​Environmental Issues

Now that we have an idea of what we might want to grow and how we could grow it, let's take a look at the physical side of our farm on Mars.

Growing food on Mars presents several significant challenges. While research on the International Space Station suggests plants can grow in microgravity, we don't really know how the reduced gravity on Mars might affect Earth crops. Several issues need to be studied and explored, most of which can be done, and in some cases has already been done, here on Earth, including:

​lighting

atmospheric pressure

CO 2 content,

content, oxygen levels, and

radiation protection

Lighting

Mars surface only receives about half the sunlight Earth does, and any pressurized greenhouse enclosure will block the sunlight even more. That means the natural light source will have to be supplemented by artificial sources​.

And that means that farming on Mars will take a lot of power.

D. Marshall Porterfield, Life and Physical Sciences division director at NASA's Human Exploration and Operations Mission Directorate. NASA has been studying how to use lower energy LED lighting to give plants the wavelengths of light they need to boost efficiency - and only those wavelengths.

It's not trivial.

As Porterfield said:

In terms of the systems engineering required, it's not an insignificant challenge.

The good news is that LED lighting is becoming a common practice in self-enclosed growing containers like ​Freight Farm's LGM 2105 hydroponic growing system.

And that means the energy requirements can be easily calculated and planned for in any settlement design.

Environmental Pressure

Since the greenhouse will be a self-contained enclosure, do we really need to keep it at the same atmospheric pressure we have here on Earth?

Researchers have been studying whether plants can survive under different pressures than normally found at sea level here on Earth. We don't want higher pressure, though -- the more pressure inside a greenhouse, the more massive that greenhouse must be to contain it.

But what about lower pressures?​

As Robert Ferl, director of the Interdisciplinary Center for Biotechnology Research at the University of Florida said:

You don't have to inflate that greenhouse to Earth-normal pressure in order for plants to grow. Maintaining a full atmosphere of pressure is difficult on a planetary surface. You can take plants down to a tenth of an atmosphere and they'll still function.

But what happens to the gardeners at pressures that low?

With one-tenth normal atmospheric pressure , humans may need to wear some sort of environmental suit to protect themselves. A lower pressure also means the greenhouse will need to be sealed off from the crew's living quarters, meaning airlocks and all the complexities that implies.

As Taber MacCallum, chief executive officer of Paragon Space Development Corp., said

Gardening in a pressure suit is going to be a real trick.

But would a pressure suit really be necessary? Perhaps a biosuit would be enough.

The Armstrong Limit, named after the founder of the US Air Force's Department of Space Medicine Harry George Armstrong, is the lowest pressure a human body can withstand before the water in our blood starts to boil -- about 6.6% normal atmospheric pressure.

That means we could survive in the low pressure environment Ferl discribes -- one-tenth normal atmosphere -- At least for short periods of time. We would need some sort of breathing apparatus, though, since the oxygen level would be so low, but it could be done.

We might also be in danger of hypoxia -- at least if no pre-breathing is done before entering the farm.

NOTE: Hypoxia can occur when the human body undergoes rapid changes in environmental pressure, like when astronauts get into a space suit. Or when divers surface too quickly. The change in pressure causes the nitrogen to boil, creating 'bubbles' in the blood and bursting blood vessels -- the 'bends'. It's why astronauts 'pre-breathe' before space walks or divers pause and acclimate before surfacing. Pressures need to equalize slowly enough for the body to adapt.

A better choice, therefore, may be to raise the pressure in our farm high enough that gardeners could comfortably operate without an environmental suit, or even a biosuit.

Perhaps an atmosphere of about 50% Earth normal - about the same as the top of Mount Everest.

That would still offer benefits to the plants, while minimizing issues for the farmers.​

Studies on this issue still need to be done to find the best option for a farm on Mars.​

CO 2 Content

We all know that carbon dioxide is critical to plant growth and development. Photosynthesis, the process through which plants use light to create food, requires it.

On earth, normal CO 2 levels range from 300-500 parts per million (ppm). If you are growing in a greenhouse, though, those levels will be decrease as the plants use it up during photosynthesis.

In a closed environment, therefore, CO 2 needs to be constantly reintroduced in order to maintain optimal levels. Luckily, there is plenty of CO 2 on Mars. If we don't get enough from simply breathing, we can always tap into air outside (Mars' atmosphere is 95% CO 2 )

But, for growing plants, we need to ask ourselves if maintaining this level of CO 2 is the best we can do. What if we increased it?

Experiments have been done that show increasing the CO 2 to three to four times the 'normal' level is actually quite beneficial for growing plants -- up to 1500 ppm,

With CO 2 maintained at this level, yields can be increased by as much as 30%!

Commercial greenhouses know this, which is why they use CO 2 generators to increase their production.

But what does that do to the gardeners?

1,500 ppm is not a problem for people. Humans can tolerate CO 2 levels up to about 10,000 ppm -- the equivalent of 1% concentration, as explained in this report from Inspectapedia, before they start to feel a little drowsy or light-headed.

​NOTE: 1,000,000 ppm of a gas = 100% concentration, so 10,000 ppm = 1%

Most people won't even be aware of the increased levels until the concentration hits 20,000 ppm, or 2%. At these levels, you might experience a heaviness in the chest and find it hard to breathe.

After a few hours, you could start to develop "acidosis" -- an acid condition in the blood, which, if not treated, could cause death.

But it isn't until a 5% concentration is reached that ​CO2 becomes directly toxic.

Luckily, our greenhouse will never need to reach concentration levels that high, but even at 1,500 ppm -- about 0.15%​ -- it would be prudent for workers who tend the farm over long periods to have breathing gear.

Oxygen

One thing most people don't think about in greenhouse operation is the concentration level of oxygen in the air.

Although we die of anoxia when oxygen levels drop below 11 percent, too little oxygen is not really the problem for a farm on Mars.

It's having too much oxygen.

Like carbon dioxide, t​oo much oxygen will kill you. It's a gradual effect -- in a high oxygen environment you will, over the course of a few days, develop an inflammation of the lungs and eventually die.

But it's not just the effect a oxygen-rich environment has on your body. The more immediate impact is the increased likelihood of fire.

It's one of the things MIT studies pointed to as a reason Mars One plans are technically flawed.

In their argument, oxygen levels rose quickly above safe levels​ and would require the introduction of nitrogen to sustain normal levels. This would quickly deplete the nitrogen that was brought with the colonists.

You can't just simply vent the oxygen. That would also vent the nitrogen.

And you need the nitrogen to maintain ​a 'safe' oxygen level that doesn't make fire such a risk.

So what's a high level? How much oxygen is 'unsafe'?

While normal atmosphere contains between 20.8 and 21 percent oxygen, ​OSHA, the US government's Occupational and Safety Health Agency, defines as oxygen deficient any atmosphere that contains less than 19.5 percent oxygen, and as oxygen enriched, any atmosphere that contains more than 22 percent.

As stated on their web site:​

Oxygen-deficient atmospheres may be created when oxygen is displaced by inerting gases, such as carbon dioxide, nitrogen, argon, or the ship's inert gas system or firefighting system. Oxygen can also be consumed by rusting metal, ripening fruits, drying paint, or coatings, combustion, or bacterial activities. Oxygen-enriched atmospheres may be produced by certain chemical reactions. Oxygen enriched atmospheres present a significant fire and explosion risk.

The plants don't really care, and humans can survive in an oxygen-enriched environment. Again, the problem is the fire risk.

We will need to find a local source of nitrogen on Mars (or possibly some other inert gas - deep sea divers use helium) or develop a way to separate the nitrogen from the air and reuse it.

Radiation

As in all aspect of Martian life, farmers and plants must also contend with the issue of radiation. Mars lacks Earth's thick protective atmosphere, so particles from space reach its surface that would be damaging to both people and plants.

Some kind of shielding or mitigation will be necessary.

As Taber MacCallum from Paragon Space Development Corp. commented:

To maintain the infrastructure is the expensive part to grow plants, coupled with the need for redundancy if something fails.

The winner of NASA's recent 3D Printed Hab Design Contest had a novel approach. They proposed building a habitat out of martian ice. Not only would that provide light during the day, it would also provide a thick layer of radiation protection.

That's one way to do it. But are there others? Could you bury the hab -- and the greenhouse?

It starts to make you think ...​