Plausibility check for a setting - Iron Giants

[krakonfour]

The time: 20,000 to 100,000 years in the future.
Humanity colonized the solar system, invented mind uploading and quantum computing. Most people are effectively immortal, as they switch their minds into a cybernetic body. At around 20k years, they have colonized two other solar systems. Earth however, gets hit by a Gamma-ray Burst Event, sterilizing it. All that is left behind is huge swathes of radioactive wasteland. The amount of ocean water that is flash-vaporized leads to a runaway greenhouse climate that boils away most of the oceans. After another 20,000 years, we are left with a mildly radioactive (lethal to biological life), barren Earth with huge polar caps and incredibly strong winds around the equator.

Nanomachines are sent across interstellar space to restore Earth and build robot bodies for the first humans to return into.

The machines fail, humanity does not return and nothing happens for 60k years. Across this time, the nanites mutate and create a iron-based biochemistry that builds nearly organic bipeds that still resemble the robot body blueprints they were originally programmed to create.
The software that was designed to accommodate the human minds becomes conscious on its own, leading to a civilization of human-shaped robots.

The Iron Giants

This is the part that I wanted you, readers, to verify and tell me whether it is plausible, interesting or needs rework.

First off, the composition. The body consists of three main elements: the mineral reserves, the active nanites and the inert structures. The nanites repair the structures (bones, skin...) using the mineral reserves.

Lifecycle: Babies are formed from a pool of active nanites mixed with mineral sand rich in iron. These nanites come from the deceased bodies of clan's elders (more on that later). Each body has its own unique nanites, containing a sort of DNA. When mixed together, the nanites try and synchronize their DNA, but the mechanism has been eroded over time to become an unpredictable mix-and-match of genetic features... much like sexual reproduction, actually. So, the dead bodies are put in the pit, mixed with the sand, and an unknown amount of time later, a young giant comes out and it is taken care of.
There are males and females, but only because the original schematics ordered them to be that way. Otherwise, they just form couples and take care of a random child.

Thermo-electric energy. The main element is a molten salt-cooled spherical breeder reactor. The neutron poison is in fact a hafnium membrane that is squeezed into ridges along the radioactive sphere to increase its surface area. The liquid salt comes out with a temperature ranging from 200 to 1100 degrees C and into a loop around the core. Between the loops are magnets. Electricity is generated magneto-hydrodynamically ( movement of an electrical conductor through magnetic fields generated electricity). This energy gets stored in capacitors where the fat reserves of a human body normally are. There are no long-term energy reserves, and the salts solidify at temperatures below 90 degrees C, so the reactor is always on, always hot.
The liquid salts pass through a heat exchanger in the belly. The cooling fluid is oil-based and is pumped through low-pressure vessels until it reached the skin. Since the skin is a highly conductive, flexible metal alloy, it is a practical radiator with a large surface area.
I've done the calculations. At maximum load (1100C core), the liquid salts go down to 500C within the exchanger, and the difference in temperature is translated into fluid velocity. The skin is brought up to 400C and can remove up to 11.4kW per m2.

Efficiency of the system is 50%.

The typical giant (giant because larger surface skin area means more power available, so we have 3m tall beings) will die in roughly 10 seconds if the MHD system is pierced. The coolant system hit is not directly fatal. Stopping the 'heart' (coolant pump) decreases coolant efficiency but the coolant still flows slowly from temperature differences. Piercing it and draining the liquid causes the heat to escape through conduction, which is much less efficient when done through the body. If the giant maintains a high core temperature with a pierced coolant system, he might risk having an irrecoverable core meltdown (the radioactive sphere melts through the container). The death happens when the electronics are fried because of too high an internal temperature.
Constantly staying 'too hot' risks reducing the active nanite count, meaning the body becomes 'sickly' quickly.

This electricity is fed mostly to the skeletal muscles. They are linear electric engine in effect, based on the magnetic interaction between two threads of magnetized iron. They function like regular human muscles, if not for the linear increase in power and speed when the power supply is increased. They are 70% efficient, but are cooled very easily because they are well irrigated by the coolant system. Electrical wires replace the nerve system and provide power.
Since they are iron-based and structurally supported by the magnetic fields they generate, they are very much like natural armor.

The joints are magnetically levitated for near-zero friction.

Bones are made up of the strongest aggregates of alloys the giant can eat.
Speaking of eating, the 'food' is mostly ground up minerals and metals, with the digestive system ending in a pit in the stomach. The stomach cavity is surrounded by the heat exchanger, so the high temperature helps breaking up the minerals.

The giants do not need to breathe, but do so to talk (damn original human design). They have lungs, but are very small. Inside these lungs, the body accumulates waste minerals or unneeded matter, and they are burned up by injecting molten sodium directly over them and exhaling. They can be washed with water too. The quantities involved are tiny though.

What's the point of having an uranium-powered iron giant? Superhero work. If the core is pushed to the maximum, electricity generation is boosted to 200kW. The useful energy at the end is 140. Just how fast can you jump around, just how much can you carry with that amount of energy available? Quite much. In fact, a bit more, since the system is mostly limited by waste heat removal.

If the body density is about 5000kg/m3, and has a surface area of 5m2 with a height of 3m, it weighs about one ton. Thsi means it can jump 12m upwards, hop left and right at speeds of 55km/h and run forwards at 144km/h. It can also carry 22.5tons, without walking. All that, without any equipment. With the eyes they have and digital processing power, they can pretty much watch everything at 60fps with diffraction-limited detail.

The limitation, of course, is that you have to keep supplying yourself with a regular source of radioactive fuel, which leads to the conflict in this setting.

More later!

The Clans

The Plains

The Wind-Castles

Warfare

[krakonfour]

A few more notes about their bodies:
Originally, the electronics in their bodies are supposed to accomodate a human brain. Therefore, there is a very powerful computer in the cranium, with memory banks in a cortial stack in the neck. The compagnon AI had a small space under all the above. Once the nanomachine bodies attained consciousness, the positioning is reversed. The neck processor takes over most functions, while the otherwise empty cranial computer becomes a harddrive for it. Practically; it means that the quickest way to kill a giant is not to headshot it, but to snap the neck.

Of course, they don't know about all this; so it is still a mystery to them why they have such a huge volume in their heads doing pretty much nothing.

Remember how the entire environment is very radioactive? Well, that radioactivity combined with the magnetic pulses released each time a giant moves a muscle means that pretty much all electronic devices are fried in their proximity, and nearly all electromagnetic communication is scrambled at long range.
The consequence is that this civilization will not discover electronic devices for a very very long time. Without any organic beings alive, chemistry and explosives are out of the question too.... they're pretty much in the medieval age of technology.

The Clans

Due to the general limitation of the rarity of the metals that enter the composition of an Iron Giant's body, the population is small.
Also, mineral depositis of the most precious resource (enriched radioactive fuel) are rare and far apart. Worldwide prodution today, with all of our technology is only 50 tons. Imagine how much a race of people that EAT IT would need.
The process of enriching them is labor intensive too, considering that they do not have access to electronics. The combined rarity, cost and value of these installations means that they will be occupied by a few giants and turned into a combined mining, industrial and fortified location. It has to be protected against the elements and other clans.

The result is communities that originate from the same birthing pool, and thus resemble each other somewhat like a real biological clan would do. Unlike their human counterparts however, there is no direct transmission of power from father to son by virtue of genetic descent, so the power is meritocratic to an extent. Furthermore, the distinction between men and women is just silly, since they do not hold reproductive roles. Therefore, power can be held by a womand just like by a man.

Wealth cannot be measured in terms of land or housing. Land has no value for the giants because they have no agriculture, and where would they put houses other than inside the fortified mining facilities? Since the latter is limited by its walls, no-one can have a lot of buildings under his or her name at the deriment of others.

The downside of having a small population that lives in one spot for a long time is that the roles within society are sharply defined. You learn one job and do that job practically forever. There aren't many 'spares' that can take over your position if you choose to change. Also, travel is strictly limited outside of regulated journies defined months in advance. After all, you are giving up a precious member of your clan to the enemy, who can just as well detain them and extract information on your defences out of them.

Why so much paranoia?
Because you've spend decades prospecting sites, digging a mine to a depth of up to 2km, building a manually operated enrichment facility, then a fortress on top of all that (these guys can jump 12m in a single bound... the walls are gonna be tall).... and you can lose it all to a single well-placed invasion force. There's only you and those of your extended family to aid you in defending this place, so every member counts, and nothing is left to chance.
In a small village simulation, successfully conquering another village doubles your production capacity and armed forces at nearly no cost. You now have a bigger force than everything in the neighbourhood, so by the time you've taken hold of a third village, it will snowball into a ginormous nation nothing can oppose.
The difference in this setting is the fortresses. The inhuman strength of the giants means they can defend the place for years without rest, and rebuild the structure by literally throwing around multi-ton slabs of rock. A huge army an be held in check by a few dozen defenders, and siege tactics do not work. Therefore, there are no huge alliances.

[Borgholio]

Radiation can have a nasty effect on tiny, lightly-shielded nanobots. You sure they wouldn't just be flash fried?

[krakonfour]

The plains:

The water levels have dropped drastically, the global temperature is now 10 degrees C and huge winds blow around the equator, with storm cells reaching the frigid polar caps.

What we have then is a mostly waterless, very flat swathes of land, smoothened by wond and always covered by a sheen of dust. Since a majority of the ocean beds are exposed, we can easily imagine our giants living on the Atlantic seafloor. Whatever remains of the oceans is in deep trenches or underground, very salty and concentrated, also, lacking life.
I also think that after 60 thousand years of freeze/thaw cycles and unbroken wind, the mountain ranges of today would be unrecognizable.

The advantage for the giants is that they can see very very far if they build a tall tower. Also, they can run at any speed they like without tripping or encountering an obstacle. Travel is therefore easy, and consequence of the constant winds, flying in a glider is actually sensible. Sole downside is the 1 ton weight of the pilot.

Anyways, I lied about the devoid of life part. Some biological species have survived the gamma burst and subsequent global climate crisis. They can be found in the setting as very hardened shrubs or grasses that absorb the moisture from the air, or tiny worms in the water. In more humid, secluded places, we can have insects and small birds... but the giants care not about these little things.

[krakonfour]

Radiation can have a nasty effect on tiny, lightly-shielded nanobots. You sure they wouldn't just be flash fried?

They were sent AFTER the disaster, to prepare the earth for the return of the humans. The remaining radiation 20,000 years after the event is low enough for the nanobots to mutate and grow.

[Simon_Jester]

I don't think sixty thousand years of erosion would change mountains "beyond recognition," you would still be able to say "yep, that's Mount Fuji" or whatever. The shapes would be different, but they'd still be in the same places they always were, and I doubt any features much more than a hundred meters across would have been removed or destroyed.

Also, remind me what caused the oceans to evaporate away?

EDIT: Another point is that I'm not entirely sure what the effects of the gamma ray burst would be. GRBs don't last more than an hour, so they would tend to fry only one side of the Earth with sheer electromagnetic effect. The real problem would be the massive depletion of the ozone layer... also, come to think of it, colonies on Mars or the Moon or inside an asteroid might well be largely unaffected, since those places don't have an ecosystem to destroy in the first place, and the radiation dose from a GRB will fail to penetrate any great thickness of solid material.

[krakonfour]

I don't think sixty thousand years of erosion would change mountains "beyond recognition," you would still be able to say "yep, that's Mount Fuji" or whatever. The shapes would be different, but they'd still be in the same places they always were, and I doubt any features much more than a hundred meters across would have been removed or destroyed.

Also, remind me what caused the oceans to evaporate away?

EDIT: Another point is that I'm not entirely sure what the effects of the gamma ray burst would be. GRBs don't last more than an hour, so they would tend to fry only one side of the Earth with sheer electromagnetic effect. The real problem would be the massive depletion of the ozone layer... also, come to think of it, colonies on Mars or the Moon or inside an asteroid might well be largely unaffected, since those places don't have an ecosystem to destroy in the first place, and the radiation dose from a GRB will fail to penetrate any great thickness of solid material.

Thanks for answering!
It's 60 thousand years of incredible winds, but yeah, they will still be mountain ranges. Passing through several ice ages doesn't help either.

A large amount of water is vaporized during the GRB, because it deposits over 10^44 joules of energy. Most of it quickly cools down and returns to the surface, the rest jumpstarts the climate into becoming Venus-like.

So now we have a radioactive, superhot Earth which makes more water evaporate in a vicious cycle, of which one side is completely unlivable. Would you stay on it or go and live on other planets of the solar system?

I still don't have a plausible reason why humanity would abandon the ENTIRE solar system though....

But maybe I should have written this earlier: The most important thing I want to check is the Iron Giant's bio-mechanics and fighting tactics.

[krakonfour]

The castles built to protect the mining/enrichment installations have to confront a dual assault: the ever-prevailing wind and the attacks of mobile enemy units.

Because they lack the proper structures to provide lighting and ventilation in long underground horizontal shafts, the giants dig straight down. Ventilation is needed not for breathing, but because having several workers with skin temperatures upwards of three hundred degrees Celsius in one underground chamber is a bad idea.

The castle is built directly over the mineshaft. Outwards-facing walls protect the bottom. They cannot be scaled unless the assailant removes his armor, leaving him vulnerable to defenders.
In the center is a tower containing reserves, living quarters and industrial installations. It can be built over 500m tall, with the base being tremendously thick. The tower is built to be aerodynamic and fully hermetic. In most cases, it is shaped like a shark's fin. The surface layer is metal-plated. This protects against debris projected by the wind and makes gripping the surface for climbing much harder.
The top of the tower is occupied by an observation post. It is equipped with rudimentary telescopes for spotting incoming invaders and for timekeeping by watching the stars. Gliders can also launch from here and be carried by the wind over several dozens of kilometers.
Right under the observation post is a missile platform. Since bows cannot contain the energy provided by the pulling power of a giant (nearly 20kN), the principal form of ranged attack is a javelin throw. Free-throwing without any bracing is limited by the thrower's grip on the ground. The missile platform consists of supports that lock the thrower's feet in place and brace the torso against the recoil, providing much better range, power and accuracy.

Midway along the tower, installed along the trailing edge, are windmills. These are a simple yet effective way to draw power from the wind, and are mostly used to turn the enrichment cylinders. They can be retracted if the wind is too strong.

The inside of a tower consists of corridors and rounded chambers. A ventilation system keeps the giants from overheating in their rooms. The outermost corridors are narrow enough to force the passage of a single occupant at a time. If the tower's surface gets penetrated, the attackers must fight in these corridors at a disadvantage.

The distances between the Wind-Castles is great. Travelers can take weeks to move from one to another, despite their inhuman speed. Gliders might only take a few days, but they risk being blown off-course by a change in the wind.

There are also several underground structures. Tunnels can be made to branch outwards, hidden from sight, and create invisible outposts. Tunneling to another tower takes years, but can lead to an overwhelming surprise attack.

[krakonfour]

Warfare! The fun part.

The first limitations on how the giants fight are bio-mechanical. A giant can increase his own core temperature in preparation for a fight. The cooling vessels dilate, increasing surface temperature and sometimes giving a reddish glow to the fighter. A cool side-effect is making the surrounding grass burst into flames.

The increased temperature means that energy production increases too. This allows the fighter to be more powerful and fight faster. However, it also means that the waste heat the body must get rid of increases dramatically. Heat loss through radiation is often not enough-- the fighter must ventilate the skin by moving or through forced air systems.

Early in the fight, combatants are slow and cold. As the fight progresses, they heat up and speed up proportionately. The fight continues until the weaker fighter heats up too much to keep up with the stronger one, or damage to the coolant systems forces a surrender of meltdown. Standing still is a sign of surrender because the energy production is severely limited.

Because of the previous mechanics, penetrating the skin and causing a loss of coolant is effective. The muscles are highly resistant to damage, so slashing attacks are unlikely to be successful. Other means of defeat include penetration of the power generation system (a belly strike) or to the circulation pump, or the back of the neck.
Attacking the electronic brain is considered dishonorable, since it does not give the opponent a chance to surrender, and will permanently kill an opponent that would otherwise have lived for over a hundred years.

Mobility:

An unweighted Iron Giant can run up to 144km/h. He or she can instantaneously hop to the right or the left with 55km/h of speed. This means that despite the relatively low top speed, a target can dodge very well. A fight in an open area can cover a very large amount of space, so localized traps are ineffective.

The greatest limitation to top speed is drag and waste heat. Both can be solved by providing an aerodynamic frame to run in. The initial drag coefficient of 1.1 can be reduced to nearly 0.3, giving a speed boost up to 200km/h. The leg motions can operate fans to force air over the body at higher speeds than the outside airflow, increasing waste heat disposal, with little extra force.

The Armor:
While a giant can be very mobile, the speed at which it can launch a projectile and the force it can strike with a weapon means that any attack is a On Hit Kill. Not instant death, but any puncture wounds means the target has to stop immediately or risk a meltdown.
The obvious solution is to wear armor. The javelins may penetrate several cm of steel with a good throw, so the armor has to be thick enough to withstand hits even at close range.
This means that the armor suits, incorporating the cooling system, can weigh several tons, with some spots reaching 10cm of thickness.
It is impractical to cover the armor with 10cm of metal, so sloping is incorporated to reduce the weight and increase mobility.

With such thicknesses involved, and the use of sloping, I have taken to WWII tank design as inspiration for the armored suits. Yes! The entire point of this whole setting is to create walking WWII tanks!

I will use medieval armor suit terminology here:

The legs are vital for survival. While the thighs are protected by thick muscles, the lower legs are not. The greaves are heavily sloped, thickening from top to bottom and overhanging the foot. This protects mainly from a downwards strike. Reduced mobility means reduced cooling capacity.

The hip is protected by a skirt extending over the legs. It is a weakspot.

The torso is the most heavily protected part. Three designs exist.
The first features a strip of very thick metal along the center ridge. Sloped armor deflects strikes away from the sides. The top-down shape is a Y.
The second features a V-shaped slope.
The third is sloped entirely to the left, forming a /. It relies on a large, overlapping besagew on the left to fully deflect a strike.

The shoulders are protected by pointed, triangular epaulieres. They deflect strikes upwards and to the side.

The left arm usually bears a shield integrated into the forearm. It can be brought to overlap the expected point of impact for additional shielding, and can be artificially sloped to create a temporary piece of unpenetrable armor. The edge of the shield can integrate a hook to catch the enemy's weapon.

The couters are strong points on the arm. The left couter is larger than the right couter for mobility reasons.

The right arm is less armored. The vambrace can hang over the wrist, or the guantlet can extend over the wrist. The right hand can be protected too, but that reduces the cooling capacity of an already ill-irrigated organ.

The head is very well protected. Most helmets are pike shaped, with vision slits place in grooves of the armor. The neck can be protected by a screen rising from the chestplate. On top of the helmet are binoculars. The user can look upwards to switch to long-range sighting. A rudimentary, short range radio is included.

The back supports the forced ventilation system in a backpack. It includes a fan that is driven by leg movements. Air is forced down channels in the armor and over the skin. A small water supply is held pressurized in a bottle. The fighter can decide to release the water into the airstream to dramatically increase his cooling capacity for a short period, allowing for a burst of speed.

As you can see, the armor is very well protected from the front. The defendant will usually face the opponent head-on, angling the armor when needed, preferably towards the left, then stepping from the right to attack in turn. Some pieces of armor are optimized for mobility, other for attack by placing all the armor on the left and forcing the user to attack while sidestepping (like in fencing).

[krakonfour]

Weapons!

The primary weapon is a spear.
It has a dense penetrator for a tip, and a reinforced body that can withstand against a full thrust. A lance is heavier version of the spear, but with more penetrative power at the expense of attack speed.

Another close-combat weapon is the hammer. It is effective in smashing in the weaker side and top armor of the opponent, but the main objective of combat, to achieve a penetrative strike, is harder to obtain this way.

Secondary combat weapons can be used instead of a shield or in conjunction with an integrated shield. These include the dagger and the hook. The dagger can penetrate weakspots with much greater speed than a spear, and can work around armor. A hook can catch an enemy spear and leave the opponent defenseless.

Ranged weapons include long and short range javelins, as well as a lasso.
The short range javelin is an expendable weapon a fighter can use to attack and gain an advantage before entering close combat. Tactics include attacking the knee, hip, helmet visor, arms or a joint, or simply denting the armor and creating an exploitable weakspot. The accuracy and power of throwing such a weapon at short range is not to be underestimated.

Some fighters do away with armor entirely, preferring to harass the enemy with a full supplement of short javelins at high speed. They can easily circle an armored opponents and attack the unarmored rear with great accuracy.

The other ranged weapon is the long-range javelin. Is is finned for stability, and can be over 10m long. The tip is short and streamlined. Behind the tip is a hook. This keeps the javelin attached to the armor if it penetrates, hindering mobility even if it does not do damage.

The lasso is an unconventional weapon. It can catch an enemy's spear if used correctly, or it can trip an opponent and make him easy pickings.

I'll submit a list of figures on the projectile speed, ranges and penetrative power shortly to give a scale of these engagements.
Some time in the future, I might upload some pictures I've drawn illustrating these suits of armor.

[Simon_Jester]

I'm a little unsure about how you arrived at "thrown spear can penetrate several centimeters of steel." Could you explain the full chain of reasoning, from the biomechanics of it to the penetration calculation? That strongly implies a spear-chucking capability with a "muzzle velocity" of ~500-1000 m/s, which is pretty hardcore even for nuclear-powered guys made of steel.

Also unsure about

A large amount of water is vaporized during the GRB, because it deposits over 10^44 joules of energy. Most of it quickly cools down and returns to the surface, the rest jumpstarts the climate into becoming Venus-like.

Just how far away was that gamma ray burst again?

[krakonfour]

Oh, it's simple.

They can jump 12 meters. Therefore, they have enough energy in their internal capacitors to push themselves that high.
One ton at 12m has 117.6kJ of potential energy.
Since muscles are 70% efficient, the actual energy stored is 168kJ.

Muscle power and speed scales proportionately with the electricity provided to it, so it's safe to say they can put all that power in their arms.
A thrown javelin with 117.6kJ of energy has a tip about 3cm in diameter. That gives us an energy on impact of 116572kJ/m2
If we consider a javelin 3m long, made of solid steel and 3cm in diameter from tip to bottom, it weighs 16.95kg.
A simple mv2 calculation gives us a velocity of 117m/s or 424km/h

In comparison, a heavy 14.5mm machine gun has 32kJ of muzzle energy. It can penetrate up over 30mm of steel at 500m.
http://en.wikipedia.org/wiki/14.5%C3%97114mm
BS round performance.

Of course, this is the upper physical limit, it is unlikely a single javelin throw uses up all of the energy reserves at once or that all of that energy arrives at the target.

The gamma ray burst... don't know. I got the figure from http://en.wikipedia.org/wiki/Orders_of_ ... e_(energy) and found it again in http://hyperphysics.phy-astr.gsu.edu/hb ... novcn.html.

Since water takes 334kJ to boil one kg of water, the GRB has enough to boil 2.9*10^32 megatons of water. Even if a fraction of that energy goes into the oceans, its going to be a whole frikken lot.

[madd0ct0r]

I'm not sure how the icecaps would work - that much ice built up at the poles should flow under gravity, spreading back out into warmer latitudes, reintroducing seas.

[krakonfour]

Maybe the rising moisture is whipped away back to the colder poles by the equatorial storm cells?

[krakonfour]

Maybe the rising moisture is whipped away back to the colder poles by the equatorial storm cells?

Anyways, here's a random Paint.NET edit of a drawing I made:


I know , I know, you don't have to tell me.

[cadbrowser]

Looks like a Zulu/Cylon hybrid. I like it. Would be nice to see it done by a professional artist in the future.

A giant can increase his own core temperature in preparation for a fight.

How? Does it voluntarily restrict coolant flow?

[krakonfour]

Looks like a Zulu/Cylon hybrid. I like it. Would be nice to see it done by a professional artist in the future.

A giant can increase his own core temperature in preparation for a fight.

How? Does it voluntarily restrict coolant flow?

Stop his heart, yes. The core temp increases, then he restarts the pump and works with the higher temperature.

The picture is not the best because if I had done a side view, then you would have seen that the front armor extends well in front of the torso, and that the shield is pyramid.
The closest I could find on the net was this: Break Blade
That design leans towards the manga-mecha side, but does feature the sloped chest armor, the increased protection on the legs and the sloped epaulieres...

[cadbrowser]

Ah, good. Thank you for clarifying.

I see what you mean for the manga-mecha style. Kudos.

I'm still digesting the rest of your world.

[krakonfour]

Ah, good. Thank you for clarifying.

I see what you mean for the manga-mecha style. Kudos.

I'm still digesting the rest of your world.

It's simple, really. I wanted something: Sentient machines running around like ninjas despite weighing a ton.
I then built a setting that would accommodate such a thing!

My ultimate aim is to make a comic. I just don;t have the artistic skill though. I've got storyboards and the scenes set up... but the art is outside my reach. I can learn... but you know, it's like learning a new language for me. By the time I'll be ready to draw the comic (I'll try and draw a giant in a dynamic position next) I might not have this project still in mind!

[Simon_Jester]

What I'm really curious about is... why do these guys fight at all? It sounds like they have such improbably tough fortifications that no attacker would ever have a realistic chance of success.
_____________

As for the gamma ray burst, 10^43 joules is the ENTIRE energy output of a gamma ray burst. It is also enough to volatilize a planet and reduce it to a cloud of vapor, so I'm pretty sure your Earth didn't soak that much radiation. It is not realistic for all, or even most, of that energy to be deposited on the Earth- that would more or less require the Earth to be parked right next to the star that gives off the burst, and the side effects of THAT would have sterilized the Earth long since.

You need to picture the gamma ray burst as a massive, conical blast of radiation which starts out at some point, then spreads out through space according to the inverse square law. The vast majority of its energy will never hit anything- the diameter of the beam when it reaches Earth will be much, MUCH wider than the Earth... and the farther the Earth is from the GRB, the wider the beam will be on arrival.

So what you need to do is look up a realistic angular width for the jet from a GRB, then do one of two things:
1) Estimate how far away the GRB must have been to have the effects you need, or
2) Estimate the effects from having already decided how far away the GRB.

[madd0ct0r]

or base them on mars. earth blew itself up,

[krakonfour]

What I'm really curious about is... why do these guys fight at all? It sounds like they have such improbably tough fortifications that no attacker would ever have a realistic chance of success.

No attacker would plausibly have a chance of taking over the tower. It is possible to break through in a spot, infiltrate a floor and take hostages. They would then be exchanged for nuclear fuel or whatever. If they get lucky, they run away with the fuel itself.

Breaking a stone wall, however thick, should not be an impossible task for a group of giants punching with several kilonewtons of force. They just have to be quick enough to not get overwhelmed by defenders. After all, if there are no easy points of access to the tower, there aren't any easy points of exit, and the narrow wall corridors means that the defenders will be able to stop the attackers, but not quickly. The defenders will have an equally hard time following the attackers until they're back out in the open.

In the open, it becomes a running battle. The best analogy is being on horseback. The attackers will run with their bounty, dodging the shots fired at them from the tower. Then, they will try and draw the pursuing defenders into a column, so that they would only have to face the nearest enemies. If that fails, then they keep running for days until they reach a friendly base that will defend them.

Usually, the attackers are well-trained warriors with superior equipment. They can actually pull this off time and time again against the numerous, weaker communities that do not have the industrial base or the know-how to make effective armor.
_____________

As for the gamma ray burst, 10^43 joules is the ENTIRE energy output of a gamma ray burst. It is also enough to volatilize a planet and reduce it to a cloud of vapor, so I'm pretty sure your Earth didn't soak that much radiation. It is not realistic for all, or even most, of that energy to be deposited on the Earth- that would more or less require the Earth to be parked right next to the star that gives off the burst, and the side effects of THAT would have sterilized the Earth long since.

You need to picture the gamma ray burst as a massive, conical blast of radiation which starts out at some point, then spreads out through space according to the inverse square law. The vast majority of its energy will never hit anything- the diameter of the beam when it reaches Earth will be much, MUCH wider than the Earth... and the farther the Earth is from the GRB, the wider the beam will be on arrival.

So what you need to do is look up a realistic angular width for the jet from a GRB, then do one of two things:
1) Estimate how far away the GRB must have been to have the effects you need, or
2) Estimate the effects from having already decided how far away the GRB.

Humm... what if the GRB was artificially caused, by an enemy? That would explain why the beam was much more power than it should have been (there are no nearby unstable stars that can cause this, not to the extend of the climate disaster I mentioned), and why humanity fled the solar system entirely despite only Earth being hit: They were scared of the new superweapon striking again.

[krakonfour]

or base them on mars. earth blew itself up,

That was my initial idea, but Mars has two problems:
-It does not have the smooth, open plains, strong winds or the concentration of heavy metals on the surface necessary for my setting to develop.
-I am not familiar with Mars's geography. It's less cool that finding out that the sea you're looking at was once the top of the Marinas Trench, 2000m under the sea.

[Simon_Jester]

Breaking a stone wall, however thick, should not be an impossible task for a group of giants punching with several kilonewtons of force. They just have to be quick enough to not get overwhelmed by defenders.

Actually, it could take an immense length of time without explosives; just slamming into a wall over and over is a lousy way of breaking it down. And given how tall the walls are, they are also very very thick at the base- there is a real risk of a tunnel caving in on the diggers, especially if the people who build the fortress are smart enough to use rubble-fill walls.

Since no remotely competent tower defenders could fail to notice someone trying to dig a hole through their own wall for more than, say, a few hours...

It would also help if the defenders had means to attack someone digging into the base of the tower...

So what you need to do is look up a realistic angular width for the jet from a GRB, then do one of two things:
1) Estimate how far away the GRB must have been to have the effects you need, or
2) Estimate the effects from having already decided how far away the GRB.

Humm... what if the GRB was artificially caused, by an enemy? That would explain why the beam was much more power than it should have been (there are no nearby unstable stars that can cause this, not to the extend of the climate disaster I mentioned), and why humanity fled the solar system entirely despite only Earth being hit: They were scared of the new superweapon striking again.

Any entity capable of causing a gamma ray burst to attack the Earth would be capable of causing similar devastation to our own sun, annihilating our planet far more thoroughly.

Moreover, it is unlikely they would NOT try to wipe out our interstellar colonies. Nor that, trying this, they would fail to do so if they set out to. It simply takes too much sheer power to accomplish such a thing.

[krakonfour]

Actually, it could take an immense length of time without explosives; just slamming into a wall over and over is a lousy way of breaking it down. And given how tall the walls are, they are also very very thick at the base- there is a real risk of a tunnel caving in on the diggers, especially if the people who build the fortress are smart enough to use rubble-fill walls.

Since no remotely competent tower defenders could fail to notice someone trying to dig a hole through their own wall for more than, say, a few hours...

It would also help if the defenders had means to attack someone digging into the base of the tower...

Humm. I was thinking of the following procedure:

Reach the base of the wall.
Use grappling methods to climb it, with something akin to icepicks to get a grip on the metal lining.
The thickness of the walls decreases very quickly with height, so the walls near the top are very very thin. A quick search puts base-height ratios at 4-6. If my tower is 300m tall, then the base will have to be 60m thick and the top only 1m thick.

I'm pretty sure base-drilling will never be attempted.

I don't know what the best techniques for digging through stone is though... I'll do some research.

Moreover, it is unlikely they would NOT try to wipe out our interstellar colonies. Nor that, trying this, they would fail to do so if they set out to. It simply takes too much sheer power to accomplish such a thing.

I see. I didn't put much thought into this. I just wanted a dry, radioactive Earth without humans. I'll try to think of other scenarios which could lead up to this.