Imagine a binary planet - that is, two earthlike habitable planets in mutual tidal lock, like the ones described in this excellent post.

Now, these two planets are populated by humans and human-like species sharing similar level of technology, ranging over time (the story span is about 100 years) from WW2-like tech through Apollo/Cold War rockets to near-future innovations (like SpaceX's ITS). I mean, both planets start from roughly the same (WW2-like) level of development (due to Precursors or just Alien Space Bats) and then progress on their own, but sharing interest in each other - so there is some technological/cultural convergence as well as notable differences (like USA and USSR).

The important thing is, that some of the countries of the planet A may be hostile towards some countries of the planet B - and vice versa. I imagine that hostilities may range from jamming radio signals (as well as broadcasting propaganda and hacking when computers are invented) to launching Interplanetery (non-)Ballistic Missiles (what other hostilities are realistically possible?).

Now my question is: given all that information (including the planetary setup described in the linked answer), what are the advantages/disadvantages of possible locations for a country, regarding the potential benefits of knowledge exchange and risks of hostilities? These "possible locations" mean primarily near/far side of a planet (and perhaps the border zone of these two).

I imagine that near side offers better opportunities for interplanetary communication and knowledge sharing (just point your antenna skyward), but at the same time is easy target for interplanetary missiles - or am I wrong? Maybe bombing the far side is not so difficult after all?

  • 4
    $\begingroup$ "Where would you like to do X?" is prone to being closed as primarily opinion-based. "How would you choose where to X?" might very well fare better. Compare Good Subjective, Bad Subjective. $\endgroup$
    – user
    Sep 29, 2017 at 19:48
  • $\begingroup$ Try to narrow down this question. There are way too many here. Breaking it down not only makes it easier for answerers but typically gets you better answers. $\endgroup$
    – worldsmith
    Sep 29, 2017 at 19:58
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    $\begingroup$ Why on earth would a single country be openly hostile towards one on another planet? $\endgroup$
    – Karl
    Sep 29, 2017 at 19:58
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    $\begingroup$ Why would the two countries on different planets be at war? What's their conflict of interest? $\endgroup$
    – Philipp
    Sep 30, 2017 at 16:39
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    $\begingroup$ Why there are intraplanetary hostilities? Or are you asking us to find you a way to make it happen? $\endgroup$
    – Mołot
    Sep 30, 2017 at 17:09

3 Answers 3


Wherever I could get the most hospitable land, resources, and be geographically difficult to access.

Basically same reason the US is so successful. Large amounts of habitable land, abundant resources and boardered by 2 big oceans that make invasion difficult. Shares 1 small easily accessible border with Mexico and one large border with Canada who is then questionably easily accessible by Russia.

At this stage in human history remote contact with another world (at the same tech level) would likely have no significant gains. A country such as the above could easily mount the resources to occupy such a "connector" country when they felt like it, when it starts to become useful.

Nations that occupy key trade paths have always been targeted by envious nations since the dawn of civilization. If you want any sizeable chance of surviving its best to not be the one making everyone envious.

Note: interplanetary missiles would be capable of hitting anywhere on the planet so there is no ideal place to be for that.

Note: Propaganda is pretty marginalized in relation to geography once the internet comes into play. Even in the case of the radio. Radio just potentially reduces how many people can bs at one time, not the fact that people are bsing. If anything, if everyone is feeding you different lies, people become jaded and more fact demanding.

  • $\begingroup$ But would there be an optimal place on the planet to place the city in relation to the tidal lock as to not be too easily accessible by the other planet for warfare but also be close enough for trade? $\endgroup$
    – worldsmith
    Sep 29, 2017 at 20:08
  • $\begingroup$ sure give me maps $\endgroup$
    – anon
    Sep 29, 2017 at 20:09
  • $\begingroup$ I noticed your answer after editing my original question - but your answer is imho still relevant, thanks for input! :) $\endgroup$
    – Ijon
    Sep 29, 2017 at 20:12

WWII technology did not have the ability to reach lunar distances, so they could not throw slugs or fire missles at each other at that time. But they could see them (telescopes) and could (accounting for minor delay) talk to them (radio). I'm going to ignore the fact that radio isn't quite that simple. Radio works by modulating electromagnetic frequencies. You need to understand the modulation to "decode" the signal. I'm going to jump to the conclusion that no matter how desparate our two races at the outset, they figured that out and can communicate. Therefore, how would technology and society change from this point?

Music and news

Without question the most commonly shared items would be music and news. The two species would initially be bonded by sharing their cultures. Technology would spread slowly as you can't simply send a digital signal via analog broadcast. It's possible, but it would be very slow and painful. Look at how long it took to get the name of the artist and song name to show up on our radios? RDS only became common in the early 90s, four decades after WWII.

Hearing about "the other side"

Eventually the two worlds would begin to realize that some portion of the news was about a side of the world they couldn't see. They'd start to wonder about what was really going on back there since they couldn't see it for themselves. Every society has its paranoid thinkers, and those thinkers would begin to make noise about what the other guys are doing in the dark (so to speak). This would lead to fear.

It's very important to remember that, with the exception of ground-penetrating frequencies (which wouldn't work well at lunar distances) all communication is line-of-sight. You can't broadcast through a planet, you must broadcast around it. Governments and corporations would quickly realize the value of working on the dark side: they can't be "heard" unless a message is repeated to the front side.

Maps become critically important

Unfortunately, while missles (once sufficiently developed) can easily hit the back side of a planet, that doesn't actually mean squat if you don't know what you're shooting at. Missles pre-dated satellite tech, so the two worlds would depend something awful on maps to keep track of the dark sides (I know they're not dark, but it sounds so demeaning to call them "back sides").

And that means spies

Spies and spy tech would grow much faster than it did here on Earth. In the beginning you couldn't send your own people, which means subverting the population over there. Obtaining accurate maps would be the first order of business. Obtaining locations of strategically important facilities would be the second.

Of course, nothing says "loyalty" like having your own person over there, so we don't want hostilities yet. No, let's use the hippie-loving liberal diplomats to physically bridge the gap! With an entire habitable world as motivation, I can easily imagine space ship technology would move faster there than it did here, too. Both countries would begin vetting people like there's no tomorrow.

Depending on how paranoid people get, the benefit of the contact might be much less than the threat of spies. Trade would be nearly non-existent due to its cost. Frankly, it would be difficult to believe that anything other than information, which could be sent cheaply, would ever be traded. What unique resource would ever be valuable enough to justify the expense? A small handful of delicacies for the very rich, nothing more. Until you invented rocketry/travel that is reusable and fuel efficient. That's a ton closer to 2050 than it is 1950.

Nevertheless, once you have a decent map of the dark side (I know, I know, "back side." Maybe "far side?" but that conjurs a faorite comic that hits too close to home with this discussion...) you can now realistically threaten your neighbor.

Our cold war would be down-right neighborly in comparison

With the very first missle combined with a good map and the location of a military base on the dark side would instantly come Mutually Assured Destruction. You'd likely have more missles bristling the dark side than the front simply because, no matter how good your neighbor's maps, you can't see them. Heck, if you fired you might not even know if you hit them. But that wouldn't stop a Kubrickene military from building every missle possible.

It would mean that nearly all scientific development, all military development, all important governmental actions, would migrate to the dark side. Planetary governments would be quickly subdued to control increasingly strategically important property. Natives of the dark side would quickly find themselves secondary to the fear of those from the front sides.

And that means satellites are all you care about

Unfortunately, increasing tensions inevitably brings paranoia about how fast the enemy can attack. This would drive satellite technology to the extreme: and along with it, anti-satellite warefare. Initially and at all times, observation would be the highest desire: intel is king. But it wouldn't take someone long to realize if your neighbor can shoot down your satellite they can shoot down your missle. Transit time takes too long! So stealthy missle- or bomb-bearing satellites would become first-strike tools. Submarines might not be invented as more than a curiosity.

It's worth noting that the greater your fear of your planetary neighbor, the less you want issues on your own planet to take precedence. If you really feared the other guy, then "local" (on your own planet) suppresion would be brutal and quick, and that's assuming that everyone doesn't just fall in line because it's far easier to fear the unknown other planet than the unknown Ted Bundy living next to you.

A satellite cold war is inevitably what you'd have by 2050. Both worlds trying desparately to entirely cover the other world for observation, communication, and first-strike. Satellites would exist at varying orbits and employ stealth technologies wholly uneeded by planes on your own world.

If economic personal transportation between the worlds ever developed, it would probably be for the sake of embassies long before vacations. But, I don't see that happening in just 100 years starting with WWII. You'd see some amazing improvements, but even today it costs a boat load of money to put a handful of people into orbit... much less move them to the moon.

...Or, possibly, everybody would be so enthusiastic about collaborating with their planetary neighbors that they would gather together in joy and happiness to share wisdom and grass chocolaty baked goods. But those movies never make money.

  • $\begingroup$ Thanks, that's really extensive analysis! I have a doubt, though: why are you assuming that targeting the far side of a planet will be no more difficult than near side, once accurate maps are provided? Sure, there should not be a significant difference in terms of delta-v, but how can you guide a missile behind another planet? In case of a near side you can just use radionavigation, but you would need a whole constellation of (friendly) satellites in order to do the same at far side. I know that real-world ICBMs use a combination of astronavigation and inertial guidance, will it work here? $\endgroup$
    – Ijon
    Oct 8, 2017 at 19:10
  • $\begingroup$ The first problem to overcome is geography (solution: cartography). The second problem to overcome is mobility (solution: spies and satellites). During the Cold War, the Russions ran ICBMs around on trains so the US didn't know where they were. The most accurate map in the world won't tell you where a mobile item is. $\endgroup$
    – JBH
    Oct 8, 2017 at 19:54

Assuming the overriding need is defence then one of the poles would be a good location. This is because a pole would be energetically more difficult to reach than any equatorial site. Any missile launched would be hindered by the rotational speed of the body it launched from in achieving a polar orbit as a polar orbit is at 90 degrees to that of an equatorial orbit.

That’s not to say that an attack could not be made, it certainly could, but a greater mass of payload warhead could be launched at an equatorial site than a polar site.

This is why the US use Vandenberg AFB for polar launches instead of Cape Canaveral AFB and the Russians use Plesetsk rather than Baikonur. Vandenberg and Plesetsk are much further north so a lot less equatorial spin velocity needs to be removed.

The availability of land, productivity of land and the temperature would probably dictate where to locate cities unless defence was the overriding concern.


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