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Water activation mechanism
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cdugas4 Offline
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Post: #1
Water activation mechanism
So today my mind became preoccupied with ways to activate the moss. We spoke a few times about possible solutions which could deliver water to the samples when we were ready to start the experiment. I originally thought some sort of plunger (syringe) mechanism actuated by one servo or solenoid would do the trick. It could be multiple plungers on one stem delivering a precisely measured out quantity of liquid to each sample right before spin up. Although I think this is still a viable option, I began to think of other, more simplistic ways to deliver the water.

I'm envisioning a tube running from the axis of rotation towards each sample and built into the sample holder. This would be filled with water and the water blocked from escaping until we are ready. We could either have something remove the blockage just before spin-up, or build the mechanism that by virtue of spinning up the satellite, the mechanism self opens (yet is still positively sealed during transport, storage, and launch). The activation mechanism could be as simple as a tab on a counter rotating part of the craft which strikes the activation levers on each sample as it starts to spin. Another option could be some sort of ringed gear that positively holds the mechanism closed, yet as it starts to spin, flips the mechanism level and locking it in the open position now. Some options for blocking the water's path off which is connected to the lever could be as simple as a gate. A gate and similar blockages may present sealing issues and ease of use issues considering we'd be relying on a relatively small torque to open them. I think a solution which may suit us is a ball check valve type mechanism (locking of course) using a BB.

Does that make sense to you guys? Have you thought of another solution to this issue?
10-14-2015 03:03 PM
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Domagoj Offline
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Post: #2
RE: Water activation mechanism
Yesterday I did some fiddling with exactly this problem. My idea was to use kanthal wire (high resistance wire for heating element) to burn through a pocket of water that would be inside each sample chamber. Imagine something like a bubblewrap bubble sized bubble of water held in thin plastic bubble with the kanthal wire coiled and glued on the outside of the bubble. When we want to activate, just pass some current through it, it heats up and cuts the thin plastic dumping the water.

I haven't had much time so I couldn't do it properly, but my tests involved cutting some 0,2 mm thick plastic (from a yogurt cup lid, similar to this).
The plastic was cut quite easily, however, there was no water on one side which might alter results. Also, I was cutting edge on, not through entire surface.

I'm having some trouble manipulating and holding the wire since it can't be soldered with standard soldering equipment and my alligator clips just won't grip the wire that is so thin (0,05mm, AWG 44).
10-14-2015 03:41 PM
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Domagoj Offline
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Post: #3
RE: Water activation mechanism
Okay, further testing shows this is not a promising technique.
Water in the bubble dissipates too much heat for this wire to melt it properly even when the wire is white hot. Also, cyanoacrylate glue I tried loses stickiness when heated so the wire detaches almost instantly when heated.
10-15-2015 04:30 AM
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cdugas4 Offline
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Post: #4
RE: Water activation mechanism
Yeah I'd imagine the water would dissipate the heat. You can actually put a lighter up to a balloon filled with water and not melt the rubber since the water conducts the heat away so quickly. Another problem is that you'd have to simultaneously pop all sample water containers and start the rotation almost instantly after for the ones attached to the spinning wheel.

I'll continue sketching out some designs this week and hopefully find something to build a test mechanism out of this weekend.
10-15-2015 05:41 AM
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Domagoj Offline
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Post: #5
RE: Water activation mechanism
The system I had in mind would be able to activate the already spinning samples. I have some slip rings that can transfer current between rotating parts. These particular ones have 12 electrical contacts, so with a capacitor on the rotating side there could be 10 samples each activated by a small MOSFET, also rotating.

I'll give this one more try, dump more energy into the wire quickly, maybe that makes a difference. After all, the wire doesn't need to survive, as long as it cuts the bubble before it breaks.
10-15-2015 06:35 AM
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Endersmens Offline
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Post: #6
RE: Water activation mechanism
What if you were to use a system where one end of the tube is open, but the other end is sealed. Done right, the water will stay in the tube because it's held in by..well, not sure what to call it. But you get what I mean. Like how you can hold water in a straw by putting your thumb on the top end. To release the water, the sealed section could be punctured, allowing air to flow in and the water to fall out. This could happen after spin up so the water will go out the correct end.

Still complex, but it could work. Not sure the water would survive launch like that though.
10-15-2015 08:30 AM
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cdugas4 Offline
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Post: #7
RE: Water activation mechanism
Actually that is one of the first designs I thought of. Have a small diameter opening at the sample, fill the reservoir with water, introduce a slight negative pressure (maybe as little as 1 ounce below atmospheric), then seal up the small opening at the end nearest the axis of rotation. Design it in such a way that the sealing surface is misaligned (the sealing surface could be a smooth disk with holes misaligned during transit which will allow air in once spinning) whenever the apparatus starts to rotate. This will allow air in, and the centrifugal motion will allow the water to drain out at the sample. This will by far be the simplest design since there are no additional moving parts. The one thing I worry about is the friction from having this disk pressed up against the rotating part, and another one mounted on the rotating part that is against the stationary part (assuming we do two gravity levels by spinning up the satellite). There is a way around that friction but I'd have to do a little testing. It would require a small spring and an inclined plane which would draw the two surfaces apart when the motor turns on...
10-15-2015 10:54 AM
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Domagoj Offline
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Post: #8
RE: Water activation mechanism
It colud take several weeks from the moment we give the sat to the launch provider until the launch. In case of throwing it out of ISS window it could take months.
If we don't fully seal the water compartment, I'm worried that the water will evaporate and the air will eventually reach 100% relative humidity, meaning the spores could activate prematurely.
10-15-2015 03:08 PM
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Endersmens Offline
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Post: #9
RE: Water activation mechanism
(10-15-2015 03:08 PM)Domagoj Wrote:  It colud take several weeks from the moment we give the sat to the launch provider until the launch. In case of throwing it out of ISS window it could take months.
If we don't fully seal the water compartment, I'm worried that the water will evaporate and the air will eventually reach 100% relative humidity, meaning the spores could activate prematurely.

This is very true, I wasn't thinking about that.
10-16-2015 08:31 AM
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cdugas4 Offline
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Post: #10
RE: Water activation mechanism
I'm not sure who you were referring to Domagoj? Leaving a small enough opening at the sample site wouldn't lead to moisture leakages. Surface tension would hold the water in and coupled with the extremely low surface area at the air/water interface, evaporation losses would be minimal. To get an idea of the size opening I'm thinking of, think of a very small pipette used in chemistry or biology class. The tips of those can get really small.
10-16-2015 10:35 AM
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