Why go fast when you can go big? That's the basic idea of Generation Ships (Worldships, Interstellar Arks, Arkships, etc.), spacecraft large enough to support multiple generations.
Host | Matthew S Williams
On ITSPmagazine 👉 https://itspmagazine.com/itspmagazine-podcast-radio-hosts/matthew-s-williams
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Why go fast when you can go big? That's the basic idea of Generation Ships (Worldships, Interstellar Arks, Arkships, etc.), spacecraft large enough to support multiple generations.
The ships typically consist of rotating sections to simulate gravity and natural environments to accommodate crews for hundreds or even thousands of years in interstellar space.
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Resources
World Ships: Feasibility and Rationale: https://arxiv.org/pdf/2005.04100.pdf
What Will It Take for Humans to Colonize the Milky Way? -Kim Stanley Robinson (Scientific American, 2016): https://www.scientificamerican.com/article/what-will-it-take-for-humans-to-colonize-the-milky-way1/
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For more podcast Stories from Space with Matthew S Williams, visit: https://itspmagazine.com/stories-from-space-podcast
Episode 52 - Generation Ships
The authors acknowledge that this podcast was recorded on the traditional unseeded lands of the Lekwungen Peoples.
Hello, and welcome back to Stories from Space. I'm your host, Matt Williams. And today, I wanted to get back into the subject of interstellar travel - going Interstellar, that dream of countless generations.
The hope and prospect of sending human beings not just robotic ships, but actual crewed spacecraft to neighboring star systems. Hopefully, ones that have been well explored so that we know that there are habitable planets there or planets we can build a home on and gradually expand the scope and reach of human civilizations giving rise to new identities, and quite possibly learning of new life forms, even making contact with other civilizations.
Now, this hope has been with us for a very long time humanity's dreamt of traveling to the stars, ever since we realized what they really were, they're not just pinpricks of light in the night sky. They're not just a beautiful thing to behold, each and every one of them corresponds to a distant solar system, quite likely, with its own system of planets, potentially habitable ones, and given the sheer number of them between 100 and 200 billion in our galaxy alone.
And that's not even taking into account the over 2 trillion galaxies there are in our universe, knowing that the universe is so infinitely large, knowing that the possibilities are so very infinite. We're determined to explore Of course, there's always been the other shoe in this conversation, which is that the energy requirements alone to reach another star are absolutely immense.
Our level of technological readiness for achieving such missions is nowhere where it would need to be and all possible means that have ever been proposed are either dependent upon exotic physics immensely massively and prohibitively expensive, or both. And much like the tyranny of the rocket equation, interstellar travel is also plagued by the competing needs for velocity or acceleration, aka delta-V, and payload mass.
Basically, the farther you intend to send this spacecraft, the more propellant it's going to need, which in turn creates a significant issue of mass and size for the spacecraft, which in turn necessitates more power and more acceleration in order to get it moving at a respectable speed, so that it might actually reach its destination in a realistic amount of time. And so this is where proposed solutions have generally run aground or just jumped the curb, so to speak.
They've either proposed that we can generate significant velocity for a spacecraft by harnessing something truly exotic like matter-antimatter reactions, detonating nuclear warheads, and harnessing the energy released from that to generate acceleration, fusing together deuterium or hydrogen pellets in order to release a tremendous amount of energy, or, in the case of the Alcubierre Warp Drive, harnessing the Casimir effect, and some highly as-of-yet still theoretical physics in order to exceed the speed of light, but without violating general relativity.
And in every single case, it either relies on future advancements, significant ones in some cases, or it just is absolutely unrealistic. As far as cost assessments go. However, there have been other proposed solutions that have gone in the opposite direction they said, rather than trying to go really, really fast, why not settle in for the long haul and build spacecraft that are large enough and outfitted with the necessary facilities, so that multiple generations can live and grow and carry on in the voyage.
And these go by the names of Worldships or Generation Ships, Interstellar Arcs have been used as well. And basically, the idea in its own way is a brilliant capitulation to the tyranny of relativity and the fact that space is just so monstrously huge. If you can't go fast, go slow and bring everything you need to enjoy the ride.
First off, any talk of interstellar travel has to acknowledge the fact that humanity actually has placed spacecraft into interstellar space already. We have technically gone Interstellar, but it's only been with robotic probes and ones that have been moving, by our standards very, very quickly, but by cosmic standards, exceedingly slow.
And these are the Pioneer 10 and 11 spacecraft in the Voyager 1 and 2 probes, and most recently the New Horizons mission. And these launched from Earth in 1972, and 73 for the Pioneer missions. 1977 for both Voyager craft, and 2006 for New Horizons. And as of the present day, these missions are either in interstellar space or will reach it within the coming years.
However, at their current speeds, these missions are not expected to reach the nearest star system, Proxima Centauri, part of the Alpha Centauri trinary system for another 16,000 to 34,000 years. And this really highlights how challenging interstellar travel would be. Robotic space probes that had the most advanced chemical propulsion when they launched, and which had the benefit of gravity assist maneuvers, they are not going to be reaching another star system for millennia.
And if we even begin to contemplate the idea of sending crewed spacecraft to another system, we automatically have to acknowledge, well, those have to be scaled up way beyond any of these probes. They need to have the living spaces, the storage spaces, and the propulsion systems, which are very, very large, and the propellant tanks, which would need to be even larger in order to accommodate the crew and to generate enough delta-V in order to break free of the Solar System at some point.
And as I said, while several proposals have been made, they are well beyond the realm of feasibility today. And this is where the idea of a generation ship really comes into play. And like most proposals for space exploration and space settlement, generation ships are a very time-honored idea. And proposals really go back to the late 19th century well before the dawn of the space age.
And the earliest known example was in a book by John Monroe, who was a science fiction author and an engineer. And it was called A Trip to Venus, and it was released in 1897. And in
this book, he described how humanity would become interplanetary and even interstellar one day. And the description he made was:
“With a vessel large enough to contain the necessities of life, a select party of ladies and gentlemen might start for the Milky Way. And if all went right, their descendants would arrive there in the course of a few million years.”
And that description sounds absolutely like the concept of a generation ship which Robert A. Goddard, the American aeronautics engineer and considered one of the forefathers of rocketry, proposed in 1918. And if his last name sounds familiar, it's probably because NASA's Goddard Space Flight Center is named in his honor. In any case, the essay he wrote in 1918 was titled “The Ultimate Migration.”
And he explained in this book how interstellar travel could be harnessed using intra-atomic energy, or placing the crew in a state of suspended animation. And as he put it:
“Will it be possible to reduce the protoplasm in the human body to the granular state so that it can withstand the intense cold of interstellar space, it would probably be necessary to desiccate the body more or less before the state can be produced. Awakening may have to be done very slowly, it might be necessary to have people evolve through a number of generations for this purpose.”
He also explained how a pilot would be kept in stasis and would be awakened periodically to make course corrections conduct maintenance and so forth. And he even went on to say how a spacecraft of this kind could actually be fashioned by an astronomical body such as an asteroid or small moon. And last, he indicated that the energy requirements for the crew and ship could be met with a combination of hydrogen and oxygen, fuel and solar energy, which very accurately predicted what future spacecraft would rely on solar panels and liquid hydrogen, liquid oxygen fuel.
And once again, credit is owed to Konstantine Tsiolkovski, another one of the forefathers of rocketry and considered the father of Soviet-Russian rocketry. And in his seminal essay, “The Future of Earth and Mankind” released in 1928, he described such a ship and even went as far as to call it a Noah's Ark. And the ship would be self-sufficient and would maintain crews for many generations.
But in his proposal, and this is really what separates generation ships from, say cryoships, is that the crews would be awake for the journey. Though centuries or even millennia would pass, the crews would live out their lives as they would on Earth. They would study, eat, drink, play, and have children, and they would do this all aboard the spacecraft generation after generation until they finally reached a new world.
Other examples include one of Robert Heinlein’s earliest novels titled Orphans in the Sky, which he released in 1941. And the story takes place aboard a giant ship called the Vanguard, which
is lost in space. And generations after the piloting officers were killed. The descendants have forgotten that there even in ship they believe that this is the world as it exists.
And in 1964, Dr. Robert Enzmann proposed fusion-powered interstellar spacecraft. And this was the most detailed concept of a generation ship to date, and is named after him the enzyme starship, and it would consist of a spherical section in the front measuring about 300 meters or 1000 feet across, which would contain all the deuterium fuel for the voyage, and a long cylindrical habitat connected to it with the propulsion section at the rear.
And fans of science fiction would recognize the artistic renditions of the ship, which were featured in Analog Science Fact and Science Fiction on the cover of their 1973 issue. And in that same year, the famed author and famed science communicator Arthur C. Clarke released his novel Rendezvous with Rama, which is perhaps the best-known example of a generation ship but in his story, the generation ship is, in fact, extra-terrestrial in nature.
It consists of a giant cylinder in space, it's traveling through a Solar System, apparently on one leg of its journey to a distant star. And astronauts boarded. It's a wonderfully interesting and detailed story of how they are discovering the self-contained world inside and all the machinery and building materials, organic and otherwise, that will go into resurrecting the species and once it reaches its destination, and famous science fiction author Ursula K. LeGuin, author of the Left Hand of Darkness and Dispossessed, she offered her own very insightful take on the idea of intergenerational space travel.
And this was in 2002, in a book titled Paradises Lost. And again, it takes place aboard the ship where after many generations, the people aboard the ship have lost perspective. And rather than forgetting that they're aboard a ship, there's a new religion where people believe that they are headed for eternity, rather than another planet, they've come to interpret their mission as a spiritual one.
And last, but certainly not least, and quite possibly the most rigorously detailed treatment of the idea was by Kim Stanley Robinson, and his 2015 novel Aurora. And this takes place aboard an interstellar generation ship of the same name. And it contains all of the Earth analog environments that would be needed to replicate Earth's biome. And these are stored in two rotating tortoises that simulate gravity that way. And it addresses the environmental, social psychological challenges that would go with making this journey in considerable detail.
And these examples are largely science fiction in nature. But many scientific proposals were made since Goddard and Tsiokovsky as well. And there's even been calculations on how large your ship would need to be how much interior space it would need for agriculture, what it would take to keep the crews healthy and physically fit to prevent recessive genes, and genetically diverse enough that they would be healthy upon arrival.
And from all this, a picture of what a generation ship would really, truly look like has emerged. And on the one hand, it's generally agreed that well, depending upon the propulsion method, or regardless of the propulsion method, really, you'd need to have some significantly large
propellant tanks. And these would carry either hydrogen fuel deuterium fuel or possibly even antimatter, that this would all be handled in a drive section, located somewhere towards the rear, and that the main body of the ship would consist of all the facilities needed to maintain the crew.
So we're talking about sleeping quarters, we're talking about open fields for planting and recreation. And of course, a lot of green space is needed in there too, because of course, they need air to breathe and that needs to be recycled and cleaned in a way that's sustainable. And the best way to do that, and scientists are certainly aware of this and are researching it for future missions to the moon to Mars, is through a bio-regenerative life support system.
So basically a system that utilizes photosynthesis, whether it's artificial or natural, and for the purpose of generation ship, if you're doing this for multiple generations, I'd say the best idea is to go with one that uses natural photosynthesis as its main producer, with a mechanical life support system, possibly one that relies on artificial photosynthesis as a backup.
And the same mechanisms are needed to clean the water, recycling the water supply so that the settlers the crew never run out of clean water to drink. And of course, the life cycle needs to be consistent for generations at a time. So we're talking about everything in this living space in this biome inside the ship. Everything from bacteria, fungi, moss, lichens to insects, and of course, to avians, mammals, and other creatures, amphibians, and reptiles, everything that's needed to ensure that all the niches inside this environment are filled. And that life itself, which is very, very good at propagating and supporting other life, that it continues to function and carry out all of its biological functions, which in turn help serve the biological needs of the whole biome.
And a very, very smart idea is to ensure that this huge volume that it rotates, so in this respect, it's very much like the O'Neill cylinder, a rotating cylinder and space that simulates artificial gravity. If you have the main section spun up, so that it can simulate either a full G Earth normal gravity 9.8 meters per second squared of centripetal force, then this will help ensure that the crew remains heel hearty and that their bodies don't deteriorate as a result of ongoing exposure to lower gravity.
And it's also been suggested that the inhabited volume consists of two cylinders, and that they rotate in opposite directions. Because it is possible, according to some research, that one rotating section rotating in one direction that is going to alter the trajectory of the ship, and it will have to make course corrections regularly in order to stay on track. So to avoid complications like that, you have two counter-rotating toruses or cylinders that provide simulated gravity for a northern and southern hemisphere.
And that idea right there that allows you to build biomes inside that are very Earth-like in nature. It's like where the two connect, you'd have your desert biomes. And at the farthest part away from each other, you'd have your Arctic and Antarctic biomes. And in between all that there wouldn't be levels of temperature increases and biodiversity. So you'd have your tropical
regions, very warm, very wet, very biodiverse, then getting into more coniferous and then Borealis regions, with all the plant life and animal life to match.
And these would replenish each other exactly as they do on Earth. And you could even simulate seasons in there, because presumably, the temperature and light exposure is something that is being seasons in there, because presumably, the temperature and light exposure is something that is being directly controlled. And the lovely idea that has been suggested for this too, and it was featured in William Gibson's Neuromancer.
And this was for a space habitat, not a spacecraft, but all the same. It rotated in order to provide artificial gravity and it had this central spire that reached down the length of this station, and it emitted light and heat. And this simulated the experience of sunlight. And much like the O'Neill cylinder, it's also been suggested that well, there should be panel-like windows in the actual hall itself.
So whereas you've got land covering all these areas here, there's a window that permits views to the outside and can let in natural sunlight and then that works rather well. in theory, for an O'Neill Cylinder. But in the case of a Generation Ship, it is not very practical. Once you're traveling in the interstellar medium, those windows are going to show just the backgrounds of space, which would make for lovely viewing at night, but during the day, it would probably best to close these windows and keep the lights on inside.
And of course, there's the issue of radiation protection, which comes up in any discussion about interstellar travel. So generation ships, like anything operating in space, would need radiation shielding. And a very, very smart, technically informed idea is that this could be done with a magnetic field.
And artificial magnetic fields generated towards the front end of the ship would help deflect cosmic rays and incoming particles, basically the most dangerous form of radiation. And, by the same token, these particles, micro-meteorites, and so forth would also be deflected, creating sort of a bow shock around the front end of the ship, that would ensure protection over time.
And, of course, it also helps to have a hole that is reinforced and impregnated with shielding, so that in case the magnetic shielding ever fails, or just as a backup, and added precaution, people inside know that they're not being exposed to levels of radiation that are beyond what their ancestors were used to on Earth.
And another lovely benefit of having an artificial biome in these living spaces, right, you're talking about a metal hole. And then between that in the surface, what people understand to be the surface. You have lots of Earth stone, everything that has been laid down in order to create a foundation for all this habitable volume, and all the plants and trees, and burrowing insects and animals that will live within it.
And this does provide natural radiation shielding. And even where this foundation would be thinnest, where bodies of water would be flowing or standing. This provides excellent radiation protection. And so the people inside would be able to carry on with their lives, knowing that the very, very hazardous environment of space is something that they are protected from with multiple layers. And so less, there are many, many challenges to consider. And as a friend of mine once said, that aboard a generation ship, you have to be prepared for any eventuality. And this has been explored in technical studies.
And, of course, in science fiction, the idea that having multiple generations of people living within this space over time, could lead to all kinds of issues. So basically, the crew would need, and examples abound in this, either some highly trained and skilled elders who have taken it upon themselves to pass along the knowledge of what to do, contingency plans, The Big Book of emergency scenarios and strategies that they would pass along for from generation to generation.
Or they would have most likely the assistance of an AI, something that can recommend different strategies for different scenarios that can be the sort of keeper of knowledge, Allah, the giver, and tell the people what they need to do in the event of any unforeseen development, or, of course, a combination thereof, a ruling council of elders and an AI that are there to guide and shepherd the younger people on their way.
Now as to what these potential issues are, well, yes, I'm a very long voyage, just about anything could happen. But the most likely scenarios, as far as I'm concerned, and as far as science fiction authors have explored, are that there will be a potential mutiny, that there will be intergenerational conflict, have explored, are that there will be a potential mutiny that there will be intergenerational conflict, that there will be conflict between different groups that people will find themselves divided along various policy or ideological lines.
So there's the potential for conflict among the people. So there have to be outlets for people to express their anger and their disagreements and so forth in a way that is constructive and creative. There needs to be respect and camaraderie among all the members of crew, generation after generation. And the children, they need to grow up understanding that they've come from a certain place, they are bound for another place.
And this mission is of great importance because whatever motivated it, we are leaving a dying planet, or there's conflict back home, or we want to be part of something new and explore beyond and find new frontiers. It's something that cannot be expected to be so easily transmitted from one generation to the next. Those who left Earth were likely very well motivated.
Those who have never seen Earth were born in interstellar space, they're more likely to want to see it. And they're more likely to question the whole idea of leaving. And they may have very, very genuine fears about what they're going to face once they get there.
And above all, there is the ever-present danger of systems breaking down. So if something breaks down, in terms of say, machinery, there needs to be a highly adept Corps of Engineers there to fix it. Highly adept machines that are there that have the technical knowledge on hand, there needs to be plenty of automated helpers, aka robots and droids that are there to assist.
And of course, if the ship has an AI, then yes, it too, needs to be a keeper of that knowledge, all things technical, subsequent generations need to understand how the machinery works to keep it functioning. This can't be completely turned over to machines, or left in the hands of people who will one day die, and before they can pass it on.
And of course, if you're relying on ecological systems and bio-regenerative systems to sustain you, you need to be prepared to address the very real possibility that one of these or several of these could collapse if they're not properly taken care of if they're not properly maintained. Soil could suffer from salt buildup, or contamination or erosion.
A species may suddenly find itself dying off due to the accumulation of harmful bacteria or predators. Or maybe the radiation shielding is not as good as we thought it was. And we're microscopic bacteria that are essential to this biome are dying off, what do we do about it. And there's always the possibility of cascade failure. One ecological system fails, triggering losses in another and then another and then another.
And there are of course, points of no return in that. If a cascade failure takes place, you may not be able to restore it. It all depends on the nature of the failure and what triggered it originally, and how it's grown over time. And there's the issue of procreation along the way, and how it will need to avoid any incest, any interbreeding because, of course, the risk of recessive genes accumulating, the people on board the ship, understand that how we populate the ship how we maintain that population, well, that is who eventually is going to settle on a new world and build a new outpost of human civilization there.
And so, basically, we need to make sure that they are a healthy genetic stock. And in that respect, several studies have been conducted over the last few decades. In 2002, Dr. John Moore, who is the current chair of the Human Genome Diversity project, and an anthropologist by training, he conducted a study to determine how large a crew would need to be, in order for there to be enough genetic diversity to maintain health during a 200 year dream. And this was followed by another anthropologist Dr. Cameron Smith, who conducted a similar study in 2014.
As part of Project Hyperion, which was a preliminary study for a possible generation ship conducted by the Institute for Interstellar Studies, or i4is. In both of these studies found that a certain degree of inbreeding would occur during this interstellar voyage that it would, unfortunately, just be inevitable.
But of course, it can be minimized by ensuring that people have a certain level of relations should not reproduce, that if marriages were going to happen for the sake of producing offspring that they needed to be done between genetically divergent people, and that this process could be kept separate from companionship or marriage, that people could marry for
love freely, but that they would need to volunteer their genetic material, whether artificially or naturally, for the sake of producing offspring that would be genetically healthy.
And between 2017-2019, Dr. Frederick and Marin of the Astronomical Observatory Strasburg, he and his colleagues conducted a number of probabilistic studies that examined what the crew of a generation ship would need in terms of space in terms of arable land to farm on, and yes, in terms of crew size that could actually accommodate healthy procreation.
And what he determined ultimately was that an initial crew of 98 would suffice that By the time it reached its arrival generations later, it would have grown to 500 people. And that it would be best to couple this crew with a cryogenic bank of sperm eggs and embryos. And in so doing, they could ensure that any chance of inbreeding and the buildup of recessive genes could be, if not entirely avoided, at least strongly minimized.
And of course, this does raise another question, the larger the crew, the more chances they will have to produce healthy offspring generation after generation. But that in turn creates the issue of isn't going to be enough supplies and farmland in order to sustain them. Because the more people that are on the ship, the more mouths to feed. And the more hands there are to work as well. But it's a complicated trade-off.
To this, Dr. Moran and his fellow researchers, they performed calculations that considered a crew of 500 and how much space they would need for farmland. And they found that a cylindrical ship with simulated gravity, so rotating, it would need to measure 1500 feet, or 320 meters in length, be 224 meters or 735 feet in radius, and contain at least 450 square meters or 4850 square feet of agricultural land.
And that's not just for producing food, but also for recycling the air, recycling the water, maintaining a living biome inside. As for fuel and energy requirements that would go into this journey, there's been research and calculations on that performed as well. And as predicted, they're all very, very high.
So upon final analysis, the generation ship does address some of the key issues there. However, it still comes with the terrible burden of cost. In order to build a ship large enough that you're set for a very long voyage, the sheer cost in terms of time, energy resources and the monetary value of such a spacecraft. It is very, very difficult to gauge.
And the fact that we really have no idea how much energy costs are going to be in the future, what the cost of materials are, whether or not money is even going to exist. And as NASA technologist, less Johnson, who we had on the show in the previous episode, as he recently related at the Eighth Interstellar Symposium, any assessment of the costs in terms of the energy, the resources and so forth, they are basically irrelevant, because we have no idea what the costs will be down the road, they could be cheaper, they could be more expensive.
We're not even sure if money is going to exist in this day and age when human beings might be motivated to build such an expensive spacecraft. And that really says something about the idea
in general there. It says that, well, this is not something we're considering building today. This is something that really could only be possible for future generations. And of course, any attempt to predict future developments, it's always fraught with peril, it's always subject to massive uncertainties.
And of course, there's the idea that, well, if we built a generation ship, sent it out to the stars, and it's traveling at a slow pace, hundreds of 1000s of years to reach even the nearest stars, there's also the likely possibility that subsequent generations back on Earth their technologies is going to have advanced significantly, and that by the time a generation ship is partway through its journey, other methods faster methods will have been devised.
And so this generation ship may find itself being just cruised past by a much sleeker, much smaller, much faster spacecraft, any or all of the above. And if they're traveling to the same destination, well that's going to complicate matters when they reach the other end. So so that is another scenario a crew aboard a generation ship would need to ponder and prepare for, right a overtake scenario.
And still, the idea is a very inspired one. And it's a very fascinating one to explore. And like a lot of concepts for interstellar space travel or just space exploration in general, it's received a fair degree of revitalization in recent years because, of course, the interest in space exploration has been renewed considerably with missions to return astronauts to the Moon in the near future are approaching and plans to send crewed missions to Mars shortly beyond that, and the many many robotic missions that we are considering sending to the very edge of the Solar System.
And even proposals like Project Starshot that want to create interstellar sailcraft, small little spacecraft there with giant light sales that are propelled by lasers that can achieve relativistic speeds, 20% the speed of light, in the case of Starshot, so that they can make the journey, make the interstellar crossing within a single generation.
All these ideas are showing that we're serious, we live in a time in which these ideas that were considered far off, but nevertheless attracted immense enthusiasm. We're now living in a time in which they once again seem entirely possible and within reach. Maybe not today, maybe not tomorrow, maybe not even in this generation, but quite possibly this century, quite possibly in a few decades. And so it behooves us to look at these ideas, consider them, take them seriously, and address the fundamental questions, be they technological, economic, socio-political, or moral and ethical.
And, of course, there is the idea of the scenario that one of these concepts may become necessary, they may become a matter of survival. Becoming an interplanetary species is often recognized as a necessity. It's argued that we need to plant the seed of humanity and human civilization on other planets in the Solar System, or in habitats in space, or risk extinction. Because either climate change and the human impact on the natural environment, it could precipitate an ecological collapse that would lead to the collapse of our civilization here.
Or it's possible a major calamity, like an asteroid strike could cause an extinction level event. As long as we are confined to Earth, these possibilities are real, and they constitute existential threats. Now, what if there were a similar threat, but to the entire solar system, in that events in the event of a major calamity that would threaten not just Earth but planets and moons beyond it? An interstellar arc may be a matter of survival. So at that point, which direction are we likely to go in future generations will need to decide do we want to pour our resources and efforts into making the ship really fast, so it can get human beings to another star quickly, or really big, so it can get human beings to another star comfortably.
And that's the subject of another episode that I'd like to address, which deals with the idea of cryo ships. It's like, “Why have a crew in a waking state consuming lots of resources, when you could have them in a state of hibernation, they would consume less resources that way, and they would only really need to be awakened when they're close to arrival or in the event of an emergency. And this could make for a cheaper voyage?”
But like I said, that's a discussion for another time. In the meantime, if you're interested in some very enlightening reading, I would strongly recommend that you check out any of the studies that I've mentioned. And in terms of science fiction treatment, I strongly recommend you read Arthur C. Clarke's Rendezvous with Rama, Aurora, Paradises Lost, and other titles mentioned, because they are very fascinating and also fun.
Inthe meantime, thank you for listening. I'm Matt Williams, and this has been Stories from Space.