The reality may, however, be much worse. The Sun has burned for nearly five billion years, but it has not burned steadily. It has continually grown hotter throughout its life, and continues to do so today. As the sun ages, Hydrogen is converted to Helium and the star’s volume contracts. This causes a gradual warming that could, according to some researchers, bring about the end of life on Earth within a billion years. The ecosystem of the Earth is fragile, and within the next billion years it is estimated that the amount of energy the Earth will get from the Sun, which is directly related to the Sun's temperature, will increase by 10%. This seemingly minor increase in energy output will spell doom for our planet.
“When scientists examine computer models for a future climate under the revved up Sun they see a Greenhouse effect gone wild. The polar ice caps will be history, and much of the fertile land will be flooded. As the Sun's output continues to increase so much water is evaporated into the atmosphere that even the stratosphere gets wet. Sunlight can then break apart the water molecules allowing the hydrogen atoms to escape into space. No more water, no more life. The world as we know it will have ended.”
The only way to escape what amounts to the death of our Solar System is to have previously-established extrastellar human colonies in place. However, the distance that exists between Sol and even our neighboring star systems is prohibitedly massive. With our current understanding of physics, (
), as an object approaches the speed of light it takes an infinite amount of energy to further increase its speed. As such we can never travel as fast as light. The nearest star system to ours is 4.5 light years away, but when moving slower than light this trip takes quite a bit longer. Even if we reach this system the odds of it having a habitatble planet are low. We know that the ideal circumstances to create earth-like planets capable of sustaining life are rare, as even our own world hangs on a razors edge of sustainability. Give or take 2% of the Earth’s distance from the sun and it could not sustain human life.
Sending an unmanned probe to another star is a daunting task on its own, but sending an Ark filled with passangers, livestock, plantlife, food, oxygen, water, enginers capable of moving all this and the fuel needed to run these engines, seems impossible by modern standards. Any current engine would require more thrust than it can produce simply to propel the fuel necessary to carry it over such a vast distance. As such interstellar travel is impossible with current technology. However, there are several theoretical technologies in the works that could be used to propel man to new systems.
Closest to modern technology, Nuclear Pulse Propulsion utilizes atomic explosions within the ships engine to propel a craft forward. The energy produced by these miniature cataclysms is vented out the ships exaust, producing tremendous thrust. However this method requires a great deal of matter to be carried onboard to sustain the reaction and as such it is less than efficient for traveling interstellar distances.
Through technological advances possible in the foreseeable future Fusion Rockets could become a viable method of transport. Reactors using fusion reactions many fold more efficient than the fission reactions of Nuclear Pulse Propulsion would be used to power ship's drives. However this method still requires fuel be carried onboard, even if it is far less than with Nuclear Pulse Propulsion.
A far more theoretical technology than Fusion, Antimatter Rockets could be used to facilitate interstellar travel. It is not yet known if Antimatter Particles can be harnessed or manufactured in a productive and technologically viable way though, and the quantity needed to power interstellar travel, even when dealing with such high-energy particles as these, may never be available.
A solution that bypasses the issue of an engine having to propel its own fuel is Beamed Propulsion making use of Light Sails. With this method a ship literally ‘rides’ a beam of light fired from Earth, traveling as fast as half the speed of light. This would pose many advantages, amongst them the Time Dilation (A perceived slowing of time that occurs for travelers moving at speeds approaching the speed of light) effect that would be experienced by passengers and the need of zero fuel onboard the ship. However this method would make the Ark in question completely dependent on its home planet over its long journey. Political shifts, wars, ecological or manmade disasters, anything that caused the laser-transmitter powering the Ark on its journey to stop transmitting would strand the Ark, dooming its passengers. This method leaves the Ark wholly dependent on Earth and the humans therein, and this defeats the purpose of the independent, self contained Arks. As such Light Sails could be very useful for unmanned probes, who exists to beam information back to earth, but Arks would require a more self-contained form of propulsion.
On the topic of time dilation, it is worth noting that at any speed approaching the speed of light, our current understanding of phyics would suggest that those onboard would experience a shorter travel time than actually occurs to an outside observer. However, this effect is poorly understood, and to gamble on this when deciding what supplies to provide for a ship would be a dangerous gamble. In addition, to recieve any extensive effect speeds well beyond what current technology, and even the near-future or distant-future technologies discussed here, could produce.
Within twenty light years of Sol there are 59 stellar systems containing as many as 81 stars, but there is no guarantee that any of these contain planets viable for colonization. As such humanity must look further. Unmanned probes which themselves take thousands of years to perform their mission must be sent to all of these neighboring star systems, and many beyond. Because of the time necessary to perform a proper survey of a Solar System, individual probes, like the Colony Ships that will follow them, must be aimed at specific systems. It takes a great deal of time for these vehicles to slow sufficiently to ‘dock’ in a system, a great deal of time to perform their surveys, and a great deal of time for this information to reach Earth. This is in addition to the original travel time the probes must endure simply to reach their target systems. As such these probes must be sent out thousands of years before the Arks, and a useable planet must be identified before any Ark is sent. The idea of a wandering Ark, going from system to system searching for a new home, amounts to playing Russian roulette with the species, only thousands of chambers have bullets and only a few are empty.
Once a probe has relayed back to Earth the position of a habitatable planet, a series of probes must be sent to measure everything about it. Soil, water, and air samples must be studied, as well as ambient radiation and any indigenous flora or fauna. Sending an Ark only to discover a deadly alien microbe in the atmosphere once humans set food on their ‘new home’ could spell the end of humanity. As such we must diversify our colonization plans. As many colonizable planets as possible must be located, and Man must send out as many Arks as we can.
However, sending an Ark is a great deal more taxing than a probe. Arks must be able to carry a human population large enough to ensure genetic diversity in a Colony’s population. Scientific estimates suggest that as few as 160 people sustain a viable gene pool, but due to genetic drift as well as the possibility of disasters on board the ship or on the colony, at least a thousand should be sent. Due to the distance an Ark would have to traverse to reach any system but our most immediate neighbors it is unlikely that, even with time dilation effects, the journey could be completed within a human lifetime. As such these Arks would need to be prepared to house multiple-generations of humans, with the decescendents of the initial crew arriving at their destination.
This flow chart shows the current standards for Nasa life support systems. The flow chart for a multi-generational interstellar Ark would be far more complex. It would likely be necessary that nothing be vented overboard, as each precious resources would need to be recycled in some form. These ships would have to be able to perfectly recycle their fuel, oxygen, food and energy. Even light would need to somehow be reused, as the nature of the journey would preclude using any fixed solar source.
A multi-generational interstellar Ark would need to be a paragon of sustainability to be even remotely viable. It would need to grow its own food, produce its own oxygen, maintain the temperature and pressure onboard, shield its inhabitants from harmful cosmic radiation and particles, all the while carring them safely and steadily to their destination, and all of this over thousands of years. From an engineering standpoint this is a nightmare. If a single system were to fail, or even lose a fraction of its efficiency, the mission would be doomed. Over such a long time period the tiniest leak or break in the system would eventually amount to a cataclysmic issue.
As such the continued maintenance by a crew that is changing each generation would be necessary. This raises social issues as well as technological and logistical ones. New generations of crew mates must be trained in maintaining the ships systems. The political and social climate on the ship must remain stable enough to allow these maintenance functions to continue over thousands of years. Also, the skills necessary to colonize a new planet, skills which will go unused through the entire journey, must still be passed on from generation to generation so those who finally reach their destination will have the skills they need to survive.
Once mankind has breached the barrier and made themselves, through technological prowess and the strength of human will, an interstellar civilization, our true history can begin. All human history to date and everything that has occurred to us up till now has been viewed from the perspective of our single tiny planet. Once we can call ourselves a truly space fairing race we will be able to consider ourselves genuine denizens of our Galaxy. If, however, we cannot escape our planet before its time has run out, we will become less than a memory, with nothing more than fading radio waves to mark our passage. This is a real issue, and from the Sun’s perspective, if not Earth’s or Man’s, most of our time to take action has already expired. If humanity does not start considering these issues and working towards solutions to them within the next millennium, it may be too late to do the work necessary for safe colonization. We may be forced into a last minute gambit, trusting our species on an Ark traveling the heavens with an unknown destination. This uncertain salvation would bring little hope to those left behind on a doomed Earth.
A few comments on your essay James
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