Aside from the technical difficulties (which are certainly real; but probably surmountable with time and funding), I would be concerned about the political side of the project(politics being...somewhat less of a solved problem... than space and blowing things up).

The technology sufficient to divert an asteroid, especially with limited warning(which precludes some of the subtler 'attach an ion drive or give it a slow shove with a laser' type schemes), is probably pretty punchy, possibly 'basically an ICBM but better at escaping earth's gravity well' punchy. It would be an unfortunate irony if, in the attempt to mitigate the city-destroying-asteroid threat, we ended up with some sort of proliferation problem or another round of delightful nuclear brinksmanship.

In an ideal world, you'd hope that people could put "Stopping asteroid apocalypse" in the category of 'things more important than your petty nation-states and dumb ethnic and religious squabbles'; but I wouldn't exactly be shocked if people largely can't and every stage of an anti-asteroid project ends up being a bunch of delicate diplomacy and jingoistic dickwaving between the assorted nuclear powers, along with a lot of hand-wringing about anti-satellite capabilities, and generally a gigantic mess.

Well, probably the de-facto legalization of every drug ever, along with cataclysmic declines in production in all sectors where working kind of sucks...

But it sounds like an absurd example of a false economy: Even at relatively cheap schools, the cost of running a student through is nontrivial. It seems like complete insanity to waste expensive instructional time on somebody who can't concentrate properly for want of a few dollars worth of calories. Nobody's interests are well served by that.

Legally, yes; but none of that kicks in until after some sort of legal proceeding actually occurs. If the cops just break down your door, shoot your dog, and seize everything that looks evidentiary and/or worth 'losing', and then no charges are filed? Well, if you have the resources to lawyer up, you could probably make a civil case out of it; but otherwise you just got protected and served.

Hasn't Peoria been a cultural touchstone for humorless reactionary behavior since whenever "Will it play in Peoria?" was coined?

Also, can they not afford enough legal advice to tell them that basically every step of this plan is practically a textbook case of 'How to incur legal exposure in absurdly obvious ways'?

You start with the ones who don't care, give them discounts on their insurance premiums or electric bill or whatever. Over the course of a few years, you futz with the prices until it's less of a 'discount' and more 'the only way to approach the price you used to get'.

At that point, the ones who do care can either suck it up and wear whatever herd-management-solution you feel like telling them to, or they can pay (probably increasingly steeply) to maintain their precious little objections.

You don't necessarily even need a hard kill, with the accompanying risks of damage/injury to bystanders and their property...

Thanks at least in part to the robust market for green diode-pumped solid state lasers, moderately alarming and dangerous IR lasers are ubiquitous and cheap. Depending on the quality of your optics and the robustness of theirs, outcomes ranging from temporary washout of the image to swift and permanent death of the imager are highly likely.

I'd assume that their legal team would be running around the company quietly busting skulls if they didn't.

"Incur significant legal exposure during the course of fucking up a high-profile project for a government client" isn't one of those good strategies.

Doing one or the other can actually be surprisingly lucrative; but both, less so.

Don't forget market power: something that no sane individual trusts a telco to exercise benignly, and which even ardent free-marketeers recognize as pernicious if abused.

If fatty were benevolent, well liked, and known for fairness and decency, there'd be no reason to kick him out just for being the fat guy. However 'benevolent', 'well liked' and 'known for fairness and decency' are not concepts you associate with the phone company. Terms like 'smirking, sociopathic fuckweasels' more usually come to mind. You don't want any of them getting their hands on more market power than absolutely cannot be avoided.

Wireless is no substitute for wireline, this much is undeniable.

How, though, is it relevant to a discussion of how to divide scarce spectrum between competing wireless use cases(doubly so when both of them inhabit markets shaped in part by a semi-substitutable wireline implementation of the service they offer)?

The question isn't whether wireless is the future (it isn't, and anybody who says it is is probably lying to save on capital investments) but whether broadcast television is the best use of an unfortunately finite natural resource; and, if it isn't, whether we owe broadcasters some sort of dignified exit strategy or whether we can just kill them and get on with our day.

Personally, I'd be the first to agree that the default 'Sell to Ma Bell or The Exaflood will eat your babies or something, something' policy is utter bullshit. Given the notable successes of ISM-band wireless protocols, despite the fact that the ISM band is kind of a slum, I'd advocate letting the poor telcoes suffer with their 4G and allocating more relatively unencumbered spectrum.

However, I'd also be the first to axe broadcast television as an institution, leaving not one transmitter upon a tower, to free up that additional spectrum. Broadcast TV is a howling wasteland and its arguments that it offers some sort of valuable public service aren't exactly getting more convincing as time goes on.

I suspect that the hover mechanism could do a fair bit of the work; but I posited additional elements because it would be a bit of a downer if the hover mechanism were tuned too far in the direction of being a good thruster/steering element, since you'd be walking a potentially touchy compromise between being capable of aggressive maneuvers and being inherently stable, rather than liable to assist you in tipping over even faster and harder that gravity would cover if you leaned too far out of the equilibrium position.

Just for the sake of consumer safety and not reducing bystanders to hamburger too often, the preferred arrangement would probably be some sort of EDF/Vectored thrust arrangement: all the advantages of a standard electric propeller (ambient-temp exhaust, none of the noise and fuel-line hassle associated with teeny internal combustion engines, runs on normal batteries rather than some sort of hobby fuel); but no exposed blades to do surprising amounts of damage upon somebody's first mistake.

You'd have to avoid going too deep into propeller-beanie-chic zones of absurdity; but if you could get the actually-hovering bit worked out, I suspect people would overlook that for the chance to zoom around at dubiously sensible speeds.

Well, you could build a thermoelectric shell around the entire earth... Of course, if you can do that, 'stop global warming' is probably something you did in high school as a busy-work lab project at your school for particularly gifted hypersentient disembodied intelligences.

My (admittedly pretty hazy at this point) memory of heat engines is that their theoretical peak efficiency depends on the thermal delta they manage to achieve. Exactly the same resource that thermoelectric materials scavenge (albeit at miserable efficiency) into electricity.

Anybody who actually has some grasp of the matter want to chime in on where and why you would use thermoelectrics (and how efficient they would have to be) rather than simple insulation or one of the various waste-heat-recovery systems that transfer some amount of the heat remaing in outgoing exhaust gases into incoming working fluids?

Is the thermoelectric advantage purely that, assuming material reliability is OK, they are a 100% solid state, trivial to scale from 'handle with tweezers and magnification' to 'pretty large', and their output is easy to transfer and useful for all kinds of things after just a little DC-DC cleanup, or are there actually situations where they might be absolutely more efficient than insulation and heat recovery, rather than just easier to tack in almost anywhere in a design that you have a few extra cubic centimeters and expect a temperature difference?

In space, 'just use rockets' is not the answer people want to hear, because mass is precious.

In an atmosphere, though, all you need is a little extra battery power to shove air in whatever direction you prefer, which works just fine for modifying your path. It wouldn't be much like skateboarding; but I suspect that if you threw some accelerometers, clever math, and a mixture of control surfaces and glorified model airplane thrusters at the problem you could have a system that can be 'steered' by shifting your body weight, as people are accustomed to, with the actual work being handled by the aerodynamic components, since you don't have solid objects to push off of.

Doesn't solve the 'make hoverboard hover' problem; but if you ignore that...

If we could fab them cheaply (and they don't turn out to be as carcinogenic as irradiated super-death-asbestos or anything), we'd probably use carbon nanotubes in everything. All sorts of neat thermal and electrical properties, strong as hell, just replace fiberglass with engineered carbon and feel the strength!

However, (aside from the pure sci-fi value) I think the reason that space elevators get the attention is that, unlike many other things that are entirely doable with lesser carbon fiber, fiberglass, aramid, etc. but would be X% better with nanotubes; the going consensus seems to be "If you want to stretch a rope from earth to orbit, it has to be This Strong, and that really narrows the options down to carbon nanotubes and, um, um...

The question of whether what we build with carbon fiber composites today will be better tomorrow is interesting; but its a 'difference of degree not of kind' sort of thing. 'Space elevator' vs. 'Haha, huddle in your gravity well like pitiful ants!' is a much more dramatic matter.