Friday, January 27, 2017

Rapid Transit on Trantor

Second Avenue Subway



In our last exciting episode we visited Trantor, or at least a city world that could pass for Trantor, an ecumenopolis of a trillion people for whom the Galactic Empire is something of an afterthought. But having come this far we ought to see more of it than just the inside of a spaceport gate or elevator foyer.

The Foundation 'verse has no teleportation tech (if you exclude jump-style hyperspace), so to get anywhere on a planet you have to go there. And if our ecumenopolis is a real city - not a mere planetwide suburbia (how boring!) - this means a public transit network.

Cars will not do, not for general use - not even Futuristic[TM] skimmer cars or whatever. Not even robocabs, which did not exist in that 'verse anyway.

It is all about geometry. Cars and highways are fine at low population density, such as tract-home suburbs - say, 5000 people per square mile = 2000/km2. But once you get up even to townhouse urban density, about 10,000/mi2 = 4000/km2, parking and roadway space become a major hassle.

Putting everyone in robocabs instead of private cars would help with parking, and the robo part would allow more roadway crowding before gridlock sets in. (Robots should drive better than we do.) Boxy little cars would help a bit, too. But these measures only get you so far.

Yes, in principle you could have multiple layers of parking garages and underground roadways below the dwellings. And since Asimov's 'verse did have aircars, you could move the garages to the top floors and the traffic jams into the air. In the Future, car accidents never happen.

But in practice, at some point it gets easier and faster to simply take the bus.

Which brings us to transit technology. In rocketpunk days it was taken for granted that even ground vehicle would never use anything so primitive as wheels. As late as c. 1990, the agency building the Los Angeles rail transit lines insisted that artists' conceptions avoid showing that its trains would run on (gasp!) railroad tracks.

Now, of course, tracks are back, including streetcars (trams, to some of you). Depending on the state of the tracks or pavement, streetcars usually have a smoother ride than buses, but don't go any faster. Their chief virtue is that a streetcar, running on rails, can be longer than a bus and thus carry more people.

But this only really matters for very busy lines, which is why most streetcars vanished around the rocketpunk era.* In any case, by the near future - no need to wait for the plausible midfuture, let alone the Galactic Era - technology could blur these distinctions.

The rocketpunk era is associated less with fading streetcars than with two other forms of urban transit. One, monorails, needs little discussion here. They are just elevated (usually) rail lines with a track too narrow for most idiots to try walking along. (The wheels are also neatly hidden from view.)

Much loved in the abstract, monorails never became popular in real life because people hate els running above their street. This is too bad, because you see a lot more of the city from an el than you do from a subway. But most people hate on els anyway, and still hate them even when the tracks are narrower and don't blot out quite as much sun. Which is why monorails remain rare.

The other great rocketpunk transit tech was the slidewalk, a pedestrian conveyor belt resembling a flattened out escalator. Step on and be carried along. These are more interesting, as a real departure from conventional vehicular transit. For one thing, slidewalks run continually, so unlike a bus or train you don't have to wait for it. This is a big deal, because people hate waiting, and long wait times can effectively wipe out the advantage of high speed.

Like monorails, some slidewalks actually exist, but also like monorails they have never really caught on. The problem is that if they are fast enough to save you much time over walking, people will stumble and fall all over when getting on or off.

Heinlein (and probably others) suggested multiple side-by-side strips, so you could start on a slow 'local' strip, then cross over to faster express lanes. Alas, unless Trantor has UBT - universal ballet training - this side-step across a speed differential is also a guaranteed pratfall generator.

With suitable magitech you might improve on the situation. Clarke's far future city of Diaspar has slidewalks made of flowing 'anisotropic matter'** that you can stand/walk on, while allowing a smooth transition from slow edges to the faster center express section.

Slidewalks are still limited in speed unless your magitech also moves the ambient air along so riders aren't facing a gale-force relative wind. Rapid transit they are not, but if you can solve the pratfall problem they might have a place along busy corridors like Seldon Street.

Indeed, for window shoppers and flaneurs, Seldon Street might even have slidewalk cafes and such. But this is more tourist attraction urban amenity than practical transit for people who just want to get where they're going.

Otherwise your basic local line, the service that goes everywhere and stops at your corner, is essentially a plain old bus. Even though the smelly diesel bus has surely gone the way of the 19th century horsecar, which also emitted a noxious exhaust.

And so a bus it is, though heavy Trantorian ridership levels - especially along busy Seldon Street - might justify streetcars/trams. We will also suppose that heavy ridership allows TERTA to provide frequent service, so you only have a short wait when connecting between lines.

But the local bus can't be very rapid, not for techological reasons as such, but because it has to fight its way through traffic, automotive or pedestrian. Even if separated from other traffic, it must stop every few blocks to let riders on and off. And it can't get up too much speed between stops because of a basic human limit.

Back in the 1930s, the R&D program for the classic American PCC streetcar determined that the highest comfortable acceleration for transit straphangers is about 0.2 g, or two meters/second^2. The maximum acceleration of the PCC was thus set close to this level - quaintly expressed as 4.75 mphps (miles per hour per second).

For surface vehicles that 'push against' the road or track, power needed for a given acceleration rises with the square of velocity; to avoid wasteful design, average acceleration for all but the most local service will be about half the maximum, a nice even one meter/second^2 or 0.1 g.

Absent magitech pseudo-gravity to allow high acceleration without bowling passengers over, technology cannot dramatically change these constraints, which is why present-day transit lines are not much faster than those of 100 years ago.

Between the acceleration limit and the need for frequent stops (with 'dwell time' for riders getting on or off), the average or service speed of local transit is limited to about 15 mph / 25 kmh or thereabouts. Fighting through traffic makes it a good deal slower, unless the the line runs on its own reserved speedway in a boulevard median - an arrangement both useful and rather elegant.

To get around this practical speed limit, large present-day cities have a two-level transit heirarchy. The local bus runs everywhere. Layered above it - or more often below it, in a subway - is a rapid transit or metro system, unimpeded by other traffic, with lines and stations more widely spaced, typically in the range of a kilometer to a mile apart.

Because the rapid transit trunk lines have heavy ridership they are commonly served by multi-car trains, not individual buses. So we will simply call the rapid transit vehicles trains, without further ado.

Longer runs between stations allow higher top speed for the same acceleration, and rapid transit service speeds are in the range of 25 mph / 40 kmh.

A two layer transit hierarchy is enough for most present day cities. Paris has a third, the RER, and London is developing one, the London Overground, upgrading and connecting suburban commuter lines for frequent all day service.

This heirarchy is not rigid - 'light rail' and 'bus rapid transit' both tend to be intermediate or hybrid cases - but it provides a starting point for discussion. And as commenters on the last post already anticipated, Trantor will need multiple layers in its transit heirarchy. Just how many is hard to say; we don't have even semi-ecumenopolitan examples to guide us.

We can start by considering a performance level that is not remotely magitech. Suppose a train accelerates at an average 0.1 g to a maximum 150 m/s, about 330 mph, then decelerates at the same rate - the public transit equivalent of a brachistochrone orbit. (This only loosely resembles how rail vehicles move, but gives us a first approximation.)

Travel time is about 300 seconds, five minutes, and the vehicle goes 22.5 km. If we let the train cruise at top speed for another 150 seconds, we go 45 km in seven and a half minutes. An express run, passing intermediate stations, can go nearly 160 km - 100 miles - in 20 minutes.

For comparison, the fastest existing transit line, the Shanghai airport maglev, runs 30.5 km in 7:20, hitting a top speed of 120 m/s. So the model performance is only modestly above current rail practice. These high speed lines can form the third layer of the rapid transit hierarchy. Below them, heirarchically, are regional trains that stop every few miles or km, then the primary metro subway (and finally the local bus).

Allowing time to get from your home to the high speed rail station, and from the destination station to wherever you're actually going, this type of system - local bus plus a 3-layer hierarchy of rapid transit, will get you pretty much anywhere in the extended neighborhood within an hour, where the extended neighborhood extends a hundred miles or so.

At typically modest Trantorian urban density, up to half a billion people live within this radius (fewer if there are geographical constraints like a coastline, large park, or the Imperial Palace grounds.) So within an hour's ride are a corresponding number and variety of jobs, restaurants, potential lovers, and whatever else the city has to offer.

But to really get around town we need to go faster. Suppose now a one hour 'semi brachistochrone' - 20 minutes accelerating at 0.1 g, 20 minutes cruise, 20 minutes decelerating. This takes you nearly 2900 km, 1800 miles, about the length of Seldon Street. Top speed is 1.2 km/s: rapid transit, indeed!

The currently popular technology for this type of service is a hyperloop. Unfortunately, in current proposals the accent is on hype - not because the tech is modestly speculative, but because promoters tend to shamelessly lo-ball things that are not speculative at all, such as the cost of building elevated viaducts.

(The name hyperloop is unfortunate in another way; it sounds more like an Awesome roller coaster ride than a practical transit service for people who may be package-laden, tired, tipsy, or all three.)

But all that said, some such technology should be viable - essentially a genteel cousin of a mass driver or coilgun - and TERTA knows how to estimate construction costs. With a nod to London, the Mother of Rapid Transit, I will simply call these Tube lines.

For the longest trips, a two hour nonstop Tube takes you up to 11,500 km / 7000 miles, nearly a third of the way around an Earth sized planet. Allowing for all connections and wait times, you can get from most locations on Trantor to most other locations in perhaps five or six hours.

A 'local' Tube running 30 minutes between stops will go a quarter as far as the baseline model, around 700 km / 400 miles. This service thus runs the length of Seldon Street in two hours, with three intermediate stations.

Conventional high speed express trains connect these stations in turn, with another four or so intermediate stops, and so on down the hierarchy to the primary rapid transit that stops every mile or less. Then there are the buses and streetcars, and perhaps slidewalks, along Seldon Street itself.

Thus a two hour trip - about the maximum for casual daily travel, whether commuting to work or meeting a friend for lunch - will get you more or less anywhere within a thousand km / 600 miles. If your destination lies close to a major transit hub you can go two or three times as far, because it will be served by top level lines, and you won't need to work your way back down the hierarchy.

The cityscape will reflect the granulation and heirarchy of the transit system. Most rapid transit stations will be nuclei of urban villages, neighborhood centers for errands, entertainment, and general public social life. Major stations will draw larger and denser condensations of the world city, some perhaps on a scale that would match our grandest Zeerust visions of the urban Future.

And while Trantor falls short of being a single practical commute zone, something in the range of 10-50 billion people probably live within two hours of wherever you are. Long distance travel might be constrained by high fares, but perhaps TERTA runs like the semilegendary subway of Gotham on the Origin World: a nickel takes you all over town.

Although not part of the urban transit system, a word about space elevators. I have argued that they are only suited to truly enormous volumes of space traffic. Well, here we are: If any world has the requirement, Trantor does. We can imagine numerous elevator lines rising from the equator, probably with ring lines connecting them at geosynch level. Commenter Eth noted last post that the elevator cables could also support a ring of solar collectors or radiators if needed for power or heat management.

Enough about the elevators; back to TERTA.

The system is extensive, with bus and rail lines totalling hundreds of millions of miles, served by up to a couple of billion buses and subway cars. The Tube network, serving only long haul trunk routes is a mere million miles or so, interconnecting perhaps a thousand stations - few enough that dedicated enthusiasts will have visited all of them.

These major stations should be suitably impressive. The levels of the transit hierarchy must become literal here, the long-haul Tube lines probably running deepest, with local lines being closer to the concourse and street entries. As with major airports today, a transit system might be needed simply to get around the station itself.

And at times it will seem as if all those trillion Trantorians are trying to catch the same train that you are.

But from suitable locations you can look down along some of the lines, with their diverging and converging switching networks and crossovers. The utter coolness of which is justification enough for this visit to Trantor.

To All Trains


* The Great Streetcar Conspiracy was real, but played only a minor role in their demise. Streetcars were unfashionable in the 1950s, and most systems were old and badly run down. So it was simpler to bus convert even the few lines busy enough that streetcar modernization would have been preferable.

** Anisotropic matter is also a term in relativity and cosmology, but I have no idea how it relates to the stuff you would use for slidewalks.


Discuss:




The image of the Second Avenue Subway comes from the New York City transit agency. Because even tiny villages like NYC can benefit from rapid transit!

The eastside Manhattan line, first proposed about a hundred years ago, opened on New Year's Day, and cost about $5 billion for a couple of miles of line - outrageously expensive even for subway lines, which are never cheap. But even at train robbery prices it will be worth the wait for the good citizens of Gotham.

And as a curious example of Google time lag, there are not yet any good post-opening images of the line, which explains the odd absence of New Yorkers on the station platform.

"To All Trains" is from the NY Transit Museum.

Sunday, January 15, 2017

Trantor: the Big Town

Trantor

As Earth awaits the official debut of America's nightmare comedy, this might be a good time to talk about other planets. So here we go! (Again!)

One minor but durable trope in science fiction is the planetwide city. (For which the geek (and Greek) term is ecumenopolis, 'world city'.) For now - until the Star Wars prequels mercifully fade from popular memory - most people will associate this trope with Coruscant. But accept no substitutes: really it means Trantor, capital world of the Galactic Empire in Asimov's Foundation Trilogy.

Just for the record, this discussion obviously lies waaay beyond the Plausible Midfuture. Also a disclaimer that I am not trying to specifically reconstruct Asimov's Trantor, but a more broadly Trantor-esque world.

I bring up this trope because one of my interests, which has gotten oblique mention here before, is urban rapid transit. And while TERTA - the Trantor Ecumenopolitan Rapid Transit Agency - never got any mention in the books, it reasonably ought to be ... impressive.

As useful background for a transit ride, a few words - well, quite a few - about the overall cityscape, starting with its population. The Good Doctor A slipped up badly on this score. His canonical figure for Trantor - 40 billion - is laughably low, only a few times current world population. We want a global city, not a world of ten-acre exurban ranchettes.

Donald Kingsbury does much better in his unofficial Foundation sequel, Psychohistorical Crisis. His version of Trantor, called Splendid Wisdom, is home to a nice, round trillion people. Spread over the whole surface of an earthlike planet, even this comes out to merely suburban average density. But if we leave the oceans wet and only urbanize the land surface, we get roughly the population density of San Francisco.

Now we're talking. San Francisco, outside the Financial District, lacks the glass and steel canyons look, but cityscapes can vary considerably for a given density. Central Paris apparently has about the same population density as Manhattan, but a very different urban look. Likewise a modest urban density could still have an impressive skyline.

The image of Trantor (nominally Coruscant) above - click to embiggen - hints at one way of finessing this. Most of the city seems to be low-rise, or at least of roughly uniform height, but with monumental structures rising above the rest for added zip.

Another consideration is that an ecumenopolis surely cannot be like an ordinary habitable planet, where humans merely skim the cream off a self-sustaining natural ecosystem. It will need something more like a spacecraft life support system, on a suitably giga scale.

The details are far above my biology pay grade, but may well imply vast sublevels of, essentially, plumbing. The subways could thus run through what amount to basements rather than true tunnels. And the oceans may effectively be sewage treatment / oxygen regeneration ponds - nothing you would want to swim in, which at least would keep shorefront promenades from being impossibly crowded.

Parts of the life support system might rise to or above surface level, and some of the megastructures could well be the equivalent of rooftop air conditioning equipment.

Also, the population density need not be uniform all over town. If you really don't like urban living, Trantor is not the planet for you. But many neighborhoods (totalling millions of km2 and a couple of hundred billion people) might well be at suburban density, balanced by high-rise urban districts, thus accommodating people who want a yard as well as those who prefer living near good shopping and restaurants.

Kingsbury mentions one such commercial district on Splendid Wisdom that is suitably Trantorian in scale. I forget its name, but since Splendid Wisdom is a rebuilt Trantor of the Second Empire, I will call it Seldon Street. Though technically a pedestrian mall, functionally it is a suitably giga-scaled version of Market Street or Wilshire Boulevard, extending for some 3000 km.

That being a long, long stroll, expect some serious transit lines to run along the Seldon Street corridor.

But before we ride, a few more thoughts on the cityscape. First, a couple of annoying practicalities. Realism[TM] is not really a key issue in this exercise, but we should give it a superficial nod.

On a world without farmland, how do you feed a trillion people? Asimov's Trantor imports its food from 20 agricultural worlds, but they could only supply this Trantor with delicacies. For basic food supply you need a planetwide array of oscillating hands: something something hydroponics, something something algae.

And, of course, all this stuff should really be on the surface, with the city life below, but we want a planet that looks urban. We will delicately assume that technology originally developed for spacehabs and such will solve food supply along with the rest of the life support challenge.

Energy supply turns out to need less handwaving than food supply. An earthlike planet absorbs on order of 10^17 watts of insolation (instellation?) from its parent star. Current average US energy usage is about 10 kw/capita, scaling to 10^16 watts for a trillion people. So cover the rooftops with solar panels and you more or less get there. Waste heat disposal is not a problem, because you are merely using energy the planet would absorb anyway.

And energy consumption on Trantor can be relatively modest. It is not an industrial world; as the Imperial capital, its chief manufactured product is government. Large cities also tend to be energy efficient - not least because people ride the subway instead of driving.

From these material concerns we can turn to social considerations. An ecumenopolis must have substantial overall social stability to function at all, but Trantor presumably has its good neighborhoods and not so good, perhaps including slums the cops only enter in army-corps strength.

Or - another familiar urban SF trope - class stratification might be literal, with the down and out living among the plumbing sublevels, while the upper classes live on upper floors, the richest in penthouses. This lends itself to a transit subtrope that goes back to 1890: dismal subways for the poor, elegant els for the rich.

Note that the district shown in the image above must be served only by subways; there are no hints of elevated lines.

Given a world of a trillion people none of this needs be an either/or: Within vary broad limits, Trantor's cityscape and social life can be as varied - including the charmingly urbane and the dystopian - as you want them to be.

On yet another note, Isaac Asimov was famously agoraphobic, and his Trantorians rarely went up to the open surface. Depending on how the life support system operates, 'rarely' might be never, at least without a quasi space suit.

But this too is not a given. An ecumenopolis, or neighborhoods thereof, may have rooftop gardens and dining patios under the solar awnings, and even (shock!) open air streets instead of roofed over corridors. When I speak of the Seldon Street corridor I say nothing about its architecture, only that it is an elongated urban district.

Trantor might even have parks, though the only open space on Asimov's version was the Imperial palace grounds. But we have not come all this way to an ecumenopolis to visit a park. You can find those on any garden colony world. So in our next exciting episode we will head for Seldon Street.

And since it is already mostly written, you won't need to wait until the Galactic Era to read it.

Discuss: 
Yes, knowing this blog's commenter community - if you have not all given up and deserted me - the discussion will work itself around to space battles.




The cityscape image comes from a blog review of Second Foundation. Alas, I know nothing of the artist who created it.


Thursday, August 6, 2015

Darker Than a Thousand Suns

Hiroshima

Seventy years ago, a nuclear weapon was used against human targets for the first time. Seventy years ago less three days, one was used for - so far - the last time.

The mythology of nuclear weapons and nuclear war is, understandably, much bound up with the element of surreal horror, from stellar temperatures and energies to lingering death from radiation. This is probably as it should be: those things stick in the imagination.

But what really sets atomic bombs apart is not the exotic horrors they release on top of the ordinarily horrific effects of blast and fire, but the mundane fact that nuclear weapons make devastation cheap. Individually they are expensive, but no more than the aircraft and missiles that carry them, and one nuclear-armed delivery vehicle wreaks the havoc that previously called for a thousand.

The good news - again, so far - is that the combination of vivid terror and stark economics has been enough to prevent a third use. It has become harder for elites to retain their illusion of invulnerability. Not only does the bomber usually get through, but if it does, a bomb shelter is unlikely to provide sufficient protection for you, your family, or your assets. These facts seem to be fairly well understood, at a fairly visceral level.

Which is a fairly thin sliver of hope to rest on, but it is the one we have.



The image of the Hiroshima mushroom cloud comes from Atomic Archive.

Monday, July 27, 2015

Stick and Gimbal: Handflying in SPAAACE

Snoopy at the Controls
Do the human roles in space include piloting spacecraft in the traditional sense of maneuvering them via direct control inputs, AKA handflying?

In an old post I said that 'handflying a spaceship is a ding waiting to happen,' alluding to a Progress supply ship that banged into the Mir space station during a Russian test in 1997. But the story is (as usual) a bit more complicated than that.

In Russian practice, handflying has always been strictly an emergency backup. And certainly their experience gave them no reason to change their approach. In the American space program, however, things were different.

Cosmonauts and astronauts were both originally chosen from among test pilots, for the same sensible reason. The basic mission was to test and exercise human capabilities in space, for which you want highly capable people. Familiarity with complex technical systems that go really, really fast was also seen as helpful.

But for institutional and cultural reasons, the early 'Murrican astronauts had much greater influence on how things were done. Mostly it was the whole hot-pilot mystique: Use the Force, Luke!

A scene in The Right Stuff - a title that encapsulates this mystique - conveyed the effects it had on American thinking about space. A German-born rocket scientist describes the prospective occupant of a Mercury capsule as a 'specimen,' but his 'Murrican audience hears it as spaceman, a term richly evocative of Romance.

A related factor might have been the historical accident that the Russians used dogs, most famously Laika, for space research while the Americans used monkeys and apes. Following in the pawprints of Man's Best Friend was one thing. Going boldly where our relatives from the primate house had gone before was a bit more awkward.

In any case, the upshot was that astronauts fiercely resisted being spam in a can, and got their way. Handflying was integral to American human spaceflight from the beginning, and right through the retirement of the Shuttle.

Moreover, it contributed significantly to Americans winning the 1960s moon race. Successful handflying of Gemini spacecraft in rendevous and docking maneuvers emboldened NASA to choose an Apollo architecture that required rendezvous on lunar orbit, and the savings in mass allowed the whole thing to go up on one Saturn V. In the mid-60s state of the art, when this decision was made, automated rendezvous and docking at lunar distance was surely a nonstarter.

Fifty years later our space technology, most of it, is not much different, but automation is obviously a different story. In the age of Google Cars, handflying is out of fashion, and new generation US spacecraft, both Orion and Dragon2, will reportedly follow the Russians in automating maneuvers, including rendezvous and docking.

So is handflying in space an idea whose time has come and gone? Just behind this question, of course, lurks the much larger one of whether human spaceflight itself is an idea whose time has come and gone. Our voyages of deep space exploration have now reached the Kuiper Belt, and the fringes of interstellar space, without their operating crews ever leaving Pasadena or its terrestrial counterparts.

It may be that at some point we will send 'mission specialists' to the planets without any need to send spacecrew along to fly their ships. For that matter, even if ship-operation spacecrew are needed, their tasks may not include handflying. But for now, let us consider handflying, as one of the classic skills we once expected of professional space travellers.

It is pretty much a given that automated systems can fly routine space maneuvers, including complex ones like rendezvous and docking, more smoothly than human pilots. And probably more safely as well, since robots are less prone to unaccountable lapses that can cause routine operations to go pear shaped.

The first question, and the traditional fallback for human intervention, is when things are not routine, and particularly when they have already gone pear shaped. This is nothing to dismiss lightly. So long as things go well, space lends itself to automation, what with Newton and all that. But once things go awry, from instrument failure to erratic maneuvers by another spacecraft, the ability of machines to easily predict the predictable is less helpful.

Moreover, a large part of contemporary AI is expert systems, essentially an encodings of prior human expertise and experience. Expert systems are convenient, cheap substitutes for scarce human experts. But it is less certain that the projected wisdom of skilled pilots who are not on the scene of a particular emergency should or can trump the judgment of a skilled pilot who is on the scene. (And setting aside the question of who trains the expert system if humans no longer practice something.)

Perhaps even more to the point, the purposes for which we go into space are human purposes, and at some point we probably want human judgment involved. In an earlier post I chose a somewhat extreme example, deciding who to rescue if not everyone can be taken. Commenter Brett rightly observed that the case was somewhat unlikely.

But more practical human decision points could easily arise at the scene of an emergency. Suppose a damaged, tumbling spacecraft has injured people aboard in need of emergency medical attention. The rescue ship can break the tumble, a time-consuming process, or perform a somewhat risky maneuver to put medics aboard while the crippled ship is still tumbling. An AI can help weigh the risks, but as Spock might say, cognitive abilities alone are not enough to make that call.

And if the decision is to attempt the maneuver, how is it managed? You probably want AI assistance in performing such a tricky maneuver, but giving verbal instructions would be awfully clumsy. A better alternative is to give the pilot something like a 'smart glove'. The glove learns the pilot's reactions - for example, distinguishing between a random muscular twitch and the beginning of a volitional action, allowing more responsiveness than a bare hand on the joystick could achieve. And if the AI packs up or starts singing 'Daisy' the pilot can disengage it and still fly the ship, even if their spirited steed turns into a carthorse plug.

This basic technology is something we are at least very close to having now, if we don't already have it. And it harnesses AI as what I believe it fundamentally is: a human mental enhancer. For routine operations we can step back and let AI handle the job. For non-routine operations the AI helps us to do a demanding job more effectively.

To be sure, the rescue example presupposes that there are humans in space to be rescued. But the basic reason that human spaceflight is so limited, and controversial, is that it is astronomically expensive. If it becomes merely expensive the justification bar will not be set so high, and in some cases the cost of human presence may fall below that of developing and providing a robotic alternative.

All of which still leaves some complex decisions to be made about handflying. If routine operations are automated, how much actual handflying experience do pilots get? And if they mostly sit passively overseeing automated operations, how alert will they be in a sudden crisis? This has already become a problem for highly automated operations such as rail transit systems.

As with handflying, so I suspect with much else, not only in space but here on Earth: AI will change many things, but probably in ways quite different from those imagined in conventional speculation about robots.

Discuss:




I previously wrote about what AIs want, or might not want, and the relationship between human and artificial intelligence. The image of Snoopy comes from a snippet on YouTube.

Monday, July 20, 2015

Luna Rising

Saguaro Moon Rising

Forty-six years ago today, the first human being walked on the Moon. And more than 40 years have passed since the last human did so. 

Those of you who have followed this blog for a long time may have noticed a quiet shift in my position regarding Earth's orbital companion. In the past I have been rather negative about returning to the Moon, while more recently The Weekly Moonship portrayed a space future that included, well, weekly travel there.

So what has changed?

Most obviously, it turns out that there is a lot of water on the moon; at least a lot of ice in polar areas where sunlight does not reach. The stuff of life is not everything, but it is a big thing, and in particular it can be cracked to make rocket fuel, something that large scale space travel can't get enough of.

Provisos apply. A lot means one thing to a scientist, something else to a mining engineer, and we have no idea (yet) whether lunar ice will be available in concentrations that make it suitable for processing. And anyone who thinks that such processing will be cheap or easy needs to cash a reality check: Nothing in space is cheap or easy. Space travel is the most difficult technical challenge that we have surmounted as a race, which is exactly why July 20, 1969, like April 12, 1961, has lasting significance.

All of that said, I have revised my perception of the Moon in the human space future, and not only for merely practical reasons. Aesthetics is also a factor, and not unjustly. New Horizons has reminded us - not for the first time, not for the last - of the sheer wonder and beauty of the Universe, including those parts of it that are already within our reach.

The beauty of Earth's companion, as seen from Earth, does not need me to expound it. Poets beat me to that punch thousands of years ago. The Greeks identified Selene, as they called it, with the goddess Artemis, mysterious virgin huntress of the night. (They gave Venus, with its hellish conditions, to the goddess of love. So far as I know, poets have not yet exploited this entertaining fact. When they do so it will be one more indication of our maturation as a spacefaring civilization.)

Seen from close up, at least in the most familiar images - those from 46 years ago - Luna seems rather less enchanting. It is about the color of a parking lot, no inducement to poetry. But while every picture tells a story, those images may say more about the circumstances than the locale.

Statio Tranquillitatis, as it is officially designated on lunar maps, is just about the most boring location you can find on the lunar surface. This is for extremely good reason: boring, in astronautics, is a technical term meaning 'probably safe for landing on.' The first human mission to Mars will also land somewhere boring; likewise the first human mission to a planet of Alpha Centauri.

Related factors also influenced those first images. The equipment was designed by people who (surprise!) had never gone where it was meant to be used. And the people using it were trained primarily as spacecrew, not photographers. All of which is to say that the Moon can doubtless be as lovely close at hand as from 384,000 kilometers. But the images that will one day enchant us have yet to be taken.

Other reasons will, in due course of time, impel us to return to the Moon. And yet others will only be discovered after we do so.

All of that said, I am in no particular hurry to send humans back to the Moon. But then, I am in no particular hurry to send them anywhere. At our current development stage the only truly good reason for humans to go into space is to learn what we can do there, which is what the ISS is all about. The time for first-hand human space exploration will come when some planetary studies postgrad goes into her advisor's office, tosses her notes onto the desk, and says 'Okay, this is really bizarre.'

Yes, there are other reasons to go to the Moon that are not 'truly' good, merely good enough, and truly human. Such as the reasons we went for the first time. I think the current betting odds are that the next visitors will come from China. One more small step for mankind, but a huge one for any emerging space program: decisive claim of a place at the big kids' table.

We will return to the Moon. Not in this decade, probably not in this generation, perhaps not in this century, but surely in the fullness of time.

Discuss:


 

I previously grumped about the Moon - but, really, more about ill-advised hype that ended up setting back our space effort.

The image comes from the Astronomy Picture of the Day archives.

Tuesday, July 14, 2015

The Heart of the Kuiper Belt

Pluto - King of the Kuiper Belt

Probably by now most of you have already seen this image, from the New Horizons probe, showing the remarkable heart-shaped feature on the surface of the King of the Kuiper Belt.

'Remarkable' is fairly weak tea, but my personal stock of superlatives has long since been worn down by the eye candy sent back from our ongoing preliminary reconnaissance of the Solar System. So it will have to do.

And I think we can declare Pluto's pity party to be officially over. Future generations of schoolkids will not remember that the largest member of the Kuiper Belt was once classed as the ninth*  'major' planet - and will be increasingly aware that there are planetary systems out there that would scoff at even mighty Jove.
* For much of my adult life, in fact, Pluto was not the ninth anything, since for a quarter century or so its orbit carried it sunward of Neptune.
If anything, some of those kids might be puzzled by old books, including much rocketpunk-era (and later) SF, that called it simply the ninth planet, back before anyone came up with our current subcategories.

Most of all, we can now officially add the Kuiper Belt to the list of places we've been, albeit so far only vicariously. Going there in person will be a demanding mission, and a ways down the road. Well before that time comes, we will return to our previously scheduled discussion of Earth's orbital space. Previous missions have passed through the Kuiper Belt, but New Horizons went there specifically to take a look-see. And the heart on Pluto is one of the first things we saw.

Discuss:



The image was snagged from Sky & Telescope.

We previously considered Pluto here, while it also came up incidentally in an amusing context. And even the phrase 'heart of the Kuiper Belt' got a previous outing here, albeit in a different sense and context, not specific to Pluto.

Friday, July 10, 2015

Ships for the Orbital Patrol

Orbital Patrol Ship
Over the last three posts we have looked at ships and travel in (mainly) Earth's orbital space, and sketched one possible path to an orbital patrol service. So now we come to the post I originally intended to write before necessary preamble took charge: the potential characteristics of Orbital Patrol ships.

The image above is unabashedly intended as a rocketpunk-era interpretation, not a strictly realistic conception of a ship built for aerobraking. Hence the forward section inspired by the B-36. Note the spacewalker casting a shadow on the nose. Also note a similar craft serving as forward-end rider atop a deep-space ship in the RM header image.

Even more unabashedly, our ship is ready to deliver something considerably more forceful than a warrant. Space warcraft you want, space warcraft you get.

Before going on to particulars, a reprise of the maneuver performance requirements table from Adventures in Orbital Space, with one difference:
Low earth orbit (LEO) to geosynch and return 5700 m/s powered
(plus 2500 m/s aerobraking)
LEO to lunar surface (one way) 5500 m/s
(all powered)
LEO to lunar L4/L5 and return* 4800 m/s powered
(plus 3200 m/s aerobraking)
LEO to low lunar orbit and return         4600 m/s powered
(plus 3200 m/s aerobraking)
Geosynch to low lunar orbit and return* 4200 m/s
(all powered)
Lunar orbit to lunar surface and return 3200 m/s
(all powered)


LEO inclination change by 40 deg* 5400 m/s
(all powered)
LEO to circle the Moon and return retrograde* 3200 m/s powered
(plus 3200 m/s aerobraking)
Mars surface to Deimos (one way) 6000 m/s
(all powered)
LEO to low Mars orbit (LMO) and return 6100 m/s powered
(plus 5500 m/s aerobraking)
* Not in source table; delta v estimates are mine.

The difference is that I have expressed speeds (more precisely changes in speed, or delta v) the way professional spacecrew probably will, in meters rather than kilometers per second. I do this for a reason: 3.2 km/s sounds picky, even a bit petty - a mere 0.0000107 of the speed of light. In the conventions of operatic space SF, hardly worth asking the diva to fire up her lungs.

But call it 3200 meters per second and it sounds like exactly what it is - fast. As in blink-and-you-missed-it fast, much faster than a speeding bullet, more than ten times jetliner speed.  

And our baseline ship will be good for nearly twice that much in power burns, plus aerobraking when the mission allows it. A hydrogen-oxygen engine and 75 percent propellant fraction (mass ratio of 4) gives it a total powered delta v of 6100 meters per second, sufficient for all the missions listed.

To flesh out the ship, a few 'design rules' for spacecraft, based on a judicious mix of current practice and sheer guesswork:

Engines: Typical chemfuel engines, e.g. for kerosene and liquid oxygen, have a thrust/mass ratio of around 75-80. For H2-O2 the ratio is somewhat lower, about 50 - the higher specific impulse means less thrust per gigawatt of engine power output.

Fuel tankage: This is most of the ship, by volume and (loaded) mass. The figures below, from the Atomic Rockets 'basic' design page, give tankage mass as a percentage of the propellant mass they hold:
  •   4 pct: Kerosene-LOX and other common propellants
  •   6 pct: H2-O2 (because liquid hydrogen is bulky)
  • 13 pct: Liquid hydrogen only (for atomic/electric propulsion)
  • 25 pct: Solid fuel - casing is also the motor
These figures are for expendable rocket stages. For reusable vehicles structural fatigue becomes a concern, not so easily guesstimated, but let us handwave that progress in materials and design will allow reusable tank structures in The Future to weigh no more than expendable tanks do today.

To a zeroth approximation, engine and tankage mass (and the propellant!) are all you need to model a rocket stage. For those playing along at home, try simming some space boosters, bearing in mind that while low orbit velocity is about 7900 m/s, losses from gravity and aerodynamic drag mean that you need about 9700 m/s worth of delta v to place a payload in orbit.

A complete, reusable space vehicle will need additional mass for needed features and equipment. Allow 15 percent of ship mass, while aerobraking, for the heat shield.

For Earth surface recovery, I'm allowing 5 percent of landing mass, compared to 4 percent of (total) mass for aircraft landing gear. I say Earth 'recovery' to emphasize that even if these ships land on a runway, like the Shuttle, they are not really airplanes. In particular, they cannot take off and fly into orbit; they need a booster stage or two. And recovery by parachute may be more robust.

I'm also allowing 5 percent for Luna/Mars landing gear. It may be that ships also tail-land on Earth, using the same gear, but in that case they'll need some propellant for the final descent burn, so we will keep Earth recovery and Luna/Mars landing as separate requirements.

Finally, we must allow for all the systems and equipment a robust spacecraft must have - electric power supply and equipment, attitude/maneuvering thrusters and their propellant, and so on and so forth.

I am simply going to ballpark these as up to 20 percent of mass without (most) propellant - not precisely 'dry' mass, since it includes payload and consumables. Spacecraft with limited capabilities - such as a recoverable top stage that merely reaches orbit, releases its payload, and heads back down, can get away with less.For aerobraking craft I'll also say up to 5 percent for aerodynamic control surfaces, fairings, payload bay doors, and such.

Whatever is left over after deducting for these structures and fittings is payload, or at least gross payload, including the crew compartment and life support, if fitted, and internal bay capacity for any payloads that must be aerobraked.

So. Here is a ship based on an unfueled mass of 100 tons, suited to launch into orbit atop a heavy-lift launch stack. In fact, the powerful engine may allow the ship to function as a second stage to orbit, needing only the big booster stage to send it on its way. (But in either case it will need to refuel to proceed beyond low orbit.)

We will call it simply a patrol ship, since the Navy has patrol aircraft, so designated, albeit with a different mission.

      7 tons main engines = ~3.5 meganewtons, ~7.5 gigawatts (770,000 lbs thrust; 350 tons)
    15 tons heat shield 15 pct of re-entry mass
      5 tons Earth recovery (5 pct) parachutes / landing gear / retro
      5 tons landing legs (5 pct) for Luna / Mars, etc
   20 tons miscellaneous (20 pct) attitude thrusters, electrical, etc
     5 tons aerodynamics (5 pct) controls, fairings, etc
   18 tons tankage body 6 pct of 300 tons H2-O2


   75 tons base vehicle less gross payload
   25 tons gross payload includes cargo bays, crew cabin, etc


100 tons unfueled mass
300 tons propellants 4:1 mass ratio = 6100 m/s delta v


400 tons total mass with full propellant load

A couple of notes to make. This ship has heat shielding only for its unfueled mass, so it is implicitly designed for 'low-high-low' missions - starting from low Earth orbit, heading outward to do business, then returning to low orbit (or recovering to Earth) at end of mission.

If a ship must aerobrake and then return to higher orbit, it will need shielding for the mass of its get-home propellant, a heavy hit to payload. This ship would need 16 more tons of shielding for the propellant needed to reach translunar space from low Earth orbit after aerobraking, leaving only 9 tons for gross payload.

On the other hand, ships optimized for high orbits and lunar space can delete aerobraking and be built as 'pure' spacecraft, using the saved mass for more propellant or a heavier payload.

Our patrol ship is not economical for commercial or logistics service. Most traffic will go in ships optimized for their specific missions - design propellant fraction configured to the mission; no landing or recovery gear for orbit-to-orbit ships; no heat shielding or fairings for ships operating on and around the Moon. Even a patrol service may use primarily mission-optimized craft. But I think there will be a place for some ships that can go anywhere in orbital space if need be.

As for the design and appearance of these and other ships in orbital space, they will generally resemble the spacecraft we already have, or have had. Non-aerobraking ships can be assemblages of engines, tanks, and modules - more compact, probably, than deep space ships of similar mass, and more sturdily built, since they must stand up to the jolting acceleration of big chemfuel rocket engines.

Aerobraking ships are different - in an appropriately 60s-era expression they are aerospace vehicles, and must have a proper airframe. Their shapes are also more constrained. Broadly I think there are two main configurations: a stout cone, like a space capsule re-entry module enlarged to the size of a townhouse; or a more elongated wedge, like the Shuttle and of comparable size.

The patrol ship, if capsule-shaped, might be 12 meters high by 14 meters in diameter; as a wedge, perhaps 40 meters high (or long) by 25 meters wide by 8 meters deep. For both configurations, interior volume is about 1200 m3, three quarters of which is propellant tankage, while surface area is around 800 m2.

It will be up to the 3D graphics designers to flesh out these shapes - the wedge types surely with wings or fins. Aerobraking ships can freely open bays and extend panels or equipment while in space, but not, obviously, in atmosphere.

It is tempting to give civil types the blunter capsule form, reserving the sleeker wedge shape (if you could call the Shuttle sleek) for military or quasi-military craft. This fits the ancient maritime distinction between sail-only round ships for trade, and oared long ships for war. But that is metaphor, not engineering. I am not sure how the trade-offs, probably modest, would actually play out.

Larger spacecraft may favor the wedge form simply because it is easier to place on top of a booster stack for initial launch, compared to the very wide and blunt cone. Ships designed for aerobraking will not be assembled in space, not in the early days - building airframes is advanced shop, not like snapping Legos together.

Gross payload is 25 tons. As a cargo ship - which it isn't - actual cargo capacity might be 20 tons, allowing for the payload bay structure and fittings. My rule of thumb for a limited-duration (two weeks max) crew compartment is two tons per person, so the ship might carry a crew of 5 plus about 12 tons of removable payload, or a crew of 10 and 4 tons of payload; adjust to taste.

My presumption is that spacecraft have a pilot or crew only if their payload is human - either passengers or the crew itself, for missions that require a human presence. Patrol missions are likely in that class, if only because there are some decisions that are specifically human, not for an AI to make no matter how smart it is.

Such as, if not everyone can be rescued, deciding who gets left behind.


From that sober reflection we may now step back to contemplate the standard patrol ship. And coming full circle, the most wonderful thing is how much it is a true, Heinleinian rocket ship. Granted it cannot lift itself into Earth orbit without a booster stage. Otherwise it can do pretty much everything that rocketpunk-era spaceships were supposed to do.

And it does them without violating a single law of physics, or even invoking magitech engineering. Given the requirement and the funding we could probably build it now.

In a rocketpunk setting it could even have the classic winged V-2 look. For Realistic[TM] aerobraking you might want to flatten the ventral side, in aviation terms the belly, and fair the wings in to that side so it can surf its own shock wave, but visually it still comes thundering straight out of the 1947 of imagination.


We might also have a smaller version, scaled down by a third, weighing in at 25 tons unfueled, 100 tons full load. This model can be launched fully fueled atop the heavy-lift booster, ready to proceed on its mission. It might carry a crew of two, or pilot and passenger, plus a couple of tons of additional payload.

Prosaically it might be a VIP transport, but you know and I know that more colorful duties are possible. Hollywood has a name for handy little ships that perform such tasks, but I will call them gunships.

And coming up we will look more closely at some of the missions that patrol ships and their gunship cousins might be called on to perform.



Discuss: