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.

Time Travel: Travelling Without Moving

One thing that seems to be almost completely overlooked when time travel is discussed, or used within a work of fiction, is location (the only example I can find that mentions it is this Dilbert cartoon strip).

This is a critical omission.

If someone was to go backwards or forwards in time just one minute they would not find themselves standing in the same place on Earth in relation to their original surroundings. They would most likely find themselves many kilometres up in the air, or embedded in rock deep underground. This is because the Earth is rotating and moving through space at many thousands of kilometres per hour as it orbits the sun, which is also moving in relation to the center of our galaxy, and so on.

The classic image of a time machine: something a person could sit in, type in a date, and then travel to that time at that particular location on the surface of the Earth. But the problem with this concept is that the Earth would not be in that location at the destination time period.

To put it simply, we are constantly moving, and so travelling in time will mean we travel to a time before the Earth was in its current location, or to a time after it has moved on. If someone travels in time just a few days they will find themselves millions of miles from Earth in deep space. If they time-travel a couple of decades they will find themselves far beyond the Solar-System in interstellar space.

Time travellers waiting to enter the machine that will send them through time. If such a machine was possible the travelers would need to be on board a spacecraft as they are likely to emerge in deep space. This is a point never considered in fiction.

But the issue of location should not be viewed as a problem. Far from it, in fact. It should be viewed as a major advantage. If we can eventually master time travel in some form it could well be the easiest and fastest way to travel interstellar distances, if only along the path the Earth will take, or has taken.

It's an incredible prospect. But can it ever be possible?

Travel into the future can be achieved, in principle, using the time dilation effect described in Einstein's theory of relativity by travelling close to the speed of light. Travelling to the past would require velocities that exceed the speed of light. This is theoretically possible using cosmic strings, wormholes, or an Alcubierre drive. A huge amount of energy would be required, which would need exotic matter, particularly matter with negative mass. It's all very complicated, and not well understood. But our understanding will improve in this area, as it always does. Sometime over the next few centuries the generation and control of such vast amounts of energy may well be harnessed, and then a device that would enable time travel could be constructed.

Assuming such a device could be built, perhaps in the form of a large orbiting facility that could transport large spacecraft across time, what would be the best way to use it?

An orbiting time portal, capable of transporting large spacecraft to other times

Sending a human crew through such a portal would be an immense undertaking.

Such an expedition would essentially be a one way trip to an unknown destination, with no possibility of return or help once the journey had begun. The spacecraft would need to be interstellar in nature, with the ability to sustain its crew and passengers for decades if necessary, as there would be no way of knowing how close a viable planet would be at the time of arrival. At best we could target the vicinity of an appropriately aged star system that we think has a good chance of hosting an Earth-like planet. And due to the impossibility of knowing the conditions of any planet found for colonisation, the ship would need to contain all the resources required to land and set up a colony in a variety of climate conditions.

However successful the mission is, no one left on Earth is likely to ever know about what happened.

If we just want to ensure the continuation of Earth life we could simply send thousands of probes to different times along the Earth's journey path and have them 'seed' the most Earth-like planets they find with the building blocks of Earth life. One day, a billion years later, perhaps a technologically advanced species would evolve on some of those worlds, an incredibly distant relative of our species.

A probe, sent through time to seed suitable planets with Earth life, arrives and begins observations

I use term 'simply' in a relative sense as this kind mission would still be difficult and complex. The probe's would have to be smart, with artificial intelligence beyond what is currently possible. They would need to observe and detect the most suitable planets or moons within their range, plot and execute a suitable trajectory, and despatch their payloads without any help from scientists on Earth.

Perhaps there are civilisations out there right now based on Earth life, evolved from simple life forms sent back through time by our descendants. If we do eventually master time travel then perhaps we go on to seed worlds a billion or more years ago, when other galaxies occupied our location. Perhaps a bipedal species, reptilian, mammalian or avian (or something extraordinarily different), will one day build a time portal to send explorers to our galaxy.

Perhaps they will find Earth and the ultimate origin of their species.

Or perhaps they will seed Earth and be the origin of ours.

Space Planes - Where Are They?

Space planes are hypersonic craft that can launch from a runway and reach and operate in space, and then return to land as a normal aircraft would. Such vehicles were first proposed many decades ago, and by now we should have a regular service in place, providing people and cargo with a rapid, economic, frequent and convenient method of getting into space. It should be a service that is considered normal, ordinary, and quite routine, just like the intercontinental flights that we take for granted right now.

Star-Raker: An early NASA/Rockwell space plane concept from the 1970s

But we are still decades away from such a service. Why is that?

The incredible lack of government support is the primary reason. Without the financial backing that only those organisations can provide, such immense projects have little hope of coming to fruition. It seems that, apart from a few small subsidies, private enterprise is left to fund such things. And they do remarkably well, all things considered.

Skylon, a British space plane concept, in flight

The most promising space plane right now is Skylon, in development by the British company, Reaction Engines. If funding is maintained, a full size version of the unique engine for the plane could be tested as soon as 2019, and actual unmanned test flights could begin in 2025. Although designed primarily as a means to deliver cargo to various orbits, Skylon can crucially be configured to carry a passenger module for 30 people. It would revolutionise how we get people off the planet, and it would be a major step forward in our ability to set up colonies away from Earth. This video shows how Skylon would operate.

Skylon docked to an orbiting station

Regular shuttle services serving the Moon, Mars and beyond could be set up with a station in Earth orbit, and Skylon space planes, based at many locations around the world, could be a very efficient means of getting equipment and personnel up to the station. Within a couple of decades we could have hundreds of people in space, travelling too and from working colonies on at least two other bodies in the Solar-System.

Such a scenario is highly achievable, and with just a little more support from governments. For example, for Skylon to be developed into a fully functioning system it would cost just over 7 billion British pounds. That is a small amount for a government, and the potential economic benefits would far exceed that.

The UK government has committed to renewing its Trident missile submarine nuclear deterrent, which would cost well over 100 billion pounds over its 40 year lifespan. It's incredible that such funds can be found for a system (as necessary as it may be) that is designed to threaten and cause immense mass destruction, but something that would cost a fraction of that, and something that would be a huge benefit economically and for the future of our species, is considered for nothing more that a paltry handout.

A Dreadnought Class submarine, which will replace the UK's Vanguard Class submarines to become the country's new nuclear deterrent. Unfortunately such a system seems to be a necessity. But what if the vast cost of such a system could be put into a space plane service instead?

Of course, a space plane service to Earth orbit, while incredibly beneficial, should only be the start. A true space plane service would allow passengers to leave Earth and travel to another planet's surface in the same vehicle, with nothing more than a refueling stop on the way.  Such a space plane would need to be configured for interplanetary voyages that would take many months or years to complete. Only a few passengers could be on board, and they would need accommodation and supplies to sustain them. It is likely that at first only the richest or most important passengers would be able to use such a service. It would be the equivalent to luxury yachts we see today. This is no bad thing. Encouraging the very wealthiest individuals and organisations to pay for such a service is a good way to get the funds to continue development and expansion, which will ultimately result in the service (albeit a much less oppulent version of it) becoming available to the general population.

A luxury space plane about to dock with an Earth-orbiting station to prepare for its onward journey to the Moon. Artwork by Alex Brady.

For the interplanetary phase of a journey the space plane could dock with an interplanetary propulsion system that would take it to orbit around its destination. The propulsion system would then remain in orbit and be serviced and refueled ready for another journey. With many such propulsion systems in orbit around key destinations a truely comprehensive interplanetary travel service could be offered, for both passengers and cargo. Colonisation of the Solar-System could then proceed with relative ease.

Such a service would require massive investment by governments and private organisations, but it would still be a small fraction of the amount spent on defence and weaponry. Humans need to fight against their primal instincts that seem to lead us down such negative paths and see the extinction that we face as a species if we do not colonise the Solar-System and beyond.

We need to stop funding our own destruction and

fund expansion and survival beyond Earth instead

A passenger space plane capable of carry over a hundred people docks with an orbiting station. Such a space plane service is required if humans are to create significant colonies elsewhere in the Solar-System. Concept by Alex Brady.

An extensive space plane service to Earth orbit, and to the Moon, should be the first priority of major governments to kickstart the development of permanent human colonies away from Earth. There are people with the right vision, drive and skills alive right now that could build it. And it could be achieved within two decades with the right motivation and funding.

As a species we would be foolish indeed not to develop such a capability as soon as we have the means to do so.

Sanctuary Entrance Found on Mars

It's quite possible that NASA has found the entrance to an underground sanctuary on Mars.

In my earlier article, 'Where Did All The Martians Go?', I discussed the dramatic change in the climate of Mars, and the need for as many of its inhabitants as possible to evacuate the planet. But most would have had to stay. I wrote about the huge underground shelters that would be required: long term havens that would enable millions to survive for many generations until they too could be evacuated, or until the planet's atmosphere and environment recovered.

The entrance to one of those havens may now have been discovered.

Near the south pole of Mars: the possible entrance to a huge underground survival facility, capable of sustaining thousands, if not millions, of Martians as their climate failed and surface survival became impossible.

Found near the south pole of Mars by NASA's Mars Reconnaissance Orbiter, the hole, hundreds of metres in diameter, is possibly one of the main entrances to a vast underground complex. It was probably used for vehicles, including aircraft and spacecraft.

And there are likely to be many more such entrances, large and small. One example can be found on the slopes of Pavonis Mons, an extinct shield volcano in the Tharsis region of Mars near the planet's equator. Shown below, the hole could have been intentionally created to allow Martians to utilise the lava tubes of the extinct volcano to access a network of underground sanctuaries. Its equatorial location would have been very useful for more economical launches of spacecraft.

Such holes can be naturally formed. This one is on Pavonis Mons, and is thought by some to be the collapsed roof of a lava tube. It could also have been intentionally constructed as an entrance to a massive shelter beneath the extinct volcano.

There has been no real evidence of unnatural surface activity on Mars, which suggests three possibilities: all of the inhabitants have now left, they are surviving solely by subterranean means, or they have all perished.

The first possibility is the most unlikely. The effort to evacuate millions of inhabitants from the surface of a planet would be a gargantuan undertaking for even the most advanced civilisation. While a huge number of Martians will indeed have left the planet, most would have had to remain. Even if evacuations continued for thousands of years, which is a possibility, the remaining population would have continued to renew as generation after generation were born. And most may have wished to remain, having physically and mentally adapted to their subterranean existence.

The second possibility of the inhabitants still surviving underground right now also seem very unlikely, at least in large numbers. There is no evidence of the emissions that would be observable if there was a massive population still living there, even underground. Of course, they could be withholding their emissions to prevent detection and living in a perfectly contained and self-sustaining biosphere, but this would be almost impossible to achieve to a level where no emissions at all were made.

A vast underground Martian city, home to possibly millions when war and climate change rendered the planet's surface uninhabitable. Could there still be millions of Martians living in such cities, undetectable within a perfectly contained biosphere?

Unfortunately the most likely possibility is that all the inhabitants left in the subterranean facilities eventually died. If the sanctuaries were designed well enough they could have survived for thousands of generations - a remarkable achievement. But many millions of years later the likelihood of the sanctuaries still functioning is minuscule. At best there may be a few hundred Martians still eking out an existence in the huge and now deserted underground cities. If so it must be a lonely and grim experience.

A cavernous space like this, clearly artificial, could be found beyond the sanctuary entrance. While the sanctuary is most likely uninhabited now, there could still be a small community of Martians living there. We need to take great care when we finally start to explore such places.

The discovery of the huge potential sanctuary entrance near the south pole of Mars reinforces the need for a substantial human colony to be established to enable its exploration. If there is indeed an abandoned network of vast underground cities on the planet we need to explore them as soon as possible.

The first colonists on Mars explore one of the entrances to an abandoned underground city

As well as the thrill of discovering the remains of a lost extraterrestrial civilisation (with the remote potential of encountering surviving members of that civilisation), we would have the opportunity to find out exactly what calamitous events happened millions of years ago which forced the planet's population to retreat underground.

Thrilling indeed...

The Evacuation of Venus

Venus may once have been teeming with life.

The planet, almost the same size and composition as Earth, had oceans and an Earth-like atmosphere for almost two billion years of its history. It's long days, which would have had the day side exposed to the sun for more than two months at a time, would actually have kept the planet cooler by increasing evaporation and rainfall, which would have shielded the land from the strong sunlight.

Venus more than a billion years ago, before climate change rendered the planet uninhabitable

There would have been ideal conditions for life to not only evolve, but thrive. And such conditions could well have lead to the evolution of an intelligent lifeform, and the development of an advanced technological civilisation.

And there appears to be some evidence for that. Studies of the detailed radar maps of the surface beneath the planet's dense shroud of cloud show what look like immense surface structures. They could well be the remains of cities, or the launch facilities that were abandoned after the last inhabitants evacuated their dying world.

There could be many reasons why Venus became uninhabitable. It could have been the result of the activity of the civilisation: war, excessive use of fossil fuels etc. (which if proven could be a very valuable lesson for our civilisation). But it is more likely to have been natural in nature. The sun has become significantly hotter over the last few billion years. This would eventually have evaporated away Venus's oceans, thickening its atmosphere and trapping more and more heat in what would have been a runaway greenhouse effect. It would have been an event that was unstoppable, even for an advanced civilisation. Fortunately such a civilisation would have been well aware of the looming crisis, and would have had thousands of years to prepare for its evacuation. This makes it highly likely that a significant number of inhabitants would have been able to leave and set up colonies elsewhere in the Solar-System, and even beyond.

If the warming of the sun was not enough, there is strong evidence that Venus has suffered high levels of volcanic activity, and on a global scale. In the past the planet has suffered periodic and massive resurfacing events by lava flows. The most recent could have been 500 million years ago. Such an event would destroy most of the evidence of a civilisation, and multiple such events would explain the transformation and thickening of the atmosphere. Combined with the warming of the sun, life on Venus was doomed.

One billion years ago: Venus is finally rendered uninhabitable by volcanic activity and the warming of the sun

Ultimately we may be better off looking for evidence of an ancient technological civilisation on Venus elsewhere in the Solar-System, and most likely in the asteroid belt (see my previous article: 'Pre-Human Technology in the Asteroid Belt'). An advanced civilisation with knowledge of its home planet's impending demise would certainly have tried to escape, and the asteroids would provide a relatively easy and abundant source of materials for habitat and spacecraft construction.

Having said that, we need to explore Venus in much more detail, especially on the surface, and below it. So far only the Russian Venera landers in the 1970s and 80s have successfully returned images and data from the surface of the planet, and they only survived the hellish conditions for a few hours.

Left: an image of the surface of Venus, taken by the Russian lander Venera 13. Right: the lander before launch

A rover is required, one that could survive for months or more. NASA's proposed landsailing rover is the most promising. With recent success in developing electronics that can function under the extreme pressure and heat on Venus's surface, such a mission is looking more and more likely to succeed. And that means it is much more likely to get the funding to go ahead. If it does, it could be launched in about ten years.

NASA's proposed landsailing rover, which would use Venus's dense atmosphere and strong winds to move it across the surface. It's expected that the rover would survive for about fifty days - a great improvement on the static Russian Venera probes that survived for a couple of hours at most.

Amazingly, there may still be life on Venus. The last remnants of the planet's once complex biosphere may be surviving in the clouds as dark streaks of microbial life. Russia and the U.S. are working on a mission that could prove such a theory, which will probably include a solar-powered aircraft that would target the dark streaks and analyse them.

We may discover that any life in the clouds of Venus is related to life on Earth, which would indicate a common ancestor. Perhaps the Venus evacuees migrated to Earth...

Venus is fascinating and brutally hostile place. There is so much to learn, and the confirmation of the existence of a civilisation that once lived there would be astounding. We need to get a sustainable mission down to the planet's surface as soon as possible. What we find could be invaluable and essential to the future of our species.

Pre-Human Technology in the Asteroid Belt

I've discussed before the possibility of an advanced prehistoric technological civilisation existing on Earth. But due to geological activity any evidence of such a civilisation is likely to have been lost due to continental plate subduction and other processes. Evidence of a pre-human civilisation from hundreds of millions of years ago will be buried many kilometres deep, and even destroyed completely by the immense pressure and high temperature found at such a depth.

We need to look elsewhere.

An ancient advanced civilisation in Antarctica. Perhaps one of the few benefits of global warming will be to reveal evidence of such lost civilisations. Studying such civlisations could reveal the secrets as to how they left the Earth, and where they went.

If a civilisation had developed to a level high enough for space travel then the moon would be an obvious place to look for signs of its existence, but even there geological processes may have destroyed any evidence. Volcanic activity may well have been occurring on the moon as little as a hundred million years ago.

Fortunately there is another region in the Solar-System where such evidence, even from a billion years ago, could be preserved. Geological activity is almost completely absent there. That region is the asteroid belt.

Of course, asteroids are not completely free of erosionary forces. Impacts would destroy surface artifacts over time, but unlike on Earth the results of activities beneath the surface, such as mining or habitat construction, would be preserved almost indefinitely.

This makes objects in the asteroid belt the prime target for research into pre-human civilisations.

And already, the first purpose built asteroid mission has found what could well be evidence of extensive mining activity.

Ceres

NASA's Dawn mission to the two largest asteroids, Vesta and Ceres, is the only significant asteroid belt mission so far. The probe is still in orbit around Ceres and will remain there indefinitely. The intriguing bright spots seen on Ceres could indeed be evidence of mining activity.

Evidence of extensive mining activity in the Occator crater on Ceres

There is also an unusual mountain, named Ahuna Mons, in another region of Ceres that could be a huge mound of excavated waste material, much like the slag heaps found near mines on Earth.

A mountain of excavated material on Ceres

Such discoveries on Ceres show that it must be explored in much more detail from the surface. A lander, rover, or even a manned mission is needed.

If one of the first asteroids to be orbited by a dedicated probe throws up such compelling evidence of a pre-human civilisation, it's highly likely that others will, too.

16 Psyche

Another very interesting body in the asteroid belt is 16 Psyche. The asteroid is unique in its composition - almost pure iron and nickel. Nothing else like it has been discovered in the Solar-System. It's possible that it once had an exterior of rock and ice, and that it was once a planet, and that that exterior was blasted away completely by an unfortunate set of collisions with other massive objects. But the likelihood of that is very small.

16-Psyche - possibly the most heavily mined object in the Solar-System

Another explanation must be found. It could well be that the rocky outer shell was intentionally removed, and if that's true it would probably be the most incredible evidence of mining that we could ever find. It's no surprise that NASA has recently announced it will be sending a probe to 16 Psyche, which will arrive in 2030.

If such a huge amount of material was mined it would be enough to construct thousand of starships and habitats, certainly enough to provide a refuge for millions for a civilisation that needs to evacuate its home world. 16 Psyche could be hiding the evidence of the ancient technological civilisation that lived on Earth hundreds of millions of years ago.

Humans explore one of the last surviving tunnels on 16 Psyche

The evidence of a civilisation that we may find in the asteroid belt may not have originated on Earth, of course. It could have been from Mars or even Venus, both of which seem to have suffered catastrophic climate changes. Such changes would have prompted any advanced civilisation on those worlds to do everything possible to preserve its species. It could have set up home on Earth (it could have formed one of the long extinct Earth-based civilisations), but at that time the Earth's atmosphere would probably have been unsuitable. What's more likely is that the species utilised the vast resources of the asteroid belt to construct interstellar starships (see my earlier article on the evacuation of Mars).

It's thrilling to think that when we do identify life-bearing planets around other stars (which I'm confident we'll do within the next few decades) the life we're observing may well have originated in our Solar-System.

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.