PRE2017 3 Groep1

Project statement

Concept

In the year 2032 the Mars One organization plans on landing the first humans on Mars and establish a permanent human colony there. The first humans will start to build an empire by building a base where people are able to live. After the first base is built, it will be developed further and further. In the end, people on Mars should be able to live there without any help from planet earth. Mars should become a self-sustainable environment.

Before we get there, a lot needs to happen. Right now, Mars does not have an atmosphere, so there is hardly any oxygen in the air. All of the water present on Mars is in the form of ice and lies far beneath the surface. Right now, no one is able to live there. Nothing is able to grow there. This needs to change.

In this project, we want to get a step closer to life on Mars. We want to do this by taking a look at the implementation of food production for the planet. We chose to focus on the plantation of potatoes, since potatoes are very nutrient and since there has already been done some research on potato plantation on Mars. We chose to for the breed Escort, since this is a long cycle potato. This means it takes about nine months for the potato to grow, but it will get way bigger than short cycle potatoes. In the end this will be more efficient for large scale food production.

For this purpose, we are going to create a fully autonomous greenhouse, which is able to plant and harvest food to fertilize and to water its crops. The greenhouse, which we are going to create, will consist of four walls and a rounded roof, all filled with a great amount of isolation material. The slightly tilted roof is necessary because of the fact that Mars has no atmosphere. Because there is no atmosphere, rocks and other junk from outer space will fall down on Mars, opposed to what happens on earth, where these rocks burn up in the atmosphere. With a slightly tilted roof, everything that falls on top of the roof will slide right off.

The isolation material in the walls and in the roof absorbs all the light coming in from outside the greenhouse. This way, we can create our own earthly cycle inside the greenhouse. This will be done using heating lamps. This is very efficient since the temperature and light can now be controlled by the same controller. An earthly cycle is favorable, because we know potatoes will grow under these circumstances.

Inside the greenhouse, the planting and harvesting will be done by an autonomous farming robot. This robot will be based on robots that are already being used on earth. The robot will look like a tractor. It will come in action only when it gets a signal that the potatoes need to be harvested. The robot will then harvest the entire field, then plow the entire greenhouse. After the ground has been fertilized again, the robot will plant new potatoes.

The fertilization of the greenhouse is also done autonomously. Over the entire greenhouse, sensors will be placed in the ground. These sensors will be measuring the nutrition in the ground, as well as the humidity of the ground. When the sensors measure the humidity or nutrition below a certain point, they will give off a signal. This signal goes to a connected sprinkler system. This sprinkler system couples to two different tanks, one with just water and another one with diluted manure. The sprinkler system switches between the two tanks depending on what signal it gets. The sprinklers will turn off once the sensors detect that the humidity or nutrients are above a certain level again.

Goal

We want to make a fully autonomous greenhouse. We want to try and do this in the form of a model. In this model, we want to consider the user needs, the strange environment and the considerations of the society and enterprise. Though it is never possible to please every single party, we want to try to compromise as good as possible and get everyone to agree with our technology. But most important, we want the primary users to be happy with the result and we want them to be able to use it in the easiest way possible.

Approach

We want to make our model by first looking at what parties are involved, what their requirements and preferences are and if there are any constraints. Based on this information, a lot of research needs to be done on the process of farming potatoes, on the environment of Mars, on the already existing greenhouses and on (autonomous) farming robots. All of this information has to be displayed clearly. From here on we can collect hard data (numbers) on what potatoes need (for instance how many water per certain time). This can then be put togheter in a simple MATLAB model.

USE aspects

Problem statement

There is a mission going on to send a group of people to Mars for colonization. In the first stage, this group consists of about 20-30 people. After this, every couple of years a new group is sent to Mars. When the first group arrives on Mars, it is important that there are enough resources to sustain. Since the plan is to stay on Mars for the rest of their lives, merely canned food will not suffice (it will run out fast). Thus food has to be tailed. As there is a limited amount of crew members in the first stage of this mission, it is favorable that as much work is done autonomous by rational agents. One of the most important things in order to survive, is the tailing and harvesting of food. In the beginning, this should be focused on nutritious food which is easy to process. For grain, as an example, it takes a lot of work to make it into something eatable, which is not favorable at this stage. We chose to look into the tailing of potatoes. This process is not yet fully autonomous.

Objectives

The objective is to make a model in Matlab and Simulink for an autonomous controlled environment for potato harvest. This includes the harvesting and the planting of the potatoes at right times, as well as keeping the environment ideal for growth.

Aspects

■ Harvesting and planting robot

■ Greenhouse

■ Climate control

■ Water and nutrition supply

Users

The users can be divided into three groups: primary, secondary and tertiary users. The primary users are the users that directly come into contact with the technology or who directly benefit from it. The secondary users usually do not directly use the technology, but benefit from it anyway, for instance, when they work on the development or design of the project. The tertiary users are mostly involved in purchasing the technology.

Primary users

■ Inhabitants of Mars

The direct users of our technology will of course be the inhabitants of Mars. The technology is designed especially for them, so that their life on Mars gets a bit easier. In the first stage of the Mars mission, all the inhabitants are going to be (mechanical) engineers, doctors, biologists, agriculture experts, physicists etc.. They are all going to be trained in advance to be able to handle all kinds of situations. They will be trained to use the technology that is sent up with them, including our technology. There are no experts for the different kinds of technology though, which means all of the technology needs to be relatively easy to understand.

Secondary users

■ (Mechanical) engineers (on earth)

(Mechanical) engineers are needed in order to design and build the technology on earth.

■ Programmers (on earth)

Programmers are needed in order to make the process of potato tilt fully autonomous. They need to implement all of the research done by other scientists in order to create the perfect environment for potatoes to grow in.

■ Biologists (on earth)

Biologists need to do research on the environment on Mars and in and how growing potatoes is possible in that environment.

■ Agriculture experts (on earth)

Agriculture experts need to establish the perfect kind of potato to grow under these extreme circumstances, as well as they need to determine the perfect conditions for the potatoes in each stage of their growth.

■ Chemists (on earth)

Chemists need to determine how to change the soil and air so that the right nutrients are in there.

■ Physicists (on earth)

Physicists need to calculate how the gravity is going to effect the growth of the plants.

All secondary users described above profit from the technology in the sense that it will be their job to contribute to the development of the technology, so they will get paid to do their jobs.

Tertiary users

■ Buyers of the technology

The buyers of the technology also play an important role of the process. These are the ones paying for everything after all. If they are not happy with the technology, they will not pay, which makes it very important to look at their requirements and prefrences as well. The buyers of our techology will probably be either NASA or the government.

User requirements

Primary users

• In the early stages of the Mars mission, people might not have the knowledge to make any complex modifications or repairs to the robot. This has to be taken into account when the robot is designed. It is important to make a design that is as simple as possible and make the programming as clear as possible. In this case, when something does break, it will hopefully be easy to fix.

• Another consideration will be the material of the greenhouse. Because the resources are limited, it is important that when the technology malfunctions, it can easily be made without using a lot of materials and specific tools. If certain materials or tools might be needed in order to fix the technology, it is important to know that in advance, so these can be taken with the crew to Mars.

• The technology needs to be easy to use. Preferably, the technology is fully autonomous so that the crew does not loose precious time while building up Mars.

• The technology needs to be efficient. It is important that in an environment, where there are so little resources like food, water, manure or energy is not wasted.

Secondary users

• Money for research.
• Enough time for research. A lot of the time researchers are set with very strict deadlines in which it is not always possible to deliver the quality of work needed for such a big project.

Tertiary users

• The technology needs to be as cheap as possible.
• The technology needs to have a long lifespan, so that it does not have to be re-purchased.

Society

Apart from the users there are two important groups left to consider, Society and enterprise. The two aspects are intertwined for some part but we will consider them separately.

First off is Society. The entire world population falls under this category because sending a small group to Mars could have a huge impact on the rest of the civilization. The Mars project is a really expensive one where only around 20 people will reap the initial benefits and get sent to Mars. This could cause a lot of uproar about the project, because some people might feel like they are investing billions of euro’s into that small group of people. Initially that feeling would be true, before a second group of people are sent to Mars, the first group is solely benefitting from the autonomous farm. However the autonomous farm could easily be implemented on Earth which would increase the efficiency of growing crops and the technology would therefore not only be used on Mars. So shifting the investment from solely Mars to both Mars and Earth might ease a lot of people into becoming less opposed to the project.

The next group of people that could start to counter the autonomous farm are the farmers. Since the implementation of autonomous farms that are more efficient than farmers could cost a lot of jobs on Earth. Farmers are a really large group of people that would all be opposing something that could eliminate their job altogether. There are different ways to deal with the farmer opposition.

The first possibility is instead of replacing the farmer with the autonomous farm, the farmer actually uses the autonomous farm to do all the hard work for him and the farmer could still distribute and sell his potatoes. However that could still mean a lot of the farmers lose their jobs since the autonomous farm does everything up and till the potatoes are harvested and collected, so distribution would be the only job left to do. And on top of that, the autonomous farms are supposed to be more efficient than a human farmer, meaning there are less farms needed to feed the same population. All things considered, letting the farmers use the autonomous farms still will not convince them of the benefits of an autonomous farm.

Another approach is to build the autonomous farms, not in more crowded and stable civilizations, but instead in third world countries. Where a single autonomous farm could feed a lot of people, causing the local population to flourish and grow. A sudden growth in population in these countries could have major effects in very different directions. One of the possibilities is that the growth and the flourishment of the country could turn it into an equivalent of the modern western societies with a lot of wisdom and knowledge getting spread throughout the country and eventually leading to a crucial country for innovation on multiple fields. An outcome to wish for, but not guaranteed. On the other hand there is a possibility that the growth of the population causes nothing more than an increasing number of people needing food and water without any progress in education or wealth in the country. With the original reason for the Mars project in mind, which is a second planet for humans so that Earth does not get overpopulated, the second scenario would only be countering the initial motive of the project. Of course in the third world country one or the other outcome could happen, or anything in between, so there is no way to know how an autonomous farm would change the country.

In conclusion, the Mars project is one of those subjects where there is always a group of people that is either opposed to the project, or a group where the investment and innovation has a negative influence on. But every big revolution and innovation has its opposition, so the Mars project should not be canceled because you cannot make every person happy.

Enterprise

Rounding of society brings us to the last important group, enterprise.

Enterprise is based on corporations and companies looking to make a profit. The Mars project is either worth investing into or not. With the benefits and downsides for society in mind, enterprise revolves around money. The autonomous farm in particular is more efficient than a farmer, so for a big company to own an autonomous farm could be enough to drive out the competition due sheer efficiency of the farm. For the company this could mean a lot of profit. When investing into the autonomous farms delivers a cheaper and even more efficient outcome, it would be even more profit. But most of the companies have no benefits from investing into an autonomous farm when it will only be used on Mars. They could invest simply for innovation and for the next step of the human race.

RPC's

In this subsection the requirements, preferences and constraints of the technology will be elaborated. With the limited resources, energy and manpower the technology used has to be altered to such an extent that all the different scenarios are to be taken in account. This will prevent early wear on the robot and its surroundings.

Requirements

All requirements are essential for the sustainability for the robot.

• Versatile mobility

The robot that can do multiple things, namely; planting potatoes, harvesting them, eliminate all remains of the potato plant to stimulate better growth for the next cycle, transport the potatoes, and do this while moving in between the different potato plants without trampling them. With that all to be taken in account the robots movement has to be versatile and reliable. Versatility is playing a large role in the development of the current technology, since this also lowers the cost of the development of the robot. The latter is due to the fact that the same technology can be used multiple times. Making it more beneficial for the enterprises, making it look better in the eyes of society and by reducing the costs it can be invested in something else needed.

• Efficiency

The means to send materials to Mars are very expensive and thereby very limited. While on earth we will be able to use means like fossil fuels and such. This is not the case on mars. A limited field of solar panels will probably be the most reliable source of electricity. Therefore the whole potato harvest process has to be as efficient as possible. Since no speed records have to be set by the robot, one can think of more dramatic ways to increase its efficiency. An example is the use of wheel motors to bring friction down to a minimum.

• Ease of transport

A system for transport is of course not difficult to implement in a robot, especially not for a vegetable like potatoes. However, the robot has to be compact even when it has a container to store the potatoes temporary. When the robot exceeds a certain size, it will be difficult to maneuver between the potato plants with care in a relatively small area. Adding too much weight will destroy the loose earth ground, maybe even to such an extent that the potatoes plants cannot grow optimally. Water that is sprayed on top could also be inhibited to get absorbed. The last, but very important, thing is that when the robot is larger, its weight will increase. This makes it less efficient due to the extra weight and resistance it has to overcome to drive. So with this in mind a system that can only carry a few potatoes might not be disadvantageous.

• Ease of maintenance

With only a very limited amount of personnel that will be send to Mars, it is essential in the first years or even decades that the amount of required maintenance stays as low as possible. The people staying on Mars will have more important issues to worry about, so some compromises might have to be made to keep the maintenance that low. For instance, when extra error margins have to be computed for, the robot might get heavier and thus less efficient, these kind of things have to be taken into consideration when designing the robot. But when something breaks in the robot, it needs to be fixed or replaced relatively easily. When designing, it can be made with different modules, which can be replaced by reserves that are to be send to Mars.

Preferences

• A connection to Earth

One cannot expect from the people, that will be send to Mars, that when the robot does not behave like initially intended that they can fix it, that is, when the problem isn’t physical. So when part of the arm doesn’t rotate for an instance, the habitants of the Mars base will probably have to fix it themselves. But the problem can be in the programming of the robot as well, when the robot cannot maneuver through the greenhouse for an instance, which might be due to difference in gravitational pull from the planets. When a connection is to be made between the robot and Earth, people like scientists, programmers and physicists can change things in the programming of the robot. A second benefit of this will be that the people on earth will be able to gather data from the robot. Like tesla is doing with their cars the data can be used to write a new program for the next iteration of the robot.

Constrains

• Size

In some views a very large robot might look like it’s beneficial, but like mentioned earlier, to be able to sustain on Mars, everything has to be as efficient as possible. Often when size increases it tramples efficiency, especially when a robot has to maneuver in a relatively small greenhouse. Making the robot smaller does however come with some challenges, the robot has to have some force for an instance to pull the potato out of the ground. Then while having finished that, drive with the potato to the next potato plant and do the same thing again, with the extra weight of the potato it is carrying around.

Scenario's

Linda

Linda is a women in her mid-forties. She has done two masters in computation science and she has a lot of experience in working with different languages of programming, but she is specialized in only one language. From a very young age, she was interested in outer space, so when the opportunity of going to Mars was there, she was the first one to apply. After lots of procedures and years of training, she made it to the final crew and she is now living amongst the first people on Mars.

On Mars, there is a problem with the technology of the autonomous greenhouse. It does not function as it is supposed to do. The system does not react to the sensors anymore. After the crew has checked everything that could be wrong, the conclusion is that the system needs to be rebooted. After the reboot certain parts of the code need to be reevaluated and possibly rewritten. Since Linda is the most experienced person on the crew, this will be her job. However, she finds out the language in which the code is written is not a language she is specialized in.

In order for Linda to solve this problem, it is important that the code is very well commended (in every step of the code it is explained what is happening in that code). It is also important that the code is a simple as possible. Since Linda has a lot of experience with coding, she will be able to understand simple scripts of different languages. Besides these requirements, it is very important that there is a possibility of contact with earth, especially with someone involved in writing the code. This person can help her with the more complicated parts of the code if needed.

Steven

Steven is a 32 year old man. He did a master in … and he has worked with a multidiscipline group on how to produce food on Mars for the people who are going to live there for two years now. He is now very familiar with all the do’s and don’ts when it comes to the cultivation of different crops on Mars.

On Mars, there is a problem with the nutrients in the soil. All the nutrients washed out of the soil thanks to a brief failure in the sprinkler system. Due to this the crops that are already growing in this greenhouse are going to die if the people don’t jump in.

After some checks of the values the sensors in the soil gave and a quick analysis of the soil it turns out that the people need to start fertilizing in the greenhouse so that the soil gets enough nutrients again to let the crops grow.

In order for Steven to solve this problem, it is important that there are enough sensors in the soil to get all the values that are needed to determine what type of fertilizer and how much of it is needed. It is also necessary that there is enough of all the types of fertilizer that are needed on Mars in stock. This way Steven can put together the needed fertilizer and can put in in the system so that it gets spread on time.

Harold

Harold is a 29 year old engineer. He did a master in … and he has been involved in the design of the greenhouse that will be put on Mars for a year now. He joined the group working on the greenhouse to know how it is going to be constructed and to lead the group who is going to build it on Mars.

On Mars, after the greenhouse has been built completely it is already operational for about two months now. All crops are planted and everything was going as planned, but then the sensors in the greenhouse showed that the levels of O₂ and CO₂ where changing rapidly. If the people on Mars do not jump in, all the O₂ and CO₂ will leak out of the greenhouse which causes all the crops in it will die, because of the hostile environment that is created in the greenhouse.

The crew goes on to check the greenhouse and its surroundings, to discover that one of the side panels was leaking gas out of the greenhouse. To repair this leaking side panel the team decides to temporarily seal the hole by screwing a small iron plate over it. After this temporary fix a new side panel is made to fit this one and it is placed over the old one from the outside. After attaching the outside-panel, the one on the inside is removed and the greenhouse works as it should again.

Theory

Conditions on Mars

Soil on Mars

Climate change on the planet Mars is discovered by detection of ground ice. The water layer is 10 - 40 cm thick and occurs in between latitudes of 30 degrees and 60 degrees. This means that water is available on Mars. Because of this carbonates can be produced. The exact substances will be discussed below.

Ions

A layer of ice has been found at a depth of 5 cm to 15 cm. In the soils around the Phoenix landing site calcium carbonate has been discovered (3-5 wt%) by scanning calorimetry. It showed an endothermic transition at around 725 degrees Celsius accompanied by the evolution of calcium carbonate and the soil had the ability to buffer pH against acid addition. Its formation in the past was due to interaction of the atmospheric CO₂ and the water on particle surfaces. The Martian soil has been further inspected, where around 10mM of dissolved salts have been found out of which 0.4 – 0.6 % perchlorate (ClO₄). The other negatively charged ions included small concentrations of bicarbonate, chloride and possibly sulfate. The cations detected (positively charged ions) included magnesium, sodium and small concentration of potassium and calcium. Besides this, an alkaline pH was measured of 7.7 (with a margin of 0.5). These findings included that the soil at Mars has changed for the past years due to the action liquid water. It has also been found out that there is a mechanism to place ice at the surface: clouds of ice crystals precipitated back to the surface and formed a daily basis. Even though ions have been found, nitrate is an important ion for the Martian soil to be able to grow crops. In the table below, the concentrations of a few ions are given.

Nitrate should naturally be formed through the oxidation of atmospheric nitrogen and then accumulate on the surface. On Mars odd nitrogen (N and NO) can eventually be turned into NO₂, which can form nitric acid. Nitrate, thus, has not yet been detected on Mars; there are only some possible detections. In table 3 multiple acid formations can be seen.

These results are bases on the Phoenix landing site in 2008. In 2014 a meteorite from Mars (EETA79001) has been investigated. When investigating this meteorite, it had been concluded that the soil composition was of Martian origin. The reason is that the detected substances within the meteorite are difficult to reconcile with terrestrial contamination. EETA79001 showed the presence of 0.6 ± 0.1 ppm ClO₄^-, 1.4 ± 0.1 ppm ClO₃^- and 16 ± 0.2 ppm NO₃^-. It has been said that because of the prenece of ClO₃^-, also ClO₂^- or ClO^- should be present. This was then produced by Cl^- and γ- and X-ray radiolysis of ClO₄^-.

Furthermore, an article was found comparing the findings on Mars and Antarctic Dry Valley (ADV) soils. The article contains tables including the concentrations of certain ions found in each place. It has been concluded that the salts of the Phoenix landing site and the salts of the meteorite are similar and that the ADV are also a good match. This also strengthens the argument that ADV is a good Mars analog environment of Earth. The occurring ions and concentrations of it in ADV and on Mars are the same within one order of magnitude. ClO₄^- is three orders of magnitude bigger on Mars than on Earth. NO₃^- may be present on Mars, but this is at a level below the detection limit of the nitrate sensor. The soil of the meteorite and on the Phoenix landing site are alike, however, on average the concentrations in the meteorite are 4% of those on the Phoenix site and the concentration Ca⁺ is 16% bigger on the meteorite.

The last article includes information about the nitrogen cycle and the ratio of the loss of nitrogen isotopes. This mainly has to do with the air activity. Therefore, it is not relevant for the discussion about the ground. There was a good explanation, however, why it is difficult to detect nitrate on Mars. This explanation is given below. A cause could be leaching. This means that the nitrate will be at a bigger depth in comparison to less soluble ions such as sulfates.

Nitrates on Mars

Some articles say the opposite of one another. Some state that nitrate has been detected on Mars and others do not. As nitrate is crucial for growing crops, it is essential to know whether this substance is actually present on Mars. The least recent articles conclude that nitrate is not present in the Martian ground. However, the most recent articles say there is. It could namely be the case that nitrate has not been discovered in 2001 but in between 2001 and 2013. Therefore the most recent articles are the wisest choice to trust.

Composition Martian soil

Several investigations have taken place in order to find out what substances are located in the soil on Mars. First of all, the Phoenix Mars Lander WCL soil has been analyzed and the Mars meteorite EETA79001 sawdust. These type of soils have been compared to soil on the Antarctic Dry Valley and to a Mars simulant. This research is about being able to grow crops (potatoes) on Mars. In order to succeed into this, the easiest way would be to do experiments with the ground which is available on Earth. This is the reason why the Martian soil has been compared to soil on Earth. To be able to grow crops, the soil should be fertile and the amount of fertilizer must be known. What is in the fertilizer and the amount of is needed, is based on the composition of the soil and the needs of a certain crop (in this case the potato). In the table below, the concentration of ions is given for the meteorite and Phoenix Landing soil. Also the values for the EETA79001 meteorite are stated here. 1 gram of soil was added to 25 mL of DI water.

Ionic species	Phoenix WCL mars (μM)	EETA79001 Meteorite (μM)
Ca2+	600 ± 300	1180 ± 1
Cl-	470 ± 90	13.2 ± 0.8
K+	390 ± 80	1.8 ± 0.5
Mg2+	3300 ± 1700	136 ± 1
Na+	1400 ± 300	110 ± 1
NH4+	ND	62 ± 2
NO3-	<1000	48.5 ± 2.5
SO42-	5400 ± 800	117 ± 5
ClO4-	2400 ± 500	1.02 ± 0.11

It has already been concluded that both of these soils are comparative for the Martian soil. It has not yet been decided which soil to take as a representative. Because of the fact that the numbers for what a potato needs are in grams, the amount of μM has to be converted into grams. In the table below, the amount of grams for each ion is given within one gram of soil.

Ionic species	gram per gram soil (Phoenix)	gram per gram soil (Meteorite)
Ca2+	6,01E-04	1,18E-03
Cl-	4,17E-04	1,17E-05
K+	3,81E-04	1,76E-06
Mg2+	2,01E-03	8,26E-05
Na+	8,05E-04	6,32E-05
NH4+	0,00E+00	2,79E-05
NO3-	0,00E+00	7,52E-05
SO42-	1,30E-02	2,81E-04
ClO4-	5,97E-03	2,54E-06

In reality, each potato has access to a certain amount soil. The potato is placed in the ground at a depth of 10 cm. The space between the potatoes in the same row is 28 cm and the distance between potatoes in different rows is 75 cm. These numbers have been taken into account in order to calculate the volume of the soil that each potato is able to use. By taking the density of the Martian soil into account, the amount of grams for each ion can be calculated. The results are shown in the table below.

Ionic species	gram total (Phoenix)	gram total (Meteorite)
Ca2+	1,26E+01	2,48E+01
Cl-	8,75E+00	2,46E-01
K+	8,01E+00	3,69E-02
Mg2+	4,21E+01	1,74E+00
Na+	1,69E+01	1,33E+00
NH4+	0,00E+00	5,87E-01
NO3-	0,00E+00	1,58E+00
SO42-	2,72E+02	5,90E+00
ClO4-	1,25E+02	5,33E-02

From the information above can be concluded that the Martian soil does not contain enough substances for the potatoes to grow on, therefore, the ground needs to be fertilized. The problem with fertilization on Mars is that there are no fertilizers. For that a solution has to be found. The 20 people who are going to Mars should produce the fertilizers themselves. This means that these people should use their own feces and pee to fertilize the ground.
Despite the fact that the Martian soil needs a fertilizer, the structure of the ground is also an important aspect. The potato plants should be able to absorb the needed water, oxygen and fertilizers. The ground on Mars has very sharp edges and water, oxygen and the fertilizers cannot reach deep enough to be picked up by the plants. This means that worms should be used. They can create holes in the ground structure to let more oxygen and water into the ground. It has been tested already by Wamelink that the worms do not die because of the sharp edges in the Martian soil. Furthermore, they have enough food from the ground and the dead plants.

Air composition

Air on Mars

The atmosphere of mars is composed of 96% CO₂, 1,9% argon, 1,9% nitrogen, 0,15% oxygen and 0,05% CO. In the section “air composition”, the most important parts of the air composition will be discussed. These conditions are far from optimal for the growth of potatoes, and thus a non-hostile environment for the potatoes has to be created. This is going be to achieved by making a friendly environment in a greenhouse. What this friendly environment entails will be described below.

environment potato

air composition

CO₂

The CO₂ level in air on Earth is about 401 ppm (0.00401 %) in which potatoes can grow well. But to get to know if potatoes can grow better in atmospheres with more CO₂, tests using FACE rings are done. A FACE ring is a ring of pipes around a field of crops which emits CO₂ so that the CO₂ values around the crops rise and measurements with different levels of CO₂ can be done. With the outcomes of these experiments it can be concluded that when the CO₂ levels are raised to 660 ppm (0.00660 %) the Leaf Area will decrease, but the activity of the photosynthesis is raised and therefore the number of tubers will increase. While the number of tubers increased, the size and weight of the tubers remained the same as on Earth. With these values in mind it would be a good idea to make an atmosphere in the greenhouse that has a CO₂ value of 660 ppm (0.00660 %). This makes the tuber yield higher and it thus creates more food from the same amount of plants.

O₂

When potato plants are just planted, they will use a lot of O₂. This means that the plants emit a lot of CO₂. The plants need the oxygen to create the haulm, which is used for the photosynthesis. It is thus necessary that there is enough O₂ available to the plants to grow at first, but when they are fully grown they will start to transfer CO₂ to O₂. Plants transform CO₂ in O₂ using the energy that they gain from light via photosynthesis, but when there is no light, the plants will start respiration. During respiration, plants do always the glucose, that is made by photosynthesis, to CO₂, water and energy for the plant to keep living. But when there is not enough light, photosynthesis rate is lower than this respiration rate.

Gravitational influence on Mars

Some questions arose whether the gravity on Mars has a significant influence on the development of the potatoes. However, it is unknown yet whether it will. The plants do grow when there is a change of gravity, but their shape is not known. In the model we will assume that it has no influence, also because certain researchers including Wamelink think that it does not have an influence.

Ground humidity

After planting, it is important that the ground is kept moist until emergence. When the seed is kept moist, a rapid emergence is stimulated. However, it is crucial that the ground is not too wet. The seed also needs oxygen and it should not suffocate.

In the stage after emergence it is important that the moisture of the ground does not exceed a soil water tension (SWT) of -0.3 MPa, for then the growth of the leafs during haulm growth is delayed. The soil water tension is the pressure needed by the plant to extract the water from the ground. It is very important that there is no over-irrigation in this stage of crop growth, as the roots of the plant then become superficial, whereas long developed roots are important for later stages.

In the period of the time just before the initiation of tuber growth, the ideal moisture of the ground is strongly dependent of the breed. Averagely, when the ground is relatively dry, initiation of tuber growth will happen faster. However, the amount of tubers per plant will decrease. The latter also happens when the ground is too wet.

For potatoes, the ideal water content in the ground is 65% ASW, when the tuber growth initiates. ASW (available soil water) is the percentage of the maximum amount of water a plant can possibly consume from a certain volume of soil. It is important that the ground moisture is sufficient and not inconsistent as potatoes are relatively draught sensitive. When there is a dry period, tuber growth is delayed. This is not only caused directly by a lack of water, but also indirectly as the leafs become less efficient in absorbing light. Also the quality of the tubers will decrease due to draught, as cracks develop and the tuber will grow in an undesired shape. It is not possible to know when the soil water content is 65% ASW. Therefore the soil water tension is taken into account. Sensors do exist for measuring the SWT, which makes this a measure to work with. The ideal water tension for potatoes can range from -20 to -60 kPa depending on the ground used to grow on, climate and the irrigation system used.

Day length

For potatoes it is of great importance that a daily cycle is involved. The potato plant can sense when it is day or night with certain light receptors called phytochrome. These receptors are positioned in the leaves of the potato plant. When days are long, the growth of gibberellins, which are growth hormones in a plant, is stimulated and this inhibits the initiation of tuber growth. When the days are short, the initiation of tuber growth thus is stimulated as the amount of gibberellins is then reduced. The length of the night in this process is rather important, as when a night break is simulated, the tuber growth is also inhibited. Therefore long nights are essential for good tuber yield.

In the initiation of tuber growth in potato plants, it is for wild potatoes more important that the days are shorter than for modern cultivars. These modern cultivars show an initiation of tuber growth quite fast relatively independent of day length (a cycle is still important however, but there are bigger margins). In other words, every cultivar has its own critical photoperiod. Whereas some cultivars cannot grow tubers when the day length exceeds 12 hours (short cycle potatoes), others can grow tubers with a day length lasting until 18 hours (long cycle potatoes). There are even cultivars that are able to initiate tuber growth with a photoperiod of 24 hours. However, the latter is definitely not an ideal situation to grow tubers optimally.

In the figure below the tuber yield from different breeds is portrayed as function of the day length. This graph shows that short days are the best circumstances for both short and long cycle potatoes.

The day cycle is mostly an important aspect between emergence and the initiation of tuber growth. When tubers start to develop, the growth habit of the potato plant is not affected as much by day length anymore. From this moment mostly other factors will determine the tuber yield.

The yield from a potato plant as function of the day length for different temperatures and different breeds.

Temperature

Potato plants are also sensitive to temperatures. Different temperatures to different plants have been inspected. From these experiments turned out that for good potato yield a cooler soil is preferred. This means a temperature around 15 ⁰C - 18 ⁰C. In the same figure as referred to in the section about day length, it is illustrated that indeed for a temperature around the 18 ⁰C, higher yield is obtained than from warmer or cooler soils.

It is found that when changing temperatures from 14 ⁰C at night to 24 ⁰C during the day can improve tuber yield by 25% with respect to a constant temperature of 18 ⁰C. This was tested with the breed “Delani”. For “Nordland” potatoes no significant changes were found. This also illustrates how great the differences in properties are per cultivar.

Other tests were done with larger temperatures to different parts of the potato plant. It turned out that whatever part of the plant was heated, it had a negative effect on the overall tuber yield. This is not desired. This has also to do with the fact that when higher temperatures arise, more gibberellins develop in the plant, which are known to be disadvantageous for tuber growth.

Just like for the length of the photoperiod, temperature as also the greatest effect on the potato plant during the period right before and during tuberization. It is thus important that temperatures in this time of the lifecycle of the plant are right. Especially for longer photoperiods, as the temperature then has an even bigger effect.

light intensity

Irradiance is an important factor as, of course, plants grow with photosynthesis. The light intensity is one of the variables that influences the photosynthesis. Research shows that for higher intensities, the growth of tubers is stimulated and thus a higher yield is obtained. For lower intensities haulm growth is stimulated, but tuber yield is decreased which is an undesirable effect. It is also known that for higher temperatures, the light intensity has a more important role than for lower intensities. For example, potatoes growing in tropical climates need a higher light intensity to have a good yield than potatoes grown in northern Europe. The higher intensity is for both temperatures better, but when the intensity decreases, potato plants in Europe can still deliver a good yield, whereas in tropical climates the yield is disappointing. The fact that yield is decreased by lower light intensities has to do with an increase of growth hormones like gibberellins, of which we know that their effect on tuberization is negative.

Manuring and nutrition

Potatoes need the following substances in order to develop themselves and grow.

Macronutrients

• Nitrogen (N)
• Phosphate (P)
• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg)
• Sulfur (S)

Micronutrients

• Boron (B)
• Copper (Cu)
• Molybdenum (Mo)
• Iron (Fe)
• Manganese (Mn)
• Zinc (Zn)

In order to make sure the potatoes receive these substances, human feces and pee will be used, which will be discussed later on this page. The macronutrients are the most important nutrients, however, it can also be assumed that there will be enough of the Magnesium and Sulfur when the other nutrients are present in sufficient concentrations. The same goes for all of the micronutrients: when there is enough of the four left-over substances, there will also be enough of the micronutrients. The amount needed of each of these four important substances needs to be calculated. It could happen that there is a surplus of one of the ions. This should not cause any problems to the potatoes, they simply do not absorb the extra ions.
Each of these four important ions will be explained when there is a shortage of it for the potato plant.

Nitrogen: Nitrogen is important for the development of the plant and ensures a better yield. When there is too less of this substance the leaves will not fully grow and a light green discoloration will be seen on the leaves.

Phosphate: Phosphate boosts the development of the tubers and it enlarges the amount of the tubers. It also ensures that the tubers are equally big. This substance actually improves everything that has to do with the tubers. When there is a shortage of it, the growth will be inhibited. A shortage of Phosphate can be noticed, because the cuttings will stand up and the color of the leave will be glazed and dark green. Furthermore, the edges of the leaves will curl up.

Potassium: This is also a very important substance. It improves the yield and its quality. Furthermore, the resistance against diseases will increase and the tuber magnitude will increase. When a shortage occurs, the plant growth will be oriented downwards and incomplete. A shortage can be noticed in the leaves as the underside is yellowing and the edges also curl up.

Calcium: A green and healthy leaf will exist because of Calcium. It ensures a better yield and quality. Furthermore, there will be less eruption during the storage of the tubers. A lack of Calcium causes internal scald and hollow tubers.

Amount of nutrition needed

As can be deducted from the section “composition Martian soil”, this soil does not contain a concentration of ions which is sufficient for growing potatoes. It is assumed as if the Martian soil contains nothing and that everything needs to be present in the fertilizer.
In the development and growth of the potato, there are certain stages where the potatoes needs more substances than in other stages. Furthermore, there is a difference between the amount of nutrients that the tubers need and that the haulms need. In the table below, the amount of the four important ions needed each day is given in mg.

	0-15	15-30	30-45	45-60	60-75	75-90
P	3	13	46	47	47	16
N	28	130	255	179	187	57
K	27	120	358	160	194	65
Ca	8	43	113	4	2	1

Each row represents a certain substance and each column represents a certain stage in the cycle, each one covering a period of 15 days. The amounts given are needed every day for each plant.

Farming equipment

Farming robots

Several articles were found on farming robotics. However, most of these articles focus on robots that are (partially) manually controlled. It has only been a couple of years since designing and experimenting with fully autonomous farming robots has begun. The hardest part in programming the robots is to make them able to see whether a fruit or vegetable is ripe, or even to tell apart a fruit or vegetable from the plant. Furthermore the robot needs to be very delicate in order for the plant not to be damaged.

In one of the found articles a robot is described that is used to farm tomatoes. In this case, color is used as a measure of how ripe the tomato is. When the color is above a certain tint, the robot picks it. Otherwise it waits until the tomato gets a darker shade. The robot, which is described, is a very small robot which climbs up the plant and cuts the stem of the tomato if it is ready. This technique is however very hard to apply in this case, since there is a focus on potatoes which grow under the ground. Though, there might be a way to use color underground if we introduce a light in our robot. Another downside to this technique is that it requires a lot of these small robots, which can turn out to be expensive. On the positive side, these robots are very precise and do not waste a lot of vegetables (once the programming is perfected). An adjustment can be made from looking at the color by looking for example at the size when it comes to potatoes.

Another article describes how a prototype is built of a fully autonomous harvesting tractor. This is used for vegetables which grow underground, but it is a very blunt device. It basically pulls out everything, including the potatoes that might not be ripe yet. In a very restricted area like Mars this is not desirable, since there are limited supplies and every potato counts.

Assumptions

Since this model will be a very first draft, lots of assumptions and approximations need to be made. All of the made assumptions and approximations will be listed below, including an explanation of why these are valid. Throughout the project, as many approximations as possible will be eliminated, in order to make a more detailed model. The assumptions will be divided over a couple of subsections, such as the things that the robot is assumed to do, the composition of the ground and the growth of a potato. This in order to try and give a clear overview of all the simplifications in our model.

Users

It is important for the developers of the technology to keep in mind what tasks the users can perform. This way the developer can make sure that the technology can be maintained as well as needed and that the technology will have a long lifetime. For this, a couple of assumptions are made about the primary users.

• The primary users are trained in solving minor problems with all kinds of technology
• There will be (mechanical) engineers amongst the primary users with the skill of performing a bit more complicated maintenance
• The Martian crew will be able to contact earth at all times
• The crew members have minimal knowledge about potato plantation
• The crew members have minimal knowledge of the specific technology

Robot in greenhouse

At the moment, there are no fully autonomous farming robots available that fit in our project. There has been done research, though, on making tractors autonomous, so the robot in the greenhouse will be based on this research. Since this robot does not yet exist, a lot of assumptions need to be made. All of these assumptions are based on the literature research.

• The robot is able to plant potatoes
• The robot is able to harvest potatoes
• The robot is able to plow the ground
• The robot is able to move forward and backward
• The robot has a small turning radius
• The robot is able to detect where in the field it is
• The robot can track where in the field it has already been
• The robot can move forward and sideward, but it can only plant, harvest and plow in one direction

Ground on Mars

In order to grow potatoes on Mars we need to know what the soil of Mars contains regarding for instance nutrients. Though, there has been a lot of research about the soil on Mars and the exact composition is hard to find. In order to make the soil right for potato growth, it needs to be fertilized. Before this fertilization can be included in the model, a set of assumptions and basic boundary conditions needs to be made.

• The composition of the Martian soil is seen as equally distributed around the whole planet
• The values found in the literature do not include errors
• Only take into account that the potato is able to take up ions from above it (so 10 cm in depth to take up these substances)
• Take size 28/35 potatoes (so width between potatoes in same row 28 cm) if size 35/55 was taken than it should be 38 cm. It is better to have more potato plants in the field, therefore, size 28/35 has been taken.
• Each potato is able to absorb the nutrients from half the distance to the next potato.
• If there is shortage in ions in the ground this can be easily dealt with by putting the shortage in the fertilizer.
• Human feces and pee will be enough to fertilize the ground.
• Other crops will also be able to grow on Mars, therefore, the dead plants can also be used to fertilize the ground.

Greenhouse

• The greenhouse is a closed system (every feces or dead plants etc. will be reused)
• The greenhouse is able to set different seasons inside it

Potato tilt

• We will look at the escort potato.
• The surface area of the potato field will be .....
• The size of a fullgrown potato will be .....

Model

In this section, a description of our model will be made. Our model consists of a MATLAB model combined with a description of what we think the greenhouse should look like. Furthermore, a section will be included which describes vital information that is too difficult to implement into the model at this stage. However, there has been done research on these subjects and thus it will be described what needs to be considered in a next version of the model, and a way to possibly implement them in the future.

Why modelling is necessary

Every ingenious invention needs to be tested before it is used and sold. The same goes for everything that goes to space. For example, the entire rocket needs to be tested, but sending the rocket to space just for testing is a huge waste of both time and money. Therefore, every section of the rocket is either tested or modelled or both. Modelling is a very efficient and cheap way to test your engineering invention. Also for our project modelling is necessary, since there is no way to test what the actual amount of potatoes is, that would be retrieved after harvesting. Because sending the entire greenhouse to Mars, simply for testing, would be a waste of both money and time.

Even though modelling is a very useful tool for physicists, for biologists it is a lot less accurate. Physicists rely on clear formulas and an understanding of the subject to clearly model whatever their problem might be. Biologists however need to deal with something called life. Modelling plants or animals is difficult because living things can always stray away from the formulas used to model them. Every plant and animal is unique and grows, feeds and festers in a different way. This makes accurately modelling the amount of potatoes gained from the entire greenhouse after the entire cycle of growth, practically impossible. But modelling can still be a useful tool. Even though it is not clear how the plant reacts on every shift in air composition or every drop of water. Through empirical research done at several places in the world, hence different weather conditions, a simple model can be constructed to give an estimate of the amount of potatoes harvested.

Another possibility for testing could be testing the greenhouse on a farm on Earth. It helps the knowledge of how the greenhouse works and what the flaws are, since it is supposed to be completely isolated with a regulated temperature, day-night cycle, fertilization, sprinkler and air composition. But once the potatoes are harvested, that specific amount does not give the full picture since the ground is not at all like that on Mars. However, it is still more accurate than modelling. To get to the optimal conditions, just like the model, a lot of iterations will be needed. When testing the actual greenhouse on Earth, it will take decades to find the optimal conditions. Furthermore, all of the different aspects of the greenhouse and the robot need to exist already. With the current assumptions that are made, the robot can do numerous things, that already exist, but are not implemented into an autonomous robot yet. That would need a lot of research before the robot has every ability necessary to fit into the greenhouse system.

The testing on Earth might be a more accurate representation of the harvested amount of potatoes, but the actual testing could only take place in the far future. On top of that, it would need decades of testing before the optimum is found. Therefore, modelling is the more efficient choice, it is cheaper and less time consuming. Even though the accuracy might be further off, plants are alive and will never be bound by formulas.

Needed values

■ Air

• Wanted composition
• Composition Mars
• Wanted pressure
• Pressure Mars

■ Soil

• Composition Mars (nitrates)
• Wanted composition (nitrates)
• Humidity Mars
• Wanted humidity

• Potatoes are wet when planted.

• Before emergence: SWT of -20 - -60 kPa

• After emergence and before tuber growth: SWT not lower than 0.3 MPa.

• After initiation tuber growth: SWT of -20 - -60 kPa

• Composition manure

■ Greenhouse

• Size
• Coefficient of heat transfer walls

■ Heat unit

• Capacity
• Energy consumption

■ Potatoes (Escort)

• Development speed
• Stages of development (with accompanying circumstances)
• Size

Dit is een deel wat niet direct toepasbaar is in het model, of het ontwerp van de kas, hoe gaan we dit noemen? En waar gaan we het laten?

Fertilization

Human feces and pee could be used in order to fertilize the ground. These substances, however, contain bacteria and parasites which can cause diseases to humans when using it. When sterilizing the feces and pee, this will not be a problem anymore. Since Mars has temperatures that could have a value of -50°C or even -100°C, this can be perfectly sterilized. The sterilization can take place outside where the feces are exposed to the cosmic radiation. This type of radiation will be capable of killing bacteria and parasites together with the extreme low temperature. According to Wamelink, when these humans preserve their feces and pee for half a year on earth as a starting package, this should be enough to fertilize the potatoes together with the pee and feces gathered on Mars itself. This also shows that a closed system will be used on Mars, meaning that everything will be used again. The ureum from the pee will be used for fertilizing the ground and the water will be used for drinking. The compost of dead plants will also be used as fertilizers.

How to realize the fertilization

Humans produce 150 grams of feces and 50 grams of pee every day. Within the 150 grams, 35% is dry and within the 50 grams of urine 65% is dry. In the table below, the percentage is given of the substances within the dry fractions of the feces and urine.

	% in feces/day/human	% in urine/day/human
P2O5	3	2.5
N	5	15
K2O	1	3
CaO	4	4.5

Now that these numbers are known, the amounts can be calculated in grams and the P, N, K and Ca should be calculated (which is done by molar ratios). Furthermore, these amounts should be multiplied by twenty as there will be twenty human beings on planet Mars. When all of these calculations have been carried out, the following table can be made. It represents the amount of the substances available in grams each day.

	grams/day
P	20.83874
N	150.000
K	24.90424
Ca	50.92117

Besides these amounts available, the human beings have also stored their feces and urine produced half a year before the landing on Mars. This is done to ensure that there will be enough available of the fertilizer.

Now that the amounts are now of the fertilizer and the amounts the potato actually needs, one can calculate when the fertilization should take place and how much should be placed each time.

It has been calculated how much all of the plants together need for one week and for 15 days. It has been decided to fertilize each week because less of the fertilizer has to be placed on top of the plants. Because of the fact that between some stages the potato plants need more fertilization than on other stages, the amount of the fertilizer placed on top of the potato plants also differs. In the table below, the amounts needed for all the potato plants for seven days long is given in grams.

	stage 0-15 days	stage 15-30 days	stage 30-45 days	stage 45-60 days	stage 60-75 days	stage 75-90 days
P	4347	18837	66654	68103	68103	23184
N	40572	188370	369495	259371	270963	82593
K	39123	173880	518742	231840	281106	94185
C	11592	62307	163737	5796	2898	1449

A calculation has been carried out, how much of the fertilizer is needed every week. It will be assumed that for every stage two weeks of fertilization take place. In order to ensure that enough of the fertilizer is available, it will be assumed that the amount needed for one week equals the amount needed for eight days. In this way, there is a certain error propagation when the potato plants are not able to take up all of the ions available. While calculating the amounts of fertilizer needed (feces and urine produced each day by twenty humans), it was noticed that there was a clear surplus of some ions. However, as explained before, the surplus does not matter for the plants, they simply do not absorb it. In the table below, the amounts of the fertilizer needed for each week is given.

	week 1	week 2	week 3	week 4	week 5	week 6	week 7	week 8	week 9	week 10	week 11	week 12
days of produced ferilizer	2	2	8	8	24	24	10	10	13	13	5	5

For some extra information: each day of the fertilizer represents 20*200 = 4000 grams of feces and urine together. In the table below, a scheme can be seen of how much fertilizer is needed per m² of the field.

	stage 0-15 days	stage 15-30 days	stage 30-45 days	stage 45-60 days	stage 60-75 days	stage 75-90 days
grams/m2	154.589372	618.3574879	3710.144928	6183.574879	48231.88406	30917.8744

From all the information given above, a part of the model will be written including the fertilization of the potatoes.

Dit gaat over seizoenen

There has already been an experiment carried out by Wamelink to see whether potatoes can grow in Martian soil in a green house. Potatoes indeed grew, however, they faced one main problem. The potatoes kept growing instead of dying. This created a lot of leaves and bad potatoes. The main cause according to Wamelink was that in the greenhouse there were no different seasons created for the plants to die. This induces that in our greenhouse, we should try to implement different seasons for an optimal result. These includes varying the length of a day and the temperature smoothly.

Greenhouse design

In this part of the wiki, several aspects concerning the design of the green house will be discussed. These are the materials needed for the walls of the greenhouse, the lamps, the sensors in the greenhouse and the sprinkler system.

Sensors

Sensors will be placed in the ground for measuring the soil water tension and the sensors will be placed in the air to measure the temperature. The sensor for the soil water tension is necessary to determine when the sprinkler system should become active. The sensors for the temperature is important to regulate the heat exchanger.

moisture

The sensors for the soil water tension are called irrometers. In order to measure the soil water tension in the best way, a shallow instrument should be used which is located 25 cm deep into the ground and also a deep instrument located 46 cm deep. Out of the model for the autonomous greenhouse, some ideal values for the soil water tension are given. When the sensors measure a moisture of above those ideal values, the input in the model will make sure that the sprinklers are switched off. If the measured value describes a lower moisture than what should be the case, then the input in the model ensures that the sprinklers spray the water onto the potatoes. When the value is as it should be again, the sprinkler will be turned off. It will not be the case that the values for the soil water tension will be too low, as the ground is dry from itself and the sprinkler will be turned off in time.

temperature

These sensors measure a certain value for the temperature. If the temperature value is too low, then the model, will give a signal to the heat exchanger to heat the greenhouse up. If the value for the temperature at the sensor will be in between ideal values, then the heat exchanger will stop heating. When the values for the temperature are too high, then the heat exchanger will make sure it cools down. When the ideal value is reached again, the heat exchanger will stop cooling.

Cosmic radiation

On earth we have the special privilege that we have a relatively dense atmosphere and an active magnetosphere. In the magnetosphere, charged particles are affected and manipulated by the magnetic field of an astronomical object, in this case Earth. These charged particles are more useful for the habitants of Earth than one might think. For instance, the solar winds that occur on our sun can launch a cloud of charged particles, which is a plasma. This plasma consists of mostly electrons, protons and alpha particles. These are redirected by our magnetosphere and this creates the phenomenon of the northern lights. Mars however does not have the magnetosphere. because it is absent, the solar winds, charged particles and other cosmic radiation reach the ionosphere of Mars directly. The cosmic radiation then strips (air)particles from Mars, making a very rarefied atmosphere in comparison to the one on Earth. The cosmic radiation also reaches the surface of Mars. If the greenhouse would be made out of a transparent material, it would also reach the potato plants. When plants come in contact with the cosmic radiation, it can change the DNA of the plants with consequences that can differ from situation to situation. For instance, it can make them inedible, kill them off completely, or make them grow even faster. Some scientist are however not completely sure what will happen, because the plants that are on Earth now have been through millions of years of relatively low cosmic radiation. But to ensure that the plants will stay roughly the same, a completely sealed greenhouse will be build.

It is not possible to stop cosmic radiation, but what can be done is to break it up. When one breaks the particles up in even smaller particles they become less harmful. Materials that are good at breaking the particles up are materials that are as small as possible. The best are Hydrogen, Boron, and Nitrogen. Now it is very important that the materials can be used as a building block as well, the materials can of course be used as extra layers in between the building and structural layers. Only with efficiency in mind, for transport (the flight to Mars) and the building of course, the walls can best be build out of these materials as a whole or at least for the largest part. The boron nitride nanotube is for this purpose a very good option. It has the shielding capabilities needed while strong building capabilities remain. Especially the boron is very effective at breaking the neutrons, the nitrogen does not reach those standards but it also breaks the neutrons pretty effectively. Furthermore, one has to think about the thickness required for the walls. Because of the fact that the cosmetic radiation is very strong, the walls need to be thick enough. According to Wamelink it would suffice when the walls are one meter thick.

Construction material of the greenhouse

Besides the walls, an extra construction material is needed for the stability. There are some very strong winds, but that will not have much effect on the construction. The atmosphere is very thin on mars which means that it will only blow up the dust. Still, some columns will need to be placed in between the walls and the material for this will be carbon. The decision has been made between steel, aluminum and carbon. A look has been taken at the costs of the materials, their strength and their weight.

	Steel	Aluminium	Carbon
Tensile strength (Mpa)	400	150	4480
E-modulus (Gpa)	200	69	245
Density (kg/m3)	7800	2700	1800
Costs (euro/kg)	0.60	3.10	50

The factors tensile strength and E-modulus both have to do with the strength of the material. As can be seen in the table, Carbon has the highest strength. In this way, one can also use less columns than when using steel of aluminum. Carbon also has the lowest density, which makes it easier to build and also easier to transport to Mars. The costs of the carbon are much higher though. It could, however, be argued that when less columns are needed, less costs will be in the transportation aspect of the material. In this way, the extra costs could be erased. Furthermore, all of these materials have a good processability and recoverability. Steel and Aluminum are a bit better in this, however, carbon is still good enough to be used. So, the decision has been made to use carbon.

Surface area of the field of potatoes

A look will be taken at the amount of surface area which is needed for the potatoes to grow on. According to Wamelink, we could assume that a potato plant has a yield of around 2 kilograms. Each plant needs a surface area of around 50 cm by 50 cm. Each man consumes 250 grams of potatoes for a meal and a female 200 grams. This indicates that on average, 225 grams of potatoes will be eaten by each person for each meal. According to Wamelink, the process of the potatoes will last three months. So, humans will need potatoes for around 92 days. The amount of potatoes consumed by the people each day is 4,5 kg in total. The amount of kg potatoes needed for those three months is 414. As each plant produces roughly 2 kg of potatoes, 207 plants are needed. As each one will need a space of 50 cm in width and in length, the total area of the field will be equal to 0.50 m * 0.50 m * 270 = 51.75 m²
Because of the fact that 51.75 m² is not that much of an area, there will be plenty of space to grow other crops. One could imagine that after eating potatoes for weeks, the satisfaction in food will drastically decrease. When experiments can be done with other crops, such as wheat, other carbohydrate rich meals can be served on Mars. In this way, the users will be more satisfied. This also goes for the scientists, as they have been able to succeed in another sort of crop. After days of eating potatoes, the users might not be satisfied anymore. Taking this into account, future research could also be done on trying to plant wheat on Mars to make pasta for example. In this project, however, we limit ourselves to the potatoes.

Lights in the greenhouse

As has been mentioned before, the experiment performed by Wamelink experienced some difficulties concerning the seasons in a greenhouse. These have not been implemented when they did the experiment. This was most likely that the potatoes were not as good as they hoped them to be. In the model for this USE-project, the day length and the temperature will be dealt with as a reflection for the seasons. According to Wamelink this should namely be enough representation of the seasons. By using lamps in the greenhouse, the day length can be adjusted. When the greenhouse has summer conditions, the lamps will be turned on for more hours than when the greenhouse has winter conditions. The numbers for the day length are present in the model, therefore, they will not be explained again in this piece of text. It has been decided to use LED lights for the greenhouse. Based on several aspects explained below, LED lights have been chosen as lamps that are used.

Before, high pressure sodium lamps were used in greenhouses on Earth, however, when using LED lights 25% of the energy in the conversion of electricity into light is saved. Furthermore, 30% of the electricity can be saved when placing the LED lights in a smart way. So, a total of around 60% can be saved. This would also be helpful for the lamps on Mars; less solar panels are needed which will reduce the costs in transportation to Mars. Furthermore, LED lights will not get hot, which makes the greenhouse easier to regulate, as the model will only need to take care of the heat transportation in the heat exchanger. Another advantage is that the lights can be placed closer near the crops when needed. The optimum of the closeness of the lamps to the crops, differs for each crop. In this way, the distance from the LED light to the crop can be adjusted easily. In addition to this, the LEDs can also be placed on the sides of the potato plants, enhancing the photosynthesis. It is not clear currently where these LEDs should exactly be placed. Because a robot has to move through the potato plants, it has been decided to just place the LEDs against the ceiling. The different colors in light can also be realized with LEDs, as each phase of the potato plants needs a different light color as an optimum. There is still some research going on in this part, so it is not clear yet which colors to use. However, if we use LEDs, it is known that its color can be easily adjusted. Light colors also have two other advantages: it will enhance the plants’ resistance against diseases and it influences the opening and closing of the stomata.
The entire ceiling of the greenhouse will be filled up with these LED lights, so this means around 50-60 m².

Sprinkler system

To ensure that the water will be equally distributed over the field of potato plants, a sprinkler system is used. As discussed the section “sensors”, the sensors will be the ones that trigger the sprinkler system based on the soil water tension.
The sprinkler system will consist of several sprinklers and a pump to push the water out onto the plants. In order to save energy costs, the sprinklers will be placed on the ceiling, meaning that less pressure is necessary, so the pump has to less work. The sprinklers are able to let the water go out in 360°, so less sprinklers are needed. A decision has to be made between buying more sprinklers, which is cheaper or less, which makes the pump work harder. The space that the sprinklers need in the spacecraft to Mars is not much and the sprinklers themselves do not cost much. They only have to be bought once. The pump needs to work for a longer period of time and the energy needed will rise, meaning that more solar panels are needed. Solar panels are expensive and bigger than a few extra sprinklers, therefore is has been decided to take more sprinklers. Furthermore, if the model can be made more complex, only a few sprinklers can be switched on when a part of the field is too dry. In this way, the system will be more efficient and ensures that the other parts in the field will not get too much water. Furthermore, the width of the tubes in which the water flows has to be decided. As the water pressure will not be high and less water is needed for each sprinkler, thin tubes can be chosen. This saves money and a bit of space in the aircraft. Also, a smaller nozzle will have to be used to let the water flow out as the pressure is low and the tubes are smaller in diameter.
On earth, a sprinkler on the ceiling could spread water for 6 meters in diameter, however, as the gravity is lower on Mars, it will be assumed that the sprinkler is able to spread water for 4 meters in diameter. The area covered by a 3.5mx3.5m square will be around the same as the area covered by a circle of diameter 4m. The total area of the field of potatoes will be 51.75 m². The length and width of the field will be 7.2 meters. This means that in length and width 3 sprinklers need to be placed. The total number of sprinklers used will therefore be 9.
The influence of the gravity must not be forgotten here. The pressure inside the tubes should already be higher than when placing this greenhouse on earth because of the fact that the gravity on Mars is smaller. When, as stated above, less sprinklers would be used, the pressure would even raise more. This high value for the pressure might be too high for the pump, therefore, it is wise that it was chosen to take more sprinklers.

Heat exchanger

Within this greenhouse, no use can be made of the sunlight heating up the inside of the greenhouse. In addition, no window can be opened to cool down. Instead, a heat exchanger will be used to get the right temperature inside. By means of the sensors discussed above and the model, the heat exchanger will cool the greenhouse down or heat it up.

Because of the fact that the system is closed, one should use cooled water and warm water to cool or heat up the system. Because of the fact that the water on Mars is in the form of ice, this should at first be heated up until it turns into liquid.
If the greenhouse should be heated, the water flowing through the greenhouse will be warmed up by the heat exchanger. This part of the system works the same as a heater in an ordinary home on Earth. Normally, an air-conditioning would be used for cooling the interior of the greenhouse, however, the system is a closed system unlike a house on Earth. Therefore, a solution has to be found to cool down the system.
It is possible to cool down the greenhouse by mean of cold water streaming in tubes inside the greenhouse. One could argue that extra cooling might not be needed because on Mars itself it is cold enough. However, as the greenhouse is well isolated, it could happen that it needs to be cooled a certain time. At daytime the temperature is higher than at night. The principle for the cooling mechanism would be the same principle as a heater, only this time the interior is cooled down. The electricity consumption for this system will be less than using an air-conditioning, because the condenser of an air-conditioning can easily reach a temperature of 50° and when cooling with water this will not be the case. The only problem with cooling by using water is that condensation can occur from the air in the interior on the tubes. This could cause the material to rust, however, one could also buy stainless materials in order to not make this a problem such as stainless steel.
Some tubes are also located in the ground. These need to be well insulated to make sure that the water inside does not freeze because of the cold Martian ground. Another reason for insulating the tubes in the ground is to ensure that only the target places will be warmed up. The ground is not the part that needs to be heated, therefore, when insulating these tubes in a proper way, the heat will remain inside the tubes and will only come out when the water reached the tubes of the interior.

Energy source: solar panels

When the autonomous greenhouse wants to work, an energy source is needed. This will be done by solar panels. The external irradiation between Mars and Earth is very different. For Earth this value equals 1361 W/m² and for Mars this value equals 589 W/m². This external irradiance on Earth is partially reflected, partially absorbed and there is some direct and diffused irradiance. Taking these things into account, 1000 W/m² sunlight hits the surface of the Earth and, therefore, reaches the solar panels. For Mars it has been decided to take the same ratio. This means that for the solar panels 433 W/m² can be used. However, on Mars there are less clouds, so the light intensity is a bit higher. On the other hand, more light will be reflected on Mars, causing the light intensity to drop. Some rough numbers can be considered here. Regarding the fact that Mars has more irradiance to pass through the atmosphere, the intensity will go up with 50 W/m², however, on the other hand, more light is reflected, so the intensity will go down with 30 W/m². This means that in total the light intensity on Mars will be 433+20 = 453 W/m². This value is crucial to find out whether solar panels are even possible. The conclusion is that around twice as much solar panels should be used than on Earth. On Mars there is enough place for the solar panels, even when we want to put them on the roof. A solar panel is about 2 m². Our roof of the greenhouse will be around 60*60 = 3600 m². By means of a solar panel calculator it has been calculated that 1355 solar panels would fit on the roof. This would give enough energy to the heat exchanger and the lamps for example. Less than 1355 solar panels will be used, however, as the exact amount of energy supply is not clear. It is difficult to determine how much solar panels are exactly needed. It is known that enough of them can be placed on the roof. Because the roof of the greenhouse is flat, the optimum angle for the solar panels can be calculated by means of the angle of the rotation axis. The angle of the rotation axis on Earth equals 23.5° and the optimal angle for the solar panels equals 35°. The angle of the rotation axis on Mars is 25°. This does not differ much with the angle on Earth. It has been concluded that the optimum angle of the solar panels will be 35° on mars as well. Even if this is not the exact optimum, the efficiency will drop with 1% when the difference is only 5°. In this case, the drop in efficiency is negligible. Therefore, the angle under which the solar panels will be placed equals 35°.

When looking at the costs of solar panels, it is quite an investment for the companies. It is however known that within 20 years one could benefit from choosing solar panels. Currently, a group of twenty people are going to look whether life on Mars is possible. This means that when it is possible, even more people could go to Mars and decide to live there. The greenhouse, therefore, needs to last for at least 20 years. Furthermore, another way to get electricity is difficult to implement on mars. One could think of wind mills; however, those are way too big to install on Mars. The twenty users on Mars will have less difficulty with implementing solar panels than building wind mills. Furthermore, the gravity will have a big influence in it, because the blades should be turning. It is also not known whether these wind mills would produce enough energy. For solar panels one could calculate the light intensity and amount of solar panels easily to find out whether this would give enough electricity.

Model explanation

Within the model, one can change a number of things and, like explained in different parts of this page, the growth of the potato reacts to all of these in a different way. To model the numerous variables, some assumptions have to be made. However, this is because of the complexity of modeling a non-numerical process, or simply because of the lack of knowledge. Not all processes are examined and mapped out in a numerical way so it can be modelled. Starting with the growth of the plant itself, in this case the potato, the growth will vary from plant to plant and this has to be taken in to account, since it will affect things like the water absorption. That absorption will affect the total needed water supply. Water absorption differs between the different phases of the plant growth, and at different times it will absorb more or less water. This is because in the different phases the assimilation rate varies. A basic assumption is that when there is a higher assimilation rate, the needed water is also higher. A specific range of soil water content that can be controlled by a sprinkler system, by hooking the sprinkler system to a PD-controller that measures the soil water content with a few sensors spread out over the greenhouse to get a good approximation of the mean water content. The water retention and hydraulic conductivity of the soil itself are other variables that control the water management. This all creates a large loop, making up the water part of the model. There are a lot more variables that are taken into account. Like discussed above, the properties of the ground are an important factor. Also the properties of how it interacts with water are important. The nutrient values are as well an aspect to take into account. Effecting the model in a different way again, since the regeneration value of the nutrition in the ground is also important. When the plants use all the nutrition, there has to be a way to refeed the ground so it matches the needs of the plant. Since the greenhouse on mars will have a way to distribute fertilizer, the refeed will be almost instant. This has to be since the ground on mars has no organic contents and thus the automatic of the Martian ground is not possible. The different variables used by the model are in data files, these files contain different sets of data, ranging over a certain time to keep somewhat realistic variable circumstances. The weather here on earth, of course, varies a lot, but in the greenhouse it can be controlled in a very precise way to achieve the best growth-time, largest potatoes and most nutritious potatoes.  

Explanation results

Nutrition

Like explained above, the potatoes need certain nitrates that are in the Earths organic ground by nature. This is modelled with 3 different nitrates, these can be added with the fertilizer sprinkler system. The three nitrates are: Nitrogen (N), Phosphorus (P) and Potassium (K). These values can range from 0 up to 100 kg/ha and do not depend on each other. When experimenting with the different values a very easy pattern is to be found, the potatoes grow in a linear pattern parallel with the amount of nitrates that are in the ground as long as there is balance between the different nitrates. Namely when one approaches zero. Making for a very easy conclusion for this part of the optimal values of the potato growth. In reality it will be a bit different of course, the 100 kg/ha does not exceed the top limit of the potato, because if so, the potato growth will approach zero.

Martian ground

The variables concerning the ground are expressed in the model as ranges. The model uses the values for the water retention and hydraulic conductivity. The calculations are done in between the most extreme values that are found or calculated on Mars. This gives a first indication in what has to be added to increase the growth of the plants and what has to be done to increase the water flow.

Literature search

To start of our project we are doing a literature research. We divided the literature search into the following areas:

1) The conditions on mars (including the effects on aggro culture due to these conditions)

2) Robots and machinery that are already used in outher space

3) Farming robots that are already being used on earth

For all of these areas papers will be searched and a summary of the overall findings will be given with refrences to the found papers.

Mars conditions

- Wei Luo (2011) Estimating hydraulic conductivity for the Martian subsurface based on drainage patterns — A casestudy in the Mare Tyrrhenum Quadrangle retrieved from: https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1268&context=geosciencefacpub

- Boersma, H. (2012). Waarom gebruiken we geen mensenpoep als mest? - Kijkmagazine. Retrieved from: https://www.kijkmagazine.nl/nieuws/waarom-gebruiken-we-geen-mensenpoep-als-mest/

- C. Leovy. “Weather and climate on Mars” (2001)

- F. Gifford Jr. “The Surface-Temperature Climate of Mars.” (1955)

- S. R. Lewis, et al. “A climate database for Mars” (1999)

- G.W. Wieger Wamelink, et al. “Can plants grow on mars and the Moon: A growth experiment on Mars and Moon soil simulants” (2014)

- Mars – Sterren en Planeten (2005-2009). Retrieved from: http://www.worldwidebase.com/science/mars.shtml

- M. Nelson, et al. “Integration of lessons from recent research for “Earth to Mars” life support systems (2006)

- S. Silverstone, et al. “Development and research program for a soil-based bioregenerative agriculture system to feed a four person crew at a mars base” (2003)

- Journal of Climate. Jun2001, Vol. 14 Issue 11, p2430. 13p. 23 Graphs..... no access

- Agriculture, Ecosystems & Environment. Feb2018, Vol. 254, p99-110. 12p....... no access

- Climate Research. 2009, Vol. 39 Issue 1, p47-59. 13p. 7 Charts, 5 Graphs, 1 Map..... no access

- Canadian Journal of Forest Research. Oct2010, Vol. 40 Issue 10, p2036-2048. 12p. 1 Chart, 1 Graph..... no accesss

- Global Change Biology. Jan2007, Vol. 13 Issue 1, p169-183. 15p. 1 Diagram, 7 Graphs, 2 Maps..... (no access)

- James I. L. Morison,Michael D. "plant growth and climate change" (2006)..... (no access)

- R. RötterS.C. van de Geijn. "Climate Change Effects on Plant Growth, Crop Yield and Livestock". pp 651–681 (1999).... (no access)

- Angela T. Moles. "Global patterns in plant height"- Journal of ecology. (2009).... access

- Wamelink, W. (2017). Regenwormen komen tot voortplanting op - WUR. Retrieved from: https://www.wur.nl/nl/nieuws/Regenwormen-komen-tot-voortplanting-op-Marsbodemsimulant.htm

- Wamelink, W. (2017). Varkenspoep als voeding - WUR. Retrieved from: https://weblog.wur.nl/ruimtelandbouw/varkensmest-als-voeding/

Potato

- Aardappel – YARA. Retrieved from: http://www.yara.nl/gewasvoeding/gewassen/aardappel/

- Adam H. Sparks. "Climate change may have limited effect on global risk of potato late blight" - Global change biology (2014).... (no access)

- Bakhtiyor Pulatov. "Modeling climate change impact on potato crop phenology, and risk of frost damage and heat stress in northern Europe"- Agricultural and Forest Meteorology. Pages 281-292. (2015).... (no access)

- D.T. Westermann “Nutritional requirements of potatoes” (2005)

- Van Ittersum, M.K. & Scholte, K. Potato Res (1992) 35: 365. https://doi-org.dianus.libr.tue.nl/10.1007/BF02357593

- H.P. Beukema, D.E. van der Zaag "Introduction to potato production" (1990)

- Pootaardappels – Carel Bouma biologisch poot- en plantgoed (2018). Retrieved from: https://www.biologischpootgoed.nl/teeltadvies-pootaardappelen/

- P.L. Kooman et al. "Effects of climate on different potato genotypes 2. Dry matter allocation and duration of the growth cycle" (1996)

- C.C. Shock, A.B. Pereira, E.P. Eldredge "Irrigation Best Management Practices for Potato" (2007)

- S. M. Bennett, T. W. Tibbitts, W. Cao. “Diurnal temperature fluctuation effects on potatoes grown with 12 hr photoperiods” (1991)

- E.E. Ewing, P.C. Struijk “Tuber Formation in Potato: Induction, Initiation, and Growth” (2010)

- C.M. Menzel “Tuberization in potato at high temperatures: interaction between temperature and irradiance” (1985)

- E.E. Ewing, P.F. Wareing, “Shoot, Stolon, and Tuber Formation on Potato (Solanum tuberosum L.) Cuttings in Response to Photoperiod” (1978)

- M. Rodríguez-Falcón, J. Bou, S. Prat “Seasonal Control of Tuberization in Potato: Conserved Elements with the Flowering Response” (2006)

Existing farming technology

- Tillet, N. (2003). Robots on the farm. The industrial robot, 30(5), 396. Retrieved February 23, 2018, from [1]

- Giles, F. (2017). Agricultural robots no longer science fiction. Florida grower, 110(2), 12-13. Retrieved February 23, 2018, from [2]

- Hill, P. (2016). 9 robots designed to enhance the farm workforce. Farmers Weekly, 165(3), 66-70,72,75. Retrieved from [3]

- Robert Bogue, (2013) "Can robots help to feed the world?", Industrial Robot: An International Journal, Vol. 40 Issue: 1, pp.4-9, [4]

- Victor Bloch, Avital Bechar, Amir Degani, (2017) "Development of an environment characterization methodology for optimal design of an agricultural robot", Industrial Robot: An International Journal, Vol. 44 Issue: 1, pp.94-103, [5]

- Bac, C. W., van Henten, E. J., Hemming, J. and Edan, Y. (2014), Harvesting Robots for High-value Crops: State-of-the-art Review and Challenges Ahead. J. Field Robotics, 31: 888–911. doi:10.1002/rob.21525

Robots and machinery used in outer space

- Rećko, M., Tołstoj-Sienkiewicz, J., & Turycz, P. (2017). Versatile soil sampling system capable of collecting, transporting, storing and preliminary onboard analysis for mars rover analogue10.4028/www.scientific.net/SSP.260.59 [Robotic arm for Mars Rover] Link to article

- Czaplicki, P., Recko, M., & Tolstoj-Sienkiewicz, J. (2016). Robotic arm control system for mars rover analogue. Paper presented at the 2016 21st International Conference on Methods and Models in Automation and Robotics, MMAR 2016, 1122-1126. 10.1109/MMAR.2016.7575295 [Soil sampling] Link to article

- Sakib, N., Ahmed, Z., Farayez, A., & Kabir, M. H. (2017). An approach to build simplified semi-autonomous mars rover. Paper presented at the IEEE Region 10 Annual International Conference, Proceedings/TENCON, 3502-3505. 10.1109/TENCON.2016.7848707 [Making a Mars Rover semi-automatic] Link to article

- Wong, C., Yang, E., Yan, X. -., & Gu, D. (2017). Adaptive and intelligent navigation of autonomous planetary rovers-A survey. Paper presented at the 2017 NASA/ESA Conference on Adaptive Hardware and Systems, AHS 2017, 237-244. 10.1109/AHS.2017.8046384 [Intelligent navigation] Link to article

- Parness, A., Abcouwer, N., Fuller, C., Wiltsie, N., Nash, J., & Kennedy, B. (2017). LEMUR 3: A limbed climbing robot for extreme terrain mobility in space. Paper presented at the Proceedings - IEEE International Conference on Robotics and Automation, 5467-5473. 10.1109/ICRA.2017.7989643 [Robot with climbing arms (maybe possible to use for planting and harvesting] Link to article

- Garrido, S., Moreno, L., Martín, F., & Álvarez, D. (2017). Fast marching subjected to a vector field–path planning method for mars rovers. Expert Systems with Applications, 78, 334-346. 10.1016/j.eswa.2017.02.019 [Vector field-path planning] Link to article

- Scopus search link

Soil on Mars

- Boynton, W.V. , D. W. Ming, S. P. Kounaves, S. M. M. Young,† R. E. Arvidson, M. H. Hecht, J. Hoffman, P. B. Niles, D. K. Hamara, R. C. Quinn, P. H. Smith, B. Sutter, D. C. Catling, R. V. Morris. (2009). Evidence for Calcium Carbonate at the Mars Phoenix Landing Site – Science

- Hecht M. H. , S. P. Kounaves, R. C. Quinn, S. J. West, S. M. M. Young,† D. W. Ming, D. C. Catling, B. C. Clark, W. V. Boynton, J. Hoffman, L. P. DeFlores, K. Gospodinova, J. Kapit, P. H. Smith. (2009). Detection of Perchlorate and the Soluble Chemistry of Martian Soil at the Phoenix Lander Site – Science.

- Kounaves S. P., Brandi L. Carrier, Glen D. O’Neil, Shannon T. Stroble, Mark W. Claire. (2014). Evidence of martian perchlorate, chlorate, and nitrate in Mars meteorite EETA79001: Implications for oxidants and organics – Icarus.

- Manning C. V. , Christopher P. McKay, Kevin J. Zahnle. (2008) The nitrogen cycle on Mars: Impact decomposition of near-surface nitrates as a source for a nitrogen steady state – Icarus.

- Mustard J.F. , Christopher D. Cooper & Moses K. Rifkin. (2001). Evidence for recent climate change on Mars from the identication of youthful near-surface ground ice – letters to nature.

- Smith M. L., Mark W. Claire, David C. Catling, Kevin J. Zahnle. (2014). The formation of sulfate, nitrate and perchlorate salts in the martian atmosphere – Icarus.

- Stroble S. P., Kyle M. McElhoney, Samuel P. Kounaves. (2013). Comparison of the Phoenix Mars Lander WCL soil analyses with Antarctic Dry Valley soils, Mars meteorite EETA79001 sawdust, and a Mars simulant – Icarus.

Greenhouse

- Bernelot Moens, H.L. (1973). Handboek voor de akkerbouw - WUR. Retrieved from: Retrieved from: http://library.wur.nl/WebQuery/wurpubs/fulltext/359567

- Leidingen isoleren – Gamma. Retrieved from: https://www.gamma.nl/klusadvies/isoleren/stappenplan/leidingen-isoleren

- Marcelis, L. (2014). Met LED-verlichting energieverbruik glastuinbouw halveren - WUR. Retrieved from: https://www.wur.nl/nl/nieuws/Met-ledverlichting-energieverbruik-glastuinbouw-halveren.htm

- Mars(planeet) - Wikipedia (2018). Retrieved from: https://nl.wikipedia.org/wiki/Mars_(planeet)

- Staal vs Aluminium vs Carbon. (2010). Retrieved from: https://bodypegasus.wordpress.com/2010/01/27/staal-vs-aluminium-vs-carbon/

- Understanding soil moisture – Irrometer. Retrieved from: http://www.irrometer.com/basics.html#depths

- Wolken - Klimaatgek. Retrieved from: http://klimaatgek.nl/wordpress/wolken/

- Zonneconstante - Wikipedia. (2018). Retrieved from: https://nl.wikipedia.org/wiki/Zonneconstante

- Zonnepanelen calculator. Retrieved from: http://www.zonnepanelencalculator.nl/huishoudens

- Zonnestraling en zonnepanelen - Het weer in Haaksbergen. Retrieved from: http://www.weerstationhaaksbergen.nl/weather/index.php/Weblog/zonnestraling-en-zonnepanelen.html

Coaching Questions

Coaching Questions Group 1