, is available power. This is an issue for two reasons. First, solar flux drops off by 1/r2, so at Jupiter, a solar array will generate roughly 1/25th the power as it does at Earth distance. Second, trips to more distant locations will typically require a greater delta V (and thus higher exhaust velocity to achieve this with a given amount of propellant). The amount of energy required to generate a unit of impulse scales linearly with exhaust velocity, so the net result is the ship’s power requirements are increased, all while the powerplant’s power density (watts per kilogram of solar array) is decreased.
Testing Beamed Power
Beamed power infrastructure would enable space coaches and solar electric spacecraft in general to operate at higher power levels for a given array size, which would enable them to operate at higher thrust levels, and to utilize higher exhaust velocities to maximize delta V and propellant efficiency. This means they would be able to accelerate faster, achieve higher delta-v, while using less propellant. In effect beamed power to SEP spacecraft will give their operators the equivalent of a nuclear electric power plant (without the nukes).
A spacecoach built for solar only operation would be able to serve as a testbed for beamed power. For example, a space coach departing Earth orbit could be illuminated with a beam that increases its power output by a small amount, say 10% (large enough to make a measurable difference in performance, yet small enough that major modifications are not required to the ship as it just experiences slightly brighter illumination while in beam). At higher light levels, this technique could also be used to simulate lighting and heat loading conditions expected at the inner planets while remaining in near Earth space. Note also that lasers can be tuned to the absorption wavelength(s) of the photovoltaic material, greatly improving conversion efficiency (and reducing heat gain per unit of power delivered). An even cheaper way to build out and test power beaming infrastructure will be with satellites and probes that utilize solar electric propulsion.
The pathway to a system based primarily on beamed power then becomes one based on incremental improvements, both for the ground based facilities and for the ships. This would result in near term applications for the beamed power facilities while the much more technically challenging aspects of the starshot project are sorted out. Meanwhile, satellite and space coach operators could test ships with ever higher levels of beamed power until they hit a limit (heat rejection is probably the main limit to how much power can be concentrated per unit of sail area, as this is similar to concentrated photovoltaics).
The chart below illustrates the power/performance curve by showing the amount of impulse that can theoretically be generated per megawatt hour using electric propulsion, as a function of exhaust velocity. Real world performance will be somewhat lower due to efficiency losses, but this shows the relationship between thrust, ve and power. We see that impulse per MWh varies from 72,000 kg-m/s (ion drive, ve ~ 100,000 m/s) to 1,400,000 kg-m/s (RF arcjet, ve ~ 5000 m/s). A Hall Effect thruster, a flight proven technology, would yield about 300,000 kg-m/s per MWh. Compare this to pure photonic propulsion, which would yield only 12 to 24 kg-m/s per MWh. Clearly photonic propulsion will be necessary to achieve a delta v of 0.2c, but for more pedestrian applications such as satellite orbit raising, launching interplanetary probes or cargo ships from LEO to BEO (beyond earth orbit), electric propulsion will work well at power levels many orders of magnitude lower than what’s required for a starshot.
Driver for an Interplanetary Infrastructure?
Closer to home there could be lots of opportunities to sell beamed power to space operators. It’s costly to launch large payloads beyond low earth orbit (which isn’t cheap in the first place). Meanwhile, payload fairings limit the size of self-deploying solar arrays, which limits the use of electric propulsion for satellites and probes. If one could launch spacecraft with small solar arrays to LEO, and then use beamed power to amplify their power budget they could use electric propulsion to boost themselves to their desired orbits or interplanetary trajectories within a reasonable time frame. The beamed power infrastructure can also be built up incrementally. Early systems would beam 100 kilowatts to 10 megawatts of power to targets measuring meters to tens of meters in diameter. This should be readily achievable, and can be scaled up from there in terms of power output, beam precision, etc. The result: lower costs per kilogram to deliver a payload to its destination or desired orbit compared to all chemical propulsion.
This could make electric propulsion for transit from LEO to GEO and beyond an attractive option. Meanwhile, the power beaming operator would accrue lots of operational experience with beam shaping, tracking objects in orbit, etc, all things that will need to be mastered for the starshot project, while providing an economic foundation for the power beaming facilities during the buildup to their intended purpose.
In fact, one can imagine the starshot project becoming a profitable LEO to BEO (beyond earth orbit) launch operator in its own right. The terrestrial power beaming infrastructure is one component. A standardized “power sail” that can be fitted to many different payloads, from geostationary satellites to interplanetary probes, is another. The power sail would consist of a self-deploying solar array that is sized to work well with beamed power, heat rejection gear, and electric propulsion units. It would use beamed power during its boost phase to rapidly accrue velocity for its planned trajectory, and then as it leaves near Earth space, would transition to use ambient light as its power source from there. Meanwhile these power sails would provide an evolutionary path from conventional spacecraft to solar electric propulsion to the nanocraft envisioned for purely photonic propulsion.
As a starting point, it would be interesting to conduct ground based vacuum chamber tests to see how a variety of PV materials respond to being illuminated with concentrated laser light tuned to their peak absorption wavelengths. What do the conversion efficiencies look like? How much waste heat is generated? How do the materials perform at high temperatures in simulated in-beam conditions? Building on that one can imagine experiments involving cubesats to validate the data from those experiments in real world conditions, and if that all works out, one could scale up from there to build out beamed power infrastructure for use by many types of solar electric vehicles.
Ambitious R&D projects have a way of generating unintended side benefits. It’s possible that the starshot initiative, in addition to being our first step toward the stars, will also make great contributions to travel and exploration within the solar system.
by Paul Gilster | Jul 3, 2015 | Advanced Rocketry |
My view is that the spacecoach, the subject of renewed discussion below by Brian McConnell and a design he and Alex Tolley have created, is the most innovative and downright practical idea for getting crews and large payloads to the planets that I’ve yet encountered. It’s low-cost and uses ordinary consumables as propellant, dramatically revising mission planning. Brian and Alex have continued refining the concept, as explained below in Brian’s essay on a modified version of the rocket equation. Have a look and you’ll see that planning long duration missions or missions with larger crews becomes a much more workable proposition because more consumables translate into more propellant. Could the spacecoach be our ticket to building a space-based infrastructure, with unmistakable implications for even deeper space?
by Brian S McConnell
The spacecoach, first introduced here in Spaceward Ho! and A Stagecoach To The Stars and on spacecoach.org, is based on the idea of using consumables waste streams, such as water, CO2 and gasified waste, as propellant in solar powered electric engines. The idea is to turn what is normally dead weight (and a lot of dead weight on a long duration mission such as to Mars) into propellant. This in turn leads to dramatic reductions in mass, and thus mission cost, because a ship that uses waste from consumables as propellant no longer needs an external stage weighing several times as much to push it to its destination. (If you or your colleagues are working on electric propulsion systems and have test data and citations to share see below)
Image: The spacecoach. Credit: Rendering by Rüdiger Klaehn based on a design by Brian McConnell.
To understand the impact this has, we developed a modified version of the rocket equation that leads with the crew consumable requirements for a given mission, and then calculates the level of engine performance required to fly the mission using only consumables waste streams (mostly water and carbon dioxide) as propellant. This, in turn, yields a minimum mission cost, as no surplus propellant is required, so the mission cost is reduced to the cost to deliver the crew and consumables to the starting point (while the ship itself is reusable so its construction and launch cost can be amortized across many missions).
The rocket equation, shown below, predicts the ship’s delta-v (change in velocity), as a function of specific impulse (a measure of engine performance) and the ship’s mass ratio (starting mass divided by ending mass).
The spacecoach equation, shown below, predicts the minimum exhaust velocity (or specific impulse) required for a cost optimized mission as a function of its delta v and consumables budget.
For programmers, this can also be written in pseudocode as:
Let’s consider a ship that has a 40,000 kg hull mass when empty that is being resupplied for a trip to the Martian moons from EML-2 (Earth Moon Lagrange point 2). With low thrust propulsion this requires a delta-v of roughly 18 km/s roundtrip. The ship has a six person crew, with a 15 kg/person-day budget for water, food and oxygen. The mission is expected to last 600 days, so the consumables budget is 54,000kg.
According to the equation, the engines will need to achieve an exhaust velocity of 21 km/s, which equates to a specific impulse of about 2,100s, assuming 100% of the waste streams are reclaimed (if engines can be made to work with gasified waste, even solids such as trash should be usable as propellant). If we assume that some percentage of the consumables waste streams (e.g. solid waste) cannot be used, say 20%, the engines will need to operate at a specific impulse of 2,900s. This is within the performance envelope of Hall effect thrusters, as well as several other electric propulsion technologies. If the engine performance is not quite good enough, that’s ok, the ship would just be loaded with more water than the crew really needs to compensate for this, or could even support a larger crew. This will increase costs a bit above the minimum possible cost, but also provide safety reserves above what the crew is projected to need.
Next, let’s compare the mass budget for a similar ship using chemical propulsion (e.g. LOX + methane). This mission requires much less delta-v as the ship can exploit the Oberth effect (aka powered flyby) when departing Earth, and on arrival at Mars. To give the chemical ship a further advantage, we’ll assume it uses aerobraking for Mars capture and for Earth return. So the round trip delta-v in that scenario is roughly 8 km/s. The downside is the engine specific impulse is much lower, about 360s for oxygen + methane. Plugging this into the rocket equation results in a propellant mass budget of almost 820,000 kg, over twenty times the mass of the empty hull. This can be optimized by shedding mass, such as waste, spent stages, etc, but not by a great deal without making compromises in terms of consumables, payload, etc (and we’ve already given the chemical ship a big advantage by assuming it can use aerobraking extensively to minimize propulsive delta-v).
Compare this with the spacecoach, where the consumables are the propellant. It would require the delivery of only 54,000 kg of consumables. This is 1/15th what is required for the conventional mission, and should lead to comparable reductions in overall mission costs. Meanwhile the mission itself is much simpler and less risky (all low thrust propulsion, no chemical rockets with catastrophic failure modes, no high G maneuvers, no aerobraking, plus the option to add more crew and/or consumables with little penalty).
The savings come from two sources. Because the consumables are the propellant, there is no need for external propellant. This effect is amplified further because electric engines have much higher exhaust velocities than chemical rockets so even the relatively small consumables mass needed by the crew is sufficient to propel the ship (if electric engines operated at a specific impulse comparable to a chemical rocket, you’d need ten times more water than the crew would consume).
And it gets even better. This is counterintuitive, but it is actually easier to plan for long duration missions with larger crews and high delta v (Ceres, Venus and the Asteroid Belt for example). This is because more consumables = more propellant = higher delta-v given the same engine performance, whereas in a conventional ship you get into a vicious circle of mass incurring more mass. Running the numbers for a 6 person, 1000 day mission to Ceres (delta v : 26.5 km/s roundtrip from EML-2), the consumables budget is 90,000 kg, and the required engine specific impulse is again in the 2000s, which suggests that a ship capable of reaching Mars will be capable of reaching Ceres due to the larger consumables budget.
And speaking of Ceres, it is an enormous water reservoir. While early spacecoaches would be supplied entirely from the Earth, developing the ability to extract water from low gravity sites like Ceres, and possibly the Martian moons, will be a priority as it will reduce the need to launch water from Earth, and thus further reduce operating costs, but even without in situ resource utilization, spacecoaches will be an order of magnitude cheaper to operate, and will be capable of reaching destinations like Ceres that simply cannot be reached by humans using chemical propulsion.
While it takes people a while to see the implications of this (the thinking about how to design a spacecraft is pretty ingrained), the math is pretty straightforward and suggests that order of magnitude cost reductions for interplanetary missions, with greatly expanded range, will be possible with this approach.
If you are working on electric propulsion technology, we are compiling data about the relative performance of different technologies and propellants, especially as it relates to the use of water and waste gases, to provide the community with an easy to search repository of SEP test data and citations. This data will be made available at spacecoach.org as well as on github. If you’d like to submit test data and citations, you can use this form. Contact Brian McConnell at bsmcconnell@gmail.com for more information.
by Paul Gilster | May 18, 2015 | Advanced Rocketry |
I’m glad to see that Brian McConnell will be speaking at the International Space Development Conference in Toronto this week. McConnell, you’ll recall, has been working with Centauri Dreams regular Alex Tolley on a model the duo call ‘Spacecoach.’ It’s a crewed spacecraft using solar electric propulsion, one built around the idea of water as propellant. The beauty of the concept is that we normally treat water as ‘dead weight’ in spacecraft life support systems. It has a single use, critical but heavy and demanding a high toll in propellant.
The spacecoach, on the other hand, can use the water it carries for radiation shielding and climate control within the vessel, while crew comfort is drastically enhanced in an environment where water is plentiful and space agriculture a serious option. Along with numerous other benefits that Brian discusses in his recent article A Stagecoach to the Stars, mission costs are sharply reduced by constructing a spaceship that is mostly water. McConnell and Tolley believe that cost reductions of one or two orders of magnitude are possible. Have a look, if you haven’t already seen it, at Alex’s Spaceward Ho! for an imaginative look at what a spacecoach can be.
ISDC is a good place to get this model before an audience of scientists, engineers, business contacts and educators from the military, civilian, commercial and entrepreneurial sectors. ISDC 2014 brought over 1000 attendees into the four-day event, and this year’s conference brings plenary talks and speakers from top names in the field: Buzz Aldrin, Charles Bolden, Neil deGrasse Tyson, Peter Diamandis, Lori Garver, Richard Garriott, Bill Nye, Elon Musk and more. My hope is that a concept as novel but also as feasible as the spacecoach will resonate.
Image: Ernst Stuhlinger’s concept for a solar powered ship using ion propulsion, a notion now upgraded and highly modified in the spacecoach concept, which realizes huge cost savings by its use of water as reaction mass. This illustration, which Alex Tolley found as part of a magazine advertisement, dates from the 1950s.
Towards Building an Infrastructure
We have to make the transition from expensive, highly targeted missions with dedicated spacecraft to missions that can be flown with adaptable, low-cost technologies like the spacecoach. Long-duration missions to Mars and the asteroid belt will be rendered far more workable once we can offer a measure of crew safety and comfort not available today, with all the benefits of in situ refueling and upgradable modularity. Building up a Solar System infrastructure that can one day begin the long expansion beyond demands vehicles that can carry humans on deep space journeys that will eventually become routine.
The response to the two spacecoach articles here on Centauri Dreams has been strong, and I’ll be tracking the idea as it continues to develop. McConnell and Tolley are currently working on a book for Springer that should be out by late summer or early fall. You can follow the progress of the idea as well on the Spacecoach.org site, where the two discuss a round-trip mission from Earth-Moon Lagrange point 2 (EML-2) to Ceres, a high delta-v mission in which between 80 and 90 percent of the mission cost is the cost of delivering water to EML-2.
The idea in this and other missions is to use a SpaceX Falcon 9 Heavy to launch material to low-Earth orbit, with a solar-electric propulsion spiral out to EML-2 (the crew will later take a direct chemical propulsion trajectory to EML-2 to minimize exposure time in the Van Allen belts). The water cost is about $3000 per kilogram. The Falcon 9 Heavy should be able to deliver 53,000 kilograms to low-Earth orbit per launch. McConnell and Tolley figure about 40,000 kilograms of this will be water, while the remainder will be other equipment including the module engines and solar arrays. From EML-2, various destinations can be modeled, with values adjustable within the model so you can see how costs change with different parameters.
The online parametric model has just been updated to calculate mission costs as a function of the number of Falcon Heavy 9 launches required. You can see the new graph below (click on it to enlarge). At a specific impulse of 2000s or better for the solar-electric power engines, only two launches are required for most missions, one taking the crew direct to EML-2, the other carrying the water and durable equipment on a spiral orbit out from LEO. It is only the most ambitious destinations like Ceres that require three launches. At $100 million per launch, even that mission is cheap by today’s spaceflight standards.
Brian notes in a recent email that the launches do not need to be closely spaced, because the spiral transfer from LEO to EML-2 takes months to complete. The crew only goes when everything else is in place at EML-2. For more on this model, see spacecoach.org. I’ll be interested to hear how the idea is received at ISDC, and how the upcoming publication of the spacecoach book helps to put this innovative design for interplanetary transport on the map.
by Paul Gilster | Jan 26, 2023 | Culture and Society |
Colonies on other worlds are a staple of science fiction and an obsession for rocket-obsessed entrepreneurs, but how do humans go about the business of living long-term once they get to a place like Mars? Alex Tolley has been pondering the question as part of a project he has been engaged in with the Interstellar Research Group. Martian regolith is, shall we say, a challenge, and the issue of perchlorates is only one of the factors that will make food production a major part of the planning and operation of any colony. The essay below can be complemented by Alex’s look at experimental techniques we can use long before colonization to consider crop growth in non-terrestrial situations. It will appear shortly on the IRG website, all part of the organization’s work on what its contributors call MaRMIE, the Martian Regolith Microbiome Inoculation Experiment.
by Alex Tolley
Introduction: Food Production Beyond Hydroponics
Conventional wisdom suggests that food production in the Martian settlements will likely be hydroponic. Centauri Dreams has an excellent post by Ioannis Kokkinidis on hydroponic food production on Mars, where he explains in some detail the issues and how they are best dealt with, and the benefits of this form of food production [1]
Still from a NASA video on a Mars base showing the hydroponics section.
A recent NASA short video on a very stylish possible design for a Mars base (see still above) shows a small hydroponics zone in the base, although its small size and what looks like all lettuce production would not be sufficient to feed one person, and that is before the monotonous diet would drive the crew to wish they had at least some potatoes from Mark Watney’s stash that could be cooked in a greater variety of ways.
I would tend to agree with the hydroponic approach, as well as other high-tech methods, as these food production techniques are already being used on Earth and will continue to improve, allowing a richer food source without needing to raise animals. Kokkinidis raises the issue of animal meat production for various cuisines, but in reality, the difficulties of transporting the needed large numbers of stock for breeding, as well as the increased demand for primary food production, would seem to be a major issue. [It should be noted that US farming occupies perhaps 2% of the population, yet most commentators on Mars groups seem to think that growing food on Mars will be relatively easy, with preferred animals to provide meat. How many Mars base personnel would be comfortable killing and preparing animals for consumption, even mucking out the pens?]
Hydroponics today is used for high-value crops because of the high costs. Many crops cannot be easily grown in this way. For example, it would be very difficult to grow tree fruits and nuts hydroponically, even though tree wood would be a very useful construction material. On Earth, hydroponics gains the highly desirable much-increased production per unit area coupled with a very high energy cost. It also requires inputs from established industrial processes which would have to be set up from scratch on Mars. Should there need to be lighting as well, low-energy LEDs would be hard to manufacture on Mars and would, initially at least, be imported from Earth.
Hydroponics is attractive to those with an engineering mindset. The equipment is understood, inputs and outputs can be measured and monitored, and optimized, and it all seems of a piece with the likely complexity of the transport ships and Mars base technology. It may even seem less likely to get “dirt under the fingernails” compared to traditional farming, a feature that appeals to those who prefer cleaner technologies. Unfortunately, unlike on Earth, if a critical piece of equipment fails, it will not be easily replaceable from inventory. Some parts may be 3D printable, but not complex components, or electronics. Failure of the hydroponic system due to an irreplaceable part failure would be catastrophic and lead to starvation long before a replacement would arrive from Earth. If ever there was a need for rapid cargo transport to support a Martian base, this need for rapid supply delivery would be a prime driver [4].
Soil from Regolith
Could more traditional dirt farming work on Mars, despite the apparent difficulties and lack of fine control over plant growth? The discovery that the Martian regolith has toxic levels of perchlorates and would make a very poor soil for plants seems to rule out dirt farming. If the Gobi desert is more hospitable than Mars, then trying to farm the sands of Mars might seem foolhardy, even reckless.
However, after working on a project with the Interstellar Research Group (IRG), I have to some extent changed my mind. If the Martian regolith can be made fertile, it would open up a more scalable and flexible method to grow a greater variety of plant crops than seems possible with hydroponics. Scaling up hydroponics requires far more manufacturing infrastructure than scaling up farming with an amended regolith if regolith remediation does not require a lot of equipment.
So the key questions are how to turn the regolith into viable soil to make such a traditional farming method viable, and what does this farming buy in terms of crop production, variety, and yields?
The first problem is to remove the up to 1% of perchlorates in the regolith that are toxic to plants. While perchlorates do exist naturally in some terrestrial soils, such as the Atacama desert, they are at far lower concentrations. Perchlorates are used in some industrial processes and products (e.g. rocket propellant, fireworks), and spills and their cleanup are monitored by the Environmental Protection Agency (EPA) in the USA. Chlorates were used as weedkillers and are potent oxidizers, a feature that I used in my teenage rocket experimentation, but are now banned in the EU.
There are 2 primary ways to remove perchlorates. If there is a readily available water supply, the regolith can be washed and the water-soluble perchlorates can be flushed away. The salt can be removed from the perchlorate solution with a reverse osmosis unit, a mature technology in use for desalination and water purification today. In addition, agitation of the regolith sand and dust can be used to remove the sharp edges of unweathered grains. This would make the regolith far safer to work with, and reduce equipment failure due to the abrasive dust damaging seals and metal joints. Agitation requires the low technology of rotating drums filled with a slurry of regolith and water.
A second, and more elegant approach, is to bioremediate with bacteria that can metabolize the regolith in the presence of water [5,6,7,8]. While it would seem simple to just sprinkle the exposed Martian surface with an inoculant, this cannot work, if only because the temperature on the surface is too cold. The regolith will have to be put into more clement conditions to maintain the water temperature and at least minimal atmospheric pressure and composition. At present, it is unknown what minimal conditions would be needed for this approach to work, although we can be fairly certain that terrestrial conditions inside a pressurized facility would be fine. There are a number of bacterial species that can metabolize chlorates and perchlorates to derive energy from ionized salts. A container or lined pit of graded regolith could be inoculated with suitable bacteria and the removal of the salt monitored until the regolith was essentially free of the salt. This would be the first stage of regolith remediation and soil preparation.
There is an interesting approach that could make this a dual-use system that offers safety features. The bacteria can be grown in a bioreactor, and the enzymes needed to metabolize perchlorates extracted. It has been proposed that rather than fully metabolizing the salt to chloride, enzymes could be applied that will stop at the release of free oxygen (O2). This can be used as life support or oxidant for rocket fuel, or even combustion engines on ground vehicles. The enzymes could be manufactured by gene-engineered single-cell organisms in a bioreactor, or the organisms can be applied directly to the regolith to release the O2 [10]. The design of the Spacecoach by my colleague, Brian McConnell, and me used a similar principle. As the ship used water for propellant and hull shielding, in the case of an emergency, the water could be electrolyzed to provide life-supporting O2 for a considerable time to allow for rescue [9]. Extracting oxygen from the perchlorates with enzymes is a low-energy approach to providing life support in an emergency. A small, portable, emergency kit containing a plastic bag and vial of the enzyme, could be carried with a spacesuit, or larger kits for vehicles and habitat structures.
After the perchlorate is removed from the regolith, what is left is similar to broken and pulverized lava. It may still be abrasive, and need to be abraded by agitation as in the mechanical perchlorate flushing approach.
So far so good. It looks like the perchlorate problem is solved, we just need to know if it can be carried out under conditions closer to Martian surface conditions, or whether it is best to do the processing under terrestrial or Mars base conditions. If the bacterial/enzyme amendment can be done in nothing more than lined and covered pits, or plastic bags, with a heater to maintain water at an optimum temperature, that would be a plus for scalability. If the base is located in or near a lava tube, then the pressurized tube might well provide a lot of space to process the regolith at scale.
Like lunar regolith, it has been established that perchlorate-free regolith is a poor medium for plant growth. Experiments on Mars Regolith Simulant (MRS) under terrestrial conditions of temperature, atmospheric composition, and pressure, indicate that the MRS needs to be amended to be more like a terrestrial soil. This requires nutrients, and ideally, structural organic carbon. If just removing the perchlorates, adding nutrients, and perhaps water-retaining carbon was all that was needed, this might not be too dissimilar to a hydroponic system using the regolith as a substrate. But this is really only part of the story in making fertile soil.
Nitrogen in the form of readily soluble nitrates can be manufactured on Mars chemically, using the 1% of N2 in the atmosphere. It is also possible nitrogen rich minerals on Mars may be found too. Phosphorus is the next most important macronutrient. This requires extraction from the rocks, although it is possible that phosphorus-rich sediments also may be found on Mars.
To generate the organic carbon content in the regolith, the best approach is to grow a cover crop and then use that as the organic carbon source. Fungal and bacterial decomposition, as well as worms, decompose the plants to create humus to build soil. Vermiculture to breed worms is simple given plant waste to feed on, and worm waste makes a very good fertilizer for plants. Already we see that more organisms are going to have to be brought from Earth to ensure that decomposition processes are available. In reality, healthy terrestrial soils have many thousands of different species, ranging in size from bacteria to worms, and ideally, various terrestrial soils would be brought from Earth to determine which would make the best starting cultures to turn the remediated regolith into a soil suitable for growing crops.
Ioannis Kokkinidis indicated that Martian light levels are about the same as a cloudy European day. Optimum growth for many crops needs higher intensity light, as terrestrial experiments have shown that for most plants, increasing the light intensity to Earth levels is one of the most important variables for plant growth. This could be supplied by LED illumination or using reflective surfaces to direct more sunlight into the greenhouse or below-ground agricultural area.
One issue is surface radiation from UV and ionizing radiation. This has usually resulted in suggestions to locate crops below ground, using the surface regolith as a shield. This may not be necessary as a pressurized greenhouse with exposure to the negligible pressure of Mars’ atmosphere, could support considerable mass on its roof to act as a shield. At just 5 lbs/sq.in, a column of water or ice 10 meters thick could be supported. It would be fairly transparent and therefore allow the direct use of sunlight to promote growth, supplemented by another illumination method.
Soil is not a simple system, and terrestrial soils are rich ecosystems of organisms, from bacteria, fungi, and many phyla of small animals, as well as worms. These organisms help stabilize the ecosystem and improve plant productivity. Bacteria release antibiotics and fungi provide the communication and control system to ensure the bacterial balance is maintained and provide important growth coordination compounds to the plants through their roots. The animals feed on the detritus, and the worms also create aeration to ensure that O2 reaches the animals and aerobic fungi and bacteria.
Most high-yield, agricultural production destroys soil structure and its ecosystems. The application of artificial fertilizers, herbicides to kill weeds, and pesticides to kill insect predators, will reduce the soil to a lifeless, mineral, reverting it back to its condition before it became soil. The soil becomes a mechanical support structure, requiring added nutrients to support growth.
Some farmers are trying new ideas, some based on earlier farming methods, to restore the fertility of even poor soils. This requires careful planting schedules, maintenance of cover crops, and even no-tilling techniques that emulate natural systems. Polyculture is an important technique for reducing insect pests. Combined, these techniques can remediate poor soils, eliminate fertilizers and agricultural chemicals, improve farm profitability, and even result in higher net yields than current farm practices. [11]
Without access to industrial production of agricultural chemicals and nutrients, these experimental farming practices will need to be honed until they work on Mars.
Given we have regolith-based soil what sort of crops can be grown? Almost any terrestrial crop as long as the soil conditions, drainage, pH, and illumination can be maintained.
Unlike on Earth where crops are grown where the conditions are already best, on Mars, it might well be that the crops grown will be part of a succession of crops as the soil improves. For example, in arid regions, millet is a good crop to grow with limited water and nutrients as it grows very easily under poor conditions. Ground cover plants to provide carbon and that fix nitrogen might well be a rotation crop to start and maintain the soil amendment. As the soil improves, the grains can be increased to include wheat and maize, as well as barley. With sufficient water, rice could be grown. None of these crops require pollinators, just some air circulation to ensure pollination.
For proteins, legumes and soy can be grown. These will need pollinating, and it might well be worth maintaining a greenhouse that can include bees. Keeping this greenhouse isolated will prevent bees from escaping into the base. As most of our foods require insect pollination, root crops like potatoes, carrots, and turnips, can be grown, as well as leafy greens like lettuce, and cabbage. The pièce de résistance that dirt farming allows is tree crops. A wide variety of fruit and nuts can be grown. Pomegranates are particularly suited to arid conditions. The leaf litter from such deciduous trees will be further input to improve the soil.
So the soil derived from regolith should allow a wider variety of crops to be grown, and with this, the possible variety of cuisine dishes can be supported. Food is an important component of human enjoyment, and the variety will help to keep morale high, as well as provide an outlet for prospective cooks and foodies.
Are there other benefits? As any gardener knows, growing food in the dirt is less time-consuming than hydroponics as the system is more stable, self-correcting, and resilient. This should allow for more time to be spent on other tasks than constantly maintaining a hydroponic system, where a breakdown must be fixed quickly to prevent a loss.
Meat production is beyond the scope of this essay. I doubt it will be of much importance for two main reasons. Meat production is a very inefficient use of energy. It is far better to eat plants directly, rather than convert them to meat and lose most of the captured energy. The second is the difficulty of transporting the initial stocks of animals from Earth. The easiest is to bring the eggs of cold-blooded animals (poikilotherms) and hatch them on Mars. Invertebrates and perhaps fish will be the animals to bring for food. If you can manage to feed rodents like rabbits on the ship, then rabbits would be possible. But sheep, goats, and cows are really out of the question. A million-resident city might best create factory meat from the crops if the needed ingredients can be imported or locally manufactured. My guess is that most Mars settlers will be Vegetarian or Vegan, with the few flexitarians enjoying the occasional fish or shrimp-based meal.
If you have read this far, it should be obvious that dirt farming sustainably, is not simple, nor is it easy or quick. A transport ship carrying settlers to Mars will have to supply food to eat until the first food crops can be grown. That food will likely be some variant of the freeze-dried, packaged food eaten by astronauts. Hopefully, it will taste a lot better. The fastest way to grow food crops will be hydroponics. All the kit and equipment will have to be brought from Earth. With luck, this system will reduce the demand for packaged food and become fairly sustainable, although nutrients will have to be supplied, nitrogen in particular. I don’t see sacks of nitrogen fertilizer being brought down to the surface, but instead, there may be a chemical reactor to extract the nitrogen in the Martian air and either create ammonia or nitrates for the hydroponic system.
But if the intention, as Musk aims, is to make Mars a second home, starting with 1 million residents, the size of the population that is large enough to provide the skills for modern civilization, then food production is going to need to be far more extensive than a hydroponics system in every dome or lava tube. The best way is to grow the soil as discussed above. This will not be quick and may take years before the first amended regolith becomes rich loamy, fertile soil. The sterile conditions on Mars mean that there will be no free ecosystem services. Every life form will have to originate on Earth and be transported to Mars. But life replicates, and this replication is key to success in the long term. There will be a mixture of biodiverse allotments and tracts of large-scale arable farming. Without some new technology to deflect ionizing radiation, the Martian sunlight will probably need to be indirect and directed to the crops protected by mass shields. Every square meter of Martian sunlight will only be able to support ½ a square meter of crops, so there may need to be an industry manufacturing polished metal mirrors to collect the sunlight and redirect it.
Single-cells for artificial food
Although our sensibilities suggest that the Martian settlers will want real food grown from recognizable food crops, this may be a false assumption. In the movie 2001: A Space Odyssey, Kubrick ignored Clarke’s description in his novel of how food was provided and eaten, with the almost humorous showing of liquid foods with flavors served to Heywood Floyd on his trip to the Moon.
Still from the movie 2001: A Space Odyssey. The flight attendant (Penny Brahms) is bringing the flavored, liquid food trays to the passenger and crew.
Because the Moon does not have terrestrial day-night cycles, the food was single-celled and likely grown in vats, then processed to taste like the foods they were substituting for.
Michaels: Anybody hungry?
Floyd: What have we got?
Michaels: You name it.
Floyd: What’s that, chicken?
Michaels: Something like that.
Michaels: Tastes the same anyway.
Halvorsen: Got any ham?
Michaels: Ham, ham, ham..there, that’s it.
Floyd: Looks pretty good
Michaels: They are getting better at it all the time.
Still from the movie 2001: A Space Odyssey. Floyd and the Clavius Base personnel select sandwiches made from processed algae. Above is the conversation Floyd (William Sylvester) has with Halvorsen (Robert Beatty) and Michaels (Sean Sullivan) on the moon bus on his way to TMA1.
This is where food technology is currently taking us.
Single-cell protein has been available since at least the 18th century with edible yeast. Marmite or Vegemite is a savory, yeast-based, food spread that is an acquired taste. Today there is revived interest in various forms of SCP, some of which are commercially available for consumers, such as Quorn made from the micro-fungus, Fusarium venenatum. The advantage of single cells is that the replication rate is so high that the raw output of bacterial cells can be more than doubled daily. The technology, at least on Earth, could literally reduce huge tracts of agricultural land use, especially of meat animals. However, it does require all the inputs that hydroponic systems require, and further processing to turn the cells into palatable foods including simulated meats. Should such single-cell food production become the basic way to ensure adequate calories and food types for settlers, I suspect that real food will be as desirable as it was for Sol Roth and Detective Thorn in Soylent Green.
Still from the movie Soylent Green. Sol Roth (Edward G. Robinson) bites into an apple, stolen by Detective Thorn (Charlton Heston), that he hasn’t tasted in many years since terrestrial farming collapsed.
Physical and Mental Health with Soil
However, even if single-cell bioreactors, food manufacturing, and hydroponics do become the main methods of providing food, that does not mean that creating fertile soils from the regolith is a waste of effort. Surrounded by the ochres of the Martian landscape, the desire to see green and vegetation may be very important for mental health. Soils will be wanted to grow plants to create green spaces, perhaps as lavish as that in Singapore’s Changi Airport. Seeds brought from Earth are a low-mass cargo that can exploit local atoms to create lush landscaping for the interior of a settlement.
Changi Airport, Singapore. A luxurious and restful interior space of tropical plants and trees.
There is a tendency to see life on Mars not just as a blank canvas to start afresh, but also as a sterile world free of diseases and other biological problems associated with Earth. Asimov’s Elijah Bailey stories depicted “germ-free” Spacers as healthier and far longer-lived than Earthmen In their enclosed cities. We now know that our bodies contain more bacterial cells than our mammalian cells. We cannot live well without this microbiome that helps us withstand disease, digest our foods, and even influence our brain development. There is even a suggestion that children that have not been exposed to dirt become more prone to allergies later in life. Studies have shown that most animals have a microbiome with varying numbers of bacterial species. As Mars is sterile, at least as regards a rich terrestrial biosphere, it might well make sense to “terraform” it at least within the settlement cities. Creating soils that will become reservoirs for bacteria, fungi, and a host of other animal species will aid human survival and may become a useful source of biological material for the settlers’ biotechnology.
If Mars is to become a second home for humanity, it will need more people than the villages and small towns that the historical migrants to new lands create. The needed skills to make and repair things are vastly larger than they were less than two centuries ago. Technology is no longer limited to artisans like carpenters, wheelwrights, and blacksmiths, with more complex technology imported from the industrial nations. Now technologies depend on myriad specialty suppliers and capital-intensive factories. Mars will need to replicate much of this in time, which requires a large population with the needed skills. A million people might be a bare minimum, with orders more needed to be largely self-sufficient if the population is to be the backup for a possible future extinction event on Earth. Low-mass, high-value, and difficult-to-manufacture items will continue to be imported, but much else will best be manufactured locally, with a range of techniques that will include advanced additive printing. But some technologies may remain simple, like the age-old fermentation vats and stills. After all, how else will the settlers make beer and liquor for partying on Saturday nights?
References:
Kokkinidis, I (2016) “Agriculture on Other Worlds” https://centauri-dreams.org/2016/03/11/agriculture-on-other-worlds/
Kokkinidis, I (2016) “Towards Producing Food in Space: ESA’s MELiSSA and NASA’s VEGGIE”
https://centauri-dreams.org/2016/05/20/towards-producing-food-in-space-esas-melissa-and-nasas-veggie/
Kokkinidis, I (2017) “Agricultural Resources Beyond the Earth” https://centauri-dreams.org/2017/02/03/agricultural-resources-beyond-the-earth/
Higgins, A (2022) “Laser Thermal Propulsion for Rapid Transit to Mars: Part 1”
https://centauri-dreams.org/2022/02/17/laser-thermal-propulsion-for-rapid-transit-to-mars-part-1/
Balk, M. (2008) “(Per)chlorate Reduction by the Thermophilic Bacterium Moorella perchloratireducens sp. nov., Isolated from Underground Gas Storage” Applied and Environmental Microbiology, Jan. 2008, p. 403–409 Vol. 74, No. 2
https://journals.asm.org/doi/10.1128/AEM.01743-07
Coates J.D., Achenbach, L.A. (2004) “Microbial Perchlorate Reduction: Rocket-Fueled Metabolism”, Nature Reviews | Microbiology Volume 2 | July 2004 | 569
doi:10.1038/nrmicro926
Hatzinger P.B. &2005) , “Perchlorate Biodegradation
for Water Treatment Biological reactors”, 240A Environmental Science & Technology / June 1, 2005 American Chemical Society
Kasiviswanathan P, Swanner Ed, Halverson LJ, Vijayapalani P (2022) “Farming on Mars: Treatment of basaltic regolith soil and briny water simulants sustains plant growth.” PLoS ONE 17(8): e0272209.
https://doi.org/10.1371/journal.pone.0272209
Gilster, P “Spacecoach: Toward a Deep Space Infrastructure“, https://centauri-dreams.org/2016/06/28/spacecoach-toward-a-deep-space-infrastructure/
Davila A.F. et all (2013) “Perchlorate on Mars: a chemical hazard and a resource for humans” International Journal of Astrobiology 12 (4): 321–325 (2013)
doi:10.1038/nrmicro926doi:10.1017/S1473550413000189
Monbiot, G. (2022) Regenesis: Feeding the World Without Devouring the Planet Penguin ISBN: 9780143135968
