X-15 rocket plane

  The link references the x-15 rocket plane of the late 50's early 60's. It could be a way to use the energy of the atmosphere as a recycled energy that could add thrust, and increase ISP, or so I speculate.

  This may be a cockeyed idea, so it goes here on the speculation blog.

  The idea is from the study of nuclear thermal engines, and Parkin's doctoral thesis, written about here many years ago. If you heat up something, and then use that heat to expand a gas, such as hydrogen; you can achieve some pretty high ISP. Or so the thinking goes here.

  At hypersonic velocities, as you travel through the atmosphere, there is a tremendous amount of heat generated. So, what if there was a way to harvest some of that, as well as some of the atmospheric oxygen, so as to lessen the amount of fuel that is needed to reach high velocities?

  Fuel can be used to cool the surfaces down so that the vehicle doesn't burn up. If that fuel were also to be used as an afterburner with oxygen gathered from the atmosphere at high velocities, would it be worth it in terms of complexities and so forth?

  Indeed, would it even be feasible to exploit that? If temperatures on the skin of a vehicle get hot enough, it can in principle, work the same as a nuclear thermal engine, or on an aeroshell that Parkin's envisioned.

  The reaction mass would be hydrogen, which is the preferred reaction mass in a nuclear thermal engine. After the massive expansion from cryogenic temperatures to a much hotter temperature, plus the added effect of burning the hydrogen, perhaps on could get an extra boost, and thereby increasing performance.

  Anyway, it is an idea.