Tuesday, August 18, 2015

Life support - Trees

This will be a background post, with deeper data by species coming later.

 Fruit and nut trees are not often considered for hydroponics, and for good reasons. They take years to mature and several meters of vertical space. Less commonly known is that many trees control flowering by the gravitational flow of hormones, so zero-G orchards may not behave in predictable ways. Also, behavior of many species is seasonal and dependent on both temperature and daylight hour changes. Trees are often less efficient at converting light and CO2 than other plants, and significant amounts of their production is in the form of wood instead of food. As a result, the edible yield of trees is not competitive with vegetables. Experience with hydroponic orchard production is very limited. Almost all trees require pollinators or hand pollination and many require different varieties for fertility.

 These are not insurmountable problems for a permanent colony, particularly one on a body with gravity. Let's look at the benefits so we can make some comparisons. Nut trees produce nutritious food that can be stored for months at ambient conditions. Fruit trees produce a variety of fruits, good for improving the diversity of the diet; fruits also often have higher sugar content than hydroponic produce. The physical appearance of trees can have psychological benefits for colonists, as can the dietary contributions. Pollen from tree flowers can likewise improve the variety of diet for pollinators. Trees themselves are quite adaptable and almost certainly have enormous untapped potential for the development of space-adapted varieties. Trees produce wood, a useful material for handles, furniture, etc. Wood waste fibers can be made into paper. The cellulose in wood fibers can be extracted and used as a film, converted to polymers or converted with nitric acid into nitrocellulose as blasting charges. A variety of spices and medicinals are only available as trees or inconveniently large shrubs. Allspice, clove, cinnamon, nutmeg, bay, mace, ginko and witch hazel are all examples. Most of these are used in trace quantities, so low productivity is not a problem. More common species like willow can be used for aspirin (for example), though it might be more efficient to synthesize it; on the other hand willow is a good source of material for making activated carbon filters. Trees can soak up the area lighting in public spaces, turning energy that would otherwise have become heat into food and air. They can help reduce CO2 concentrations when a lot of people are in one spot and provide some fallback capacity if the air system is temporarily offline.

 My early data for fruit trees is based on semi-intensive orchard growing on Earth using semidwarf trees. Apples seem to be the best producers at around 5 kg/m², followed by pears and plums at 3 kg/m² and cherries and peaches at 2 kg/m². Noncommercial species like pawpaw or quince yield around 1.2 kg/m². In daily terms that's only 5.5 to 13.7 grams per square meter per day. It does mean that apples can be more productive than barley (for example, at about 12g/m²*day) on an energy basis, but not even close on a volume basis. Nuts, unfortunately, are much less productive than fruits; almonds weigh in around 0.2 kg/m² or about half a gram a day per square meter. Almond milk is not likely to find itself on the menu.

 For fruits, the difference in yield by species has little to do with inherent productivity. Apples have been the focus of commercial orchard breeding programs for longer periods and larger budgets than the other species. It's true that peaches and cherries are also undergoing heavy investment and there seems to be no reason why their yields could not exceed that of today's apples. Pears and plums have not been so intensively developed, though they started with a bit better output and have still seen improvement by many dedicated researchers and breeders. Crossing over into intensive hydroponic production has generally meant incredible productivity gains for most crops. Average yields can be expected to double at the very least simply by eliminating disease, pests and competition and providing optimal levels of light, water, nutrients, temperature and air composition. A more accurate projection might be to use Earth record yields instead of average yields. Space-specific pruning and training plus a good breeding program and the potential for shortened production cycles should at least double that number again. If everbearing varieties could be developed then yields could be pushed even higher. I think given enough time and resources that apple yields could be brought as high as 120 g/m²*day, comparable to many vegetable species. We won't know until it is attempted, and given the time it takes for each generation to mature this is a process that will take 2-3 decades of sustained effort.

 The drawbacks are pretty significant and need to be addressed. Not all species have suitable dwarfing rootstocks for grafting. (Most fruit trees are a franken-tree made from one variety or species {the rootstock} that resists pests and has good growth plus another variety {the graft} that has good flavor and yield.) At this point we must assume any orchard crop will require gravity, so they are restricted to some unknown threshold probably above 0.5 g. Even mini-dwarf apples require 2 meters of aboveground clearance while the smaller semidwarf trees need nearly 4 meters if they are pruned according to normal methods. The solution I think is to emphasize the psychological aspect and place trees in public spaces. They do not need the high light output, long light hours and high CO2 concentrations of super-productive vegetables, so their growing conditions are compatible with habitation areas. Trees can be trained to grow into space-saving shapes, a practice called espalier which can produce fencelike barriers; this produces a visually pleasing structure that can screen out noise and unwanted sights while producing edible fruits. These trees will provide a sense of steady change combined with a sense of permanence and will contribute to making public areas feel more organic and living. If you think that sounds like a bunch of hippie BS, consider that just having a couple of bean plants on the ISS made a significant measurable improvement in astronaut mood and outlook. Depressed people do not get along well; mental health is critical in an environment where carelessness can kill.

 I think a large enough colony will benefit from the investment of trees. I also think a successful program of adaptation will take much longer than similar programs for vegetables and other single-year crops, and much of the work will require access to reduced-gravity growing areas. In other words, this kind of research will be enabled by spin-gravity colonies or research stations; early stations will not be able to bank on specific productivity numbers if they include trees in their design.

Earthside - Nemo's Garden

Supporting ourselves in space means developing and demonstrating technologies on Earth.

 This is one excellent example: Nemo's Garden, a project to build underwater hydroponics bays. A structure is anchored to the seafloor a few meters underwater; compressed air is used to inflate it. Plants grow as they do in any other hydro environment. The system collects fresh water from evaporation and condensation, so no external water source is required. The temperature and humidity are very stable and pests are eliminated. Gas exchange with the seawater (presumably) allows for O2/CO2 transport. Nutrient solutions would still be required, as well as some electrical power for monitoring, pumps, etc.

 This is something that can be deployed without large real-estate expenses, without straining fresh water supplies and without the risk of weather-induced losses. Under the right conditions these systems could produce clean fresh water as a byproduct. Island nations with minimal arable land could meet their food needs without imports even as rising sea levels threaten their growing areas.

 Something interesting: plants in the test systems grow faster than they should. One theory is that the increased pressure at depth may allow for more efficient respiration. If true, that means the hydro bays of future colonies could be operated at greater than 1 atmosphere for increased efficiency. It's at least something to consider during engineering trades. It's possible this is simply that the partial pressure of CO2 is closer to ideal at normal concentration and increased total pressure, in which case a reduced-pressure atmosphere with high CO2 concentration might achieve the same result. We won't know until someone does the research.

 In the long run, the technologies required for permanence in space will enable human habitation of the worst Earth has to offer: deserts, tundra, mountaintops, deep caves and under water. Those same technologies could make life easier and safer for people who live on the margins today.

Monday, August 17, 2015

Life support - Goats

Another entry in the series of animal yields and requirements.

Let's consider a herd of 100 producing goats, just as we did for dairy cattle. The required protein in feed is 16% (with short periods at 20%); as ruminants these animals require plenty of bulk fiber. (It is possible to raise goats without roughage, basically forcing them not to develop their rumen; this is protein-intensive and cannot be used for herd replacement.)

Mixing feed inputs

To hit the right crude protein for animal feed given two ingredients:
Low protein ingredient A
High protein ingredient B
Target protein content C
Proportion of first ingredient X

X = (C-B) / (A-B)

For example: A is 10% protein, B is 45% protein and C is 16% protein
X = (.16 - .45) / (.1 - .45)
X = .8286
Mix about 83% of ingredient A with 17% of ingredient B.

Friday, August 14, 2015

Life support - Pigs and Cattle

This is a follow-on to the previous post about raising animals for food. I won't go into detail about background issues like I did last time, I'll just dive right into the numbers and then compare.

To review, on a per kg ag waste basis we can produce one of:
490 g edible insects
290 g chicken eggs
140 g chicken
140 g catfish or tilapia
100 g rabbit

As a cheat sheet, here are my results for this post:
 90 g pork
 16 g beef + 1.094 kg cow's milk

Thursday, August 13, 2015

A mass-produced booster concept (updated costs and SPS notes)

This is an idea I had kicking around for a while before SpaceX started getting serious about reusable rockets. It seems wasteful somehow, but if we had an urgent need to start lifting a lot of mass in a short time I think it could still be useful.

 Consider a booster family constructed entirely of modular tanks and one or two types of engine. All components are sized to fit inside standard shipping containers. The fuel is liquefied natural gas and the oxidizer is liquid oxygen. One or more launch platforms can be built out of converted floating drydocks or oil-rig tugs; add a solar-powered cryogenic oxygen plant and docking facilities for both commercial LNG tankers and commercial containerized cargo ships.

 A container ship delivers the components for several launches. The booster is assembled on the deck of the platform using cranes and quick-lock connectors. A LNG tanker delivers the fuel and the on-platform plant delivers the oxygen. Customer payload is delivered by air if it is light enough, otherwise by sea. Any nearby vessels clear the area, then the booster is launched. Wash, rinse, repeat. If there is enough onboard storage, the fuel and components for several missions can be taken onboard and then launched as fast as they can be assembled while the next shipment is in transit.


I have a spreadsheet I use for estimating the mass of fuel tanks. It has been useful for indulging my obsessions, so I'm posting it here in case someone else finds it useful. Or wrong. I'd love to hear about either.

It has two tabs, one for spherical tanks and one for cylinders with spherical endcaps. I'll consider doing a 2:1 endcaps tab if someone actually wants such a thing. The spherical tank tab assumes you only want one fluid in the tank, while the cylindrical tab assumes you want two fluids separated by a flat circular bulkhead.

Tuesday, August 11, 2015


I've mentioned several times that plastic can be produced from agricultural waste and/or CO2.

 The plastic of interest is polyethylene, or rather ultra high molecular weight polyethylene (UHMWPE, UHDPE, polyethene or trade names Spectra or Dyneema). It is formed of very long single chains of carbon, so the unit formula is CH2. This material is a thermoplastic, melting around 130 °C (or less if it contains solvents and/or crystalline defects). In normal use it should be kept between -150 °C and about 80 °C, so in-space applications will typically require a protective coating such as thin-film aluminum.

Life Support - Animals for food

It is often assumed that animal protein is not reasonable in a space habitat. Certainly if we try to feed high-quality grains and soy to an animal and then eat it we will have wasted significant amounts of calories, protein, electricity and other resources. Meat requires finding ways to use biomass that would otherwise be wasted.

Monday, August 10, 2015

Life support - growing plants for fun and profit

In the first life support post I discussed removal of CO2 and water vapor from residential air. Now we look at what happens to them downstream.

 Plants require water, carbon dioxide, light, a set of 14 essential minerals and reasonable temperatures. Many plants can handle microgravity and low pressures without difficulty. Some have useful properties like extracting pollutants from water, growing edible food or producing medically useful compounds. Their two main uses in space are to convert CO2 to oxygen for breathing and to produce food.

Early Days

 Unless some cataclysmic event occurs, we are not going to be building huge thousand-person colonies in space any time soon. It's just too expensive, with uncertain payoffs, unknown risks and very long time scales.

 The only way to get around that is to solve problems cheaply and use the available materials. For example, we have multiple rovers on the surface of Mars. These have operated for long periods of time and have taken photos and rock samples across an impressive track of travel in a very hostile environment. What could we do with a rover the size of the Mars Science Lab (Curiosity) on the Moon, with equipment for gathering resources?

Friday, August 7, 2015

Life support - CO2, humidity, air conditioning

First up is carbon dioxide. People exhale around 0.998 kg of CO2 per day and consume 0.835 kg O2 per day. The OSHA limit for normal exposure is 1000 ppm, while NASA's 1000-day limit is 5000 ppm. (Granted, NASA is specifying a 70-kg man in peak condition; the population will be mixed gender and age including children, but a little excess capacity doesn't hurt.)

 Zeolites (a type of molecular sieve that can be used for CO2 capture) work by adsorbing a specific gas until the structure is full, then releasing the gas under heat and/or vacuum. This release is called the regeneration phase and normally takes less time than the adsorption phase. For continuous operation the system requires twice the amount of zeolite needed for the adsorption phase; adding a third measure provides a good safety factor and could also provide emergency capacity if needed. The behavior of zeolites depends strongly on their molecular structure and they can trap more than one kind of molecule, so a detailed design will consider water vapor and other gases.

 NASA currently uses a four-bed system with silica/13X beads to adsorb water and 4A beads to adsorb CO2; the beds are exposed to vacuum and strongly heated to reject the CO2 into space. This takes a lot of power and wastes the CO2. The silica beds also have to be heated over 100 °C to force the water out.

Monday, August 3, 2015

Where to?

To get into deeper detail requires settling on one or more locations.

 I think we can rule out any free-space colonies just on the basis of radiation shielding. The required mass is just so enormous that there does not seem to be any cost-effective way to collect it. A habitat for 10,000 people could take up to a few hundred thousand tons of shielding. NASA's asteroid retrieval mission was set to retrieve about one thousand tons for one to two billion dollars. Granted if one wanted to capture a hundred asteroids the economies of scale would drive down the cost, but we would still be talking about tens of billions of dollars.


A colony in space will need a wide variety of resources to survive. Let's look at some of them and where to find them.

 Earth's atmosphere is roughly 78% nitrogen, 21% oxygen and 1% argon. Nitrogen and argon are inert; as air we need them only for bulk. The pressure in a colony affects how much of each gas is needed; you can have a half-pressure atmosphere with 42% oxygen, 30% nitrogen and 28% argon and breathe just fine. You could also breathe a pure oxygen atmosphere at one fifth pressure, but this is extremely dangerous; the slightest spark can start a very rapid fire even in materials that aren't normally flammable.


Radiation. Scary word. Makes us think of fallout and glowing waste.
The truth is, most radiation is harmless. That warm feeling of sunlight on skin? Radiation. Microwave ovens? Strong radiation sources. Same for wi-fi, cellphones, broadcast TV, radio, infrared heat lamps, blacklights and remote controls.

Radiation takes two forms: electromagnetic and particle.
 Electromagnetic radiation is packets of energy carried by photons (or one could say waves of energy). This is defined by the electromagnetic spectrum. Most of this radiation is harmless or even useful as long as it is at the visible level or below.

The Basics

Some say space is hard. Things break, people die.

It's still true.

We are in our infancy, struggling to find our feet and set out on the path to a sustainable and permanent presence in space. We have learned an enormous amount from the first pioneers. We have a framework, we do tests, we simulate. Still, things go wrong. It's unavoidable.

Set aside for a moment our current state. Look to the future. How would a permanent human colony look?


This is a digital workspace for me to collect my thoughts about humanity becoming self-sufficient in space. I promise only that there will be errors in my work.

Comments welcome. I will turn on moderation if necessary.

In case future humans ever actually read this...
I'm a college dropout (physics major) with a talent for technology. I work in the broadcast industry as a technician. The contents of this blog are not generated by an expert, merely an obsessed amateur.