This entry is a continuation of Obstacles to Manned Space Exploration: Part I - Propulsion and will eventually be submitted to Peer Review. Is it not necessary to read Part I in order to understand and enjoy this entry. It is, however, necessary to stand on your right foot with one hand over your left eye under the influence of a few of the local mind-altering substances to understand and enjoy this entry.

We will attempt here to construct a logical and detailed look at the obstacles to creating a viable spaceborne personnel carrier. When we discuss the subject of 'space travel' we are really combining two different types of off-earth transportation; long-duration, and short-duration.

Long-duration space travel has many factors to consider that influence the final outcome of the mission; length of time in space, distance to destination, number of crew, etc.. In comparison, while short-duration space travel is affected by the same factors, it does not have the same limitations because the crew and ship have a shorter distance to travel, therefore are in space for a shorter period of time, and are closer to aid if something goes wrong.

In fact, if the reader so desired, a trip to the local DIY shop would supply him/her/it with all the necessary components for the construction of a craft capable of short-duration space travel¹. In light of this, for the purposes of this article, we will consider the term 'space travel' to imply 'crewed long-duration space travel and colonization' because the obstacles to long-duration travel and colonization of a hostile environment are very similar. Where convenient, will point out the differences in requirements between long-duration and short-duration craft.

How to eat, drink and make love in space.

Our first foray into the subject of obstacles to space exploration discusses necessary technologies required to make our ship move; the motor, if you will, of our space car. In that entry, the existence or non-existence of a crew in the ship was irrelevant. In this entry, however, we will address this incredibly important aspect of manned space exploration: the crew. Without the crew aspect, we are not discussing manned space exploration anymore and we may as well skip forward to Part III of this essay, 'Bringing Rocket Rugby to a Spacepitch Near You'. With that in mind, with the understanding that this essay deals specifically with the human element in space travel, we now bravely stumble forward towards the Truth.

There are five main items that we must address;

1. Food,
2. Air,
3. Exercise and sleep,
4. Waste Disposal, and
5. Entertainment.

Without any of these five, a mission is doomed to disaster of the sort that makes the Titanic look like...erm...a really bad boat crash.

We will now look at each of these in turn, discussing in each section three things;

1. The outline of the problem and how it affects the outcome of a mission,
2. The state of present technology and whether it is suitable or insuitable to the needs of the crew, and
3. Possible solutions to the problems we will inevitably unearth in our discussion.

Food: Where do we get it and what do we eat?

Sadly, the number of fast food restaurants and convenience stores in outer space has been dwindling since the Outer Space Nuclear Arms Treaty of January 27, 1967 and we are thereby required to find other food sources for crew consumption. The idea that food is an important aspect of manned space travel is essentially self-evident, but there are many problems associated with food, namely, these; where do we get it, what should we eat, how do we ensure that proper dietary requirements are met, what is the shelf-life of the food we take with us, and where do we store it?

If music be the food of life²...

It would be wonderful if the only thing needed to survive was an old Led Zeppelin 4 cassette and a Sony walkman, but sadly this is not true. Humans need food less ephemeral than rock and roll. For the sake of simplicity, let us assume that Earthly sustenance has two possible sources. The first is the friendly neighbourhood grocery store, where one can buy milk, bread, canned beans, and sundry other items good for eating. The second is our garden, where we grow our vegetables, keep our chicken coops, and tie up the cow. We can make the same assumption about food in space. In essence, there are only two sources. We either have to bring our food with us after buying it in the shops, or grow it, breed it, and raise it on our ship. However, one item that allows for no debate about its source is water. We must bring water with us. There are no known intergalactic natural springs so we must take a good percentage of the water we will need with us. We will discuss the importance of this, and solutions to the problem, below in the waste disposal section.

Packed sandwiches and a picnic cooler.

The great thing about bringing your own food with you is that you only need a microwave and water to prepare it. Freeze dried biscuits, ice cream, lasagna, and chow mein have all been created, most specifically for the space program. When one is hungry, one goes to the cupboard, takes out a package, opens the top and plunks it in the microwave with a few drops of water. Two minutes later, we can suck our beef bourgignon out of the convenient extra-wide straw in the top of the package. There are problems with this. Shelf-life, while incredibly long for freeze-dried items, is still limited. In the case of a trip longer than a year, this would become critical. The nutritional value of preserved foods drops off drastically after between six months and one year, while unpreserved foods are nutritious for even shorter periods. Nutritional supplements, like pills, creams, drinks, etc., can help but still will not supply everything the body needs.

While convenient, in terms of who has to cook dinner that night, bringing our food with us is difficult because of the sheer mass of food required. A short trip is not a problem as you only need a few sandwiches, an apple, and a thermos of tea.

Assume the average adult, in total, requires 2500 kilocalories of food and 2 litres of water a day. Let's say that the 2500kCal makes up 2kg of food. That means that for every day, we need 4kg of food and water (because 1L = approximately 1kg). For a 2.5 year mission, which is what some say is necessary for a Mars round trip, each person would require over 3.5 tonnes of food and water. Luckily, because half of that is water, which can be recycled³ with little loss almost indefinitely, we can reduce the total required sustenance mass to, as a guess, 2.5 tonnes. Three people times 2.5 tonnes equals a lot of extra weight(otherwise known as 7.5 tonnes).

And how much space would that food take up? If the food was packed as densely as possible, and assuming the food had the same density as water (which isn't far off), we would need 7.5m³ of space to store all the food. A cube that is approximately 2m wide by 2m tall by 2m long. Doesn't sound like much? Consider that the volume of the Apollo capsule was about 7.7m³, one is better able to see why this is a problem. Also, if the reader has already seen the previous installment of this series titled 'Propulsion', she will already know that extra mass is a bad thing when designing space missions. Obviously, a better solution is necessary.

Grow-your-own

What seems to be the only other possibility is to grow our food as we go. The benefits of growing our own food are various and are laid out below.

• Less total mass is brought along in the case of long-duration missions.

Although the mass of a hydroponic growing system would be high, compared to the total mass of the food one would need for a three year trip, it's negligible. There are also subsidiary benefits which will be discussed later on in the article.

• Food would remain fresh for the entire trip. If an astronaut wants an apple, she picks it off the hybrid ultra-multi-tree in the corner of the games room.

Fresh food makes for happy people. Crunchy lettuce. Orange carrots. Freeze dried ice cream may be fun the first 43 times one eats it, but once the novelty has worn off, a simple carrot could potentially go a long way to aiding crew morale.

• Nutritional value stays high.

This, more importantly than morale and weight concerns, is probably the greatest argument against bringing all the necessary food from Earth. The importance of good nutrition cannot be overemphasized, especially for a group of people who will be millions of kilometres from home. Far from "just" making one physically healthy, nutrititional levels have been shown to influence mood, sexual desire and ability, and intellectual capabilities. Very little would be more of a danger to the crew on a cramped spacecraft than a grumpy, foolish, computer engineer who can't get it up. Naturally there is also a downside to carrying a farm around in your backpocket.

• Limited Variety

No matter how good a farmer one is, there is always a limit to the number of different crops one can grow on one field. If that field happens to be a 5cm deep swimming pool with nutrient rich water under UV lamps in the cramped back corner of a space ship? The reader is sure to understand.

• Limited Volume

While packaged food may be heavy and eventually tasteless, a small farm is much less efficient in terms of calories per cubic metre. We can pack billions of calories into a space only 2m cubed with pre-packaged food, but a farm requires dozens of square metres of area in order to grow enough food for an entire crew. The farm itself may mass less, but the corresponding increase in the size of the ship necessary to carry a farm would easily outbalance the loss in total food mass.

Solutions and Conclusions

With what we have discussed thus far, we can come to the conclusion that though packaged food is a poor solution in a number of ways, it is probably the best for both short-duration and long-duration missions. Why? Because of the sheer volume requirements for a farm on board a ship. In order to have a farm, a ship would by necessity by two or three times bigger in volume just to have room for it. This sort of reuirement is beyond the ability of humans to achieve when we have a suitable, though flawed, alternative in freeze dried food. There would have to be a much more pressing reason for including a farm on board a ship.

Luckily enough for the hydroponics industry, there are two, and we discuss them both in the next two sections.

Where does air come from Daddy?

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¹ Please note that this will be the subject of an intensive study by the author. His findings will eventually be offered to the Guide as an entry titled, "How to destroy your neighbourhood using one litre of kerosene, a hand cloth, and a pink toilet brush for under 100 local monetary units."
² All quotes in this entry will be misquoted out of principle. What principle? The author is unsure, but is sure that there is a principle in there somewhere.
³ See the Waste Disposal section below