Hello. I've regained a certain interest in lighter-than-air-craft recently. To satisfy this interest, I wish to construct a small, rigid, unmanned, moored, hydrogen balloon within the bounds of reason. I'm most definitely not an engineer to any extent, and as such, I have many questions. First, is hydrogen too dangerous to even consider as a lifting gas in a tethered balloon? I realize hydrogen is looked down upon as a lifting gas for obvious reasons, but the fact is, many airship designs safely used it. Take zeppelins for example, of course there is the tragic Hindenburg (of which a source of ignition has not been determined, so I would not like it mentioned any further), and many early zeppelins met a flaming end, but many sophisticated hydrogen based designs safely transported passengers all around the world, both commercially and militarily. Second question, which ties with the first, is hydrogen a legal lifting gas in the United States? Are there separate regulations for manned and unmanned balloons? Also, are there any FAA regulations for unmanned tethered balloons? There were not any that I could find. Third, is a rigid tethered balloon even practical? This may sound like a foolish idea, but it would be used for experimental purposes. If it were within the bounds of reason, what might the frame look like (i.e. material, and wire size.) Fourth, what is the buoyancy of hydrogen, assuming 100-1,000 meters above sea level and average equatorial air pressure and temperature. If what I hear is truth, this should be around 1.1 kg per cubic meter (or 0.075 lb. per cubic foot.) Finally (thank you for sticking with me thus far), what material might the envelope be made of, and how could I stitch it together with hydrogen proof seams? I hear that neoprene might suite this purpose well. Once again, thank you for reading through this mass of questions.