I was looking at JP Aerospace's Airship to Orbit project: http://www.jpaerospace.com/atohandout.pdf I was with it until the third phase: What is the mechanism of electric propulsion? Is it simply a propeller? (I was under the assumption that a propeller would be fairly useless at that altitude due to the low air density) For a big airship to perform this feat, I would assume that drag is minimal at this high an altitude, but will accelerating to escape velocity at this altitude still cause massive amounts of heat on the surface on the airship? Will a heat shield be necessary? Does anyone think this is feasible?