Roof chillers can easily exceed 55db. It seems that 80-100db at source is quite possible without noise attentuation. Depending on wind and frequency distribution that could still be extremely annoying at a distance of hundreds of yards. https://sdashrae.org/images/do...

Humidity/ water content of air at 30k feet and low temperature is very low. My understanding is that taking water to hydrate the outside air would be too heavy, and recycling the water content before purging might have similar issues to recycling the air in the first place.

The selection of games I made probably reflects some of my own preferences. Maybe I am a bit too impatient for turn-based games in multiplayer. I'll give it another look, though. Thanks a lot.

cool, when I last looked it wasn't yet free. thanks for the great tip.

Probably not as practicable, but isn't http://opencores.org/ kinda missing from this list.

Also, a lot of fun to be had with FPGA-based boards (http://www.fpga4fun.com/, http://hackaday.com/2008/05/22/fpga-projects-roundup/)