Living Inside Asteroids

For humans to live long-term in space we would need a healthy environment. This would mean somewhere spacious, with plenty of the comforts we find on Earth. And most importantly, we would need gravity, or at least a simulation of it.

Large space stations could be built with all of the above. With a large enough diameter they could be spun at less than two revolutions per minute, which would eliminate the uncomfortable symptoms of the Coriolis effect that would be experienced at the higher revolutions of a small rotating space station. Due to the huge amounts of material needed for construction of such stations, and the immense cost of launching it from Earth, the materials to construct the space stations would realistically have to be mined from asteroids.

A large diameter space station under construction in the Asteroid Belt. A single large asteroid will provide more than enough material for the construction of the station. Concept by Deep Space Industries.

Asteroid mining will not only provide the huge amount of construction material necessary for space habitats. If the asteroids are mined in a certain way, making large cylindrical chambers through the asteroid's centre of rotation, we could then convert the chambers into living spaces. Once mining is concluded the rotation of the asteroid could be altered until a high-enough centrifugal force provides enough artificial gravity comfortable for humans on the chambers' outer walls.

Such chambers, several kilometres in diameter, could well provide what may become the safest and most comfortable human living spaces away from the Earth.

Of course, the idea of hollowing out space inside an asteroid is not a new one.

This image was created in the 1960s by Roy Scarfo when the exploration and colonisation of the asteroid belt was being researched by Dandridge M Cole.

In the 1960s Dandridge M Cole, an aerospace engineer and futurist, was one of the first to propose hollowing out an asteroid and spinning it on its long axis to simulate gravity. Illustrated above, he envisaged a large single void within the asteroid with fields, lakes and villages. Sunlight would be reflected into the interior using mirrors. It would be a spacious and comfortable environment.

It's an impressive concept, but there are numerous problems with it, and not least the idea of a single huge chamber and relatively thin wall. It would make the asteroid habitat vulnerable to complete decompression if the wall was compromised in some way. If the rotation provided one gee of gravity the forces on the wall, especially at the asteroid's equator, would cause it to fly apart as soon as any cracks or flaws developed.

The very green and pleasant interior of Dandridge's asteroid habitat concept

It would be far better to cut several cylindrical voids, and have the outer walls very thick - several kilometres at least, depending on the overall size of the asteroid. Each chamber would be connected to the next, but with the ability to quickly seal off a particular chamber if it was compromised and at risk of decompression, or indeed some other dangerous event. Those living in the effected chamber could easily be evacuated to another chamber, making such asteroid habitats safe and with plenty of redundancy.

Once the chambers have been excavated the asteroid's speed of rotation can be increased slowly, until the right level of simulated gravity is reached. To generate an equivalent of one gee (the same as what we experience on Earth) the rotation speed would be quite substantial, and it would mean that, at the very least, loose boulders and dust would be thrown off the surface of the asteroid. It would also put considerable stress on the outer surface, which would rule out low density asteroids due to the high risk of instability.

A natural habitat for Earth life, many kilometres in diameter, created inside a hollowed out cylindrical chamber within an asteroid. Typically there would be a few such chambers. All would be linked but each could be sealed off should a disaster occur, which would protect the other chambers.

A supporting series of collars around the equatorial region of of the asteroid would negate many of the issues that such a high centripetal force would cause. It would be a huge construction task to build such collars, but no more than the excavation of the chambers themselves. Of course, the excavated material would provide everything required to build the collars, each of which could be many kilometres in width. They would be held in place by deep supports.

Visiting spacecraft would using large docking areas at the poles of the asteroid, situated at each end of the axis of rotation. People and cargo would then be transported through the asteroid along the axis of rotation. Essentially there would be zero gravity in this area. When the destination chamber is reached the visitors and cargo would be delivered to the surface using elevators. People descending in these would experience a steadily increasing sensation of weight as they approached the surface.

A diagram showing how the interior of a rotating asteroid colony could be divided up into separate chambers. This would provide higher levels of safety (colonists could be evacuated to another chamber if their own is compromised), and more structural integrity than a single large chamber.

It's likely that people arriving at the asteroid will have spent many months travelling in zero gravity so acclimatisation areas at the regular points down to the surface should be built to allow people to adapt gently to the full gravity of the facility.

As well as fairly static colonies inside asteroids in the Asteroid Belt, or in the Trojans, asteroids that are on highly elliptical orbits - that head in to the inner Solar-System and then out beyond the orbits of Neptune and Uranus - would make very useful passenger ships. As the asteroid gets close to Earth (and the probable large colonies on the Moon and Mars) passengers who need to travel to the outer Solar-System could rendezvous with it. They could then spend the next couple of years living in comfort in relatively Earth-like conditions as the asteroid's orbit takes them closer to their destination.

Ultimately, such asteroids could become our first interstellar star ships. They would make voyages lasting thousands of years, with a hundred generations or more of humans living out their lives in comfort until the asteroid is captured by the target star system. With the right energy generation technology such as nuclear fusion that could provide light and warmth during the interstellar period of the voyage, humans would have a relatively good chance of reaching their destination.

Converting asteroids into large human habitats, and then into interplanetary and interstellar spacecraft, seems to be a logical and necessary step as humans embark on colonisation beyond Earth, and it is likely to be an essential step towards securing the future of our species.

The vast resources and protection that such objects can provide must be utilised at the earliest opportunity.

The Ice Billionaires

One day, when the human population away from Earth reaches a certain level, new economies will emerge, ones that are almost completely independent of our home planet. And not long after that the new economies' first Earth-independent billionaires will emerge. But what service or product will generate such wealth?

Providing construction material will be one way. Finding enough suitable material to construct human settlements, whether in space or on the surface of a moon or planet, is a difficult and awkward task. It would not be long before businesses are created that specialise in mining and distributing such material. The most successful will enjoy an ever-increasing demand for their materials as colonies expand and new colonies are started.

Another profitable service would be transportation. There will be a constant need to transport people and cargo of all kinds around the Solar-System. Businesses will be set up to provide reliable and regular transport services. Eventually huge spacecraft with the capability to move millions of tonnes of cargo, and hundreds of passengers, will be making journeys between the mining facilities and the colonies and outposts. Leaving Earth to work at one of the colonies for a few years, and then returning home or moving on to a different colony will become a relatively routine, if still lengthy, process. The large interplanetary ships will at least provide a high level of comfort and simulated gravity, which will be much healthier and safer than what we could provide travellers at the moment.

A typical mid-sized cargo ship. As well as cargo carrying ability, this ship has a large crew and passenger section which rotates to provide artificial gravity. Eventually there would be thousands of such spacecraft, some much larger, providing cargo and passenger transport between the colonies and mining facilities, and of course Earth.

But there is one product that will create the most riches for the people that set up businesses to mine and deliver it. That product is ice, and especially water ice.

There is a relative abundance of water ice in the Solar-System. Even Mercury, the closest planet to the sun, has water ice preserved in craters that are in permanent shadow.  There are many ice moons around Jupiter, Saturn, Uranus and Neptune, and Saturn's rings are 90 percent water ice. And then there are the Kuiper Belt objects beyond Neptune, which are mainly composed of ices, including water ice. And beyond that in the far reaches of the Solar-System, on the border with interstellar space, there is the Oort Cloud which is the source of many of the comets that periodically make their way into the inner Solar-System. It's likely to contain enough ice equivalent to several times the mass of Earth.

I expect the ice industry will be split into two: with one part specialising in ice mined on a planet or moon's surface and with it's customer base restricted to the body on which it was mined (due to the cost of transporting it out of the local gravity well), and the other part dealing with ice mined on asteroids, comets and other small bodies. Such ice will be easily transported to space-born colonies and orbital facilities, and to the small rocky worlds such as the inner Solar-System asteroids, and the moons of Mars: Phobos and Deimos. Those bodies will certainly have human activity on them as materials for construction are mined. Their demand for water ice will be high.

Surface-Bound Ice Mining

In the higher latitudes of Mars, close to the planet's north polar ice cap, lies the Korolev Crater: an almost 82 kilometre-wide impact crater filled with water ice. The base of the crater is more than two kilometres below the rim, creating a cold air trap that's allowed the crater to fill up with the ice to a depth of 1.8 kilometres.

Korolev Crater: An ideal location for a large human colony due to the vast amount of water ice contained within its rim. The first ice mining business is likely to be set up here. It will be the start of what will become a global corporation supplying essential ice to the entire planet.

The crater's location close to the polar ice cap, and just south of the expansive dune-filled region known as Olympia Undae, and it's abundance of water ice, makes it an ideal location for a large human colony, and the best example of a massive and conveniently located source of water. The area surrounding the crater will be relatively easy to traverse, making the construction of roads towards the north pole, and south towards the equatorial regions, straightforward. It is the most likely location for the first of the planet-bound ice mining businesses to be set up.

The person who will become the very first ice billionaire may well be living on the rim of the Korolev crater in several decades time just as material self-sufficiency from Earth is achieved. His or her vision and drive will enable the rapid expansion of the colonies on Mars, and become the inspiration for others elsewhere on the planet and far beyond.

The crater could well become the site of several sizeable towns, even cities, whose inhabitants are specialised in mining water ice. The towns would be located on the rim of the crater. Access in to the crater will be easy as the slopes are gentle and natural routes for roads would be easy to find.

A close-up of part of the Korolev crater's rim, which is typical of where most of the human settlements will be located. Roads will be built down into the crater to provide easy access to the ice mining facilities. Roads will also be needed that head out of the crater to allow exploration of the areas beyond, and for transporting the ice south to the settlements in the equatorial regions.

The ice mining business's first contracts will be with Earth governments as they hand over the extraction of the ice to a private venture, but within decades, as the colonies themselves separate from direct Earth control and become truly independent, the contracts will be with Mars governments, and with other business sectors that have developed on the planet. By that time ice mining will have expanded to the north and south poles. It will be an efficient global industry that will allow millions of humans to live and thrive on the planet.

The same is likely to happen on other worlds that are suitable for human colonisation, with Saturn's moon Titan a prime example. There will be differences, of course. Mining anywhere on Titan, and the other ice moons will result in plenty of water ice being found. Many more smaller competing businesses are likely, which will ultimately merge to become a handful of large corporations.

Interplanetary Ice Mining

Space-bound colonies, either in orbit around planets, moons or the sun, will become a significant presence in the Solar-System once human colonisation away from Earth becomes established. They will be constructed from material mined from asteroids and most likely constructed in the asteroid belt (or from the Trojan asteroids that share Jupiter's orbit) and transported to their ultimate destination once complete. Such structures, each built to house thousands of people and to be as independent and self-sufficient as possible, will still need regular deliveries of water ice (and other volatiles). There will be no shortage of people ready to exploit that need, and the earning potential it represents.

Transporting water up from the surface of planets and the larger moons will be difficult and very expensive, due mainly to the effort and energy required to get millions of tonnes of ice out of such deep gravity wells. Such efforts would be foolish to attempt, and could never be considered as a viable business plan.

For such space-bound colonies the efficient solution is to mine the ice from small objects with a negligible gravity well, such as Kuiper Belt and Oort Cloud objects.

An artist's impression of the dwarf planet Eris, that resides in the Kuiper Belt. Eris is currently the most massive known Kuiper Belt object. Despite its size (over 2,300 kilometres in diameter) its low gravity of 0.083g would probably be low enough to make the export of ice volatiles viable. Eris could end up being one of the most active and profitable ice mining locations in the outer Solar-System. Image by S M Pritchard.

The objects in the Kuiper Belt, which lies just beyond the orbit of Neptune (and includes dwarf planets such as Pluto, Orcus and Eris), is the most conveniently located of the two. Once there is a human presence in that region mining operations with transport infrastructures will be set up to exploit the abundant ice riches that are available. There will be a regular fleet of cargo ships, largely crew-less, making their way inwards to the large space-bound colonies that are likely to exist around the major planets and moons. Their trajectories will be slow, but very efficient, and their regularity will ensure a constant supply of ice volatiles to a hungry and highly populated inner Solar-System.

A cargo ship prepares to dock with a massive space-bound colony in the inner Solar-System. Such a facility would need a regular supply of ice volatiles, including water ice. Supplies mined from objects in the Kuiper Belt or beyond would arrive at least annually to fulfil the needs of the thousands of colonists. Image by Bryan Versteeg.

Very large space-bound colonies have a distinct advantage over planet-bound colonies: those living there can live with Earth-level gravity, due to the ability to rotate the colony. With a large enough diameter any unpleasant coriolis effects can be eliminated (as the rotations per minute can be kept very low - less than one per minute if the colony's rotating section is 1,000 metres or more in diameter). It is likely that the ice billionaires would chose to live in such facilities due to the obvious space and luxury they could provide.

The interior of a space-bound habitat. With a diameter of hundreds of metres it would be able to rotate at a quite leisurely pace and still create enough artificial gravity to match that of Earth. The interior would be very spacious and would be the preferred home of the future ice billionaires. Image by Bryan Versteeg.

The motivation of the ice billionaires (and those in other industries) to expand their businesses further to increase their own wealth will be an important factor in the speed at which human colonisation spreads further and further away from Earth. Such activity needs to be encouraged. It is one of the ways to ensure that our species will endure if a catastrophe - either natural or of our own making - occurs on our home planet.

This kind of insurance against our extinction is essential. Governments on Earth are too slow, fickle and bureaucratic to provide that insurance any time soon. We need to embrace the commercialisation of space colonisation.

The future entrepreneurs that can exploit the business opportunities in the Solar-System are quite possibly alive as children today. They will one day leave Earth and create the most far-reaching corporations in human history. They will be motivated by profit, but inspired by the innate desire in all of us to survive as individuals and as a species.

Uranus Mission: Essential and Urgent

Of the larger planets in the Solar-System, Jupiter and Saturn, and their moons, seem to get almost all of the attention when it comes to orbiter and lander missions. That's understandable, of course. There's a huge amount of fascinating bodies in those systems, and many mysteries to solve and theories to prove. And the fact that those systems are relatively easy to get to helps.

But a mission dedicated to Uranus and its system of moons is long overdue.

The planet Uranus: the coldest planet in the Solar-System

Since 2010 there have been five proposed missions to Uranus. These have been by the United Kingdom (Uranus Pathfinder), ESA (MUSE and ODINUS) and NASA (Oceanus and NASA Uranus Orbiter and Probe). It’s disappointing that none of them has yet been given the go-ahead, and none of them are likely to be given it due to budget constraints and the priority given to other missions, particularly those to the Jovian system.  Even if one or more of the Uranus missions was given the go-ahead, the earliest any of them would arrive at Uranus would be the mid to late 2030s (with ODINUS not even launching until 2034).

A Uranus orbiter and atmospheric probe

There is clearly the need for much more urgency and ambition. And there is a need to use a means of getting to Uranus that does not require a cruise time of up to 15 years (due the requirement for coventional rocket propulsion to make use of multiple gravitational slingshot maneuvers using Venus, Earth, Jupiter and Saturn). A more advanced method of propulsion is required: one that is much more powerful and sustained than current rocket technology. Nuclear thermal rockets, which have been developed and tested for decades, but never used, would allow for an orbiter mission to be launched on a direct trajectory to Uranus. The journey time would be reduced to just a few years.

But why would there be such an urgency to get an orbiter mission all the way out to Uranus so quickly? It's simply because there are many mysteries about the planet that need answers. And the sooner we know those answers the better.

One of the major mysteries about Uranus is that, unlike the other planets in the Solar-System, it seems to generate almost no heat at all. There seem to be no reasonable explanations as to why. It's quite possible that the heat energy could have been extracted from the planet by some extreme geo-thermal power generator. Indeed, the planet's unusual axial tilt, which makes the planet appear as if it's laying on its side compared to the Solar-System's other planets, and its magnetic field, which is at an extreme tilt in relation to the planet's rotation and is also off-centre by quite a margin, all point to unusual and potentially unnatural events that occurred as the planet's resources were utilised.

There is a likelihood that long ago the Uranian system was the location of some intense activity by an ancient extra-terrestrial civilisation: perhaps from Venus or Mars, or maybe even from Earth many millions of years ago (see my article 'Pre-Human Technology in the Asteroid Belt'). A vast engineering project of some kind may have been implemented. The evidence of such activity, even if it ceased hundreds of millions of years ago, will still be there for us to discover. We need to know what was going on, and why.

The most likely place we'll find that evidence is on the planet's moons.

Miranda, the smallest and innermost of the major moons of Uranus

The moons would provide all the resources needed for a civilisation as it worked. The moon Miranda, the smallest of Uranus' major moons, certainly has the appearance of a moon that has been heavily mined. As it's composition is mainly water ice its surface could have been the main source of water, oxygen and hydrogen for fuel.

The planet's largest moons, Titania and Oberon, do not show signs of mining, but they would make ideal locations for habitats and deserve detailed surface investigations. Ulimately, a strong human presence is required for a thorough investigation (and of course for the more general reason of helping ensure the survival of our species if/when something catastrophic occurs on Earth).

At the very least, a human colony in the Uranian system would be an ideal base from which to explore the outer Solar-System.

Human colonists on Miranda enjoying ultra-low gravity recreational activities 

A small human outpost on Titania, the largest moon of Uranus

An orbiter mission to Uranus and landers for its moons are essential. Sooner rather than later we need to know what happened in the Uranian system. And ultimately we need to establish a permanent human presence there to help ensure our long-term survival.

Human Colony on Titan

Titan is Saturn's largest moon (and the second largest in the Solar-System after Jupiter's moon, Ganymede). It is unique in many ways, most notably for its thick atmosphere, weather patterns, including rain, and its lakes and rivers. It is one of the best places in the Solar-System for a large human colony. It has the potential to support millions, in fact.

And there is, of course, the potential to discover a completely different form of life and biology to that of our own.

Saturn's largest moon, Titan. Left: a true colour image. Right: overlaid with an infra-red view of the surface.

Here's why Titan would be a promising place to build a colony:

• Titan's thick atmosphere and air pressure, that's just above that of Earth's surface, would eliminate the requirement for bulky pressure suits. A suit would simply need to provide warmth and oxygen.
• The hydrocarbon lakes would provide the materials to make plastics that could be used to make all the required structures for living and working.
• The atmosphere would provide excellent protection from radiation and meteorites, and make any leaks or failures of habitats a problem rather than a lethal failure (the indoor and outdoor pressure would be the same and therefore any leaks very slow).
• Drilling into the surface would provide all the water a colony could ever want. And from that could be extracted oxygen, and hydrogen for fuel.
• The low gravity would make return to space relatively easy, and the thick atmosphere would make aircraft particularly easy and economical to fly. Human-powered flight is possible.
• If there is any life on the surface of Titan it is likely to be methane-based, which should mean it would be unable to survive in a human environment. The danger of either life-form infecting the other would be minimal. It's very likely they could coexist without any problems.

There are significant challenges to overcome, but none are in any way insurmountable:

• The surface temperature is extremely low at about -180 degrees Celsius. This is significantly colder than even the coldest locations on Earth. New types of clothing and insulation will need to be developed to cope with this.
• It is currently unknown exactly how detrimental to health living in such a low gravity environment would be. Those born and raised on Titan may well be unable to leave the moon due to the weakness of their bodies. They would certainly never be able to visit Earth.
• The journey time from Earth to Titan would be many years using conventional rocket technology. Unless the ship had a rotating section to generate artificial gravity, and effective radiation protection, the crew would suffer significant health issues. Nuclear propulsion would significantly reduce journey times (this has been researched heavily but never used).
• There is a possibility of water-based life existing in the subsurface oceans. The water extracted for use by the colonists would need to be thoroughly studied and sterilised to prevent contamination and infection.

A view of Titan's surface from an altitude of 70 kilometres

Creating a Self-Sustaining Colony

Landing on airless moons is always problematic due to the need to rely solely on rockets to slow down enough for a safe landing. A large amount of fuel needs to be transported each time. No such problem exists at Titan. The thick atmosphere and low gravity of the moon makes it easy to take advantage of aerobraking techniques and relatively small parachutes (compared to the large parachutes that would be required in the thin atmosphere of Mars).

Because of this very large landing craft, carrying hundreds of tonnes of cargo, or even hundreds of colonists, should be able to land quite easily.

Before colonists arrive in large numbers a sizeable 'town' of habitats will be needed, with power generation and crop growing facilities to enable self-sufficiency. It needs to be well planned, with plenty of redundancy, factories (making use if the liquid hydrocarbons), and with roads and airstrips, and space launch facilities.  There will be no chance of rescue for a colony so far from Earth.

The initial habitats will have to be sent by unmanned missions. They will be built robotically. The first humans will then arrive to expand the facilities and establish what will become the first self-sustaining colony. It's likely that this initial stage would take two or three decades to complete. Essentially, the first generation of colonists would be living in a frontier town, with limited but slowly improving comforts.

A shuttle takes off for a journey to an orbiting station around Titan. Once the colony matures and fuel and manufacturing factories are established there will be regular trips to and from the moon's surface to other colonies in the Saturnian system.

The second and future generations would benefit from the growing colony, with spacious homes, more recreation time, and a growing system of orbital facilities to support life on the surface including communications, and transit to and from the surface and to other colonies that will no doubt have been established elsewhere in the Saturnian system and beyond.

At this point, when survival is routine rather than the main task of each colonist each day, research and scientific discovery can take priority. And it will no doubt focus on the indigenous life that is quite possibly abundant on the moon. Such life could well be complex, with the lakes especially teeming with larger creatures that are just impossible to detect without a surface presence.

A large methane-based complex life-form living in one of the hydrocarbon seas on Titan. The actual life on Titan is likely to be less extravagant than that shown in this image, but it still could have evolved into an array of sizeable creatures.  

Titan could have a diverse ecosystem, far removed from what we know here on Earth. It is the most exciting location in the Solar-System to look for life. There will be no shortage of scientists willing to live there when the time comes to send them.

Robotic Exploration

Before any human colonisation of Titan can start we need to know much more about the moon and its surface conditions. We must send surface exploration missions there at the earliest opportunity.

Some missions have been proposed since 2008, such as the Titan Saturn System Mission. It's an ambitious proposal consisting of an orbiter, a balloon to explore the atmosphere and photograph the surface, and a lander that would splash down in one of the methane lakes.

Another proposal is the Titan Mare Explorer. It's a relatively low cost mission that would put a lander on one of Titan's seas. Unfortunately it did not receive funding, but the lander could end up as the lander for the Titan Saturn System Mission if that ever gets off the ground.

Kraken Mare, Titan's largest sea, seen from a high altitude. NASA is researching the possibility of sending a submarine to explore the sea's depths. If it goes ahead it would be a remarkable mission, and one that has the potential to encounter what could be a complex ecosystem of methane-based life.

Flying in Titan's atmosphere is easy due to it's high density and the moon's low gravity. AVIATR proposes sending an aeroplane that would spend a year flying aound Titan, before attempting a landing. And there is ongoing research into a submarine that would explore Kraken Mare, the largest sea on Titan.

None of the above proposals are ever likely to launch. But there is a proposal that has a reasonable chance of getting full approval. Dragonfly, as it is known, would send a rotorcraft (similar to a quadcopter drone) to explore the moon. It would have the ability to fly at speeds up to 10 metres per second and reach altitudes of up to 4 kilometres. It would land and recharge from its radioisotopic generator during Titan's long nights. While landed it would sample the surface composition. It’s an ambitious and cost effective proposal.

The Dragonfly drone: an essential mission to Titan, and one that could be launched in the next decade

In July 2019 NASA will select either Dragonfly or CAESAR (a comet sample and return mission) for launch in the mid 2020s.

Titan's huge importance cannot be stressed enough, both to help ensure the future of our species by being one of the best places for a sustainable human colony, and by being the likely home of a completely new form of life.

Both of those reasons must ensure that Dragonfly is chosen.

They simply must.

Secret Colonies Beween the Stars

We tend to think of human colonies beyond Earth as being located on planets or moons around stars. The abundant energy resources at such locations certainly make such thinking logical and sensible.

But such locations are also the most visible and desirable. And that makes those locations the most likely places where we may encounter a competing and hostile civilisation.

While we should certainly colonise other star systems, we should also consider colonising deep interstellar space. We should create clandestine colonies; ones that limit contact with the star-bound colonies. Those clandestine colonies would need to be large and self-sustaining, and most importantly  they would need to be 'silent', with no emissions, including light, detectable from even just a single light-year away.

A clandestine interstellar habitat under construction. A rogue asteroid is used to provide the resources required.

Such colonies would be our insurance. They would passively monitor the surrounding human colonies, watching and listening for signs of distress. They would ensure our continuation as a species should our star system colonies suffer natural or unnatural catastrophes.

In an earlier article titled 'Living on Rogue Planets' I explored how life could evolve on planets between the stars, how humans could colonise them and reasons why such planets would be safe from various threats. But finding such worlds would be difficult, and they would be unlikely to be in the right locations. It would be better to create our own rogue worlds in exactly the locations we want, and where they would not drift close to star-systems for millions of years.

Simply put, the clandestine colonies must be located in the right places to be able to remain hidden essentially forever.

But how could such remote colonies be created and sustained?

One possibility would be to create generation starships that would intentionally 'stop' in the void between stars. Such spacecraft would,  of course, need to have very efficient and self-sustaining ecosystems and the means to provide appropriate energy generation. This could be fusion-based, or even antimatter-based. This would provide enough energy to create the light and warmth for growing food to maintain a significant human colony.

Resources would be required for manufacturing replacement parts, new equipment and topping up air and water supplies. Comets from the very outer reaches of star systems (such as the Oort Cloud in our Solar-System) could be redirected to pass close enough to the clandestine colonies to be easily mined.

A comet in the Oort Cloud is moved closer to the clandestine human colony nearby. It's resources will help sustain and grow the colony for centuries or more.

Such redirection would be relatively easy as objects in the Oort Cloud are very loosely bound to the sun due to their vast distance. Those objects are essentially just a nudge away from being truely interstellar.

Of course, the Oort Cloud itself is about one to three light-years from the sun, which puts it in interstellar space. This would enable some interstellar colonies to remain shrouded in darkness and secrecy while having access to a sparse but relatively abundant set of resources.

The Oort Cloud in relation to the rest of the Solar-System and its closest neighbouring star-systems. It would be an ideal location for secret human colonies, with relatively easy to find resources from the mass of comets in that interstellar region.

If such clouds of objects are common around most stars it would make setting up such colonies much easier. It should be an essential component of any interstellar colonisation missions that humans embark upon.

Creating sustainable colonies between the stars will be a formidable task, but it is a crucial one. Those colonies will be our backup, and the skills learned by those surviving (and hopefully flourishing) there will be invaluable as the human species spreads throughout the galaxy and beyond.

Humans on Callisto within 15 Years

Human colonies on the Moon and Mars are almost inevitable, but that is simply because of their proximity to Earth. But the best location for the first human colonies beyond our planet may not be the Moon or Mars. It could well be one of Jupiter's ice moons. The intense radiation in the inner Jovian system is a major problem, but one of the largest outer moons, Callisto, has great potential.

Callisto, the second largest of Jupiter's moons, and the easiest and safest one on which to establish a human colony

As far as human colonisation is concerned Callisto offers much the same resources as the other three Galilean moons, but there is one thing it offers that the others cannot: a low radiation environment. Such an environment, which is still protected by Jupiter's magnetosphere,  means that crewed spacecraft will need minimal radiation shielding, and habitats on the surface of Callisto are possible. On top of that, its old surface indicates that it is geologically stable. And there is also strong evidence of significant amounts of liquid water beneath the surface (which itself contains plenty of water ice).

As well as water ice, the surface is made up of significant amounts of carbon dioxide ice, rock, silicates and hydrocarbon compounds, all of which can be mined to help a colony achieve self-sufficiency (water oxygen, fuel, metals etc.).

Callisto appears to be an almost perfect choice for colonisation, and also as a base to launch the colonisation missions of many of the other outer Solar-System bodies, such as Enceladus, Titan,  Triton, and the trans-Neptune objects beyond.

An aggressive, but achievable, time line for Callisto colonisation is as follows:

• 2019: the Callisto orbiter launched. Construction of crewed spacecraft begins.
• 2020 - 2022: an unmanned supply spacecraft is launched with surface habitats and supplies for the future Callisto colony.

An unmanned Callisto supply spacecraft is prepared for launch in Earth orbit

• 2024: the orbiter arrives and begins detailed visual and radar mapping of the Callisto's entire surface.
• 2025 - 2027: the supply spacecraft arrives and enters orbit around Callisto. Two surface locations are chosen for the first colonies. The equipment for the two surface bases lands at the desired locations. The equipment includes human habitats, power generators, food and food growing bays, drilling machines, and oxygen/fuel creators (to extract hydrogen and oxygen from the surface water ice to create fuel for return journeys, and of course to make oxygen for breathing). The now empty supply spacecraft returns to Earth.
• 2027: the first crewed spacecraft launches with eight occupants.
• 2029: as the empty supply spacecraft arrives back in Earth orbit, the second crewed spacecraft launches, again with eight occupants.
• 2030: an unmanned Europa lander launches from Earth.
• 2031: the first crewed spacecraft arrives in orbit around Callisto. Six of the occupants land on the moon, three at each location, and set up the habitats. The drilling of underground habitats, and mining, begins. The two remaining crew members stay in orbit in the detached orbital station section. The empty crewed spacecraft returns to Earth.

The first colonists explore the crevasses and caves of Callisto

• 2032: The unmanned supply spacecraft leaves Earth orbit and heads back to Callisto.
• 2033: the second crewed spacecraft arrives and docks with the first one in Callisto orbit. Six of the occupants land on the moon and join the earlier colonists. There are now six at each location. The orbital station is enlarged with a new module.  It now has a permanent crew of four. The empty crewed spacecraft returns to Earth.
• 2034: the Europa lander arrives and lands on the moon's surface. The crew orbiting Callisto take control of the Europa mission, using tele-operation to control the surface rover and the penetrator to explore the ocean beneath. They will do this for all future unmanned Jovian missions.
• 2035: the underground habitats on Callisto are now occupied. They consist of large pressurised caves with habitat domes within, and also greenhouses for growing food. Tunneling continues to expand the habitats. The surface habitats are now used solely for science purposes. The first launch from Callisto with two occupants, and using fuel maufactured on Callisto, successfully docks with the orbital station.

Large man-made and pressurised caverns beneath the surface of Callisto would make ideal human habitats

• 2036: the unmanned supply spacecraft arrives. Supplies are sent to the surface colonies and the orbital station, and then the spacecraft heads back to Earth.
• 2037: the third crewed spacecraft with eight occupants leaves Earth and heads for Callisto.
• 2038: the fourth crewed spacecraft launched from Earth.
• 2039: the first baby is born in the Callisto colony.
• 2041 - 2042: the two new crews arrive in Callisto orbit and dock with the orbital station. New modules are added to the orbital station. The now very large station keeps a permanent crew of eight, while the rest head for the two surface colonies. The empty crewed spacecraft return to Earth.

One of the manned spacecraft arrives in the Jovian system and, after a close pass of Jupiter, closes in on Callisto

• 2042: with fuel on Callisto now plentiful regular round trips from the surface to the orbital station begin. Crew rotations are performed, giving all the chance to work on the surface and in orbit.
• 2043: two more children are born in the Callisto colonies.  There are now 27 colonists on the surface.

If the above plan were to be followed there would a sizable and thriving human colony on Callisto within 30 years. As it grows over the following decades humans would have an ideal base from which to launch colonisation missions to other outer Solar-System regions, and from which to conduct science and exploration work, manned and unmanned, from within a much more manageable gravity well.

SpaceX has recently presented its concept for a large and fully reusable interplanetary manned spacecraft. It's a highly impressive proposal, with a long term goal of having 100 or more passengers per trip. It would be an incredibly efficient and fast way of building a colony.

SpaceX's interplanetary spacecraft, which could eventually carry 100 passengers to colonies on Mars and the moon's of Jupiter. The image shows the spacecraft after landing on Enceladus, a moon of Saturn.

Although the initial target planet is Mars, SpaceX has said that the vehicle is suitable for use on the moons of the outer planets, too. With the extreme ambitions of organisations like SpaceX, a colony on Callisto is possible within the lifetimes of many who are reading this.  Let's hope more organisations, and some governments, rise to this challenge.

It is essential for our survival as a species.