Perhaps you saw the news recently about astronauts in the International Space Station eating their first home grown lettuce? It's just a beginning, but in the future, could they grow all their own food and get all their oxygen from plants?
The astronauts of the ISS eating their first home grown lettuce in space. Actually, it's a first only for US astronauts. The Russian cosmonauts have been eating half their crop on the ISS since 2003. The US astronauts have just had the food passed as okay for them to eat it as well.
Could they grow all their own food and get all their own oxygen from plants?
We probably won't recreate the tropical jungles and other mini ecosystems of Biosphere 2 in space, at least, not until we can build much larger habitats than the ISS. But what about those smaller scale suggestions for growing food in Lunar or Martian habitats.
Those are space habitats too, in vacuum or near vacuum conditions like the ISS. Could the ideas for these habitats be used in Low Earth Orbit as well?
Early experiments with prototype space habitats for Mars or the Moon were so promising that in the 1980s, scientists were looking into the possibility of a biological Controlled ecological life support system, for future space stations in orbit around the Earth as well. For instance here is a conference on the topic in 1984.
Though most have heard of Biosphere 2, probably not many have heard of the (originally rather secret) closed habitat experiments the Russians did with their BIOS-1, 2 and 3 in the sixties, continuing right through into the eighties.
They produced all the oxygen and nearly all of the food for a crew of three, from a surprisingly small volume of habitat of 315 cubic meters. That included 237 cubic meters set aside for growing crops. Their longest test was 180 days with a crew of three, with nearly everything recycled.
Biosphere 2, which is what most people think about when you suggest a closed habitat.
It's great for studying closed ecosystems, but it wasn't designed for space.
- The trees and bushes need lots of space to grow.
- Most of what you see in this photograph is inedible.
- The plants chosen are not especially quick growing.
Something like this might be great in a Stanford Torus type habitat with lots of space, and especially if you have some use for wood and other products from the trees and bushes.
For a small space habitat you need rapidly growing crops, to get as much food as quickly as possible from a small area. Also the faster it grows, the more oxygen it produces. And you want as much of it edible as possible. In short, you want something more like BIOS-3.
Bios 3 - facility in Siberia which was used for a series of ground breaking experiments in closed systems for space habitats in the 1960s through to the 1980s. And still exists today.
This is a model of the habitat. As you see they had it set out with three rooms devoted to growing crops, and one room for the crew quarters. The crops provided all their oxygen and nearly all their food, in a series of experiments in Russia, for a crew of 3. Longest test was 180 days.
They grew ten different crops, including dwarf wheat which they used to make all their own bread. Only 13 square meters of growing area was needed, per person for 78% of their dry food requirements and nearly all their oxygen.
They were by no means the only ones working on this. But they got closer to 100% recycling than anyone else in the field at the time.
They kept healthy. They needed some extra food supplied, such as dried meat, but all the bulky food such as carbohydrates, they grew themselves, and nearly everything else. They baked grains harvested from dwarf wheat and made all their own bread, for instance, from that small growing area, as well as greens, radishes, beets etc. It sounds like a healthy and tasty diet.
(You can get this article as a kindle ebook)
DOES THE ISS HAVE ENOUGH VOLUME TO GROW ITS OWN FOOD?
Is there any chance of doing this in space? The 315 cubic meters of BIOS-3 is large, but not impossible for a space station.
The ISS has a total volume of 32,333 cubic feet, or 915 cubic meters. Nearly three times the volume of the BIOS-3 experiment. So that is enough to grow nearly all the food for eight people at least, including living space for the crew, and provide all their oxygen from the plants.
Then, the BIOS-3 experiments weren't particularly optimized for volume, as you can see from the model. There is lots of free unused space above the crops. So, you could probably grow food for many more than eight crew, in the volume of the ISS. That is, if the methods of BIOS-3 can be adapted to zero g.
Of course I'm not suggesting that we turn the ISS over to crop growing in space. They need that space for other things. But this preliminary rough calculation is promising enough to look at this more closely.
Also don't think of it as like your allotment or garden or house plants. There would be no pests in space; no insects at all except the ones you take up with you. And the plants would be grown in sterile conditions using aeroponics with their roots dangling in moist air supplied with nutrients, and in containers or modules separated from the crew quarters. This is a mature and practical technology on Earth and it's already been shown to work in space. The system would be largely automated with minimal work for the crew.
RELIABILITY OF PLANTS
The crew of the ISS have had many issues with their machines for generating oxygen. The Russian Elektra, and the US OGS for splitting water to make oxygen, and the Sabatier system for recycling CO2 have all had issues, needing to be fixed, and sometimes not functioning for long periods of time. The astronauts often rely on "top up" oxygen from Earth in other forms, including oxygen air tanks and solid oxygen generators. And the system isn't yet closed. Even with the Sabatier system when it is working properly, they only recycle 50% of the oxygen, and the rest has to be supplied from Earth as water. It's not a mature technology yet.
They continue to research into this. Currently the aim is to increase the efficiency until they recycle 75% of the oxygen. But the Russian algae system in the 1970s already achieved 100% recycling of oxygen, as well as producing food. So, is there any potential for looking to algae to solve these problems?
Unlike machines, plants and algae always work and don't need to be repaired. Your dwarf wheat won't suddenly break down and need parts shipped from Earth to keep it making wheat grains and absorbing CO2 and producing oxygen. And your green algae will never break down either, it's as reliable as brewing beer or using yeast to raise bread. Nature, through evolution, has sorted that all out millions of years ago. All you need there is reliability of the lighting, plumbing and pumps; a rather lower level of technology, at least if we can get them to grow in space as well as they do on Earth.
Here is a discovery channel program about growing plants using aeroponics in space.
GETTING STARTED - ALGAE FOR OXYGEN
Though crops would be what you want to grow in the future, you would probably start with growing algae for oxygen, as the Russians did.
In the early BIOS-1 experiment they had already shown that you can produce all the oxygen you need for one person from just 20 kg of water and algae (that's 0.02 cubic meters), spread over 8 square meters of surface area.
This apparently shows the chlorella cultivar used in the originally rather secretive Russian BIOS-1 experiment. Image from this paper I can't find much by way of details of its construction so far and how it worked - do say if you know more, in the comments. But the principle was simple anyway - supply lots of light to Chlorella algae and it photosynthesizes, absorbs carbon dioxide and produces oxygen. In the first experiment it was in a separate room, tended from outside, and supplied all the oxygen for a single volunteer. In BIOS-2 they put the cultivar inside the habitat, recycled other wastes as well, and produced some crops. In BIOS-3 they made the habitat larger, with a crew of 3, and changed to growing crops as their sole source of oxygen.
In the algae experiments, 20 liters of algae and water (20 kg) spread over eight square meters of lit surface provided all the oxygen for a single person.
That's small enough so you can consider flying it in even a small module, perhaps even a Bigelow inflatable BEAM module would be large enough.
The inflatable BEAM module, from Bigelow aerospace, which will fly to the ISS later this year is 4 meters long, 3.2 meters in diameter and has 16 m3 living volume, and weighs 1.36 metric tons.
The total volume for all the algae and water, for a crew of six, would be 0.12 cubic meters. Most of the space would be to supply it with lighting and make sure there is plenty of exposed surface area for growing. The lighting for an algae bioreactor can be supplied in many ways with the general aim to make sure as much light gets into as much of the solution as possible. For instance the algae flow in tubes, or you insert light pipes into the solution.
I haven't been able to find out the details of the system the Russians actually used in their early green algae experiments, particularly, I can't find a figure for its volume.
But, let's suppose, just for the sake of calculation, that you have 0.25 of head room for each square meter of algae for the lighting, pumps etc (although more likely to be done as tubes or light pipes etc). Then, you could fit 48 square meters of surface area into a volume of 3 by 2 by 2 or 12 cubic meters. That's enough surface area to supply all the oxygen for a crew of six. So, that suggests the 16 cubic meters of the BEAM module might already be enough to supply all the oxygen the ISS needs.
The air inside the growing containers is moist, and this is condensed to supply drinking water for the crew.
Artificial lighting of course uses a fair bit of power. For the later experiments with food as well, for crew of 3, the Russian experiment used twenty 6 kW xenon lamps per chamber, three chambers and one of them had all the lights doubled in later experiments. So it used a total of 480 kW of power. (The chambers are called phytotrons in the literature - special research greenhouses built for studying interactions between plants and the environment).
The ISS has maximum power of 120 kW and is often in darkness. So this just couldn't work, there is not enough power available.
For algae only they used rather less power, three lights, or 18 kW per person, but that still would be 108 kW for a crew of six, which is still not feasible for the ISS.
But with modern LED lights you could reduce those requirements hugely. And especially so, with modern grow lights optimized to produce only the light frequencies the plants need for photosynthesis.
Let's just check the commercially available high efficiency grow lights for aeroponic growers. As of writing this, August 2015: this High Efficiency Full Spectrum LED Grow Light - uses 20 watts of power to illuminate 0.2 square meters. So that's 100 watts of supplied power needed per square meter. It is recommended for crops that require bright sunlight such as lettuces in this roundup: Top 10 Best LED Grow Lights, and so seems roughly comparable with the Russian lighting system. So, that would be 800 watts for 8 square meters, or 4.8 kilowatts for the light needed for algae for a crew of six. That's a rough estimate of course, but it now seems far more manageable for a space station.
Using modern high efficiency LED grow lights like this a crew of six could provide all their own oxygen with 4.8 kW (rough calculation).
The rest of the system - pumps etc, requires less than 1 kW.
By comparison the Russian Elektra electrolysis unit, when it was working, needed 1 kW to supply all the oxygen for a crew of 3 or 4. (I can't find the figures for the power requirements for the US OGS - if anyone knows do say in the comments). The green algae needs more electricity than you need for electrolysis of water, but it is 100% recycled, needs no resupply of water from the Earth, and also absorbs the CO2 as well and recovers some of the carbon as food.
You could also use fiber optics solar collectors to collect sunlight for the spacecraft to reduce the power requirements, and it could then use even less than the ISS. We'll come back to this later.
Here is an ESA video about the idea of using Spirulina to produce oxygen in space.
Spirulina is better than the Chlorella used in earlier experiments because it is edible unlike the almost inedible Chlorella.
Spirulina which has been harvested for food in Africa and South America for centuries. This image is credit ESA. It could produce all the oxygen and some of the food for astronauts on board the ISS. Experimental algae bioreactors using Spirulina will fly on the ISS in the near future. And they have already flown cultures to the ISS several times to test how they grow under zero gravity conditions. See the Melissa project.
Spirulina is nutritious and safe to eat. It doesn't have the toxic byproducts such as BMAA of some other cyanobacteria. It contains about 60% protein, and contains all the essential amino acids, though with less methionine, cysteine and lysine compared with meat and milk (and doesn't have any vitamin B12 usable by humans). Basically it's a decent source of protein but needs to be supplemented with B12.
But it's not such a good source of carbohydrate. Humans need carbohydrates, even the Inuit, it turns out, eat a fair amount of them because of their habits of eating raw meat, fermenting meat, and eating animals with high levels of winter glucose stores.
You can use algae for food, but the mix of proteins and carbohydrates means they can't be the only source of food.
NEXT STAGE - FOOD
More space is needed for non algae foods because you need head room for the crops. But still, with the crops they use in BIOS-3 such as dwarf wheat - not a huge amount of clearance is needed. With the BIOS-3 experiments they had a total of 237 cubic meters set aside for growing crops. But it is clear the experiment wasn't set out to be optimized for volume as they only grew the crops in a single level.
With 13 square meters of growing area per crew, conveyor belt system, growing wheat, sedge-nut, beet, carrots, and other crops, ten crops in total, they reduced the daily substance requirements for dry food for the crew from 0.924 kg to 0.208 kg, and for oxygen from 1.22 to 0.35 kg, and didn't need drinking water or water to hydrate the food at all, with a saving of 5.133 kg a day for water.
So that's only a little more growing area per person than was needed for the algae. It's clear from the photographs that they weren't optimizing for volume, as there is lots of spare headroom above the plants and just one layer of crops in the room. If those 13 square meters per person are all that you need to illuminate, then that makes it 7.8 kW total power for the lighting for a crew of six.
There seems plenty of space for three or four layers if you had them in trays. The wheat was used to make bread. So, that growing area of 237 cubic meters is very much an over estimate.
"Wheat plants of various ages showing the "conveyor" approach that was used in the Bios experiments, Young wheat plants are in the foreground, with more mature plants toward the back. The aisle between benches is narrow (to leave as much space as possible for the crops). The post, with some environmental sensors attached, further obstructs the aisle. Crew members planted various herbs and other special plants in the corner and next to the wall to the left, space that would otherwise be wasted." photo from here
I can't find an estimate of the total volume needed for the crops themselves if it was used in a space station with minimal overhead space above the crop. But it looks as if you could easily fit them within a third of the space.
COMPARISON OF BIOS-3, MELiSSA AND THE ISS
In her 2006 masters thesis Living in Space, for the Swedish Physics in Space program at Uppsala university, Maria Johansson compared the Russian BIOS-3 with MELiSSA and the current ISS system.
The main difference between BIOS-3 and MELiSSA is that in BIOS-3 the inedible plant wastes are burnt in an oven - returning CO2 to the air which is then used by future generations of crops to make more food. In MELiSSA the wastes are decomposed by micro-organisms in biological reactors, basically, they are composted and used as nutrients for the algae and hydroponically grown plants.
She assumes that light is provided using fibre optic solar collectors, with a mass penalty of 338 kg per kW, and 46 watts per kW used for tracking for the solar collectors.
Hamiwari sun tracking solar collector - the light is collected, focused and sent through fiber optics to the interior of the spacecraft where it can be used as a light source for algae or growing crops. The light is collected using fresnel lenses - harmful frequencies in the UV and IR range are not collected, so it is optimized for photosynthesis.
Details of how this would work for spacecraft, see page 319 of Peter Eckart's book: Spacecraft Life Support and Biospherics.
Her figures for average power needed are.
ISS: 1.2 kW
MELiSSA 4 kW
BIOS-3 0.92 kW
So in this situation if you have solar collectors instead of LED lighting, BIOS-3 actually uses less power than the ISS systems.
Note - this calculation doesn't take account of times when the ISS is in shadow. That depends on the beta angle - the angle between the satellites orbital plane and the sun. For the ISS, whenever the beta angle goes above 69 degrees, as happens for some weeks around summer solstice, it is in constant sunlight. At other times of the year, it goes into darkness for a while on every orbit, every 45 minutes.
So if you need constant sunlight, the solar collectors would need to be supplemented by artificial lighting at times. But perhaps it is good enough to have sunlight most of the time with the sunlight switching off and on every 45 minutes for part of the year.
Then the mass for the system in her comparison is
|System||Startup mass||Supply mass per day|
|ISS||1773 kg||6.5 kg|
|MELiSSA||15,711 kg||1.4 kg|
|BIOS-3||6,250 kg||0.5 kg|
That's not including the modules needed for the growing volume though.
Most of the mass for the BIOS-3, which is mainly aeroponics, is for the oven (1.305 tons) and the solar fiber optics condensers to produce light (4.225 tons).
For MELiSSA as a basically hydroponics system the water takes up most of the mass at 8.89 tons, and much of the rest is taken by the centrifuges at 2.8 tons.
For ISS, though nothing particularly stands out by way of mass, the hygiene water supply system is the most massive at 0.706 tons.
She found that BIOS-3 and the ISS system used about the same power and that BIOS-3 breaks even with the ISS on equivalent mass after two years. MELiSSA takes longer to break even, 7.5 years because BIOS-3 has a lower startup mass and less supply mass. But the MELiSSA system, being bacteria based to a large extent, is more controllable than BIOS-3.
As for state of readiness:
ISS - systems already in use, but not yet totally reliable, needs occasional repair with new components from Earth and the ability to "top up" with oxygen when the systems fail.
BIOS-3 -system not designed for micro-gravity so would need to be redesigned to be used in space.
MELiSSA system - currently being actively developed but should be considered at an early stage of development still.
It's taken a while to learn to grow plants in zero gravity, also pollutants in the atmosphere of space stations can harm the plants. For some of the early attempts, see Robert Zimmerman's 2003 article "Growing Pains" in Air and Space magazine. Nowadays they seem to have figured it out growing lettuces and dwarf wheat for instance, successfully, with similar yields to Earth crops.
THE MATHEMATICS BEHIND IT
It might surprise you to know, but actually the main waste product of a human, apart from water, is not feces. It's CO2.
You produce only 0.03 kg dry mass of feces a day. But you exhale 1 kg of CO2 every day. And breath in about 0.84 kg of oxygen a day. For details see Design Rules for Life Support Systems (NASA document).
A crew member needs about 5 kg total per day. Much of that is water which is recycled already in the ISS. Apart from the oxygen, the main other non water component of the crew needs is dried food solids, 0.62 kg per day.
If you can capture that 1 kg of CO2 and turn all of it back to food, you save on the 0.62 kg for food. But you also save on resupply of 0.84 kg of oxygen. as well. The total comes to more than 1 kg because the food, even dried food, contains oxygen and hydrogen as well, not just carbon.
HOW IT WORKS ON THE ISS
The oxygen is produce by electrolysis of water. Originally this was done by the Elektron unit which requires 1 kilowatt to supply the oxygen needs for a crew of 3 or 4. So 2 kilowatts for a crew of six. They also have the US Oxygen Generation System. As well as the "topup" oxygen supplied in various forms when these systems break down or are not working optimally.
This reacts the hydrogen waste product from the water electrolysis with the carbon dioxide breathed out by the astronauts to produce methane and water. The methane is then vented to space.
To recover all the water that was originally split by electrolysis, then all the hydrogen would need to be combined back with the oxygen from the CO2. Since half the hydrogen is wasted in this reaction, only half the oxygen can be recovered (unless you supply the extra hydrogen from the Earth). So with the Sabatier system alone, you still have to vent half the CO2 to space.
The ISS has a Sabatier system installed and when it is working can achieve near to 50% recovery of the oxygen to water so that it can be reused again.
OTHER TECHNOLOGICAL SOLUTIONS
The methane from the Sabatier reaction could be split at high temperatures by pyrolysis, or recovered in other ways, making an almost complete cycle, with only carbon as the waste product.
You could also split the CO2 completely to C and O2, by using laser light: .
You can also use the Bosch reaction CO2 + 2H2 → C + 2H2O which, unlike the Sabatier reaction, recycles all the oxygen to water in one go. But this requires higher temperatures in the range 450 to 600 °C, and is technically harder to do in space.
There are several other ways you can improve on the Sabatier reaction.
100% RECOVERY OF OXYGEN WITH PHOTOSYNTHESIS
With plants, the basic equation is
6CO2 + 12 H2O → C6H12O6 + 6O2 + 6 H2O
There the atoms shown in bold are the same atoms on both sides, so technically the oxygen comes from the water rather than the CO2, but the end effect is the same.
The end effect is that all the CO2 gets used up and an equivalent amount of oxygen is produced. So you get 100% recovery of the oxygen from the CO2. You also recover the carbon too, as glucose, which can be recycled into food.
Techy aside. You might think that the plants are splitting the CO2 - but no - actually the oxygen in photosynthesis comes from splitting water.
The oxygen from the CO2 goes into the glucose, and into water. Indirectly that H2O from the CO2 might well end up as O2 if it gets taken up for photosynthesis later on, but it is not split directly.
This has been proved by using isotopes to tag the oxygen in the CO2 and the water.
See and (see page 5 there for a useful diagram of how it works).
HOW IT WORKS WITH FOOD AND ALGAE
The way it works is quite neat. If you can recycle all your own oxygen, you produce the same mass of plant food as your originally ate as food.
Normally only half of the crop is food, so that means, if you grow enough crop to meet all your food needs, you get an excess of oxygen.So then the excess plant mass you created to produce all that oxygen needs to be burnt or composted, and this will use up the oxygen and turn it back to CO2 which then can be used for new crops, or turn it directly to organics to use for crops. So it's automatically self balancing like that so long as you burn or compost any excess plant crops.
In more detail, what matters is the harvest fraction, how much of the plant growth from the exhaled CO2 gets turned into food and so can be eaten again.
With typical harvest foods, half of the plant material is edible, and the other half is plant wastes. You may be able to go higher than that, for instance with edible algae, 100% of the mass is edible. But, for purposes of this calculation, to show how it works, let's suppose that half of the plant material is edible.
In a closed system, nearly all the carbon in the plant comes from the exhaled CO2 of the crew. And nearly all the carbon in the food is exhaled as CO2.
The two equations are photosynthesis:
6CO2 + 12 H2O → C6H12O6 + 6O2 + 6 H2O
C6H12O6 + 6O2 → 6CO2 + 6 H2O
If the oxygen used up in respiration is all recovered through photosynthesis, then to make the two equations balance, the amount of CO2 respired must also balance the amount of glucose produced in the plants. E.g. for every 6 oxygen molecules used up in respiration, one glucose molecule is eaten. If all those six oxygen molecules are recovered in photosynthesis, then one glucose molecule is produced in the plants.
So in a closed system, the total amount of glucose produced as crops has to match the amount eaten.
But then if only half the glucose produced is edible, that means, that the amount of glucose produced as food is only half the amount you ate originally.
If on the other hand you grow enough crops to supply all the food you need, with harvest fraction of 50% again, then the plants will supply double the oxygen requirements, you end up with two much oxygen, and also too much glucose, which gets into the inedible food wastes.
So if you supply all the food from crops, the food wastes need to be incinerated or composted to return the carbon back to the plants again to close the loop. The extra CO2 from incineration or the extra organics created by composting the food is needed to continue with plant growth.
That's why MELiSSA relies on bioreactors (basically high tech composting) and BIOS-3 uses ovens to burn the CO2.
PAYLOAD SAVING FROM GROWING CROPS
If you can grow all the food in space then you save 0.84 kg for oxygen per day, and 0.62 kg for the dried food solids for a total saving of 1.46 kg per person per day, or 3.197 tons per year for a crew of six.
If you can produce oxygen only, then (by a similar calculation), that saves 1.84 tons per year.
Currently the ISS is able to produce about half of the oxygen it needs, when the Sabatier system is working, so saving about half of that 1.84 tons a year. And when the Sabatier system isn't working, all of that mass has to be provided from the Earth, either as water or as oxygen.
PAYLOAD SAVINGS OVER DURATION OF MISSION
Three tons per year is a significant amount of extra payload for an interplanetary mission or a long duration mission to the Moon or to an asteroid or comet. And it's a considerable saving for a long duration space station also.
The ISS launched in 1998 and had its first resident crew in 2000. The crew fluctuated, but for our calculations let's suppose the future station has an average crew of six.
The ISS is expected to last until 2028 now, if so, at three tons per year, you could save nearly 90 tons of mass over that time period, so nearly six times the 14.515 tons of the Destiny module.
One Destiny module with a pressurized volume of 106 cubic meters would probably provide enough space to grow food for three people, if it's right that the 227 cubic meters of the BIOS-3 includes a lot of unnecessary head space above the plants - so you'd need only two of those for the crew of six. So after accounting for that, it's a total saving over 60 tons.
Also, since Progress has a payload capacity of 2.35 tons, you'd save around 25 Progress launches (60/2.35) worth of payload, if you put up two extra modules to grow the food, and had close to 100% recycling of oxygen and food.
If you recycle just the oxygen, you'd still save over 51 tons over a 28 year lifetime of a space station (and in this case negligible extra mass, perhaps a couple of tons max, for the module itself).
In future, the modules are likely to be lighter, e.g. the Bigelow aerospace inflatable module, the BA330 is only 20 tons for 330 cubic meters of living area, more than enough volume for all the food and oxygen for a crew of six probably. So then you'll pay back the mass of the module sooner.
Proposed BA330 from Bigelow - mass of 20 tons, and internal volume 330 cubic meters. By comparison, the Destiny module is 14.5 tonnes for 106 cubic meters of pressurized volume.
Future habitats will have more space available for growing crops for the same mass. So you'd save on the payload for the crops module(s) sooner.
FASTEST PAYBACK FOR ALGAE
With oxygen from algae the payback could be much faster. The BEAM module weighs 1.36 metric tons. The startup mass for an algae bioreactor for a crew of six is negligible, fraction of a ton. And the payback is 1.8 tons a year.
So you'd pay back both module and the bioreactor within a year. This would seem to make it worthwhile to send an algae bioreactor module to the ISS to use as its main system for oxygen, in the near future. That is if the MELiSSA experiments prove that the method works in space. As a bonus, the algae produced by the module can be recycled as food.
With the more complex systems, the payback time is longer, but still, it could be well worth doing, even with the limited lifetime left for the ISS especially if you can use the larger inflatable modules like the BA330. These modules could also be detached and re-used in future space stations when the ISS is de-orbited so extending their lifetime and payback time.
Anyway that's looking rather far ahead. So far we don't have any bioreactors or biological closed systems ready to fly into space. MELiSSA is the system being developed most actively at present. From Maria Johansson's figures, it would seem that a system based on BIOS-3 would also deserve attention as a competing system, since it seems it could use less power, less startup mass, and require less input mass to the system each year.
Engineers tend to see machines as more reliable and controllable. But in practice the machines on the ISS for generating oxygen and recycling CO2 have gone wrong often and been out of order for long periods of time.
So far, we have no machines that are anything like as reliable as, e.g., yeast, or algae, or dwarf wheat. There is no need to get resupply of components from Earth to fix your algae. So long as you provide them with the conditions for growth, they won't let you down.
So long as you can make sure there are no insect pests, or crop diseases, and can avoid contaminating the algae with other microbes, and give them the light and temperature and water quality they need, then you have nothing to go wrong.
And if something does go wrong, say, the lighting or pumps fail and the crop dies back before they can be repaired - well, so long as you have some seeds and some algae still alive, it can regenerate itself, you can grow your algae and crops back again, as they found out with the BIOS-3 experiments. Try doing that with machines.
So this seems to have a lot of future promise. And on the Earth with BIOS-3 it proved to be very reliable. We will soon find out if it similar approaches live up to their promise in space conditions as well.
HUMAN WELL BEING AND HAPPINESS
As a fringe benefit, if we can grow food in space, this is likely to lead to a happier crew. We aren't machines, and most human beings enjoy having plants around and growing plants.
First, there's the taste. Fresh food, lettuce leaves and tomatoes picked from the plant, and bread you bake yourself, from wheat you grew yourself tastes much better than food that is dried and reconstituted, which is all you'd have otherwise in a long duration journey.
Also most people enjoy having plants around and tending plants.
It's true that you can survive fine without plants. If you are a prisoner in solitary confinement, you have no choice, and may find that you adjust fine to your situation. And many hermits in the past, and even today, spend years on end in caves and other confined small places, without any plants or much of anything except blank walls, and come out of their retreats happy. It is the same also for the crew of rowing boats and such like on long distance voyages, for instance when rowing across the Pacific, they live in confined quarters for weeks or months on end, and are happy in those situations.
However, that's not for everyone. Having plants around in the spaceship, and fresh food that they have grown themselves seems likely to contribute to overall happiness and well being of the crew. This is often mentioned as a fringe benefit in the literature. And in a small way, this has already happened - in the ISS tending their small crop of plants has a calming effect on the astronauts and cosmonauts.
Cosmonaut Mikhail Tyurin, Expedition 14 Flight Engineer, performs his regular daily inspection of the BIO-5 Rasteniya-2 (Plants-2) experiment in the Russian Lada greenhouse in the Zvezda Service Module. Image NASA
A happy crew will make better decisions, and are more likely to come up with inspired and creative solutions to problems, and so may be better at completing mission objectives. And in any case, all things being equal, surely it's better to go for a solution that is more enjoyable for the crew.
Especially on long duration missions, far from Earth, where their plants in their spaceship may be the only green thing there is for many light minutes, many millions of kilometers, in all directions. Even on the far side of the Moon, the green plants in their spaceship may be their one direct tangible link with the ecosystem of the Earth which they can no longer see in the sky.
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