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Fortifying a planet


jrphilps

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In some works of science fiction, a space farring empire will need to fortify their planetary colonys from assaults launched by rival factions, privateers, terrorists, and the occasional alien scum. One fine example of this is the galactic empire from star wars. Their fortification schemas had a layered pattern to prevent intrusions into the planet. The first line of defense was battle stations located at lagrange points, where patrols could be conveniently launched from. The second was a huge number of surface based ion cannons to shoot down any craft which entered orbit. The third was dozens of garrison bases with enough troops, tanks, and aircraft to repel an invasion force.

Of course, all this brings up an interesting question. When the empire needed to conquer a world that was not under their direct control (maybe it was part of the hutt clan, or the corporate sector authority) and rapidly fortify it against counter-attack, would this schema still be appropriate? Could they get all the infrastructure into place quickly? Would fortifying the planet be more desirable than guarding it with star destroyers (ships which could be better put to use on other missions)? Lets get some discussion going!

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38 minutes ago, jrphilps said:

In some works of science fiction, a space farring empire will need to fortify their planetary colonys from assaults launched by rival factions, privateers, terrorists, and the occasional alien scum. One fine example of this is the galactic empire from star wars. Their fortification schemas had a layered pattern to prevent intrusions into the planet. The first line of defense was battle stations located at lagrange points, where patrols could be conveniently launched from. The second was a huge number of surface based ion cannons to shoot down any craft which entered orbit. The third was dozens of garrison bases with enough troops, tanks, and aircraft to repel an invasion force.

Of course, all this brings up an interesting question. When the empire needed to conquer a world that was not under their direct control (maybe it was part of the hutt clan, or the corporate sector authority) and rapidly fortify it against counter-attack, would this schema still be appropriate? Could they get all the infrastructure into place quickly? Would fortifying the planet be more desirable than guarding it with star destroyers (ships which could be better put to use on other missions)? Lets get some discussion going!

It would be easier to rapidly fortify something by simply throwing spikes around the planet in a "Kessler syndorme" esque scenario. Ofc course,that also prevents you from leaving, at least until you can destroy your own defenses.

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36 minutes ago, fredinno said:

It would be easier to rapidly fortify something by simply throwing spikes around the planet in a "Kessler syndorme" esque scenario. Ofc course,that also prevents you from leaving, at least until you can destroy your own defenses.

If the invading ships have excellent armor, then debris might not be sufficient. This also holds true for ships with excellent sensors: If they detect the debris, they can maneuver out of the way or vaporise it with their weapons. At a minimum, you would need asteroids with some means of actively going after intruding ships (maybe a thruster to steer itself, or a proximity fused mine). Orbital debris would be only a stop gap.

Edited by jrphilps
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For 'low magic' solutions, I'd be thinking in space-stations loaded with a massive amount of small, self-guiding rockets. Those have to travel a lot less than anything launched from the ground, can change course fast enough so a manned and armed spaceship can't just steer out of the way in time. I also imagine the torpedoes could do some manuvering, so unguided point-defence won't take them down from too far.

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Well if you want something pretty realistic have heavy lasers deep inside the solar system like around mercury orbit. This can be used for direct fire but you also have another fancy option. 
Take lots of probes with an mirrors this probes will be passive and hard to detect, think mines, on signal they fold out mirror and point toward target, you then fire the gigawatt laser.  

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You send the captured rebels to the asteroids, they fill bags with regolith, then some of sandbags are used to build fortresses, others - orbiting the planet as a "Kessler Line".

Also this is the most efficient way to colonize the asteroid belt and to begin the asteroid mining.

Edited by kerbiloid
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59 minutes ago, Nibb31 said:

Science fiction = Magic.

Just dream up whatever makes a good story.

This. In practice I think planetary defense would boil down to a question of 'can I blow enough incoming rocks into small enough pieces before they take out my important infrastructure and/or render my biosphere uninhabitable?'

That Star Wars model makes sense in a universe with force-fields in which space battles revolve around wet-navy tactics. Anywhere else it makes no sense at all.

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4 minutes ago, More Boosters said:

Giant solar powered laser station very close to the sun so its masked well and so it can fire rapidly.

For example, it takes about 8 minutes for laser beam to walk from the Sun to the Earth.
Say, the enemy ship being targeted is 1 km in diameter.
So, any random movement with dV = 2 m/s makes the beam to miss.

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5 minutes ago, kerbiloid said:

For example, it takes about 8 minutes for laser beam to walk from the Sun to the Earth.
Say, the enemy ship being targeted is 1 km in diameter.
So, any random movement with dV = 2 m/s makes the beam to miss.

Barrage fire! Plus you would probably stay at least 1 light minute away from the sun lest you get vaporised. Or you know, harness the power of the sun and melt those silly Martians. Your ion cannons on the ground can deal with the enemies shadowed by your planet, we have decent ASAT missiles already.

Edited by More Boosters
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33 minutes ago, magnemoe said:

Well if you want something pretty realistic have heavy lasers deep inside the solar system like around mercury orbit. This can be used for direct fire but you also have another fancy option. 
Take lots of probes with an mirrors this probes will be passive and hard to detect, think mines, on signal they fold out mirror and point toward target, you then fire the gigawatt laser.  

Thats definitely another option. By using solar panels to collect huge amounts of energy from the local star, you can power an array of directed energy weapons which could wipe out whole fleets. Although the light speed delay is an issue.

Another question for this thread: If you were to emplace gun batterys on the planets surface, how many would you need to completely cover the sky arc of an earth sized planet?

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Star Wars might not be the best genre to base the discussion in......because the principal enemy of the Galactic Empire made it a habit to tiptoe around the Empire's defensive perimeters--or sneak right through them using hijacked Imperial shuttles with stolen clearance codes.

The Empire vs. the Rebellion was a case of asymmetric warfare, with the former faction finding their defensive networks mostly useless and the latter only using planetary defenses to stall Imperial offensives while they evacuated.

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If the infiltrating ship is enough fast and chaotically performs evolutions in random directions, light delay (minutes) makes its current position unpredictable and you should build hundreds of such superlasers to occasionally shoot it down.

Btw there are your own ships and orbital stations around it.

Edited by kerbiloid
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37 minutes ago, kerbiloid said:

For example, it takes about 8 minutes for laser beam to walk from the Sun to the Earth.
Say, the enemy ship being targeted is 1 km in diameter.
So, any random movement with dV = 2 m/s makes the beam to miss.

That's why magnemoe's suggestion involves redirecting the beam with mirror probes closer to the enemy. The main laser several light minutes away would only have to track a nearly immobile, friendly target. The mirror would then focus the laser on whatever needs to die.

Of course, if you have orbiting solar power facilities, you don't exactly need the near-sun laser in the first place; you just use the solar stations as mirrors (perhaps install the ability to pull extra reflective sheets over the photovoltaic arrays). A 40% effective solar power satellite that can produce a gigawatt worth of power to send down to the planet can, in this way, be instantly turned into a ~2 GW orbital laser cannon, by a principle similar to a magnifying glass pointed at ants. Yes, it would be quite large an conspicuos, but the enemy will still have troubles with the fact that any lasers they shoot at it will be reflected, and any physical projectiles they shoot at it will melt... if the ship launching them doesn't melt first. :P And if your civilization is capable of (and willing to) deploying gigawatt class solar power satellites, you probably have several dozen of them, if not hundreds.

Edited by Streetwind
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2 hours ago, Nibb31 said:

Science fiction = Magic.

Just dream up whatever makes a good story.

Well, I'll ask you this:

Are electric subs magic? Was the Moon Landing magic? Was the flip phone magic? Is nuclear power magic? What about flat screens? Video calls? All of these  things are from science fiction, in stories written and published decades before the real thing actually happened. 

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53 minutes ago, Streetwind said:

the enemy will still have troubles with the fact that any lasers they shoot at it will be reflected

Nope, once you get past about UV light, mirrors don't work except at exceedingly shallow angles... no 90 degree reflections.

By the time you get to gamma rays, they don't work at all (but then it seems pretty much impossible to focus into an offensive laser as well)

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Meh, we could argue about this all day, given that 'Science Fiction' as a genre covers everything from short stories exploring the consequences of actual physics all the way through to brick-thick space operas. However, for most of your examples, I would turn your question around. Where did the writers of those stories get their ideas from? I would argue that the answer is in the name. There's a reason why we call this genre science fiction after all.

Before nuclear fission was developed as a scientific concept (let alone a practical reality), any story about 'nuclear power' may as well have been magic, or more kindly:  'a name attached to a plot device to make it sound good but which has absolutely no basis in reality.'

Verne's From the Earth to the Moon certainly predated the actual Moon landings. But to write that book requires a certain cultural and scientific background to even conceive of getting to the Moon by shooting yourself out of a giant cannon.

Electric submarines - kinda hard to write about them before the concept of electricity.

As far as the original post is concerned (planetary defense based on a Star Wars model), 'Science Fiction = Magic' seems entirely appropriate given the number of get-outs and what-ifs you would need to make that model even vaguely plausible.

Edited by KSK
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1 hour ago, KerikBalm said:

Nope, once you get past about UV light, mirrors don't work except at exceedingly shallow angles... no 90 degree reflections.

By the time you get to gamma rays, they don't work at all (but then it seems pretty much impossible to focus into an offensive laser as well)

I stand corrected, then. But I still like my idea :P

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1 hour ago, kerbiloid said:

Another btw: nanobots.

Clouds of nanobots orbiting your planet and eating invaders' ships, making new nanobots.
And nanobots on the surface doing the same with unrecognized drop pods.

And then someone's wifi goes out momentarily and...grey goo.

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Tactically speaking, you are asking how to fortify a city at the bottom of a valley surrounded by high hills/mountains (I'm assuming that the planet is at the bottom of a significant gravity well).  You don't put the fortifications on the planet, you put them in orbit, and probably beyond them as well.

One of the basic ideas of medieval castle design was "defense in depth" (it was called bailey design then).  This keeps be rediscovered every time someone needs to fortify something.  Another thing is that the further away your defenses are, the longer they can detect and react to an offense.  This might be less important with lasers and near-C neutron particle beams, but for missiles and such it could be critical.  As of now, the most dangerous conceivable attack (ignoring "global thermonuclear war") would be redirect a comet from the Oort cloud.  As noted in recent "planet 9" hype, we can't directly detect things that far out, it would be on course before we knew it.  By the time it was detected, we would have a couple of months (instead of multiple years needed for present tech vs. asteroids: see recent Scott Manley video).  A large array of detection and interception would be needed for defense at high speed.

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4 hours ago, Streetwind said:

Of course, if you have orbiting solar power facilities, you don't exactly need the near-sun laser in the first place; you just use the solar stations as mirrors (perhaps install the ability to pull extra reflective sheets over the photovoltaic arrays). A 40% effective solar power satellite that can produce a gigawatt worth of power to send down to the planet can, in this way, be instantly turned into a ~2 GW orbital laser cannon, by a principle similar to a magnifying glass pointed at ants.

And if you absolutely, positively MUST annihilate any conceivable incoming fleet, use Earth-orbit-sized superconductors' magnetic fields (i.e., "magic") to induce solar flares that are then manipulated to route part of the sun's energy output directly into a world-sized laser (i.e., "even more magic").

(Credit: Larry Niven, Ringworld series)

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5 hours ago, Bill Phil said:

Well, I'll ask you this:

Are electric subs magic? Was the Moon Landing magic? Was the flip phone magic? Is nuclear power magic? What about flat screens? Video calls? All of these  things are from science fiction, in stories written and published decades before the real thing actually happened. 

Well, there is classical saying about sufficiently advanced science being indistinguishable from magic. But there is also "magic" as explanation for (hopefully entertaining) silliness and stupidity. Not all fiction is a science fiction, and I think it's pretty obvious where SW stands.

4 hours ago, kerbiloid said:

Another btw: nanobots.

Clouds of nanobots orbiting your planet and eating invaders' ships, making new nanobots.
And nanobots on the surface doing the same with unrecognized drop pods.

Or viruses engineered to be fatal to untreated organisms. Bees or other animals attacking individuals not possessing recognized pheromones  (not my idea this one). You can make your biosphere hostile to attackers in many ways.

IMO best defense of planet is being a planet. Who would care for anything at bottom of gravity well? I believe real spacefaring civilization is based on most economical resources - asteroids, comets, planetary rings…

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7 hours ago, magnemoe said:

Well if you want something pretty realistic have heavy lasers deep inside the solar system like around mercury orbit. This can be used for direct fire but you also have another fancy option. 
Take lots of probes with an mirrors this probes will be passive and hard to detect, think mines, on signal they fold out mirror and point toward target, you then fire the gigawatt laser.  

 

7 hours ago, More Boosters said:

Giant solar powered laser station very close to the sun so its masked well and so it can fire rapidly.

These would likely not be able to fortify something quickly, which is what OP wants

 

1 hour ago, HebaruSan said:

And if you absolutely, positively MUST annihilate any conceivable incoming fleet, use Earth-orbit-sized superconductors' magnetic fields (i.e., "magic") to induce solar flares that are then manipulated to route part of the sun's energy output directly into a world-sized laser (i.e., "even more magic").

(Credit: Larry Niven, Ringworld series)

Or, launch nukes to make the magnetic field belts a giant radiation-filled monster. That would shut off communications and leave the enemy much weaker.

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