© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

21.4.2  Galactic Trade Routes

Generally speaking, trade routes are fixed along the shortest possible physical pathway between the sources of the principal commodities shipped and the major centers of consumption.¹¹⁶⁹ Each regime of travel has a unique set of physical characteristics that dictate the distribution of optimum routes. On land, surface conditions such as mountain chains and passes, accessible waterways, impassable swamps and deserts are determinative. On the sea, the curvature of the Earth, ocean currents, wind patterns, and the presence of iceberg fields, monsoon tracks and other hazards to navigation are more critical. In the air, trade routes are fixed mainly by political considerations, distribution of major population centers, jet stream and other atmospheric conditions, and so forth. In the realm of interstellar commerce, too, a unique set of problems prove determinative.

Probably the single most important parameter in deciding which trade routes should be utilized by an extraterrestrial civilization is the level of sophistication of transportation technology. Starships restricted to speeds below 50%c will gain no benefits from relativistic time dilation. Time of flight between neighboring stellar systems in the Disk will average on the order of decades for the vessel’s crew. Even if physiological longevity is greatly extended, starships will probably have to call at inter mediate ports to take on fuel and fresh crews. Even vessels able to pull 99%c won’t do significantly better. For such starships, the time dilation factor will cut trip time down to about 14 shipboard years per 100 light-years of travel. While it is certainly possible to imagine traveling for decades without pausing to refuel, resupply, or recrew, the longer the flight time the less likely starships will not stop at intermediate points.

In other words, starships limited to 99%c or less probably will not be able simply to aim at target star systems anywhere in the Milky Way and journey directly towards them (though "leading the target", of course, to account for proper stellar motions during the journey). Rather, since the distances are so vast and the travel times so long for the crews, manned trading missions most likely must follow certain prescribed routes as they crisscross the Galaxy engaging in interstellar commerce. (Unmanned robot cargo ships are another matter -- they can be "aimed and shot.") Regular ports will be visited and many planetfalls made as starvessels "hop" from solar system to solar system along paths calculated to cost minimum time or energy. Eventually these may be legislated into law as a matter of convenience by the ET Interstellar Transit Authority.

Intragalactic trade routes may also be fixed in accordance with physical heterogeneities in the Galactic environment. For instance, hydrogen gas is an order of magnitude more plentiful along the spiral arms than in the interarm regions. Hence xenologists expect that Bussard ramscoop vehicles might adopt trade routes called "ring routes" by network theorists. Ring routes follow a clockwise or counterclockwise pathway around the circumference of the Galaxy (the arms of the Milky Way) and then follow a radial route inwards to the final destination. Using an external ring route the trip path will be about 250% longer than a simple direct (straight) route; using an optimized internal ring route, however, this excess distance may be reduced as low as 37%.²⁶²⁹

It will also be recalled that the number of habitable star systems (classes F, G, and K) is only a few percent higher in the spiral arms than in the interarm regions, so self-fueled starships will not tend to follow trade routes aligned with the Galactic spiral structure. To an economic galactographist, the Galactic Disk is essentially uniform with useful star systems. However, there are certain clumpings of stars which impart valuable heterogeneity to the intragalactic environment. One example of this is the galactic or "open" cluster.

Galactic clusters contain from a few dozen to nearly a thousand suns, usually confined to a more or less spherical volume ranging from 5-65 light-years in diameter. About 500 clusters are known (see table next page for a few of them), and it is estimated that there are about 20,000 scattered throughout the Milky Way.¹⁹⁴⁵ While this imples a mean distance between them of about 1000 light-years, this figure is very misleading because clusters are largely confined to the spiral arms. Taking this into account, the true mean separation works out to perhaps 100-300 light-years.

Galactographic considerations suggest that civilizations located in clusters may form close-knit economic units. This is possible because solar systems in galactic clusters typically are separated by a mere 0.5 light-years, which is an order of magnitude closer than normal stars (such as our Sol) in the Galactic Disk. Interstellar trade routes may be designed as a series of overlapping arcs connecting series of galactic cluster trade associations around each spiral arm. (Each cluster may represent individual political units, small pockets of interstellar civilization scattered across the Galactic wilderness.)

There are many other nonuniformities in the galactic distribution of stars which may have economic implications for galactic governments. Stellar belts, associations, and galactic star clouds (bright "knots" of suns found in Cygnus, Scutum, Sagittarius, etc. in our own galaxy) are more diffuse aggregations than clusters but may serve to concentrate trading activity to some degree. Globular clusters, metal-poor and probably also planet-poor, may be exploitable without danger to sentient lifeforms (since such clusters most likely harbor none). With 10⁴-10⁶ Population II stars each, globulars (Table 21.5) represent rich lodes of fusionable hydrogen and a possibly very lucrative mining venture for industrious galactic entrepreneurs.

Another major heterogeneous feature is the general density gradient of suns in the Galactic corpus. Stars are about an order of magnitude more numerous near the Core than in the outer Rim regions of the Disk. As we move inward from the Rim, number density rises continuously. Stellar metallicity is also about ten times higher in the Core than in the Disk, so more planets, lifeforms, cultures, and mining ventures are possible nearer the more central regions of the Galaxy. (This is also where globular clusters are most abundant.) Economic and sociopolitical activity is expected to concentrate towards the Core.

Galactic communication routes may tend more to be line-of-sight than trade routes. These systems may be organized hierarchically with extremely complex network designs.²⁹⁹¹ One writer suggests the following:

Local terminals handling ten worlds are constructed in space, presumably circling a star for free energy. The civilizations in touch with each terminal might range from a few hundred to a few thousand light-years away. The terminal receives signals from each and rebroadcasts them to the other members; in addition, it bumps a duplicate of the signal to a junction station further up the network hierarchy. From the junction it receives, and passes along to its member worlds, the full output of the galactic network, a great glut of information, perhaps edited in advance for potential interest to each idiosyncratic world. The more complicated junction stations in turn report to a large central station. A network of one central station and 1000 junctions, each in turn corresponding with 100 local terminals, could handle 1,000,000 worlds. Each society then would require only a single antenna, aimed at its local terminal.²⁶⁰⁷

Other designs, perhaps analogous to the decentralized nonhierarchical military ARPANET system or the ALOHANET packet radio network, may be more practical for complex interstellar communications.^2484,2483

Last updated on 6 December 2008