Not Included

Material culture thoughts, chiefly as it turns out concerning power-supplies.

• Someone might (you see it happen often) take exception to me saying that things like anti-gravity might be used in buses and airships, after I explicitly compared that kind of ultra-tech to nuclear fission. We'll leave nuclear-powered spacecraft, which have already been fielded, to one side, not least because the Soviets were less than meticulous in their disposal of the scary pieces. But the thing is, fission is a special case; we need weird radioactive substances to pull it off and it's easy for the reactions to get away from you. That's not the case for, e.g., fusion, which simply stops happening when you stop making it happen (which is why we can't use it for power yet), although other issues with fusion probably require a certain minimum facility size. It probably wouldn't be the case for most things involving the Casimir effect. (Antimatter, on the other hand...)
  
  I was thinking that all those hand-held ultratech devices in our fiction would probably strike a future society much like the Ford Nucleon strikes us, but then it occurred to me that a lot of science fiction still seems not to understand that fusion is incredibly dangerous—just because it doesn't go critical or require uranium doesn't mean it's not a nuclear reaction that involves loads of lethal radiation and megakelvin temperatures. It's extremely doubtful fusion can ever be produced, as a power-source, in anything much smaller than a fairly good-size fission facility. Fusion power-plants almost certainly require lots of room and lots of sheer brute mass, between the fact fusion produces temperatures beyond any process that ordinarily happens on a planet, and the radiation, both EM and particle. (Even if aneutronic fusion were remotely feasible right now, and it's orders of magnitude less so than many things we still don't actually know how to do—even helium-3 isn't wholly aneutronic unless you fuse it to itself instead of deuterium—you'd still need huge facilities to magnetically contain the protons).
• The space-requirements of fusion, of course, means that the planes and buses (and mecha) in my books use some kind of battery. I've reexamined AMTECs (alkali-metal thermo-electric converters), and decided that their energy-density (2-3 kW·h/kg) isn't really that great. Think I'll go with silicon-air batteries, since they're almost as energy-dense as lithium-air (8.47 kW·h/kg for Si-air vs. 12 kW·h/kg for lithium-air) and yet made of the eighth most common element in the universe (second-most in the Earth's crust), rather than an element rarer than platinum, palladium, neodymium, and cerium. Those are theoretical energy densities, mind, not the ones we're gonna actually get for the foreseeable future, but it's set in the 24th freaking century, so I figure I can get away with that.
  
  An electric motor is three to four times more efficient at driving a propeller than an internal combustion one. If we assume an average improvement (3.5 times as efficient), then to propel, say, an Ilyushin Il-18 transport plane, which has four Ivchenko AI-20M internal-combustion turboprops with a power of 3,170 kW each, would require only (12,680/3.5=)3,623 kW. If we assume the same mass of batteries as the Il-18 carries fuel (30,000 liters, which has a mass of 23,850 kg given the density of jet fuel), then the battery provides (8.47*23,850/3,623=)56 hours of operation, which is plenty respectable. Dividing its listed max range by its cruising speed gives 10.4 hours, for which you'd only need 4,448.5 kg battery.
  
  An electric motor is 2.5 times as efficient as an internal combustion engine in powering a car—again, electric motors spin, and what does a drive-train do? To propel a Prévost X3-45 bus (the kind used by both the current and previous US Presidents, as well as by bus-lines like Greyhound), which has a 324 kW Volvo D13 engine, you need (324/2.5=)129.6 kW. If we assume the same mass of battery as it currently carries fuel (787 liters, which masses 582.4 kg given the density of gasoline), the bus gets 38 hours of operation. Dividing its tank by its fuel economy (1.58153 km/l) gives a range of 497.6, which takes 6.63 hours at highway speeds. To power the bus for that time with batteries takes only 101.4 kg of battery.
• While we're at it, an M1 Abrams tank has a power-plant of 1100 kW, which an electric motor could replace with 440 kW; at 1406 kg of battery, the mass of its 1900 liters of gas, it gets 27 straight hours of operation. Dividing its range by its top speed gives 6.36 hours operation; the silicon-air batteries to power that are only 330.4 kg.
  
  A, say, Honda Accord, has a 138 kW engine (=55.2 kW electric), and carries 65.1 liters of gas, which masses 48.2 kg. Carrying a comparable mass of Si-air battery means it gets (8.47*48.2/55.2=)7.4 hours of operation, which translates to over 550 miles range at highway speeds. Dividing its tank by its fuel economy of 14.88 km/l gives 4.375 hours activity, which can be powered by 28.5 kg of battery.
• Of course, a mecha is not a car. Let's take the example of, say, TOPIO, the Vietnamese ping-pong playing robot, since ASIMO is a poor model for military hardware. TOPIO uses a 48-volt, 20 ampere-hour battery, which is probably derived from an electric scooter battery. All the scooters I can find with that battery have 15 horsepower engines, so we can assume that it's got an effective 11.2 kW power plant. If we scale the 188 cm, 120 kg TOPIO 3.0 up to 10 meters tall, we get a weight of 18.1 megagrams, which presumably needs 1,686 kW to power it. If it carries as much battery as the similarly sized (17.7 megagram) M18 Wildcat anti-tank armored gun carried gas (624.6 liters, massing 462.2 kg), we get...2.3 hours of continuous operation.
  
  Whoa, I guess they weren't kidding when they said a bipedal design is power-intensive! Hang on, though, y'all, I got this. I never put a ring on silicon-air batteries' finger, we maybe can go with something else. Lithium-air gives us (12*462.2/1,686=)3.3 hours. Maybe do the whole "the mecha never go far from some other form of transport" thing? ...Come to think of it, Asimo's battery is a whopping 1/8 its mass; just stick 2,262.5 kg of lithium-air battery on the thing, that gives us 16.1 hours. We can go half that to get 8 hours operation, which is all anyone expects of a tank, as the Abrams demonstrates, above. Plus, 1,131(.25) is only 3.07 times the weight of the Tesla Roadster's battery, and the Roadster only masses 1,235 kg.
• Androids, I think, might have to use something a little weirder, since if they use a battery the size of ASIMO's (7.7 kg), then, even if it's lithium-air, they'll only get eight and a quarter hours off the charge. Then again 22.4 kg, the amount of lithium-air battery you need to get a day's activity, isn't unworkably heavy. It's basically slightly more than the mass of an average human's torso, but androids don't have organs or need to make sure that tubes running through their body (one of which opens at both ends) aren't interrupted.
  
  Maybe they'll store the power supply in structures more like those sticker-batteries, but presumably thicker, all over their bodies, under the skin—since we're just now beginning to work with lithium-air batteries, it's possible we'll have figured out how to make them work like that in the mid-2300s. The reason I suggest they'd have a "battery" layer is that, well, humans store our energy like that—it's called fat. If we assume an android with an overall mass of 120 kg, like TOPIO 3.0, 22.4 kg is only 18 and 2/3 percent its body mass, which is right between the male and female recommended body-fat percentages of humans. Maybe some lighter-duty models only mass 60 kg and have enough battery for 12 hours (or only need half as much power since they're moving half the mass).
  
  ...Holy shit. So a little further reading reveals some lithium-air batteries aren't solid, but use gel-polymers based on, basically, polyvinyl, both to separate their cathode from their anode and as an ion-transport medium. And the way metal-air batteries work is they need to be oxidized. My androids need to breathe! Even better, when they get injured? I have something for them to bleed that's not only more directly important than coolant (or hydraulic fluid, which I hadn't used but had considered), it pretty much actually is blood!
• Finally, I think I mentioned that mecha weapons carry their own power-sources. The rail-rifle I conceived of, that operates like a tank gun, would propel a projectile much like a modern KE-penetrator. Assuming tungsten carbide (in a ferromagnetic discarding sabot), and comparable dimensions to modern penetrators (an average of 2.5 cm diameter, an average of 55 cm long—volume of c. 270 cm³), it would have a mass of 4.22 kg. With a muzzle velocity of 2,000 m/s (very modest), each shot takes 8.44 MJ. That's the equivalent of 2.34 kW·h; a single-kilogram lithium-air battery gives sufficient energy for five shots (tanks usually carry around 40 rounds, which is the equivalent of 8 kg of Li-air battery). A total mass of c. 300 kg, counting the magazine and its battery, seems reasonable—and puts the rail-rifle more in the size-range of an anti-tank cannon like the 25 mm Hotchkiss Mle. 1934 than a tank gun. Except its bullets are twice as long as a typical anti-tank cannon's.
• All those people who think robot, or, God forbid, cyborg arms could have whatever number of times greater strength nanowires offer over muscle? Uh...what's powering that?
  
  If they're moving hundreds of times as much mass as a human can, or a humanlike mass hundreds of times faster, they're going to be using hundreds of times that much energy, and as I've just demonstrated, it takes the whole weight of an average human's torso to power a robot of normal strength for just one day, with the theoretical optimum of a currently-experimental battery.
  
  Also, of course, good luck finding materials to make those robots out of. A robot that has to be made of materials as costly as wholly-hypothetical orbital insertion structures like space elevators just to resist the strength of its own muscles...doesn't sound like a good idea to me, how 'bout you?
• If you think about it, the scale of outer space essentially (lacking FTL) puts space-expansion on the same time-frame that humanity's original expansion over this planet was. It took myriads of years for humanity to leave Africa; it took several more for them to leave Eurasia. The great civilizations of the New World, in the Renaissance, seem to have been roughly comparable to where Europe was 13-20 millennia ago—because it took them that long just to get over there. The Maya, whose last major center fell into decline in the 1200s AD, were not measurably superior to the Epi-Olmec (neither had anything over the Olmec but writing), and the Olmec began in the 1500s BC—much as many Neolithic Old World sites were inhabited by recognizably continuous material cultures for thousands of years, compared to the rapid upheavals of the Bronze and Iron Ages.
  
  We think of space-travel as slow only because it is only possible to people whose material culture has given them the ability to circumnavigate the globe in a bit under a day and a half. But what if you could give Neolithic people interstellar rockets? Would they think of reaching Alpha Centauri in forty years with Project Longshot (which I think would have an average speed of 12% lightspeed) as very long? How long did it take to settle Polynesia, or the Valley of Mexico? Two generations to reach a new place is pretty typical, actually, in prehistory. Admittedly that's mostly because foragers and pastoralists (not to speak of subsistence farmers) have to travel much slower than the actual top speed of humans on foot, but the point is that "we arrive in a new place and set up our new center generations after we left our old one" is not, taking the broad view, actually some new phenomenon for the human race.