As (I think) I explained before, it was never my intention to use lighter-than-water concrete as ballast, but because my budget is as close as I can get to zero, I was trying it out. Expanded shale didn't work. Without resin, it's already denser than water. Polystyrene in portland cement was slightly lighter than water, but I don't think it would have stood up to much pressure. I was planning on reinforcing it with some sort of polypropylene, but that's a lot of work for such a small component. So I am incredibly happy about what I just received in the mail.
The best thing about working for a big university is that people give you free stuff. This is about one cubic foot of epoxy resin syntactic foam. I talked to the company that manufactured it and when I asked them what the smallest amount I could buy was, they told me the scraps they have lying around are larger than what I needed. Since I was a student, they would give it to me for free. Quite a lucky break. So thank you, thank you, thank you to Forum Energy Technologies. After I build my pressure vessel and a fairing to go around it, I'll mill a piece of this to fit inside the fairing. It will be beautiful. I'm also going to cut out a bunch of small tubes that will make the tether neutrally buoyant. I'm not sure what the quickest, most efficient way to do that will be. I want to cut several hundred tubes with minimal waste. That will take some thought.
The best thing about working for a big university is that people give you free stuff. This is about one cubic foot of epoxy resin syntactic foam. I talked to the company that manufactured it and when I asked them what the smallest amount I could buy was, they told me the scraps they have lying around are larger than what I needed. Since I was a student, they would give it to me for free. Quite a lucky break. So thank you, thank you, thank you to Forum Energy Technologies. After I build my pressure vessel and a fairing to go around it, I'll mill a piece of this to fit inside the fairing. It will be beautiful. I'm also going to cut out a bunch of small tubes that will make the tether neutrally buoyant. I'm not sure what the quickest, most efficient way to do that will be. I want to cut several hundred tubes with minimal waste. That will take some thought.