Has anyone had ideas about any unique advantages of spinning spacecraft when it comes to passive temperature regulation?I ask because I've noticed my small (1.5 L) bottle garden has been going without any outside interference for nearly 5 years now. It is definitely self regulating (it's going through another phase of foliage growth and the cycle happens several times a year as far as I can tell).The project I can imagine would was basically be "spinning bottle garden in space", but one major stumbling block I can see is having a (mostly) passive mechanism to regulate temperature in space. Imagine a thermal mass of several hundred kg but with an energy budget of a cubesat. Launch it beyond the Van Allen Belts and observe to see what 10+ years of interplanetary radiation does to small insects/plants/lizards etc.
[...] What plants?
What animals, if any?
[...] Are there plants that don't absorb most of their water through their roots, but through humidity? [...]
Thermal control might be as simple as a reflective coating on the glass/container, with passive radiation handling the rest. There won't be a lot of electronics, so your main issue is absorption of sunlight/Earthlight, rather than internal heat production.OTOH, light timing might be an issue. Most plants are not going to be bothered by a 90/90min light/shade cycle during their "day" (no different from clouds or dappled light through trees), but what plants can handle a complete lack of a night cycle? (Ditto animals.) Or do you need a sun-shield over half the container and slow-rotate it once-per-day.Another issue is the water cycle. In terraria, the water condenses on the glass, then runs down and collects at the base, where it's reabsorbed by the plant roots. No gravity, no water cycle. Are there plants that don't absorb most of their water through their roots, but through humidity?Or are you better off having a water-filled aquarium instead of a terrarium? At least for the early, simplest version.
Another issue is the water cycle. In terraria, the water condenses on the glass, then runs down and collects at the base, where it's reabsorbed by the plant roots. No gravity, no water cycle. Are there plants that don't absorb most of their water through their roots, but through humidity?
Assuming the non-illuminated side of the sphere is radiating all of this energy as fast as the sunlit side is absorbing it:
I was trying to put some numbers around the temperature considerations, and I came up with the following thought experiment. Could someone check my math please?1) Imagine a spherical pressure vessel, containing water, in a high orbit around Earth. It's in geostationary orbit or higher so that it receives constant illumination from the sun, and the amount of Earthshine is negligible.Let's say the radius of the sphere 0.564 meters - an odd number chosen because this means the surface area of sphere being illuminated is exactly 1 square meter. At 1 AU the solar radiation on the sphere of 1 square meter is ~1361 Watts.Assuming the non-illuminated side of the sphere is radiating all of this energy as fast as the sunlit side is absorbing it:E = T4 (where = 5.670367×108 W·m2K4 is the Stefan–Boltzmann constant)So I think that gives us an equilibrium temperature of 393.6 K or 120.45ºC.
Ye-ouch, let's try some smaller sizes.a) A sphere with an area of 0.5 square meters (r= 0.399m, 680.5W) gives an equilibrium temp of 331.0 K or 58ºC b) A sphere with an area of 0.333 square meters (r= 0.326m, 453.6W) gives an equilibrium temp of 299.1 K or 26ºC c) A sphere with an area of 0.25 square meters (r= 0.282m, 340.25W) gives an equilibrium temp of 278.33K or 5.3ºC
The equilibrium temperature is size invariant (this is the classic "Goldilocks Zone" calculation) because the radiating area changes proportionally.
<reflective coating>... doesn't solve the heat-loss in shadow, since that comes from the outside of the ball. In theory, it does slow the internal heat loss, but conduction between the interior/exterior makes that largely irrelevant. Annoying. I was hoping to avoid heaters as much as avoid heat exchangers.
the end state of most attempts at doing this will probably be some form of floating algae / fungi goo puddle. I take it as a goal of the thread is that the ongoing state should be at least somewhat aesthetically pleasing, and/or helpful towards creating a closed loop ECLSS.
Why would you need either if you have sufficient thermal mass? A few hundred kg is not out of the realms of possibility for the type of mission you described in the OP.
OTOH, light timing might be an issue. Most plants are not going to be bothered by a 90/90min light/shade cycle during their "day" (no different from clouds or dappled light through trees), but what plants can handle a complete lack of a night cycle? (Ditto animals.) Or do you need a sun-shield over half the container and slow-rotate it once-per-day.
Or are you better off having a water-filled aquarium instead of a terrarium? At least for the early, simplest version.
Interesting idea, I really like it.Personally other than designing radio systems and having a keen interest in our expansion into the cosmos, I also grow veg in our garden following organic-no-dig principles, and I have a planted aquarium which I'm running as an eco system, changing water as little as possible, reducing water filtration to the minimum and so on, whilst not killing the inhabitants.Small is a relative term, IMHO I would want something as big as possible, it gives an eco system stability, it needs to be big relative to the size of the largest element. I would describe a large ecosystem as one that contains a large number of the highest life form in that system. A 40gallon aquarium with 100 shrimp as the highest life form is thus bigger than a system that only just manages a single elephant. Even so, a larger system will have less temperature fluctuation, and slower chemical and biological variations which allows the denizens to adapt. I would also look for creatures with a very short life cycle as it will allow their numbers to track available resources better, which stabilises everything.I would also start with soil. All life on land begins and ends with soil. If we are to progress into the cosmos we will need to be able to grow food in space, we are learning that soil biology is a marvellous thing allowing plants to thrive where your average soil test would tell you it can't. That's because the soil biology is providing access to micronutrients on a "as needed basis" rather than the plants directly taking nutrients from the soil itself, so if the soil has zero magnesium that isn't a problem if a fungi has found a rock deeper down with that element and can allow a plant that needs it to access it. I'd want to see that amoeba, fungi, nematodes, arthropods, protozoa etc can all do their thing, and keep a range of plants and small animals alive. One also needs to control the light availability, not everything likes unrestricted sunlight, a careful measure of that need to be kept, my aquarium needs the lights to be dimmed somewhat otherwise algae takes over.In an ideal world I'd start with a series of small eco systems, learn all I can with those, then move up to larger ones, maybe ten times the volume, apply the lessons from the small systems to those and observe how the larger ones perform, gradually optimising before going larger again.
1U
