This is an update on my article about JP Aerospace's Airships to Orbit program, covering a few points not mentioned in it, but mainly, the idea is to give a short summary of the main challenges his program faces. So first, if you haven't come across it before, John Powell's idea is to build airships that can fly in the upper atmosphere, above 300,000 feet and travel at supersonic and then hypersonic speeds and eventually accelerate fast enough to reach orbital velocities, at which point they would then gradually accelerate further to higher and higher orbits. They aim to get to around 240,000 feet just through buoyancy. Can they do it? It seems impossible at first sight. But we do achieve seemingly impossible things with technology every day. So is this another of those things that seem impossible until it is done, or is it truly impossible?

As an example of something that seems almost impossible, let's look at the precooler for the innovative Sabre rocket engines for the Skylon space plane. It aims to fly as a high tech version of an airbreathing jet at up to more than five times the speed of sound by cooling the incoming air from 1000 C down to -150 C in a hundredth of a second. Even more imporessively, it does that without causing any condensation or blockage from frozen water vapour. That seems almost impossible too, yet they have actually done it in tests. They keep the details secret for commercial reasons but had to disclose some of the details in 2015 for a patent, which reveals that they use 3D printing technology to create a part that couldn't be made using more conventional approaches.

They use some of their liquid hydrogen fuel (at -238 C) to cool liquid helium which in terun cools the incoming air from 1000 C down to -150 C in a hundredth of a second.

https://en.wikipedia.org/wiki/SABRE_(rocket_engine)#Precooler