I have taken down the Starship Generations website, it was flawed. The reason is my estimate for the number of acres per person needed to grow food was vastly overestimated. Here are, in my opinion, some better estimates:

The General Food Guide Pyramid recommends a daily diet consisting of the following:

Cereals & Grains recommended 6-11 servings daily, where one serving is equal to 42 grams of dry wheat flour (made into bread or pasta) with 153.72 Calories. Current farm yields of wheat are about 66 bushels per acre, and each bushel is 60 lbs gross, and yielding 42 lbs dry wheat flour. Therefore 6-11 servings of cereals & grains is equivalent to 0.0132-0.0242 bushels of wheat per person daily. In terms of land usage this ranges from 0.073 - 0.134 acres per person, assuming just one crop harvested annually.

Fruits recommended 2-4 servings daily, where one serving is equal to 154 grams of chopped fruit with 80 Calories, or 1 medium fresh apple. Apple orchards yield about 150 bushels per acre. With 100 apples per bushel, that's 15,000 apples per acre. In terms of land usage 2-4 servings of fruit per person daily works out to 0.487 - 0.973 acres per person, assuming one crop harvested annually. Keep in mind here that apple trees can grow 10-15 meters high, and are used for about 20 years and then replanted.

Veggies recommended 3-5 servings daily, where one serving is equal to 100 grams of cooked veggies such as Broccoli, and a total of 25 Calories. Broccoli can be harvested 5 times per year under controlled conditions and current crop yields are about 120 crates, or 42 lbs per acre. This is about 19,091 servings per acre, 5-times a year. To satisfy 3-5 servings daily would require 0.0115 - 0.0192 acres per person, with 5 annual harvests.

Legumes, beans, nuts (or meat) recommended 2-3 servings daily, where one serving is 85.05 grams of Soybeans with 382.725 Calories. Soybean crop yields are about 90 bushels per acre, with 60 lbs each, and this is the same as 28,860 servings per acre. To satisfy 2-3 servings daily would require 0.0253 - 0.0380 acres per person, assuming 1 crop annually.

On the basis of Calories consumed daily the totals are as follows:

Grains & Cereals = 922 - 1691 Calories
Fruits = 160 - 320 Calories
Veggies = 75 - 125 Calories
Legumes = 766 - 1149 Calories
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Total = 1923 - 3285 Calories per day

The same food pyramid recommends 2-3 servings of milk, yogurt & cheese. However I do not believe these foods are actually required, since they come from cow's milk, and a substitute may be easier to provide on a space habitat, versus launching cows into orbit. And it is obvious that meat would be virtually impossible to provide. We also know how important fats, oils, sugars, spices & seasonings are, for example chocolate, butter, birthday cakes, etc.!!! But they can be grown in fallow (unused cropland) and stockpiled, since they are used sparingly, i.e. not in large quantities.

In terms of land usage the totals are as follows:

Grains (wheat) = 0.073 - 0.0134 acres/person
Fruits (apples) = 0.0487 - 0.0973 acres/person
Veggies (broccoli) = 0.0115 - 0.0192 acres/person
Legumes (soybeans) = 0.0253 - 0.0380 acres/person
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Totals = 0.156 - 0.290 acres/person

Information on serving sizes varies only slightly depending on the source. Crop yields vary geography and there is a great deal of information on the subject. Land usage should vary significantly depending on the crop being grown. The above numbers for example are estimated based on farming wheat, apples, broccoli, and soybeans. These are just one possible crop for each food group. It would be preferable to grow a variety to prevent catastrophic losses from infestation and disease, to maintain a viable stock of seeds, to use crop rotation to increase soil quality, etc. A fantastic database for the caloric values per unit weight of various foods is found at the U.S. Department of Agriculture website:

Nutrient Laboratory Database

China provides a real-world comparison for this result. China is closer to achieving agricultural self-sufficiency than any country in the world. Currently about 10% of China’s land area is arable land, or 932,641 square km (230,459,687 acres). For a population of 1,273,111,290 people this works out to approximately 0.181 acres of farmland per person. This is within the range calculated above.

This suggests fairly strongly that land area needed to sustain 10,000 people with a 50% safety margin, i.e. a space colony, is 2340 - 4350 acres (3.7 - 6.8 square miles).

In terms of energy efficiency the above totals break down as follows:

- 1 acre = 4046.873 square meters
- Average sunlight in the Midwestern USA = 61.15 Watts per square meter
- 1 acre receives 7.8041 trillion Joules per year

Cereals & Grains – 66 bushels wheat = 6,588,000 Calories food energy per acre

Fruits – 150 bushels apples = 1,200,000 Calories food energy per acre

Veggies – 120 crates broccoli, 5-times per year = 2,386,375 Calories food energy per acre

Legumes – 90 bushels soybeans = 11,045,444 Calories food energy per acre

Photosynthesis efficiencies are therefore:

Cereals & grains (wheat) = 0.353 percent efficient
Fruits (apples) = 0.064 percent efficient
Veggies (broccoli) = 0.128 percent efficient
Legumes (soybeans) = 0.592 percent efficient

As we can see the efficiency of photosynthesis is much less than 1 percent. This is in spite of the fact that plant’s chloroplasts could potentially absorb 28 percent of the sunlight that reaches the ground. This inefficiency is caused by a number of factors:

- Plants do not grow year-round at high latitudes
- Not all land is used to grow crops
- Photosynthesis stops at temperatures below 10 degrees Celsius
- Photorespiration losses are high at temperatures above 30 degrees Celsius
- Leaves form an unbroken canopy and block sunlight to leaves nearer the ground
- Low atmospheric carbon dioxide levels limit plant growth
- Water shortages and nutrient deficiencies limit plant growth