The Sky Hotel

https://www.youtube.com/watch?v=ZrodDBJdGuo

It's impossible screams everyone!!! Well, as of 202X, the video's design and technological base is. 

But the concept is cool, what's the feasibility with technologies that appear quite possible to us in the current day?

1) Perpetual Power (Nuclear) - this is probably the core of the concept. Nuclear power is so dense and powerful that it enables ideas that simply aren't possible with what we think of in terms of oil / gas / chemical rocketry. Here's a good little primer: 

https://energyeducation.ca/encyclopedia/Energy_density

The money diagram is "table 1" under fuel energy density. UM, how many more zeroes is that? Yes, nuclear power is 100,000 times more dense. 

But currently used fission nuclear reactors are huge behemoths. The fusion nuclear reactor in the article is pure fantasy, the ITER in France, the preeminent jewel of sinking fusion reactor research dollars, is 1000m x 400m.

The easy part of nuclear concepts is the effectively unlimited range, because the density of the fuel is so high. The challenge for nuclear vehicles is getting a compact reactor that produces power/weight ratios, and oh yeah, making it safe for occupants of a vehicle.

As part of the Air Force nuclear bomber project (where the Air Force would have a long range bomber aircraft that could deliver bombs and would rarely / never land), the Oak Ridge National Laboratory designed several key reactor concepts:

https://en.wikipedia.org/wiki/Aircraft_Reactor_Experiment

I believe the key number here is a targeted 350 megawatt powerplant for the eventual production reactor, but that was never fully developed. The ARE reactor was only 2.5 megawatts, and was the last one before the project was cancelled due to funding concerns by John F Kennedy. 

Essentially, the LFTR/MSR reactor design underpinning the Air Force's nuclear bomber could drive very high temperatures, which is important in aircraft because it means that brayton cycle engines (which is the engine cycle of turbofans) can be used for high efficiency power output. The Air Force had confidence that the design would lead to a high speed, high-endurance, long range (perpetual range) bomber aircraft.

Of course, the military has less concerns around crew safety and nuclear pollution than non military (especially the Soviets who were also working on this concept). Billions of dollars of research would likely be needed, but the fundamentals are there. Modern aircraft engines output 50 megawatts at peak liftoff. A 350 megawatt reactor would be able to do perpetual peak power output for seven of those.

But this was also almost 75 years ago. 75 years of aircraft design, materials engineering, reactor operation, etc. And the aircraft reactor experiment is fundamentally very scalable in size: from a closet-sized reactor to much larger ones as needed.

Essentially, the core power generation and perpetual flight aspects of the nuclear sky hotel are very much feasible in physics theory and in technology. The real issue with any nuclear reactor feasibility is the cost of development (billions) and the safety (we'll get to that).

2) Airframe design

Who knows if the video's actual shape/design is feasible. There is a joke that with enough power a pig can indeed fly.  Let's assume from what seems feasible in the nuclear power feasibility that we have enough power to make any reasonable air wing of any size fly. Fundamentally an airbus A380 is a big bulbous glob with wings, and it flies quite well! Other examples like the Antonov AN-225 and other military transports show that you can make quite a lot of large shapes as shown in the video fly close to Mach 1.

https://www.flyingmag.com/comparing-the-worlds-largest-airplanes/

There is also the concept of the big massive flying wing, the most common concept is the B-2 stealth bomber. Essentially, you gain efficiency by making the entire plane a wing, and if the plane is big enough, the wing is where people stay in the plane. Flying wing concepts are in heavy development in the aerospace world in order to gain efficiencies for lowering carbon impact of air travel. For example, here is the "blended wing" concept from airbus:

https://www.wired.com/story/airbus-maveric-blended-wing-jet/

It doesn't take a lot of imagination to scale that out and the wings become part of the passenger accommodations. 

And if we are talking about massively sized aircraft, there is also something else that can be integrated into the design: the fact that blimps/airships improve in efficiency and capability as they get bigger. If we are going to talk about a massive flying machine, then we are already moving into the scale that using airship techniques could also improve feasiblity, especially in the economic sense.

So the essential question: can you make something that big fly? Yes. Very achievable with just a propelled plane, and very much with an airship.

Making big airplanes fly was basically solved in the era of bombers by the air force and air travel industry. Airplane size tops out at the current sizes not because of physical or engineering limitations, it is simply a matter of economics first, and secondly infrastructure for landing them.

3) Infrastructure / Facilities

The essence of the concept however is the fact it doesn't ever land in practical terms. This is of course unrealistic. Some total overhaul would be necessary. Perhaps if, like the cruise ship and transport industries, so many were built that eventually a practical maintenance-free or maintenance-lite design was conceived. 

But aside from the "hotel" aspect is all the uses of large ocean ships come to mind. Passenger ships are point-to-point destinations. The longest commercial flight is 19 hours and 10,000 miles roughly. However people would likely pay a lot more to travel in hotel or near-hotel conditions and get there in 24-36 hours instead, assuming a slower speed. 

Likewise, priority cargo transport would be point-to-point and involve landing and unloading. In reality, this is what would stimulate the construction of ground facilities for landing.

The obvious approach would be it would never land ... on land. It would land on sea. There are some pretty big planes that can take off from water:

https://en.wikipedia.org/wiki/AVIC_AG600

A sea-based landing would remove a huge infrastructure cost of making someplace for it to land. 

As for loading/unloading of a perpetual flying hotel, this is where a mixed airship/airplane design comes into play, because it enables two things:

First, it enables the aircraft to possibly slow down to very slow speeds safely. If the airship's can slow safely to 40-50 mph, that is a very doable speed for "drops" or hooked cargo catches or some other handoff scheme. Those speeds would also be feasible for helicopters, and dirigibles to catch up and dock.

Second, if there is an airship aspect, there would be room for a landing strip for planes or helicopters/VTOLs. Because the flying hotel is already moving at decent speed, the length requirements are lessened for takeoff and landing. Aircraft carrier techniques could also be employed with snag cables and catapults.

4) Safety

Well, it has a nuclear reactor. A reader may not know this, but a MSR design from the aircraft project is fundamentally safer than nuclear reactors in use for power generation, because they do not use solid fuel rods. The liquid fuel can turn off/remove criticality of the reaction on demand. 

But we still have the issue of crashing. We can armor the reactor, but for a crash on land? The obvious solution is that the plane never goes over land for any substantial time. For nuclear waste, water is an excellent shield, so if the reactor from a crashed megaplane sunk into the ocean, it is automatically well shielded. 

Perhaps if certain key crossings, like the Panama crossing or something similar, could result in a land crash, but planes can glide for as much as 60 miles and the Panama crossing is less than that. A crossing would be attempted only if the plane was in good operation.

That would leave catastrophic failure/crashes in only certain small sections of land, and that can obviously be mitigated by making them over nonpopulated lands.

As for the AI turbulence, it isn't clear to me that this would be needed. Bigger planes experience less turbulence effects per this seemingly very thorough analysis:

https://www.quora.com/Does-the-size-of-an-airplane-affect-the-amount-of-turbulence-a-passenger-feels

Sky hotel / passenger transport would likely target slower speeds at cruise, probably 300-400 mph, although nothing about the nuclear aircraft experiment suggests that a high speed couldn't be engineered. The perpetual range aspect means the aircraft could simply fly around bad weather, while the fuel efficiency aspects of air transport means that planes will simply fly through bad weather. 

5) Economics

Okay, well, who knows with this. Something like this could only be budgeted if there was existing economies of scale and interests aligned. That would probably  require:

- a very robust and mature market for LFTR / MSR nuclear reactor designs in commercial/civilian operation and probably the US navy moving its nuclear reactors from the current design to a LFTR design

- the US military taking extensive interest in a rapid mass transport of cargo / military hardware by sponsoring the initial nuclear mass transport aircraft

- a very reliable market for very affluent customers using this transport mode, for people willing to spend likely 10,000$ per trip or experience, and possibly more.

While the availability of rich clients is feasible given what is being seen with space tourism, something like the sky hotel is not happening without especially the development of the LFTR/MSR in very wide use with multiple generations of refinement, and currently there isn't even a commercially operating MSR, although China is bringing a MSR online very soon. 

This likely would take a grand military investment and revitalization of the MSR inside military/national laboratory/US government with sustained funding. There is new MSR funding coming in the national laboratories, so there is hope.

It may also require the success of large cargo-transport airship startups to achieve commercial viability. That would produce large scale airships and airship infrastructure that could be one-offed/enhanced to achieve the "air cruise ship". 

It may also require a host of advancements in materials engineering such as extremely cheap carbon fiber or graphene/nanotube strength materials to vastly reduce the weight of the frame.

Something like this only happens as a side interest to a fundamental shift in the logistics industry, where nuclear power produced a significant economic reduction in the speed and cost of transporting things that petroleum or other schemes couldn't compete with. It would only happen as the brainchild of some multi-hundred billionaire who likely made such riches in successive stages of the underlying revolutions necessary in nuclear technology and airship/air transportation.