Imagine if you will, that scientists were able to say definitively that Kepler 22b was habitable, and a generational spaceship was built to go there. Would you be willing to board?
The rest of my life trapped in cramped conditions living on strict rations with a large number of other people, constantly haunted by the knowledge that if the radiation doesn't sterilize us all before we make it to the heliopause, anything built by the lowest bidder will never last any longer than it takes those responsible to be safe from consequences?
Imagine if you will, that scientists were able to say definitively that Kepler 22b was habitable, and a generational spaceship was built to go there. Would you be willing to board?
Most likely whatever is optimum for a minimum viable population. I haven't calculated the ideal ratio, or the number of people needed aboard this ship.
Most likely whatever is optimum for a minimum viable population. I haven't calculated the ideal ratio, or the number of people needed aboard this ship.
For a generational ship, 1:1. For several reasons:
1. Population stability is the goal while in transit, not growth. There might be room on the ship for growth, but the food production capacity and long term supplies are strictly finite.
2. General societal stability: Most human societies that practice imbalanced mate sharing in either direction have suffered conflict as a direct result. Communal living might make sense in the situation than traditional family units, but that still means an even split.
3. Any gender disparity will be erased in the first generation anyway.
For a sleeper ship, now, where the initial passengers wake up at their destination, things get a lot more fun. You can plan for population growth in this scenario, which can mean a male:female ration in the 1:2 to 1:4 range.
The entry barrier for this kind of colonization is a lot higher, though. Everyone who boards a sleeper ship has to be physically and mentally up for the task of building a colony. A generational ship has the luxury (and potential danger) that the population that arrives at the colony will be so far removed from the one that boarded the ship that it almost doesn't matter.
A generation ship is far from the best option for interstellar travel, even taking into account our rather primative technologies. The best aproach would be to accelerate continously Reaching relativistic speeds within a few months, and providing the advantage of time dilation, making the trip duration far shorter for those making the journey than it would be to outside observers.
Of course sleeper ships are more fun. There's not much of a downside to going on a sleeper ship, and you get to enjoy the fuits of your investment. That's why asking about a generational ship is much more interesting.
A generation ship is far from the best option for interstellar travel, even taking into account our rather primative technologies. The best aproach would be to accelerate continously Reaching relativistic speeds within a few months, and providing the advantage of time dilation, making the trip duration far shorter for those making the journey than it would be to outside observers.
The trip to Kepler 22b would still be 600 years at the speed of light.
The trip to Kepler 22b would still be 600 years at the speed of light.
You're forgetting time dilation. For example, at .9c, the relativistic factor is roughly 2.29. It would take 667 years from an outside point of reference, but only 291 years from an internal point of reference. At .95 c the relativistic factor is 3.2. So while the travel time is 631.5 years, it would only be 197 to those on the ship.
Of course sleeper ships are more fun. There's not much of a downside to going on a sleeper ship, and you get to enjoy the fuits of your investment. That's why asking about a generational ship is much more interesting.
The trip to Kepler 22b would still be 600 years at the speed of light.
Not for those on board the vessel due to time dialation that can be calculated by findiing the Lorentz Factor, which will make both the distance traveled and the time it took to travel the distance seem much smaller to the passengers of any such vessel.
You're forgetting time dilation. For example, at .9c, the relativistic factor is roughly 2.29. It would take 667 years from an outside point of reference, but only 291 years from an internal point of reference. At .95 c the relativistic factor is 3.2. So while the travel time is 631.5 years, it would only be 197 to those on the ship.
At .999 c it is the Lorentz factor is 22.3 and so to the passengers aparent travel time sould be just under 30 years. Getting even closer to the speed of light makes the Lorentz Factor much larger, making aparent travel time much shorter.
I think you missed a 9. At .99 it's only 7.08.
Handy toy for the discussion: http://www.1728.org/reltivty.htm (decimal portion of c int he top box, click the C=1 button, bottom number)
Though these are only partial calculations, assuming you instantly accelerate and then simply slam into the planet at full speed upon arrival. In reality you'd have to spend the first half of the trip building up to these speeds and the second half shedding it again so you're below escape velocity when you arrive, at which point you spend a pretty substantial portion at each en dof the trip with a Lorentz factor somewhere closer 0.
I think you missed a 9. At .99 it's only 7.08.
Handy toy for the discussion: http://www.1728.org/reltivty.htm (decimal portion of c int he top box, click the C=1 button, bottom number)
Though these are only partial calculations, assuming you instantly accelerate and then simply slam into the planet at full speed upon arrival. In reality you'd have to spend the first half of the trip building up to these speeds and the second half shedding it again so you're below escape velocity when you arrive, at which point you spend a pretty substantial portion at each en dof the trip with a Lorentz factor somewhere closer 0.
You correct I left out a 9, I will correct.
And you are correct about the acceleration/deceleration, but if one were intelligent about it they would probably slingshot off of stars providing a much higher rate of acceleration, and probably calculate paths to provide gravitational braking as well.
With that distance and the use of the gravitational fileds of star systems they may get closer to c than .999.
There would be a lot involved in calculating the optimum trip. As you reduce the aparent travel time you reduce the amount of materials that you must carry, but you increase the amount of energy required to reach those velocities. However, the hassles of keeping equipment functioning over multiple generations makes multi-generational travel problematic.
I cannot imagine the trip lasting more than about 30 years from the passengers perspective. At 30 years you can have a small group of crew and educators, and children as the eventual colonists. It would be best to have more female children than mle children the exact ratio determined by travel time and number of colonists, Adult crew would probably be close to 50/50 or alll one gender or the other..
You're forgetting time dilation. For example, at .9c, the relativistic factor is roughly 2.29. It would take 667 years from an outside point of reference, but only 291 years from an internal point of reference. At .95 c the relativistic factor is 3.2. So while the travel time is 631.5 years, it would only be 197 to those on the ship.
I saw on a Stephen Hawking documentary that if the ship reached 99% of light speed, the time dilation would be so that the crew would only experience a day for every year of travel. So 600 years = 600 days for the crew.
Sorry had a brainfart about the relativity. However moving at relativistic speeds is still a bad idea. At those speeds, particles of dust would hit with the force of a warhead.
Sorry had a brainfart about the relativity. However moving at relativistic speeds is still a bad idea. At those speeds, particles of dust would hit with the force of a warhead.
The best aproach would be to accelerate continously Reaching relativistic speeds within a few months
Hmmmmmmmm -scratches chin-
Average weight of human, 80 kg.
Let's assume each passenger will need 120 kg of support (renewable food, medicine, etc).
Let's also assume we have 100 humans to start a small colony.
We now have a 20,000 kg spacecraft, which is pretty much the absolute minimum. The kinetic energy of such a ship going at 0.95 c is gonna be ....
KE = m c^2 [(1-v^2/c^2)^(-1/2) - 1] ≈ 2.2 m c^2
≈ 4 * 10^21 Joules
For reference, the *world* energy production in 2008 was 4.7*10^20 Joules.
So it would take the total output of the world's electricity 10 years to accelerate this craft. Double that, actually, since the propellant coming out the back would have to have the same energy going the other way.
The point of it is that it's feasible within modern technology - we have the propulsion and food production technologies on smaller scales and have proven they can be scaled, ultimately we're only really missing the orbital construction capacity to build something of that size.
Cryogenics, however, hasn't even been established as possible on humans. Only a few vertebrates have been frozen and revived, and only over short periods of storage with low success rates and drastically reduced life expectancy afterward. Even all our cryogenically stored corpses are just expensive caskets - reviews of the facilities have shown that even if it were possible, their technique causes more irreparable damage than standard embalming does, and isn't even done properly most of the time.
I saw on a Stephen Hawking documentary that if the ship reached 99% of light speed, the time dilation would be so that the crew would only experience a day for every year of travel. So 600 years = 600 days for the crew.
Like most of his stuff that wasn't written for the scientific journals, it's a bit simplified. At 99% of c, you'll experience one day for every seven days of travel. Doing a little playing with the calculator in my last post, you get to the 1 day=1 year point at roughly 99.999621% of light speed. (factor 363.21670029572545 - almost close enough to account for leap years even).
Well a generational ship could be done with today's technology, or near future technology. We're not that close to relativistic travel or inertial dampers. Or cryostasis chambers for that matter.
The best aproach would be an electron beam emitted from the vessel to place a negative charge on any dust particles which would allow the particles to be deflected magnetically.
Hmmmmmmmm -scratches chin-
Average weight of human, 80 kg.
Let's assume each passenger will need 120 kg of support (renewable food, medicine, etc).
Let's also assume we have 100 humans to start a small colony.
We now have a 20,000 kg spacecraft, which is pretty much the absolute minimum. The kinetic energy of such a ship going at 0.95 c is gonna be ....
KE = m c^2 [(1-v^2/c^2)^(-1/2) - 1] ≈ 2.2 m c^2
≈ 4 * 10^21 Joules
For reference, the *world* energy production in 2008 was 4.7*10^20 Joules.
So it would take the total output of the world's electricity 10 years to accelerate this craft. Double that, actually, since the propellant coming out the back would have to have the same energy going the other way.
Utilizing the gravitational fields of stars starting with our very own sun to accerate and decelerate could reduce energy consumption considerably. Imaging the speed one could obtain over the severl months of droping in for close pass of our sun from a distance out past Pluto.
Like most of his stuff that wasn't written for the scientific journals, it's a bit simplified. At 99% of c, you'll experience one day for every seven days of travel. Doing a little playing with the calculator in my last post, you get to the 1 day=1 year point at roughly 99.999621% of light speed. (factor 363.21670029572545 - almost close enough to account for leap years even).
A bit simplified? A week is a lot shorter than a year!
Gravitational slingshot only works if the object you're using is also moving in the approximate direction you're trying to go, and you need to start from outside it's gravitational influence (these two combine so that you're "falling" much longer than you're "rising" after perigee so you get a net gain). If you start from an orbit around the object, getting back out to that distance will rob you of what speed you gained. That's why probes don't slingshot out of earth orbit, they use boosters and slingshot on a second pass.
Another issue is one of fuel for propulsion. If you are using rocketry (since we haven't discovered subspace-distortion-based impulse drive or inertial damping), then to get up to near-light speeds, the only fuel that would work is antimatter. Fusion would not work, as the energy released would be about three hundred times less than for antimatter, which would result in needing impractically large (and heavy) fuel tanks.
Another issue is one of fuel for propulsion. If you are using rocketry (since we haven't discovered subspace-distortion-based impulse drive or inertial damping), then to get up to near-light speeds, the only fuel that would work is antimatter. Fusion would not work, as the energy released would be about three hundred times less than for antimatter, which would result in needing impractically large (and heavy) fuel tanks.
Antimatter isn't necessary... and for that matter, not feasible with current technology, or our current understanding of the stuff. We haven't found a way to produce it without expending more energy than it'll release in annihilation (not to mention the fantastic expense involved), we haven't managed to store multiple particles at once, or single particles for more than a few seconds, and don't even have a viable theoretical means to do so.
Acceleration doesn't need to be done all at once. Because of the distance involved and the need to be accelerating or decelerating for most of it to attain minimum travel time, sustainability is more important than output. Ion engines exist and are ideal for this kind of use, and you wouldn't even need something as exotic as fusion to power one.
Gravitational slingshot only works if the object you're using is also moving in the approximate direction you're trying to go, and you need to start from outside it's gravitational influence (these two combine so that you're "falling" much longer than you're "rising" after perigee so you get a net gain). If you start from an orbit around the object, getting back out to that distance will rob you of what speed you gained. That's why probes don't slingshot out of earth orbit, they use boosters and slingshot on a second pass.
Fair enough.
I would have to go back and recheck some things, but as I recall a fusion ram jet becomes viable at about .5c and .5 c can be obtained by using an Orion project typr of propulsion system.
Or forget the ramjet and go Orion Project all the way. A nuclear warhaed in the 1 megaton range can release about 4.184 petajoules, which is about 4.184x10^15, and there are much higher yielding devices than that.
Antimatter isn't necessary... and for that matter, not feasible with current technology, or our current understanding of the stuff. We haven't found a way to produce it without expending more energy than it'll release in annihilation (not to mention the fantastic expense involved), we haven't managed to store multiple particles at once, or single particles for more than a few seconds, and don't even have a viable theoretical means to do so.
Acceleration doesn't need to be done all at once. Because of the distance involved and the need to be accelerating or decelerating for most of it to attain minimum travel time, sustainability is more important than output. Ion engines exist and are ideal for this kind of use, and you wouldn't even need something as exotic as fusion to power one.
It has nothing to do with the magnitude of the acceleration, and everything to do with how much energy can be extracted from the fuel. The less energy in the fuel, the more of it you will need. The bad news about that, though, is that fuel consumption increases exponentially with your desired maximum velocity.
To put this all in perspective, a spacecraft traveling at 0.999c has a relativistic kinetic energy equal to about ten times the energy of annihilating its rest mass in antimatter.
As such, to get 0.999c with fusion power would require literally trillions of times your payload mass in fuel unless a Bussard ramrocket can be made workable.
Comments
Yeah, I'll pass.
What's the male/female ratio?
Most likely whatever is optimum for a minimum viable population. I haven't calculated the ideal ratio, or the number of people needed aboard this ship.
No cryo systems. You live on the ship, and raise a family, then in a couple thousand years, your decendents colonise the planet.
For a generational ship, 1:1. For several reasons:
1. Population stability is the goal while in transit, not growth. There might be room on the ship for growth, but the food production capacity and long term supplies are strictly finite.
2. General societal stability: Most human societies that practice imbalanced mate sharing in either direction have suffered conflict as a direct result. Communal living might make sense in the situation than traditional family units, but that still means an even split.
3. Any gender disparity will be erased in the first generation anyway.
For a sleeper ship, now, where the initial passengers wake up at their destination, things get a lot more fun. You can plan for population growth in this scenario, which can mean a male:female ration in the 1:2 to 1:4 range.
The entry barrier for this kind of colonization is a lot higher, though. Everyone who boards a sleeper ship has to be physically and mentally up for the task of building a colony. A generational ship has the luxury (and potential danger) that the population that arrives at the colony will be so far removed from the one that boarded the ship that it almost doesn't matter.
The trip to Kepler 22b would still be 600 years at the speed of light.
You're forgetting time dilation. For example, at .9c, the relativistic factor is roughly 2.29. It would take 667 years from an outside point of reference, but only 291 years from an internal point of reference. At .95 c the relativistic factor is 3.2. So while the travel time is 631.5 years, it would only be 197 to those on the ship.
Not for those on board the vessel due to time dialation that can be calculated by findiing the Lorentz Factor, which will make both the distance traveled and the time it took to travel the distance seem much smaller to the passengers of any such vessel.
Time Dilation
At .999 c it is the Lorentz factor is 22.3 and so to the passengers aparent travel time sould be just under 30 years. Getting even closer to the speed of light makes the Lorentz Factor much larger, making aparent travel time much shorter.
Handy toy for the discussion: http://www.1728.org/reltivty.htm (decimal portion of c int he top box, click the C=1 button, bottom number)
Though these are only partial calculations, assuming you instantly accelerate and then simply slam into the planet at full speed upon arrival. In reality you'd have to spend the first half of the trip building up to these speeds and the second half shedding it again so you're below escape velocity when you arrive, at which point you spend a pretty substantial portion at each en dof the trip with a Lorentz factor somewhere closer 0.
You correct I left out a 9, I will correct.
And you are correct about the acceleration/deceleration, but if one were intelligent about it they would probably slingshot off of stars providing a much higher rate of acceleration, and probably calculate paths to provide gravitational braking as well.
With that distance and the use of the gravitational fileds of star systems they may get closer to c than .999.
There would be a lot involved in calculating the optimum trip. As you reduce the aparent travel time you reduce the amount of materials that you must carry, but you increase the amount of energy required to reach those velocities. However, the hassles of keeping equipment functioning over multiple generations makes multi-generational travel problematic.
I cannot imagine the trip lasting more than about 30 years from the passengers perspective. At 30 years you can have a small group of crew and educators, and children as the eventual colonists. It would be best to have more female children than mle children the exact ratio determined by travel time and number of colonists, Adult crew would probably be close to 50/50 or alll one gender or the other..
What's the point of that??
I saw on a Stephen Hawking documentary that if the ship reached 99% of light speed, the time dilation would be so that the crew would only experience a day for every year of travel. So 600 years = 600 days for the crew.
Not if we have inertial dampeners.
Hmmmmmmmm -scratches chin-
Average weight of human, 80 kg.
Let's assume each passenger will need 120 kg of support (renewable food, medicine, etc).
Let's also assume we have 100 humans to start a small colony.
We now have a 20,000 kg spacecraft, which is pretty much the absolute minimum. The kinetic energy of such a ship going at 0.95 c is gonna be ....
KE = m c^2 [(1-v^2/c^2)^(-1/2) - 1] ≈ 2.2 m c^2
≈ 4 * 10^21 Joules
For reference, the *world* energy production in 2008 was 4.7*10^20 Joules.
So it would take the total output of the world's electricity 10 years to accelerate this craft. Double that, actually, since the propellant coming out the back would have to have the same energy going the other way.
The point of it is that it's feasible within modern technology - we have the propulsion and food production technologies on smaller scales and have proven they can be scaled, ultimately we're only really missing the orbital construction capacity to build something of that size.
Cryogenics, however, hasn't even been established as possible on humans. Only a few vertebrates have been frozen and revived, and only over short periods of storage with low success rates and drastically reduced life expectancy afterward. Even all our cryogenically stored corpses are just expensive caskets - reviews of the facilities have shown that even if it were possible, their technique causes more irreparable damage than standard embalming does, and isn't even done properly most of the time.
Like most of his stuff that wasn't written for the scientific journals, it's a bit simplified. At 99% of c, you'll experience one day for every seven days of travel. Doing a little playing with the calculator in my last post, you get to the 1 day=1 year point at roughly 99.999621% of light speed. (factor 363.21670029572545 - almost close enough to account for leap years even).
The best aproach would be an electron beam emitted from the vessel to place a negative charge on any dust particles which would allow the particles to be deflected magnetically.
Utilizing the gravitational fields of stars starting with our very own sun to accerate and decelerate could reduce energy consumption considerably. Imaging the speed one could obtain over the severl months of droping in for close pass of our sun from a distance out past Pluto.
A bit simplified? A week is a lot shorter than a year!
Antimatter isn't necessary... and for that matter, not feasible with current technology, or our current understanding of the stuff. We haven't found a way to produce it without expending more energy than it'll release in annihilation (not to mention the fantastic expense involved), we haven't managed to store multiple particles at once, or single particles for more than a few seconds, and don't even have a viable theoretical means to do so.
Acceleration doesn't need to be done all at once. Because of the distance involved and the need to be accelerating or decelerating for most of it to attain minimum travel time, sustainability is more important than output. Ion engines exist and are ideal for this kind of use, and you wouldn't even need something as exotic as fusion to power one.
Fair enough.
I would have to go back and recheck some things, but as I recall a fusion ram jet becomes viable at about .5c and .5 c can be obtained by using an Orion project typr of propulsion system.
Or forget the ramjet and go Orion Project all the way. A nuclear warhaed in the 1 megaton range can release about 4.184 petajoules, which is about 4.184x10^15, and there are much higher yielding devices than that.
It has nothing to do with the magnitude of the acceleration, and everything to do with how much energy can be extracted from the fuel. The less energy in the fuel, the more of it you will need. The bad news about that, though, is that fuel consumption increases exponentially with your desired maximum velocity.
To put this all in perspective, a spacecraft traveling at 0.999c has a relativistic kinetic energy equal to about ten times the energy of annihilating its rest mass in antimatter.
http://en.wikipedia.org/wiki/Rocket_equation
http://en.wikipedia.org/wiki/Specific_impulse
As such, to get 0.999c with fusion power would require literally trillions of times your payload mass in fuel unless a Bussard ramrocket can be made workable.