JAFAL in Flat Black

In reading the historical background material for Flat Black, I find that the big hole in my understanding is exactly how JAFAL works. That seems to affect those early colonization ventures in important ways, but I can’t envision what those effects are. Maybe I’ve missed something in the material so far that already explains it; if not, I’d be very interested in such an explanation, set out fair and square with no contradictions, as the Shirefolk would put it.

I understand that this is an acronym for Just As Fast As Light (akin to Le Guin’s NAFAL). But here are the questions that leaves me with:

° "JAFAL isn’t meant literally, is it, since human passengers (at least) have nonzero rest mass?
° What sort of technology do flingers use to send something out at that speed? Is this a variant on launching lasers (Niven’s idea, I think?) and lightsails?
° Since no such technology exists at the other end, say at Tau Ceti, at least early on, how does a craft traveliing fractionally slower than c decelerate to in-system speeds?
° Of course I’ve read about time dilation effects in Time for the Stars and Tau Zero. But do they actually apply in this case, to the observers actually on board the JAFAL ships, since they aren’t actually accelerating in a closed loop that brings them back to Earth, and there are no telepathic twins on board to complicate things with FTL communication? I confess I haven’t been able to make sense of the relativistic arguments; it seems that during the voyage itself the people on board can just as validly say that Earth and Tau Ceti are moving fractionally slower than lightspeed and are being massively slowed down. Or are we not dealing with those complications?
° Assuming the standard SF version of time dilation—in a literally JAFAL craft, of course, no time would elapse on board during the voyage. By choosing a speed sufficiently close to c, you could make the voyage arbitrarily short for the colonists. But it seems that the first batch of colonists for Tau Ceti had time enough to elect a prom king and queen, as it were. Did they experience the trip as taking 11.9 years, or a single evening (under Elf Hill, so to say), or something in between? (This becomes more important for the remoter primary colonies; it would take a peculiar sort of person to sign up for a trip that their grandchildren would finish half a century later.)

“So many a year has gone, though I’m older but a year.
From your eyes your mother’s eyes cry to me.”

(Queen, “39”—the most truly sfnal song I know of in popular music)


Warning: contains pseudoscientific gibberish!!! Do not learn from this post

I did try long ago to build a history for Flat Black in which laser-pumped lightsails were used either to despatch colony ships or to establish an infrastructure for technologically primitive FTL (instantaneous) travel. But the Tau Ceti and the other colonies of the core got too far ahead of the periphery, the power requirements of the launch lasers scared me, and the inventor of FTL ended up with not enough legitimacy. So in this version you have the Ramotswe-Raerino modified Alcubierre warp encapsulator, or “flinger”. I don’t want to say too much about the Ramotswe-Raerino-Alcubierre warp bubble. Any statement about its physics would be mere corroborative detail, intended to add an air of artistic verisimilitude to an otherwise bald and unconvincing tale. The first problem with that is that a decorative statement (such as “the warp has such negative density of gravitational energy as to exactly match the mass of the ship and other contents, leaving the capsule with zero net mass”, or “all information about the interior of the capsule is temporarily unavailable to the outside universe, leaving conserved quantities such as mass, charge, entropy, and spin as property of the capsule’s surface”) always turns out to imply something that I don’t want, and that my friends with science degrees figure out for me while meaning to be helpful. The second problem is that a statement that sounds sciency to me with my sophomore physics is SoD-busting gibberish¹ to a reader or player who knows science. “Keep a still tongue in a wise head.”

So here’s what a flinger does, at the level of “set the date you want to go to with this dial, turn the machine on with this key, hold down this safety and press the green button”.

A Ramotswe-Raerino warp encapsulator (popularly “flinger”) is a large, delicate, and expensive piece of apparatus, several hundreds of kilometres long, consisting of myriads of field generators held in place by a framework, and with an open channel along its axis. You build them in orbit, and they only work properly 2.2 1.7 AU from Sol, because of gravity and tides. Accelerating or rotating a flinger is a pig of an operation, because all the pieces have to be precisely in place and orientation. If any of those kilometre-long struts bends, if any of those ten-kilometre stay cables stretches, the thing will need an expensive overhaul.

So you have a flinger in deep space. You point it at the star you want to travel to, replenish the consumables, put a spaceship in the middle, turn on the power and the computers, and press “go”. Machines start doing things, generators glow with what would be Cherenkov radiation if you weren’t in vacuum. Lines of sight through the flinger start rippling and quivering like heat haze. After a few tens of hours the distortions settle down to a regular pulsation that slows down like the beating of a guitar string coming into tune. When its frequency reaches zero there is a violent convulsion. The ship is gone. Many of the components of the flinger are white-hot. Some have failed. A vapour of coolant is spraying from ruptured lines. Almost everything is at least a few microns out of place. Cooling, refilling, checking, and adjusting everything to prepare for the next launch is automatic, but takes days.

What the flinger does is to “encapsulate” the ship (whatever is in the middle of it) in a Ramotswe-Raerino warp capsule, which is an exotic solution to the equations of General Relativity, kind of like an Alcubierre warp, but not all that much like it. “Have you heard of a Alcubierre warp?” “Yes.” “It’s not really like that.”

  • A Ramotswe-Raerino warp travels at the speed of light
  • The canonical form of an R-R capsule travels though flat space; the practical version is an approximate solution that travels through sufficiently-close-to-flat space. When it reaches sufficiently curved space it distorts, tears open, and ceases to be: an energetic event that is conspicuous to detectors
  • A fully symmetrical R-R capsule goes “straight uphill” and “straight downhill” in a gravitational field, “straight on” in flat space. Travelling slantwise induces asymmetries that curve the path, distort the capsule, accelerate through feedback, and burst the warp. But you can calculate that backwards, setting a warp with carefully-calculated asymmetry out on a very slightly oblique path, just precisely adjusted become more symmetrical and straighten its course as the asymmetrical effects of oblique gravity work on it.
  • A warp capsule cannot be steered once it is formed.
  • A theoretically perfect warp capsule in flat space goes on forever, with no beginning and no end. The practical ones actually used only approximated that, and were unstable. They could be formed within Time, in curved space. They were unstable; they disintegrated in excessively curved space and unravelled in finite time.
  • No time passes inside the warp between its formation and its rupture.

Bifrost was built in a elliptical solar orbit with its aphelion at 2.2 1.7 AU, non-rotating. That had a shorter period than a 2.2 1.7-AU orbit (which gave it more frequent launch windows), and by Kepler’s Third Law meant it was moving more slowly at aphelion, so it spent longer in the launch cone (more launches per window). But it had continual problems with precession and tidal effects. It worked, but at such cost that no-one did that again.

Later flingers were built in ~2.2 1.7-AU circular orbits, rotating synchonously. Each one provided a potential service to any star within a narrow band of sky on either side of the plane of its orbit, for a week or two once every 2.2 years, approximately. The width of the band and the duration of the launch window were not hard-edged, but limited by the increasing instability of the capsules with increasing launch angle.

Flingers were expensive to build and comparatively cheap to run. The salvage value of a used flinger was small compared to its construction costs (sunk costs were large). And it was difficult and expensive to change their orbits once they were built². The result is that when a flinger was built to serve a colony project, if the project failed to live up to projections it was more economic to keep running the flinger for a short-run profit on variable costs than to liquidate it and crystallise the long-term losses.

Given any two destinations, a flinger could be built to serve them both at the same cost as a flinger that served only one. It was thus trivially easy to spread the cost of amortisation over two colonies.

Each flinger spent less than 2% of its time “pointed at” each colony it served. The rest of the time it was pointed at a little patch of sky dictated by timing the characteristics of its orbit. If another destination happened to be in that patch another potential launch service was available towards it, at no increase in the capital cost of the flinger. That meant that habitable worlds sometimes got their interstellar transport infrastructure built as a free side-effect of building transport infrastructure for somewhere else. Later, many habitable worlds were discovered in the accessible bands of existing flingers. Transport to those worlds could be had very cheaply.

As technology improved between AD 2059 and AD 2353, and as the flinger industry expanded, flingers gradually became significantly cheaper to build and run. Over the same span of time existing flingers became more valuable as new colonies were established in their ambits. Simultaneously, the steady discovery and confirmation of more habitable and terraformable planets meant that there were ever more opportunities to build a flinger that might serve multiple colonies. Usual practice after AD 2200 or so was to build each new flinger in such an orbit that it provided lucrative access to one of the established and desirable colonies, thus defraying the cost of providing access to a new colony (and, increasingly, incidental access to other low-demand colonies and yet-unsettled worlds).

The upshot of all that was that from AD 2250 or so there were lots of habitable worlds that were not attracting mainstream migrants, and to which JAFAL transport was available cheaply. While at the same time an increasing share of the population were coming to accept emigration. Secular and religious utopist and separatist projects found it ever easier to buy a planet and get there, requiring any ever-narrower base of support to do so.

¹ Like “Lord John Marbury” explaining his titles to Toby Zeigler in that episode of The West Wing.

² Inclination changes. Ugh.


So then the practical answer is “You get in at Sol, you wait for the flinger to come up, and then you get out at Tau Ceti, with no perceived delay,” right? Or is it “You get in at Sol, you wait for the flinger to come up, a bit over a decade passes in total isolation from outside stimuli, and then you get out at Tau Ceti”?

The former.

You wait for your launch window at Earth, then travel to the flinger and board your colony ship. You wait for hours in a cramped uncomfortable cheap low-spec spaceship for the flinger to come up, then suddenly you’re in orbit around Tau Ceti. You indulge in a bit of rocketry, spend days or weeks in space in the Tau Ceti system, then land on Tau Ceti III with a cheap one-use landing system.

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(Usual provisos apply: this is your setting, I’m trying to point out the weak spots rather than break them, obviously you do what you need to do in this piece of relatively deep background that has little relevance to play, I just like playing with this stuff, etc.)

I think the astrodynamics may not quite work. An orbit has a period proportional to the the 3/2 power of the radius, so roughly 3.3 years for the 2.2 AU orbit.

If the flinger is rotating to match its revolution, you must allow a fair amount of slop in order to have more than one launch per orbit. (You have a solar orbital speed of about 20km/s. Scaling up from 2.2AU to 11.9LY, your straight-line destination point scans across the Tau Ceti system at about 23 times the speed of light.) “2% of its time” suggests it’s turned by about 7.2 degrees; let’s call it a 3.5° tolerance on the boresight angle.

ETA: if you put it in a 2.2AU circular orbit and non-rotating, you can keep it permanently pointed at its destination and launch to the same place over 50% of the cycle. Yes, tidal forces will need to be compensated. Seems potentially worth it compared with getting to use it only 4% of the time (for two different targets) (plus possibly more later as discoveries happen). Put it in an orbit perpendicular to the direction of the target, and you can launch 100% of the time!

Mars has an orbital semi-major axis of 1.6 AU and a period of 2 years, so just check that you don’t have Kepler’s Second Law back-to-front.

My dear @RogerBW , I am sorry. I did the arithmetic correctly some time ago — 2.2-years for a 1.7-AU orbit — but absent-mindedly typed time values in place of the distance values when I wrote the above post. And then didn’t check what you were saying when you corrected my error. Nor check what I had written. I am ashamed.

I want slop of at least 1.5°–1.8° so that the ambit of a flinger is a band across the sky and not a geometrically narrow great circle.Otherwise I don’t get cheap transport to later colonies as a by-product of flinger construction. Without that cheap transport no-one forms outer colonies until the nearby few are getting crowded. I think I would be pretty happy with 3.5°, but if it gets too much larger too much of service time is available for the high-value destinations and not enough constrained to use for incidental destinations or not at all.

1.8° of slop makes the launch window 3.6°, or 1% of service cycle. 1% of 2.2 years is eight days. I can adjust the transport capacity of the flingers by adjusting the cool-off and re-set time. The ambit of the flinger would be a band 1.8° either side of a great circle: 3.14% of the sky. Bythe time 640 habitable planets were confirmed flingers would each serve on average twenty destinations and have load factor of 20%.

With 3.5° of slop the primary and secondary launch window are each about ~2% and the ambit of a flinger is 6.1% of the sky.

Boresight angle is not the chief constraint. The chief constraint is that you have to fire directly away from the Sun, give or take a degree or two. If it were otherwise then yes: you’d build each flinger in an obit with plane normal to the line-of-sight to destination, and could launch at 90° to the gravitational vector towards the prime destination any time you liked. 100% of service life would be available for the prime use and I’d get none fo the effects I want in encouraging a diaspora.

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Okay. Those two sentences were bad, and they led @RogerBW astray. What I ought to have written is something like this:

“Each flinger spent less than 2% of its time in position to fire at each colony it served. The rest of the time it was only able to shoot for at a little patch of sky directly anti-Sunwards of its position in its orbit.”

I’m going to try harder at answering @whswhs’ question in the “set dial, push button” style, with less distracting gibberish.

  • A flinger is a big thing, consisting of a structure of struts and cables that hold “field generators” precisely in place. It is hundreds of kilometres in size, but not very massive because it is mostly empty framework.
  • A flinger is fairly expensive, and a lot of the cost is sunk — the salvage value is small compared to the construction cost.
  • It’s not practical to make a flinger rigid enough to keep its bits in place under acceleration. In fact, it’s an expensive pain in the arse readjust all the things on a flinger after it has been stressed by force or torque.
  • A flinger will only work when it is at least about 1.7 AU from Sol (or an equivalent distance from whatever star, not that any were built around other stars).
    • When they built Bifrost the Interplanetary Society tried a trick using an elliptical orbit that was only far enough from the Sun where it needed to be. That turned out to be a bad idea because of precession and tides. It worked, but it make everything needlessly expensive and cumbersome. So no-one did that again.
    • Everyone since built their flingers in circular orbits a little further out than Mars, that had periods of 2.2 years.
  • A flinger will only shoot straight¹ outwards from the Sun, give of take a few degrees.
    • So you wait until the time when your flinger’s orbit brings it in between the Sun and the star you are making for.
    • Then you point² the flinger at the destination³
    • Then you replenish all the consumables, switch everything on, and check all the adjustments
    • Then you put a payload such as a spacecraft or a space probe in the “firing chamber”
    • Then you make final adjustments
    • Then you press the “Go” button
    • Then a bunch of things happen that look like special effects to you, but they make physicists swear under their breath and check their radiation dose meters.
    • The payload vanishes.
    • The flinger needs days of cool-down time, replacement of consumables, checks, and maintenance.
  • Years later, light-years away⁴, the equivalent⁵ of ~1.7 AU from some other star, there is a violent paroxysm of space-time, a flash of gamma rays and assorted particles, and a pulse of gravitational waves.Your payload appears out of nowhere.
  • As far as your payload is concerned it has teleported instantaneously. No time has elapsed for it.

¹ It’s not really a straight line, but close enough to visualise it so.

² Some adjustment can be achieved without re-orienting the flinger, thank the Dog, because rotating a flinger is a cow of a job. You need the flinger pointed in approximately the right direction, but you get a bit of play to adjust the shooting direction. How much depends on tech improvements and having invested in adjustablity.

³ It’s not precisely straight at the target. You have to make an adjustment if you’re shooting at an angle from directly straight outwards.

⁴ The number of light-years is equal to the number of years.

⁵ There is no conceivable advantage to me of defining what “equivalent” means in this case. It can only get me into trouble.