Tuesday, 21 February 2017

How to Live on Other Planets: Jupiter

A look at how we could colonize Jupiter and its Moon. Fittingly long for our largest planet!


Jupiter is big. It masses more than twice of all the other planets combined. Appropriately, it has the lion's share of the moons in our solar system: 67 as of today's count. A faint planetary ring crowns this behemoth.

Layered like a big hydrogen snowball.
In interstellar terms, Jupiter is a rather average gas giant. It is mostly hydrogen, with about 25% helium and rare traces of other elements. The only solid surface is its core of metallic hydrogen, kept at the crushing pressure of 200GPa. Further extremes are reached at the centre of the planet. 

The upper atmosphere is more interesting. A mix of ammonia, water and even some sulphides makes for a diverse colour palette. The 1 bar (100000 Pascal pressure) 'surface' of Jupiter is at a hot 67 degrees Celsius. The top of the atmosphere, at 1000km altitude, is so hot that it glows during the night. In between are multiple layers of frigid hydrogen gas. 

Unlike most planets, Jupiter has a very dynamic cloud and storm system. It is powered by the rotation of the planet, thereby moving clouds at over 45000km/h. The Great Red Spot is one of the largest features, at 12000km tall and up to 40000km wide. 

These features are even more impressive from the view point of Jupiter's moons. The largest are called the Galilean moons: Io, Europa, Ganymede, and Callisto. All but Europa are larger than our Moon, and two are larger than Mercury. 

Jupiter follows the 'orbital spaghetti' school of moon systems
Accompanying these moons are a plethora of smaller bodies, such as Amalthea (167km), Himalia (170km) and Thebe (100km).


Living on Jupiter's solid surface is not possible. 

The transition to metallic hydrogen that creates a solid surface involves temperatures and pressures that no habitat or spacecraft can resist. It might be possible, however, to float in the upper atmosphere.

Jupiter will offer titanic vertical landscapes.
Generating lift will be difficult. Filling balloons with the lightest gasses, such as hydrogen and helium, will not work as the atmosphere is already composed of those same gasses. A 'lighter than air' balloon does not exist here! The problem is compounded by Jupiter's gravity: 2.5G. This means that you would need to produce much more lift than on Earth.

The only solutions to generating lift would require the continuous use of energy: hot gasses are less dense than cold gasses, so something like a hot air balloon would work. A quick calculation tells us that if we try to maintain the altitude where pressure is 1 bar (Earth's sea level pressure) on Jupiter, the temperature is about 180 to 200K and density is 0.16kg/m^3. If we can heat up the air inside a hot air balloon to a blistering 450K (the maximum safe temperature of Kevlar), the density inside the balloon would be 0.08kg/m^3. This would provide a terrible lift to volume ratio of 1kg per 12.5m^3 of hot gas. In comparison, a helium balloon on Earth provides 1kg of lift per 0.9m^3. Even then, most of the lift capacity on Jupiter would be lost to the heavy insulation the balloon would require.

The other option would be mechanical lift: helicopter blades or wings. Obviously, these cannot be made large enough to support a large habitation base. With the Jovian atmosphere nearly eight times less dense than our atmosphere and with 2.5 times more gravity, an airplane would have to travel twenty times faster to take off, or require wings twenty times bigger and heavier.

Hypersonic... at liftoff?
Something like a 737-800 would have to travel at 7500km/h (Mach 6) to stay in the air!

Even if hopeful colonists manage to stay in the air, they will find themselves in the Jovian equivalent of a desert: no useful volatiles, poor energy resources and exacting living conditions.

Jupiter's atmosphere is starved of water and oxygen-containing compounds. They, along with elements such as sulfur or nitrogen, are held in the lower atmosphere, where pressures of 10 bars or greater make their extraction difficult. 

Considering the issues with generating lift and finding resources, habitats on Jupiter would have to stay very deep in the atmosphere. There, they trade crushing pressures and high temperatures for denser air and access to wispy clouds of ammonia and water.

At least, at those depths, the habitats would not have to worry about radiation hazards or meteorites. These same hazards make living in close orbit around Jupiter very hazardous. Automated factories would suffer from rapid degradation of their electronics, so even an unmanned presence is unsustainable.  

Moons of interest

Living in or around Jupiter does not seem to be worthwhile, at least with conceivable technology. Staying on one of the moons orbiting the gas giant would be the better deal... but which of the moons is the most promising target for colonisation? 

We will look at the Galilean moons first. Together, they represent 99.997% of the mass orbiting Jupiter. 


Io is the Galilean moon orbiting closest to Jupiter, at just further than the distance the Moon orbits our Earth (421000 vs 384000 km). It is a remarkable moon in many ways, but habitability is not one of them: it is the most geologically active object in the Solar System, but also the driest (least water to mass ratio). Its distinctive yellow tint comes from the sulphur compounds churned out by volcanoes and shot up to 500km from the surface. The volcanoes themselves are incredible peaks, like the Boƶsaule Montes reaching twice Mount Everest's height at 17km!
Volcanic eruptions in low gravity are spectacular.
This moon is a champion in another statistic: density. At 3528kg/m^3, it is the highest in the solar system, surpassed only by a few metallic asteroids. 
Io orbits Jupiter in a mere 42.5 hours, wobbling enough to cause tidal forces to lift the surface by as much as 100m. As it does this, it flies through the most intense parts of the gas giants magnetosphere and gets bathed by 3600 rem of radiation per day.

This is 6 times the level that caused Chernobyl workers to die in months, every day. The safe limit is 360 times lower. 

This is 18000 times the yearly radiation we encounter on Earth, per day!
In terms of temperature, the surface varies between sulphur ice fields at 143K (-130 C) and volcanic spots hot enough to melt steel at 1922K (1649 C). Io has an extremely thin atmosphere, composed mainly of the scorching remains of volcanic emissions. It glows in the day and collapses as snowfall when the moon passes behind Jupiter. 

Due to the ions being stripped away by Jupiter's magnetosphere, Io builds up an incredible charge across its surface, reaching 400 million Volts. Lighting strikes discharge a potential of 3 million Amperes on Jupiter's end. 
The plasma torus visualized
In other words, Io is a fascinating place, with a great many potential uses, but it is worse for colonisation than even the sun-facing side of Mercury or the acidic hell of Venus. 


Where are not exactly sure what the orange-red striations are caused by.
It is the smallest Galilean moon, with a surface gravity of only 0.134g. It is a smooth ball of ice, marred only by crevasses and spikes created by faint sunlight. 

Temperatures on Europa are actually quite mild.
Tidal heating is the main source of Europan energy. Ice plumes are quite dangerous as they shift the ice unpredictably.
On the surface, they vary between 50 and 110K. But, the atmosphere is only a very thin haze of oxygen radicals at 0.1 micropascals, meaning that it acts as an insulator. Buildings on the surface might as well be built like spacecraft - insulated and pressurized. Underneath the hard-as-rock cover of ice, however, is an ocean. 

This ocean consists mainly of ... water. It flows and buckles the ice above it, peaking out at crevasses to form 'chaotic terrain', and shooting out as geysers. 

Two models have been put forward to describe this ocean. 
The two possible models for the Europan ocean.
In one model, it is a fluid at a comfortable 277K (4 degrees Celsius). A mere 200m of ice separates the ocean from space, meaning it is easy to reach. Because bouyancy is independent of gravity, floating in the Europan ocean requires habitats to be built like modern submarines.  

A second model believes that the ice extends much deeper below the surface. The hard outer layer is 10-30km thick, while a slush-like 'mantle' goes as much as 100km below the surface. A thin layer of liquid water surrounds the rocky core, at the bottom. 

Whichever of the models is correct, living on Europa would be very interesting, but for entirely different reasons than on Io. Access to huge amounts of water at relatively warm temperatures makes everything easier, and protecting yourself from the deadly 540 rem of radiation becomes trivial. 


Ganymede is the least interesting of the four Galilean moons, but that is like saying it came last place on the podium.

It is larger than Mercury at 5268km diameter, and would have been classified as a planet in its own right had it not orbited Jupiter. In many ways, it is a miniature Earth. It has a liquid iron core that spins to create a magnetic field. A rocky mantle extends halfway up the planet. It has a respectable surface gravity of 0.145g, just under that of our Moon. Up to 100km of salty, dense seawater is trapped between two layers of ice, one thin layer on the surface and one surrounding the rocky core ... which is probably where the similarities end.

The Ganymedan landscape resembles a dirty glacier. Long streaks of smooth surface bordered by darker crater walls and ridges, pebbles and meteoric fragments scattered all around and deep crevasses opened by earthquake-like movements of the ice, their depths opening up to darkness possibly kilometres below. 
What a dirty glacier looks like on Earth. Instead of pebbles, the Ganymedan surface contains meteoritic fragments
Ganymede's sub-surface ocean contains more water than on all of Earth.

By observing how auroras move over the moon, scientists inferred both the size and salinity of Ganymede's ocean (massive and ten times less salty than our seawater). However, they also think that this ocean is located 150 to 200km under the moon's surface, making it very difficult to access. 

Radiation levels are just 8 rem per day, insignificant compared to the sterilizing bombardment on Io and Europa. However, they are high enough to be compared to the maximum safe dose for humans per year. At the equator, the moon's magnetic field can reduce the radiation doze down to 1 rem per day. Either way, it is best to live underground.

The bare surface might be of some use still. Ganymede is brown-grey, while Europa is a dazzling white. The difference lies in the dust and impurities on Ganymede's surface. These can be scraped off to provide vital minerals and metals to a sub-surface colony.


The outermost of the Galilean moons, Callisto is also the least moon-like. It only has a surface gravity of 0.126g. However, it is nearly the size of Mercury at 2410km diameter. This suggests that it is quite lightweight, with most of its volume occupied by ices rather than rock.

In fact, Callisto is a mess.

Tetragonal, cubical and hexagonal ice are the forms water takes under very high pressures and low temperatures.
It is a giant half-half mix of rock and ice in any random order. There are no discernible layers, only an uneven increase in density towards the core. Callisto is undifferentiated, meaning it is structured more like an asteroid than a moon. 

Callisto is far away enough from Jupiter to not suffer large tidal forces. This means that Callisto does not suffer the tidal heating that melts Europa's oceans and keeps Ganymede's core molten. It is the least active Galilean moon.

The distance from Jupiter (1.86 million km) provides another effect: less radiation. It measures only 0.01 Rem per day, which is survivable without any protection at all. 

Some craters on Callisto date back to 4.5 billion years ago. The surface is saturated with impacts.
The fact that Callisto receives practically no energy from Jupiter is very good for colonisation. As evidenced by the undisturbed billion-year-old craters found saturating the moon's surface, Callisto is a very calm place. Structures on the surface do not need excessive amounts of radiation protection, while subsurface structures won't fear a sudden shift in the ice.

The ice layer surrounding Callisto continues all the way to the core. It is riddled with useful minerals and metals, such as magnesium and iron in hydrated silicates and ices such as carbon dioxide and sulphur dioxide. Ammonia might represent up to 5% of the ice by weight, providing vital nitrogen for biological activities such as farming. 

Building on Callisto can be as simple as carving out hollow structures into the ice. Reinforcing the walls with fibres, such as Pykrete, can even allow for relatively roomy spaces that support full atmospheric pressure: even 4% by weight reinforcement makes the ice mix as strong as concrete. 

Other Moons

As noted above, Jupiter has dozens of moons in addition to the Galilean moons. They are insignificant in mass, and the largest after Europa is Amalthea at 250km and Himalia at 170km. The rest are single-digit km in size. 

They are islands in comparison to the larger moons. Most are low-density clusters of rocks and ice, containing all of the elements found on the moons, but lack the size, mass and gravity to protect colonies from radiation, meteorite  impacts and long-term low-gravity effects.


What industrial benefits does Jupiter and its moons provide? How do they compare to the rest of the Solar System, and what can they trade?

Let's start with energy.

The size of the solar panel on the Juno probe. It has three of these to produce electricity.
Jupiter orbits at 5.2AU. Due to the inverse square law, sunlight at that distance is 27 times weaker than on Earth. Relying on solar energy is therefore a costly affair.

Nuclear energy is a powerful and compact solution, well suited for space travel and habitation. However, it uses on fission fuels. These are hard to find and even harder to refine. This places a colony at the risk of over-estimating the amount of fission fuels available in its surroundings, and running out entirely!

No, the best long-term energy source around Jupiter is geo-magnetic energy. This focuses on the special relationship between Io and Jupiter, specifically, the connection formed by plasma particles originating from Io's atmosphere and orbiting Jupiter due to the influence of its magnetosphere.

Jupiter's incredible magnetic field. 
As Jupiter siphons away Io's atmosphere at a rate of 1 ton per second, an electrical imbalance is created between Io's Jupiter-facing side and its opposite. This is, in other terms, a voltage. 

All that is required from potential colonists of the Jupiter system is to install conductors between the two ends of Io. If they are extended around most of Io's 11400 km circumference, they will tap into a 400000 volt differential  for limitless electrical energy.

Converting this voltage into an electrical current reduces its potential. In other words, if the colonists siphon off some of this energy, the voltage will be reduced. This will require them to shoot off material of their own to compensate.  

At 1 ton per second of material ejected from Io, the current is 3 million amperes. Power (Watts) is equal to voltage times current, so Io has a capacity of 1.2 terrawatts. 

An electrodynamic tether around Earth. 
Another option is electrodynamic tethers. These long conducting wires generate electricity when dragged through Jupiter's magnetosphere. NASA experimented around Earth magnetic field, such as with the Propulsive Small Expendable Deployer System, which generated 35 to 250 volts per kilometer of length. Jupiter's magnetosphere is 14 times stronger and the plasma velocity is 10 times higher, which could mean charge potentials of 5000 to 35000 Volts per kilometer. These tethers would generate electricity and beam it by laser to the ground. In doing so, they sacrifice altitude until they hit the atmosphere and are destroyed.

This abundance of energy is crucial to solving one of the problems with living around Jupiter. Due to the gas giant's strong gravitational field (equivalent to 2.56G), travelling between the moons is very expensive in terms of deltaV. For example, travelling between Callisto and Io requires 6km/s, and going from Io to Low Jupiter Orbit requires a whopping 11.8km/s. For comparison, going from Earth to Mars requires only 5.6km/s, and the distance travelled there is about 200 times greater.

Another issue is that low-thrust rocket engines end up having very low thrust-to-weight ratios. This leads to significant gravity losses, so even more deltaV is needed in practice.

High specific-impulse rocket engines are needed to travel efficiently around the Jovian system. Beamed power would solve the thrust-to-weight issue, as it removes the need for a heavy on-board reactor. 

A power transmission concept relying on photovoltaic panels on the moon.
Despite those solutions, the deltaV requirements do have an effect, especially when the power transmission infrastructure has not yet been built. 

The further you are from Jupiter, the cheaper it is to travel. Coincidentally, the further you are from Jupiter, the lower the radiation levels. This strongly favours concentrating industrial activity as far away from the gas giant as possible. Far-flung rocks such as Pasiphae, Megaclite or Sinope would become industrial centres, exchanging raw materials between them and only pushing finished goods down the gravity well to Callisto.

Strangely enough, it is cheaper to transport items to other planets than to send them to Low Jupiter Orbit and back. The only drawback is the time required to travel the huge distance that separates Jupiter from the rest of the solar system. On a Hohmann trajectory, a spacecraft will take over 2 years to reach Mars, and 2.6 years to reach Earth.

Overall, a Jovian colony is self-sufficient. It has vast amounts of water, ammonia and light elements available in the lunar ices. It has protection from radiation and has possible 'warm' environments under Europa's ice and Callisto's surface. There's an abundance of metals and minerals in the countless smaller moons and rocks, providing a resource base for expansion limited only by how much electricity is being extracted from Io's and Jupiter's magnetospheres. 
The only thing that the inhabitants of Jupiter's moons would lack is heavy elements. These include Neodymium for magnets, Palladium for hydrogen chemistry and Uranium for nuclear reactors. It is unlikely that these elements remain in significant quantities around Jupiter, as the giant's gravitational pull would have separated them from the lighter elements early in the moons' formation.

One trade that can be set up between Jupiter and the Inner planets is energy for energy. Jupiter can sell kinetic energy, while the Inner planets sell nuclear energy. Nuclear energy is of critical concern to military forces, as it allows the use of spaceships that can operate independently of any energy network.

Jupiter's kinetic energy 'exports' take the form of small robots, under 100 grams. Micro-satellites, in essence, with miniature thrusters and accurate guidance systems. Using the power network around Jupiter, they are accelerated away from Jupiter using laser beams, or simply shot in the right direction with a railgun. A minimum velocity of 13km/s is required.

13km/s is the orbital velocity of Jupiter. Shooting the miniature satellites 'backwards', or 'retrograde' at that same velocity cancels out their motion relative to the Sun. The Sun's gravity pulls on them, and they start to fall. 

Tested in KSP's Real Solar System mod: 37758m/s after falling from 778 to 149 million km from the Sun.
From an altitude of 5.2AU, they pick up a lot of speed while travelling inwards. At 1AU, Earth's orbital altitude, they reach 37.8km/s! Relative to a spacecraft orbiting Earth, they can have a velocity of up to 67.8km/s, up to 75.6km/s in LEO.

The micro-satellites operate as kinetic impactors. They explode into a blast of high-velocity plasma when striking a target. This plasma can be redirected by a magnetic field to provide thrust. At 67.8km/s, the robots provide much more kinetic energy than they were initially provided with, making for a form of high efficiency and high specific impulse rocket. Streams of these impactors are shot down from Jupiter to skim the orbits of Mars, Venus and Earth. Spaceships 'ride' these streams towards their destinations. In return, they sell nuclear materials to Jovians.

Trade between Jupiter and the Inner Planets would become much more feasible once the energy market opens up. Jovian spaceships would have a choice between the free aerobraking around Venus or Earth, or the slightly closer Martian system. Inner Planet merchants would demand that rescue and recovery infrastructure be built in Low Jupiter Orbit, despite the exorbitant cost in deltaV, so that they too might skim the gas giant's clouds for an extremely effective Oberth boost towards other destinations without fear of losing the payload.  

A much more interesting client for Jupiter's industrial production would be Saturn, Uranus and Neptune. The Outer Planets are difficult to reach from Mars or Venus, but not so for Jovians. 

Trojan asteroids around the Solar System
Trojan asteroids concentrate around Jupiter too, and they would be a prime target for asteroid miners due to their size and number. Sending them to be captured and refined around Jupiter, instead of all the way down to Mars or Venus, is an interesting deal. 

The Colony

Due to the variety of environments the Jovian colonists can live in, there is no single design for a colony. 

The HOPE program targeted Callisto.
The first colonists are likely to settle on Callisto. They would need a nuclear reactor, either to power the spacecraft that they travelled in or to provide reliable energy to the colony, or both. 

The main building material would be cellulose-fibre reinforced ice, called Pykrete, and aramid fibres, such as Kevlar. These can be harvested from plants grown simply by using the abundance of ammonia and carbon dioxide on Callisto. 

Here is an example of an early Callisto settlement:

The nuclear reactor is used to heat and melt the ice. The water is used to melt a larger and larger hole in the ground, forming a vertical tunnel with the reactor at the bottom. A pool of water protects the colonists from a radiation leak from the reactor. 

Once a sufficient depth is achieved, pykrete is made from plant fibres and ice. It is required to build strong walls to hold in an atmosphere at 100kPa. Storage spaces are unpressurized and only need to be insulated from interior heat to prevent deterioration of the walls. 

A parallel tube would probably used to prospect for rock deposits, forming the basis for industrial activity. Callisto's ice is littered with such deposits, which would provide the metals and minerals required to further expand the colony and build installations such as a mass driver, early solar panels (27m^2 is required for 1kW of output), rocket fuel refineries and so on. 
Ice caves!
The colony expands in three dimensions. Mining tubes can be closed and pressurized to become habitation spaces. Eventually, finding rock deposits will become harder and harder, requiring deeper tubes with impractical amounts of structural support. As the colonists would not have a large number of nuclear reactors, cheap melt-through methods of digging becomes impractical. This would be the colony's first limitation: energy.

Solar panels on the surface, as described before, do not provide much energy. They would not even be very efficient, as the rare metals and high-tech industry we take for granted on Earth might not be available to produce efficient versions. 

So, colonists would start shooting off electrodynamic tethers into orbit. These would transmit electricity back down to the surface, but they are quite inefficient in terms of resources spent over returns. It would be essential to make industrial production more efficient, and the tethers more productive. Both objectives can be solved by moving industrial activity to the furthest moons in the Jovian system. Electrodynamic tethers would have a greater gravitational potential energy to convert into electricity, and lower launch costs. Industrial products require less deltaV to move, and might end up costing less than digging another kilometer through the ice.  

Eventually, Io would have to be exploited. Orbital stations would capture the plasma stream through Magnetohydrodynamic effects, while surface-based installations use the large charge difference between the two faces of Io. These are transmitted by laser beam back to Callisto. The same laser beams can be used to propel spaceships. Efforts to exploit Jupiter's magnetosphere could lead to an 'artificial Io' that shoots off a stream of ions and creates a second plasma torus focused on itself. It would be place in Low Jupiter Orbit, where the magnetic field is highest.

The other Galilean moons are unlikely to be colonized. Europa's oceans could be inhabited as an extension of scientific research, or when Callisto is saturated (high population density creates too much heat to keep the ice stable) or simply if people prefer living underwater than in ice bubbles. Ganymede is large, but it resembles Callisto with more radiation and without the rocks.


  1. Callisto is tidally locked

    1. Thank you. I will correct it.

      What do you think of the rest of the post?

    2. English is not my first language, so I am sorry for the poor english below.

      Radiation and gravity make Jupiter a harsh place to live, but how about collecting hydrogen for fusion reactor, using a platform like Jupiter Orbital Mining Platform?
      I understand that it is still a long way to commercialize fusion power, however, by the time human can colonize Galilean moons, it may become a useful power source.

      The Kinetic Impactor remains me the boostbeam from Orion's Arm.

    3. Collecting hydrogen from Jupiter is very very costly in terms of both energy and deltaV. This means the value of that hydrogen has to exceed the costs by a good margin, which is only the case if the hydrogen consumption elsewhere in the Solar System far exceeds local production capacity.

      Basically, if the entire Solar System is using lots of fusion energy, then Jupiter might be interesting. If we're still extracting Deuterium from our oceans and covering all energy needs locally, then Jupiter won't be interesting.

      Development of fusion might be independent of whether the Galilean moons are colonized or not.

      I've never heard of boostbeams, but they're interesting. Kinetic impacts seem to be the more realistic and practical version of this concept.

    4. http://www.orionsarm.com/eg-article/460c3685cd4c4

      Boostbeam is similar to the Kinetic Impactor, a more futuristic and faster version.

  2. You must really hate fusion. C'mon, not even a word about it when the colony's literally surrounded by hydrogen of all varieties ? :)

    1. I don't *hate* fusion, its just that I started this series explicitly as a near-future, off-the-shelf technology look at colonizing the solar system. I cannot reasonably base a comparison of the planets on technologies we do not fully understand or have made work yet.

      This is the same reason I haven't suggested super-strong carbon nanotube materials for building vacuum ballons to float on Jupiter, or antimatter collection space stations using Jupiter's magnetic fields to scoop up anti-protons for fuel....

    2. Still, the idea of a city throwing away it's power stations after only a few uses is INCREDIBLY inefficient. One can use chemical sources if no other options present themselves, and it would still be more efficient. Wasteful but still better....
      Come to think of it, you may have identified a reason to go to Jupiter in the first place: it's massive magnetosphere would make it an attractive destination for magsails.

    3. I assume that 'throwing away power stations' is referring to the electrodynamic tethers. I agree that it is wasteful, but it might not necessarily be very expensive and it would only be an intermediary solution between solar energy and Io plasma energy.

      Magsails are quite useful around Jupiter. A lightsail and a magsail can be combined into a spaceship that can accelerate quickly away from the sun and stop at Jupiter and vice versa.

  3. If your environment depends on good submarine construction techniques, then it stands to reason you'd be very good at it.

    Jupiter's incredibly harsh atmosphere might also make a good (uninhabited) 'proving ground' for aero-drone designs to be used in exploration of other gas giants.

    Consequently, do you think that these 'Jupiterians' might make a living designing plane and sub designs and e-mailing them to earth (and elsewhere)? I imagine Venus would have a better hold on commercial and military aerospace industries, but Callistans and other might try and corner their own exploration niche....

    1. Hmm. I would consider that sort of reasoning as backwards. If I were to design a colony to inhabit the Jovian system, I'd seek to reduce the possible costs, complexity and mass requirements. I'd avoid Jupiter's atmosphere in the first place.

      If I had to design a colony specifically in Jupiter's atmosphere, I wouldn't drop people in there and then expect them to become better t submarine building later.

      I'd use proven techniques that require the least amount of super-materials and least overall mass. So, something like a giant flying wing, held together by inflated segments instead rigid supports, pushed through the atmosphere at supersonic speeds by a nuclear-ramjet. Inflated wings exist, nuclear ramjets have been designed, and big flying things are old news.

      Sure, it won't be terribly energy efficient. Sure it won't be long-term-sustainable or even provide better living conditions than a flight cabin, but it will keep its inhabitants alive reliably and long enough to perform their task. If they want long-term sustainable and confortable habitats, they'd return to the main colony on Callisto.

      Practical testing of full-scale objects seems to be dying out in favor of computer simulations.

      Jupiterians make a living by trading with outer planets, servicing asteroids, providing mag-sail return journeys against lightsail outbound trips, pumping kinetic streams into the inner solar system and selling water.

      Water is decently cheap from Jupiter if it is extracted from a very low gravity rocks on the edge of Jupiter's Sphere of Influence. It would arrive quicker than asteroid water, and be less deltaV expensive than planet-bound water. According to Hollister (http://hopsblog-hop.blogspot.co.uk/2012/06/inflated-delta-vs.html), an SOI to SOI transfer of water from Jupiter to Earth can be as low as 3.5km/s, plus an Earth SOI to LEO burn of 3.6km/s. It might be energetically advantageous compared to Lunar water (6km/s from Lunar surface to LEO).

    2. Those are all important 'primary' industries, absolutely! I have to ask though.... do you foresee ANY semblance of a mixed economy occurring over time or will it just be kinetic impactors and magsails/ water and travel services indefinately?

      I hope I'm not asking the same question again (if so my apologies), its just that my whole approach was to write sci fi with the perspective or 'long duree' of a historian (fearing that I couldn't do a PhD and didn't want to waste my hist BA degree). My science knowledge is terrible (as I have shown), but I am trying one last time to see if my historian background can be of any use in this endeavour. Thus seeing how a colony develops over time and if there can be any 'changes' catches my interest.

      I hope that makes some sense. Tiredness is creeping up and if I don't stop re-writing this post it'l never get done. *shrugs*

    3. Hum. That's an interesting question.

      I see two types of secondary industry arising from having both plentiful energy and resources: services and transformation.

      By services, I mean expansion up and down the economic chain that links the consumer on Earth (or elsewhere) to the bare rock of a Jovian moon. It starts with extraction, initial processing, bulk transport to local refineries, intra-system transport to major transport hubs, interplanetary transport ect. A Jovian company that has access to cheap energy can decide to buy out intermediaries and improve its profit margin.

      Jovian Rocks and Ice Co. becomes Jovian Interplanetary Co., then Jupiter Industrial Solutions and so on.... it then branches off into setting up banks to fund mining ventures or handling warehouses on the client's end of the chain.

      Transformation ties into the expansion of services. If you are transporting your own ore, it makes sense to build spaceships for yourself. If you have spaceships, you can start offering passenger transport. Some might be tourists, who would be interested in luxury accommodation. Now Jovian mining corporations are running hotels in Low Earth Orbit. Why not start building farm-wheels? Why not open up your own genetics R&D for the next generation of space-grown food? These industries 'transform' the available resources into higher value products (spaceships, space stations, scientific data). It is not done on an energy-saving basis or even an economic basis, but on a financial one.

      In other words, Jovian companies can move into research and tourism not because it is cheap to travel from Earth to Jupiter or because a laboratory on Callisto is more effective than on the Moon.... it is because the Jovian company can leverage the secure 'primary industries' into large, low-interest loans that fund high-profit margin ventures. Terran banks will want to lend to Jovians, the safe bet that is also growing rapidly, than to exhausted Terran companies.

      An example of this sort of sweeping corporate expansion is the British East India Company. It became so encompassing that it thought that moving governments and ruling foreign populations was a good expansion to its shipping services.

      Be aware that these ideas (to be crystallized in an Interplanetary Trade post) are definitely not the Mercantilist oversimplification in 60s SF or the popular theories of Comparative Advantage or Monetarism. This is the Uni-level Finance that I study.

  4. Thanks for the interesting article. I am working on a sci-fy novel where the Protagonist is from a science academy located at the bottom of Europa's ocean and is going to pilot a fusion driven star ship built on Aneke, the workers of which live on Callisto, and Himalia; then obtaining hydrogen for the star ship from Jupiter's atmosphere. It sounds like my science credibility is nearly spot on from your article. My problem now is travel distances. I will need my commutitor ships to travel at better then .5% of C, and I was hoping to use a Jovian gravity assist to aid in the star ships acceleration, but distances make that impractical because a planetary gravity assist is pointless unless the vessel is moving less then 200,000 kph, which would take many hours starting out from the outer Jovian. Also the Antagonist lives in the asteroid belt. So some of this is back to the drawing board. But thank you still.

    1. Your numbers are not quote correct, but the rest is.

      .5% c is 1500km/s, which is insanely fast. For comparison, Jupiter orbits at 13km/s and the Saturn V lunar vehicle left Low Earth Orbit for the Moon at 3.5km/s.

      At those speeds, a gravity slingshot around Jupiter is utterly pointless. It'd be like trying to run faster by flapping A4 paper like wings.

      Around Jupiter, a slingshot is still useful for velocities at up to 100km/s, or 0.03%c, or 12000000km/h.

      If you want fast ships to pass near Jupiter, instead of relying on gravity slingshots, why not have them use laser power transmission or kinetic streams instead?

    2. Not familar with laser power transmission or kinetic streams.

    3. 0.005 = 0.5%

      Laser power transmission: Due to the abundance of electrical energy available, it can be used to power rockets by beaming lasers onto them. Externally powered rockets can end up having both the high exhaust velocity and the high thrust-to-weight ratio that allows for fast travel across the Jovian system.

      Kinetic streams: Tiny little robots use Jupiter's magnetosphere and/or laser beams to boost themselves into very energetic orbits. They have a very tall apoapsis (tens of millions of km) and a very short periapsis (skimming the target's surface). The spaceship carries a large magnetic ring that produces a large magnetic field. At the right time and place, it puts itself in the path of one of the kinetic streams. It launches a plastic disk into the middle of its magnetic ring. A robot hits this disk and gets vaporized. This creates a cloud of plasma that expands rapidly. Through interactions with the magnetic field, the plasma is slowed down and the spacecraft sped up. This is a very efficient method of travel, as it allows lightweight spaceships to accelerate rapidly, using only a small supply of plastic disks as propellant.

    4. I so want to read your book so badly,sadly it's extremely unlikely you will see this response and say how the book's going.fingers crossed i find it randomly or you respond after 8 years

    5. I wanna read their book too! Hopefully they answer :)

  5. For operating inside the Jovian atmosphere, can a chemical ramjet function? On Earth ozone is produced in the upper atmosphere by cosmic radiation bombardment. A ramjet design can convert the ozone into oxygen and the resulting heat propels the gases out. It furnishes continuous operation without the need to store fuel. The reactive gas is regenerated by radiation; human-scale flight can't deplete Jupiter's atmosphere.
    Might humans not hit upon a similar pair of reactant and product for continuous operation at a proper atmospheric layer and temperature? The radiation is very bad for humans but great to (re)generate high-energy chemical reactant gases for powered flight.

    1. Its going to be very, very difficult. First of all, the ratio of ozone to hydrogen is greatly tilted towards a hydrogen-rich ratio. It would be hard to sustain an oxygen/hydrogen flame with such little hydrogen. Second, there's just less gas than on Earth. It's reduce drag, but you'd have to be travelling quite fast to collect enough hydrogen to produce thrust out of it.

      This implies hypersonic speeds at a minimum. But, you'll never get enough oxygen to burn in the hydrogen to produce enough thrust to sustain hypersonic speeds. This means that the only practical way to travel in Jupiter's atmosphere is by using nuclear-powered air-breathing rockets like those designed for Project Pluto (https://en.wikipedia.org/wiki/Project_Pluto).

      Inside Jupiter's atmosphere, radiation levels are negligible because the gas absorbs most of it.

      If you really want a chemical ramjet, you're going to need an external power source that spends time extracting oxygen from the atmosphere, accumulating it, storing it in liquid oxygen tanks, and providing it as 'fuel' to the aircraft before it starts flying.

    2. Yes, ramjet is what I was thinking, with an onboard means of super heating the hydrogen to begin a fusion reaction, and quickly get my star ship up to 40% of C. I need a ten year one way to Proxima b, a fifteen year settlement, and a twelve year trip back to fit the time line I have for aging my Protagonist 37 years by the end of the story.

  6. You guys have some really great ideas and insights. There are 3, maybe 4 outer moons I can put small colonies and industry on, all of Callisto, and almost anywhere under water on Europa and Ganymede. I really like the idea making Io into a giant battery. But making believable commutes for people working on those outer moons are still a thorn in the side. Even with a Jovian system mass space transportation system, I don't think I can make people living on Himalia, and going to work on Elara believable, and especially since there are times when even very close moons are on the other side of the planet from each other.
    Unless I either put settlements and industries on the same moons, or use matter to energy transporters like Star Trek. Perhaps I should consider Saturn. Way more useable moons that are closer together, less radiation, and hydrogen that is more pure. Except that F ring is way out there. Much to think about, and thanks again for the feedback.

    1. You are welcome!

      Remember, even on Earth, a lot of our work is done online and with colleagues sometimes in other countries, often on the other side of the plant. Telecommunications will allow a lot of cooperation between people on Himalia and people on Callisto. Also, most of the grunt work on the furthest rocks will be done by robots. Its only when they break down that you need to send a human out there.

  7. One thing which makes Jupiter and the Jovian system exciting for me is that "everything" is there in close proximity. You have energy from the magnetosphere, resources scattered across 67 moons and relatively close travel distances between them. Industry could be developed to take advantage of the massive radiation fields around Jupiter, and external financing should be relatively easy to get by selling water ice to the inner Solar System.

    In short, the Jovian system could be an almost entirely self contained system, and evolve and an independent polity of immense size and power (political, economic, social and even military) inside the larger civilization of the Solar System. Given the vast numbers of moons, and even greater numbers of available bodies in the Trojan asteroids, the problem of the closing of the frontier will also be centuries in the future for restless Jovians looking to find a fresh start.

    This could lead to Jupiter being the analogue of the growing American state in the era between the founding in 1776 and the "closing of the frontier" in 1890. Of course, if the civilizational foundation is different, this might resemble the Tsarist conquest of Ukraine, the Caucuses, Central Asia and Siberia instead.....

    1. I like that analogy.

      Scattered Jovian colonies and outposts that strike their corporate banners and default on their debt to Mother Earth to become their own unified state. What could Earth do? Jupiter is so far away and has everything it could ever need from energy to water and rocket fuels!

    2. The Jovians might have the opposite problem if the 67 moons and thousands of Trojan asteroids all become independent polities instead.

    3. There is historical precedent to this: India and Pakistan. Remove the big colonial influence and the squabbling factions are free to air their grievances.

    4. To add into this discussion, I think you could have a scenario that encompasses both; A number of colonies and outposts all collectively strike their banners and give a collective fuck you to Earth, before all collapsing into civil war with nothing to keep them unified.

    5. Depending on what the author wants, the Jovian polities could be re-united by fear and terror, and end up being oppressed worse than under Earth... It could even be a seasonal project, like the reunification of China!

  8. So if I'm reading this right, there's a lot of potential here for some interesting stuff. Namely, for automated mining outposts on the likes of Ganymede staffed by drones with rotating crews like oil rigs. Only, with a permanent city/ cities on Callisto, Callisto becomes the population hub of the entire system, regularly sending out rotating crews of maintenance techs out to support the drones. Lots of room for Alien-esque scenarios where a crew are trapped in a station for certain amount of time.

    1. That's kind of the whole objective of this blog: inspire readers to go forwards, armed with new information, to create interesting worlds of their own!

      If you want a really high-tension scenario, consider an interplanetary asteroid, diverted from its solar orbit into an intercept with Jupiter. Normally, the Jovian Laser Transport system catches it in its beams and provides the energy for it to slow down. It would then be 'attacked' by mining drones that strip it of valuables while the crew rotates out...

      But what if the laser's don't arrive? What if there's an error and the lasers sear off the asteroid's braking thrusters? The crew are stuck on-board with the choice of a risky aerobraking manoeuver, a high deltaV rescue mission Corporate doesn't want to pay for, or a slow death in interplanetary space... maybe the crew pirates the ownership records of the asteroid and sell it from under the Corporation to some shady Jovian middle-men in return for a rescue attempt...

      The possibilities are endless!

  9. I agree with the above, so I'm going to keep my colonies in the Jupiter system. I like Matter Beams suggestion of laser power transmission or kinetic streams for commuting between moons. But my main characters are on a ship that will be used for interstellar exploration, and my opening is of them speed testing the ship.

    It will have 2 stage fusion, 3 stage fission, VASIMR Ion drive, and a device that nullifies gravity and inertia to make the engines propel it as if it has no mass. I took out Jupiter for the gravity assist, and will use the Sun instead.

    So now my challenge is making a believable one way from Jupiter to the Sun in 10 hours or less for that grav. assist to supplement the fusion drive. I need it to come out to around 8% to 12% of C before the sling shot. Fission and VASIMR are too slow, and fusion is too fast.

    1. This is toughsf, so I feel obligated to tell you that you don't really need magical gravity/inertia nullifiers to make your spaceship go fast. Just increase the power output. For example, instead of a magical machine that makes you feel 10 times lighter, just use an engine 10 times more powerful to the same effect.

      For interstellar travel, I strongly suggest only 2 stages: one for departure, one for arrival. VASIMR is not going to be useful because the exhaust velocity is too low for near-lightspeed travel. Fusion is perfect because its exhaust velocity is already measured in %c.

      For example, if you want to travel at 30% the speed of light, you need 60% c in deltaV. If you use VASIMR with a maximum exhaust velocity of 120km/s, the mass ratio is 7.5e651. That's 7.5 with six hundred and fifty one zeroes. If you use a pure fusion thruster (http://www.projectrho.com/public_html/rocket/enginelist.php#he3dfusion) with 7840km/s exhaust velocity, then mass ratio is 'only' 95 billion.

      Travelling at lower fractions of c, of course, reduces the mass ratios.

      If you are using pulsed propulsion, with your 'propellant' being stacks of bombs, then the mass ratio doesn't really matter: just stack enough bombs until you have enough.

      Fusion is great because you can increase or decrease thrust however much you like. It is never 'too fast' or 'too slow' for any sort of manoeuvre!

  10. Thanks again for your input. I need the magical gravity/inertia nullifiers because I want the ship to make 85% of c, and from what I've researched on predicted max velocities of nuclear space craft, fission reactions (except Orions) can make 3% - 5% of c at best, unless you're using much heavier fissionables that run several atomic splits, Like element 106 that splits into carbon and plutonium then the plutonium splits. I called them stages, but I think it's actually called a multiple generation reaction. Those can double your fission power output. Likewise with fusion,it supposedly tops out after making 60% to 65% of c. But hydrogen fusing into helium, then carbon, then oxygen, then magnesium can get you a lot more. Again, I called them stages when generations is probabley correct. But even usin both fission and fission multiple generational reactions together will not likely give me my 80% c.

    Because Einstein said increasing power for greater speeds becomes exponential to the also increasing mass from the greater speeds. But if the mass were zero, then the available power should produce much greater speeds. The VASIMR is supposed to be very small in boosting, but more for cruising a stable speed with very slight increases over a long distance. I didn't think it's exhaust velocity is too low for near-lightspeed travel, but would hold whatever speed was reached. Fusion is of coarse the star of the show. I will rethink the VASIMR, and the gravity/inertia nullifiers if I can come up with a believable mix of fusion with fission. One thing I did forget is submersible propulsion, because the starship's departure point is the bottom of Europa'a ocean.

    1. Just note that there is no 'maximum speed' to a rocket, just a practical limit.

      For example, consider a chemical rocket with a mass ratio of 1 million. Exhaust velocity is 4.5km/s. It can reach a velocity of 62km/s! That's much higher than most designs for electric rockets, or even VASIMR, are capable of.


      Is it practical to hold one million tons of propellant for each ton of dry mass? Not really.

      So, a fusion rocket can contain enough deltaV to reach the speed of light twice (0.5c going out, 0.5c braking at target, and again to return home). It just needs to hold more propellant.

      There is no maximum speed, just a practical limit to what you deem is 'acceptable'. So, a VASIMR rocket can have more deltaV and reach faster velocities than a fission or fusion rocket. It will just require much more propellant.

  11. Hey by chance do you have any idea how fast a spacecraft can be going and still get a useful gravity assist from the Sun?

    1. Well, one thing I know is that swinging around the sun will only help to change your direction, not to speed you up or slow you down like around other planets. It's not orbiting anything, after all. It can be used for an Oberth effect.

      Read here: https://en.wikipedia.org/wiki/Gravity_assist#Limits_to_slingshot_use

      A chemical rocket gains a lot from an Oberth effect. An electric rocket, less so. A fusion drive which has an exhaust velocity measured in % of speed of light has nearly zero benefit from going around the Sun.

      Basically, there is no reason to pass by the Sun when leaving the system.

  12. Unless I'm missing something, I don't get the kinetic energy trade. Why would Jupiter colonists go through the trouble of spending their already limited energy supplies to essentially bombard the inner solar system with kinetic kill vehicles (and why would inners agree to this?). The method of having to shoot these vehicles with plastic discs so they vaporize and then use the plasma to accelerate with magnetic fields already seems difficult enough, but compounded with the fact this would only really work when Jupiter is roughly at opposition to your spacecraft and only accelerate you TOWARDS the Sun... the proposition seems unlikely.

    1. Hi Alan.
      The kinetic energy trade is developed in much more detail in this later blog post: https://toughsf.blogspot.com/2018/06/inter-orbital-kinetic-energy-exchanges.html

      The value of the trade is that the value of an energy source around Jupiter gets multiplied many times to someone receiving that energy around Earth. And, it would allow for massively decreased propulsion requirements when compared to chemical rockets, and it is much cleaner than nuclear rockets in terms of radiation risk or fuel cost.

      The collision of an interplanetary projectile with a plastic target creates a plasma expanding in all directions at a velocity many times greater than the collision velocity. For example, a 1kg projectile striking 1kg of polyethylene at 50km/s relative velocity would slow down to 25km/s due to momentum transfer but create a plasma expanding at 57.8km/s. You can therefore climb 'up' a mass stream if needed by placing the target behind the magnetic loop and catching the plasma as it expands in the direction you want to go.

    2. Nuclear is cheaper. Nuclear is always cheaper. Nuclear is also better. Nuclear technology is mature and well developed even at present tech. All our issues with cost of nuclear power are political, not technological.

      So, you can build megatons of tethers, inefficient lasers, and kinetic transfer devices, or you can run a gigawatt generation IV reactor on 300 to 500 kg of fissionables per year.

      Also, open cycle gas nuclear rockets are very much near future tech, and in interplanetary space are perfectly fine (your radioactive exhaust dilutes to background levels almost immediately) and can give an ISP of 5000s, giving you a deltaV of 50kps on a mass ratio of 3. That makes jetting around your jovian system trivial.

    3. When all of your nuclear fuel has to be mined, processed and refined on Earth, then launched into orbit, then carried over interplanetary distances to where you need it, it becomes a very expensive resource. There's also the time delay involved: if you need to fuel up a ship to launch a mission from Jupiter now, the supply lines would have a delay of up to 2.7 years!

    4. Who says all your fuel has to be mined, processed, and refined on earth? Fissionables are rare in the Jovian system, not absent. The trojans will have more. And with your 5000s rockets, rocketing around the region is relatively trivial.

      Meteors have about 0.008 ppm uranium. Hektor has a mass of 8x10^18 kg. So this asteroid alone could have up to a million tons of Uranium, and a couple of million tons of Thorium.

      That's enough to run 10,000 gigawatt reactors for 600 years.

      And that's just one asteroid.

      Nuclear is ALWAYS cheaper.

    5. It is reasonable to assume that a Jupiter colony will be attempted long before the nuclear fuel chain has been recreated off Earth. The cost of doing this is enormous, even after it becomes technically possible... likely more expensive than shipping the uranium. At that point, electricity generated from windmills and tether might still remain the better option.

      But, I agree with you that in the long term, this is one problem that can be solved and nuclear energy will prevail. Having many nuclear reactors will allow you to breed fuel out of more common fissiles, so you don't have to enrich as much, which in turn makes the whole thing cheaper and more abundant. It is hard to predict what other innovations or problems might arise in the long term though!

    6. We won’t be getting out there until late this century or the next century. We’ll have space infrastructure by then.

  13. I love what you guys tend to be up too. This sort of clever work and coverage!
    Keep up the good works guys I’ve added you guys to blogroll.

  14. Both the Moon and Mars have known deposits of Uranium. There will almost certainly be extensive lunar industry before we attempt a Jupiter colony, since lunar industry is pretty much a requirement if you want to make big spacecraft on the cheap. With GenIV reactors, the nuclear fuel chain is easy: Refine your ore. No enrichment is necessary.

    Your ship is already nuclear powered. Just load up a few tons more and you have your energy needs set for the decade or so you need to start mining and refining ore on what is essentially a giant rock with no gravity in space. Your lunar industry experience has already taught you how to do it.

    I don't think it will take long at all, and will certainly require less infrastructure investment than a kinetic transfer or tether system.

    In space, nuclear is king.

    1. At this level, it is the details and assumptions being made that will determine the best options.

  15. Have you looked at gliders in the Jovian atmosphere? It sounds crazy but this may be feasible. I know you can get pretty crazy wind speeds there, so it might just work if you were to lower the sailplane to a low enough altitude, where the atmospheric density is high enough to get the lift you need.
    I see two methods of keeping altitude that may work: thermal currents and dynamic soaring.
    Thermal currents are straight forward: you circle in a rising thermal current, and as long as the sink rate of the glider is lower than the upward speed of the air column, you have a net gain in altitude. Here we rely heavily on getting to low enough altitude to increase the gas density and hence the lift, as well as the faster than earth winds and a super optimised unmanned glider, to compensate for the increased sink rate.
    Dynamic soaring is the crazy one, but also potentially the most powerful. It relies on a gradient in wind speed. The glider cycles between the fast and slow moving air masses, making turns in each. It gains speed like a ping-pong ball being bounced between two rackets (except the rackets are hurricane winds on an alien Planet). On earth, the current speed record for dynamic soaring is above 840kph... So imagine what you can do with a Jupiter level storm. The one problem is that you need a reliable and steep airspeed gradient to take advantage of, which on earth usually means flying behind and above a mountain ridge. On Jupiter we have no such luxury, but flying in and out of fast air currents might still be possible. I should note that this has to be robotic, as dynamic soaring gliders easily pull in the 100s of g's here on earth alone. Since these earth gliders already are in the transonic regime, I wouldn't be surprised if Jovian gliders operate exclusively at supersonic speeds.
    One advantage of such a system is that it also provides you with an easy to tap reliable source of energy. You can tap off energy with a small propeller and motor working in reverse (the same you use to make occasional small boosts in emergencies).
    So yeah: supersonic gliders riding an alien storm from hell. Let me know what you think

    1. Yes! These are great ideas. The loops would have to be gigantic on Jupiter though, as the size of the atmosphere is huge and there is no terrain to force sharp gradients of wind speeds, but it would be useful for very long distance travel.

      I see that dynamic soaring is achieving 8-10x the windspeed. On Jupiter, this might mean 4000 km/h but the difference in windspeed between layers you can practically reach might be much lower.

      Also remember that hydrogen has a faster speed of sound. At room temperature, hydrogen's speed of sound is 1270 m/s or 4570 km/h.

  16. A 2011 reanalysis of Galileo data casts some doubt on Callisto being undifferentiated; if that's true, then Ganymede and Callisto start to look more similar (OK, the former is more irradiated, but not unmanageably so), going down the gravity well to the Galileans looks less attractive, and Jovians face an even more pressing metal shortage and dependence on the Inner Solar System. So I wonder if a Jovian setting might plausibly instead look more like an asteroidal empire centred on the outer moons, kept together by proximity compared to the asteroid belt proper with Himalia as capital, and some influence into the Trojans and Hildas.

  17. Oh, and also:

    "At 3528kg/m^3, it is the highest in the solar system, surpassed only by a few metallic asteroids."

    The four inner planets also surpass Io. :)

  18. @planet watcher how's the book going?

  19. Trade negotiations...
    Jovians: You give us heavy elements, and we give you kinetic energy to propel your spaceships.
    Terrans: I'm sorry, but we don't like the proliferation possibilities.
    Jovians: Ok, new proposal: You give us whatever we want, and we *don't* send you kinetic energy impactors to propel your cities into orbit.
    Terrans: Well, when you put it *that* way...

    1. Most propulsion schemes are well-behaved weapon systems!

    2. It occurs to me that given Io's high density, it might well also serve as a local source of heavy elements in the long term. Yes, the radiation would be very high, but the OP also proposes using Io for geomagnetic energy, which would equally require a physical presence.

      Europa's density suggests it could also work, but then you're mining the ocean floor. At least there radiation is not a problem.

      So I suppose Jovians do not totally lack heavy elements; they are just inconveniently positioned for initial exploitation. There might therefore be an evolution as the colony develops from being an "asteroidal empire" centred in the outer moons and trading with the inner system for metals to fully tapping Jovian resources by moving inward to the Galileans. All the things the colonists would likely be learning about radiation protection could well give them a distinct identity.

      What I do wonder is how the inners could push back against this kind of interplanetary blackmail. I suppose Mercury could retaliate via giant laser, but all the other inner planets would probably object to that idea equally hard. :)

  20. I just saw your comment. I have lost everything I had written. The power cord to the laptop it is on, has stopped working, and I can not find a replacement. The thumb drives I had backed up to are currupted. Besides that, I can not begin to afford a publisher anyway.
    Paper books are no longer in much demand. Nearly all publishing is entirely on line these days.

    1. Wow, that's terrible. I hope you find the motivation to try again...