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The short answer is, both. There's a smaller core team that works more or less full time on this, and a lot of other part time volunteers. Personally, I volunteered temporarily on one of their research trips only (I'm unsure if I'm counted in the "over 100 volunteers" figure, though).

Edit: I forgot to respond to the second part. It is also very complicated - it has already required a lot of research that hasn't been done before, and a lot of angles need to be considered, not just in various fields of physics and chemistry but also biology, economics and law to mention a few.