I believe I read that two methods of cut-away are required in the standard EOS amateur balloon launches. So, at a minimum, we'll need to do that. Both mechanisms will need to be tested to very low temperatures as well. Nichrome wire around the rope is common. But, to answer the question you posed Jordi, if it still doesn't release, we'll get to see how far it goes! I'd like to use two downlinks: one along the lines of XBee (short range and two-way), the other using packet via amateur radio so conceivably we could get position reports across the rest of the US if the batteries hold up. That is assuming we launch in the US one day. The regulations are another whole topic...