Procrastonauts

https://docs.google.com/presentation/d/1Vj7GdMn3AZ1a8fj2gJKysKoKEQ1vSch7/edit?usp=sharing&ouid=110920689771458909897&rtpof=true&sd=true

https://github.com/NicolaGiardino/SpaceApps2021

A complementary food production system is mandatory for a crewed mission on Mars, because of the necessity of fundamental vitamins such as B, C and K, but also to provide a differentiated diet to the crew, minimizing the risks of a fixed diet. To achieve this goal the most important decision is the choice of the crop to harvest. We decided to go for mushrooms. 

Why mushrooms?

The reasons for this choice are multiple:

• Mushrooms can be grown rapidly, with an harvesting time of approximately 7-10 days from the colonization of the substrate;
• They require a fraction of the water needed for other crops, for example they require 7% of the water used for potatoes;
• They can be also eaten raw or dried, making them storable almost indefinitely, allowing the reuse of the extracted water;
• Spores and mushrooms are quite radio-resistive, and some studies from NASA and others affirm that they feed on radioactivity, while remaining edible for humans [1];
• Research studies already confirmed that mushrooms can grow in a microgravity environment: in this condition they grow in the direction of the light source [2];
• Mushrooms are very rich in nutrients, having a high vitamin content, especially B, C and K, while also containing remarkable quantities of proteins and mineral salts [3].

Basics of mushroom cultivation

We studied the standard harvesting process used on Earth [4], adapting and suiting it for our necessities. The mushroom cultivation process can be divided in four steps:

• STEP 1 (on Earth): Growing out a chosen mushroom culture on agar filled petri dishes: This involves placing mushroom spores on a nutrient rich media. This will allow the spores to grow, forming a culture known as mycelium. This step would be done in-lab on Earth, allowing the crew to bring samples of live mycelium in petri dishes, always ready to start new harvests. 

fig.1: Mycelium culture in petri dish

• STEP 2: Transferring the mycelium onto sterilized hardwood sawdust pellets: It’s done by extracting a sample of mycelium and transferring it into a package of sterilized hardwood sawdust pellets (Pellet’s been chosen to avoid sawdust particles flying around in the spacecraft). The mushroom mycelium will start to grow out, running across and devouring the sawdust, eventually taking over the package, forming the so-called spawn.

   fig.2: Hard sawdust pellets spawn

• STEP 3: Inoculate a suitable substrate with the spawn: The spawn is used to inoculate a substrate on which the mushrooms will eventually grow. It’s done by mixing it with the provided substrate material (depending on the type of mushroom chosen) and some water. The bags must rest in a warm environment to let the mushroom mycelium to run across the substrate, consuming nutrients and engulfing it.
• STEP 4: Inducing mushrooms’ fruiting by altering the environmental conditions: Once the entire substrate is engulfed in mycelium, it’s time to induce the fruiting state. Small cuts are made on the bags and by altering the environmental condition of the chamber, dropping the temperature and increasing the humidity, the mycelium will start to form little knots which eventually turn into pins.Many of these pins will continue to grow, drawing up water and nutrients from the substrate and rapidly turning into full sized mushrooms.

fig.3: Fruiting bodies on a bulk substrate

If a proper environment is maintained, a healthy substrate can produce numerous flushes of mushrooms, allowing to harvest the mushrooms up to 4 times before recycling.

Design

The food delivery system we designed is based on a foldable, inflatable growing chamber (IGC) (fig.4), first darkened and heated to allow the mycelium to grow, and then cooled down to ambient temperature, humidified and illuminated for the fruiting of the mushrooms.

fig.4: The inflatable growing chamber (IGC) deflated and inflated.

The IGC consists of two rigid shells on the top and the bottom, three side walls made of inflatable materials to obtain structural integrity and a transparent access door on the front, occasionally covered by unfolding a dark curtain. The shells have 3 hooks each on the inner side, used to keep the substrate bags in place. 

In this setup the IGC would approximately measure 70x35x40cm in its inflated form, and 70x35x10cm in its deflated form, reducing its volume by 75%. The bottom shell contains the soft deflated walls when the structure is closed and stored.

The top shell contains the electronics (fig.5):

• A controller board to drive sensors and actuators;
• Sensors for humidity, temperature, oxygen and substrate moisture;
• A fan to guarantee the correct airflow inside the chamber;
• A water nebulizer to control the humidity rate during the fruiting state;
• An heater used to increase the environment temperature during the mycelium growth ;
• A Real-Time Clock and a LED strip used to keep a good day/night cycle;
• A display and some buttons as user interface for the astronauts to check all the data needed.

fig.5: Electronic circuit prototype.

A demo code is provided in the GitHub repository attached.

Use

The composition of the substrate depends on the species of mushroom chosen. We went for the Pleurotus Ostreatus, commonly known as Blue oyster mushroom. It’s one of the easiest to harvest and it has a really fast growing rate. The best substrate for this species is hardwood sawdust (in the form of compressed sawdust pellets), giving a higher overall Bio-Efficiency (BE) compared to other materials[2].

To start the production a certain amount of hardwood sawdust pellets is needed. We opted for a clean and space efficient solution: 

• Pre-made 250g sawdust pellets packages (SPP) are stored vacuum sealed (fig. 6);
• A set of empty custom mushroom grow bags (MGB) is provided to the crew; 
• One single SPP would be inoculated with the mycelium and used as spawn;
• It would then be mixed with a substrate made of five other brand new SPP (1,25kg in total) and a fixed amount of water in one of the MGBs (fig. 7);
• The chamber can host up to three 1.5kg MGBs that will be hooked to both the shells waiting for the mycelium and mushrooms’ growth (fig. 8);
• One single MGB can produce up to 1.4kg of mushrooms in one month divided in 3 to 4 flushes.

fig. 6: A sealed sawdust pellets package (SPP)

fig, 7: Full 1.5kg mushroom graw bag (MGB)

fig. 8: IGC as fruiting chamber, loaded with 3 MGBs

It’s important to point out that the spent mushroom substrate (SMS) can be indefinitely recycled to make new substrate in the suggested proportions: 70% SMS (∽1 kg), 15% new sawdust pellets (∽250g, one SPP), 15% spawn (∽250g, made from one SPP). It would achieve a BE of approximately 84% compared to the previous 95% of the fresh substrate [5] (fig.9), providing up to 1.2kg of mushrooms per MGB until the next cycle.

fig.9: Bio-efficiency of the substrate using different SMS percentages.

Given that one cycle lasts for approximately one month, this whole procedure would be repeated up to 7 times in the trip back to Earth, meaning that the total weight of the materials required for our proposal, recycling the spent substrate, would be about 13.5kg plus the weight of the chamber and the petri dishes.

Extras

Commercial artificial supplements can be added to the substrate to increase its nitrogen, protein and sugar content, helping the mycelium growth and the fruiting process. We haven’t found any relevant or reliable studies about the BE increase using this kind of supplements, so further investigations are needed.

Another IGC can be used to speed up the process using them both at the same time: one chamber can be used to let the mycelium grow, while the other is used only as a mushroom fruiting chamber. This way the two different environments are separated, requiring the operator to swap the bags midway.

Alternatively additional IGCs can be used to increase the production, allowing the crew to recycle the extra spent substrate accumulated with the past harvests.

Mushrooms can be a precious resource even on the Martian surface: while sawdust is the most viable substrate for the trip back to Earth, it’s not the only one that can be used; in fact many mushroom species can grow on compost. During the round trip to Mars a decent amount of human manure and organic food waste is accumulated; once on the surface of Mars these wastes could be processed and turned into compost, inoculating it with the sawdust spawn from a more suitable mycelium culture (such es Agaricus bisporus), and letting it fruit, creating a small and independent mushroom farm. 

Conclusions

This setup would provide a grand total of almost 26 kg of mushroom during a 7 months long trip from Mars to Earth.

We’ve tried to achieve the maximum rate of automation. The astronauts will just need to let the mycelium grow and harvest the mushrooms, leaving them with the only duty of checking the sensor’s data once in a while and renewing the substrate once a month.

We used both the documents provided by NASA, VEGGIE and Advanced Plant Habitat. We based our idea of a production system on the ones already used on the ISS, improving it and making it easier to deploy, while adapting for mushroom harvesting, maintaining the ease of use and automation of those systems.

More in the depth: we based our system mostly on the VEGGIE system from NASA, being the easiest to deploy and the one with a lower volume while folded. The APB was also useful for the sensors it contains, but was too big and complex for the challenge we were faced with.

Inspiration for selecting the challenge:

We decided to choose this challenge because the exploration of Mars and the challenges that it brings excite us. But also because it is the best one for our skills and knowledge.

Approach to reach the goal:

We approached the project by going for steps, in a sort of Top-Down scheme. 

We began by choosing the right crop, being the choice that impacted the whole system’s prototyping.

Then we considered the possible approach to solving the problem, using the resources given to us by NASA and the ones we found by ourselves. 

The hardest part was to design a space-efficient solution, while keeping it easy to use and automated. We prototyped the system by ourselves, basing it on previous existing mushroom farming methods and adapting it to a zero-g environment.

We used the C++ programming language to code the microcontroller piloting the actuators, sensors and display, giving a complete demo of the final system.

Problems faced:

• Find a space-efficient and weight-efficient solution
• Having both a foldable and rigid system

Achievements:

In the end we found the most viable solution that is also usable in situ, giving fresh food to the crew in a short period.

[1]- https://www.sciencedirect.com/science/article/abs/pii/S0044405777800300

[2] -http://davidmoore.org.uk/Assets/Printed_documents/my_reprints/1991_Moore_mushrooms_in_microgravityMycologist.pdf

[3] - https://fdc.nal.usda.gov/fdc-app.html#/food-details/168580/nutrients

[4] - https://link.springer.com/article/10.1007/s00253-009-2343-7

[5] - https://updatepublishing.com/journal/index.php/rib/article/view/2452

#mars #VEGGIE #foodsystem #mushrooms #harvest #plants

This project has been submitted for consideration during the Judging process.