X-15 rocket plane

12/13/25:

  A consideration to the subject of being "worth it" to do this, would be in how much energy could be expected to be recovered from this? A calculation from the Nuclear Rocket pegged the energy to thrust ratio at about 1 Mw per 50 lb of thrust. Hence, if 10 Mw could be recovered, then 500 lb of thrust could potentially be produced.

  So that question must be answered before you could answer the question as to whether or not it would be "worth it". You'd also have to consider the additional weight added to the vehicle, because if you add more weight than thrust, it wouldn't be worth it at ground level, but maybe at high velocities and altitudes. It all depends.

  For example, the Space Shuttle did not achieve orbit with the hydrogen tank and main engines. It achieved only 98% orbit velocity. Then the tank was dropped into the Indian Ocean, and the OMS thrusters took the Shuttle the rest of the way. The Shuttle massed out maybe 150 tons,but those OMS thrusters did not generate that kind of thrust.

  The point being that you wouldn't need a great amount of thrust, but you would still need enough in order to make it all worthwhile. What would that be? Looking at energy potential recovery as one consideration, there are others. Among these is weight added through this additional capability, and complexity in terms of reliability and so forth.

12/12/25:

  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.