However, if you are interested in the what and how to maintain it once there, I strongly suggest reading these two posts by Patty Jansen: So you want to be a space farmer (part 1) and Growing crops in space (part 2). She has a background in agricultural science and hence is significantly more knowledgeable than I on the matter.
Getting off the ground
Lifting anything off Earth into orbit requires a large chunk of energy. Exactly how much depends mainly on the weight (and a little bit on the size, in the sense of how big—and hence heavy—the spaceship doing the lifting needs to be). To get something off Earth (pretty much to anywhere further away than the moon, though it's not that different for the moon either), we need to give it enough energy to overcome the energy of Earth's gravitational pull.
Some basic terminology first:
- Kinetic energy is the energy something has due to its movement. It mostly depends on how fast the object is moving, but also on its mass. A faster object will have more kinetic energy, but of two objects moving at the same speed, the heavier one will have more kinetic energy. The formula for kinetic energy is
- Potential energy is stored energy that has the potential to turn into a more directly useful form of energy. For example, if you lift a brick off the ground, you're giving it the potential to turn gain kinetic energy when you drop it. In fact, thanks to conservation of energy, the amount of potential energy you add to it when you lift it up will be equal to the kinetic energy it gains as it falls and just before it hits the ground. What we are interested in is gravitational potential energy. You can have other types, like spring potential energy, which is the energy stored in a spring when it is stretched or compressed. The general formula for gravitational potential energy is
- Conservation of energy is the law that says energy cannot be created or destroyed but can only change forms. Hence, potential energy can be transformed into kinetic energy and vice versa, but neither can appear out of nothing. (On a macroscopic level. Things get a little bit more complicated on a quantum scale, but that's not relevant here.)
- Escape velocity is the velocity required to get something off the surface of a planet. It's basically the amount of kinetic energy required to overcome the potential energy stored between your object and the planet. It's found by equating the kinetic and potential energies above (ignore the minus sign, it's just a convention). Doing that, the mass for the object, m, cancels out and we find a common escape velocity depending only on the mass of the planet, M, and the radius of the planet, R. (This is assuming we're trying to get off the surface. For other distances, replace radius with distance from the centre of the planet.) Incidentally, Earth's escape velocity is about 11 kilometres per second (more than 40 000 km/h). The general formula for escape velocity is
OK, so that's the basics. To get something off the ground and into space, we need to make it go pretty fast to overcome Earth's gravitational pull. However, we don't do it all in one go; it's just not logistically a brilliant idea. Among other things, the faster you go within Earth's atmosphere, the greater air resistance (the friction air exerts on the spaceship) is. This is why rockets usually have stages. The space shuttles, for instance, had two initial boosters to get it off the ground, another large rocket to get them out of the atmosphere, then some small rockets which stay attached to the shuttle (the others are discarded when the fuel is used up) for orbital manoeuvring and coming back down to Earth. Here is an infographic from Wiki.
The tricky thing, when we're talking about getting the elements of an ecosystem off the ground, is how much they weigh. I don't know of any reason why crops wouldn't be transported as seeds which, compared with plants weigh a lot less and take up a lot less room. Depending on where you're taking them, giving them enough water and the right kind of soil is likely to be much more of a problem. In most cases, I think it would be best to mine the necessary water from whatever nearby source you can (the rings of Saturn, mayhaps?) and possibly ditto with the minerals needed for soil, but see Patty's posts linked to up top because I'm far from an expert.
Animals, however, would be a lot harder. With our current technology, we can't really transport a bunch of animals in foetus form and then grow them when we get to wherever like we can with plant seeds. Animals weigh a lot and eat a lot and produce a lot of waste products. That sort of thing (while making good fertiliser for our off-world plants) would be very difficult to transport.
To put this in a bit of perspective, let's look at the weight and lifting capacity of the space shuttle (which have almost all been decommissioned now with only Atlantis having one mission left). According to Wiki, an empty space shuttle weighs close to 70 000 kg, has a maximum payload weight of 25 000 kg and the payload bay is 4.6 times 18.3 metres (doesn't say how tall, but let's assume tall enough for cows). Twenty-five thousand kilograms may seem like a lot, but remember that the shuttles have been used to lift several bits of International Space Station into orbit. So a cow weighs around 500 kg, depending on the type, but let's run with this number because it's round and convenient. That means theoretically, we could squish 500 cows into a space shuttle and lift them into orbit. Well, that's not very helpful because we're ignoring all the food and water they'd need. I also think they wouldn't quite actually fit into the payload bay. Let's say cows need a metre by two metres of space to stand around in. That leaves us with only around 70 cows in our cargo bay. Well, OK, that means we could use the rest of the space for that pesky food and water I keep mentioning...
Let's say a cow eats 50 kg of hay a day... WolframAlpha tells me that hay weighs around 380 kg for a cubic metre (when pressed, because anything else would be silly in this context...) Our 70 cows would eat more than nine cubic metres of pressed hay a day and since getting to anywhere other than the moon takes at least months... we quickly run into problems being able to carry enough, even without worrying about the water.
It's fair, at this point, to mention that the space shuttles were obviously not designed to carry cows anywhere. They were designed to carry bits of ISS and other space-based equipment into orbit and not further. But in terms of lifting power they and the Soyuz rockets are all we've currently got. Also, cows probably aren't the best thing to start off carrying to other planets, I was just trying to make a point.
It takes a lot of energy to launch anything into space, let alone an ecosystem. Unlike the ISS which was built by launching bits up in manageable chunks, it's not really practical to do that with live animals. Flora poses less of a challenge and the difficult part becomes setting it up sensibly on the other end. Also the part where we haven't actually sent people on very long space flights yet.
More on this topic at a later date.
If there were ever to be livestock transported into space, it would be the type that transports easily. Cattle would be on the very, very bottom of that list (and then they'd take calves). Not only do they weigh a lot, they are also not very efficient in the food/product stakes, for the reason that they're ruminants. You're much better off taking fertilised eggs into space, or baby bunnies. I could even see an opening for the culture of certain insects as basis for protein (locust burgers, yum!).
ReplyDeleteI do, however, see a certain necessity to take some animals into space if a colony is to survive independently long term. People say: we can make proteins artificially, but, there are three buts:
1. Even these products are animal derived at some stage
2. Protein production from plants is much less efficient
3. The taste, smell and texture of food is enormously important for people's long term motivation. We simply feel good eating things that are real. Sure, a lot of the diet will involve semi-artificial food, but I think some real food will lift people's spirits.
Whenever I mention this in my fiction, I always have lettuce and cherry tomatoes grown aboard (they're easy to grow hydroponically) and have people eating chicken, eggs and don't forget the other easy to grow type of animal: fish.
I know cows aren't the most efficient animals to keep for food, especially in space, they were just the first thing that popped into my head and seemed easy enough to do calculations for.
ReplyDeleteI can't help but feel that our current technology would have difficulty transporting fertilised eggs + all the infrastructure to grow them to maturity at the other end. Much like the actual transportation side of it, I'm not sure we're quite there yet.
Protein-wise, have you considered quinoa? NASA is, apparently, considering it for future space-crop endeavours (http://www.hort.purdue.edu/newcrop/proceedings1996/v3-632.html) and it is chock-full of protein. Lettuce might be easy to grow, but it's not that full of nutrition, is it (or am I getting it confused with cucumbers)? I think, initially, a mostly or entirely vegetarian diet would be much easier to set up. You could then possibly start bringing in animals after the plants are working happily. (And logistically live animals, even chickens or rabbits, would be a bit of a nightmare to transport in space. Maybe guinea-pigs would be less affected by zero-gee conditions... I vaguely recall reading that they don't get motion sickness.