bhauth
After being “launched” from the despinner, you would find yourself hovering stationary next to the ring.
Air resistance.
That is, however, basically the system I proposed near the end, for use near the center of a cylinder where speeds would be low.
This happened to Explorer 1, the first satellite launched by the United States in 1958. The elongated body of the spacecraft had been designed to spin about its long (least-inertia) axis but refused to do so, and instead started precessing due to energy dissipation from flexible structural elements.
picture: https://en.wikipedia.org/wiki/Explorer_1#/media/File:Explorer1.jpg
a space habitat design
That works well enough, but a Vital 200S currently costs $160 at amazon, less than the cheapest variant of the thing you linked, and has a slightly higher max air delivery rate, some granular carbon in the filter, and features like power buttons. The Vital 200S on speed 2 has similar power usage and slightly less noise, but less airflow, but a carbon layer always reduces airflow. It doesn’t have a rear intake so it can be placed against a wall. It also has a washable prefilter.
Compared to what you linked, the design in this post has 3 filters instead of 2, some noise blocking, and a single large fan instead of multiple fans. Effective floor area usage should be slightly less, but of course it has to go together with shelving for that.
overengineered air filter shelving
First, we have to ask: what’s the purpose? Generally aircraft try to get up to their cruise speed quickly and then spend most of their time cruising, and you optimize for cruise first and takeoff second. Do we want multiple cruise speeds, eg a supersonic bomber that goes slow some of the time and fast over enemy territory? Are we designing a supersonic transport and trying to reduce fuel usage getting up to cruise?
And then, there are 2 basic ways you can change the bypass ratio: you can change the fan/propeller intake area, or you can turn off turbines. The V-22 has a driveshaft through the wing to avoid crashes if an engine fails; in theory you could turn off an engine while powering the same number of propellers, which is sort of like a variable bypass ratio. If you have a bunch of turbogenerators inside the fuselage, powering electric fans elsewhere, then you can shut some down while powering the same number of fans. There are also folding propellers.
The question is always, “but is that better”?
electric turbofans
Yes, helium costs would be a problem for large-scale use of airships. Yes, it’s possible to use hydrogen in airships safely. This has been noted by many people.
Hydrogen has some properties that make it relatively safe:
it’s light so it rises instead of accumulating on the ground or around a leak
it has a relatively high ignition temperature
and some properties that make it less safe:
it has a wide range of concentrations where it will burn in air
fast diffusion, that is, it mixes with air quickly
it leaks through many materials
it embrittles steel
it causes some global warming if released
Regardless, the FAA does not allow using hydrogen in airships, and I don’t expect that to change soon. Especially since accidents still happen despite the small number of airships.
In any case, the only uses of airships that are plausibly economical today are: advertising and luxury yachts for the wealthy. Are those things that you care about working towards?
see also: These Are Your Doges, If It Please You
IKEA already sells air purifiers; their models just have a very low flow rate. There are several companies selling various kinds of air purifiers, including multiples ones with proprietary filters.
What all this says to me is, the problem isn’t just the overall market size.
Apart from potential harms of far-UVC, it’s good to remove particulate pollution anyway. Is it possible that “quiet air filters” is an easier problem to solve?
I’m not convinced that far-UVC is safe enough around humans to be a good idea. It’s strongly absorbed by proteins so it doesn’t penetrate much, but:
It can make reactive compounds from organic compounds in air.
It can produce ozone, depending on the light. (That’s why mercury vapor lamps block the 185nm emission.)
It could potentially make toxic compounds when it’s absorbed by proteins in skin or eyes.
It definitely causes degradation of plastics.
And really, what’s the point? Why not just have fans sending air to (cheap) mercury vapor lamps in a contained area where they won’t hit people or plastics?
cancer rates after gene therapy
some questionable space launch guns
As you were writing that, did you consider why chlorhexidine might cause hearing damage?
https://en.wikipedia.org/wiki/Chlorhexidine#Side_effects
It can also obviously break down to 4-chloroaniline and hexamethylenediamine. Which are rather bad. This was not considered in the FDA’s evaluation of it.
If you just want to make the tooth surface more negatively charged...a salt of poly(acrylic acid) seems better for that. And I think some toothpastes have that.
EDTA in toothpaste? It chelates iron and calcium. Binding iron can prevent degradation during storage, so a little bit is often added.
Are you talking about adding a lot more? For what purpose? In situations where you can chelate iron to prevent bacterial growth, you can also just kill bacteria with surfactants. Maybe breaking up certain biofilms held together by Ca? EDTA doesn’t seem very effective for that for teeth, but also, chelating agents that could strip Ca from biofilms would also strip Ca from teeth. IIRC, high EDTA concentration was found to cause significant amounts of erosion.
I wouldn’t want to eat a lot of EDTA, anyway. Iminodisuccinate seems less likely to have problematic metabolites.
As a “physicist and dabbler in writing fantasy/science fiction” I assume you took the 10 seconds to do the calculation and found that a 1km radius cylinder would have ~100 kW of losses per person from roller bearings supporting it, for the mass per person of the ISS. But I guess I don’t understand how you expect to generate that power or dissipate that heat.