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SciFi writer needs space travel help!

  1. Aug 24, 2012 #1
    My novel is coming together rather rapidly, but I've left some pretty big holes in my descriptions of the setting. It takes place on a generational ship traveling from Earth to a New hypothetically hospitable planet.

    Essentially I would like to know the amount of time that has passed on both Earth and the golden ship when the story takes place.

    Imagine catastrophe hits in 20 years time. Economic collapse, multiple international wars, the works. Nasa spots a planet way off in the distance which passes every test they throw at it in terms of the substance of its atmosphere and surface, and they are essentially convinced that it could be hospitable to humans.

    So with the guise of producing mining endeavors in the astroid belt of our solar system, they begin carving out an asteroid and build a ship in secret. The ship is tube like, and it is filled with all types of Earth material. The finished product has lakes and rivers and mountains and cities all living inside safely.

    News gets out of this and the US is attacked. 10,000 lucky citizens are sent off to board the ship and it takes off. Somewhere during the trip the society of generational colonists develop newer and faster technologies that begin to increase the momentum of the ship drastically. It reaches near light speed travel. Being science fiction, I merely allude to a large nuclear force, since I do not need to necessarily explain everything mathematically.

    So here's what I'm wondering. The total amount of time for the trip aboard the ship should be 200 to 500 years, depending on what sort of celestial bodies exist that far off (any opinion on this matter?) Say 200 years have passed on this ship. How many times has planet Earth circled the sun, in other words, how much time would have passed on our calanders as we continue our lives and the lives of the people on the ship have reached year 200?

    Thanks in advance!
  2. jcsd
  3. Aug 24, 2012 #2


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    You only need to calculate the value of gamma which is the reciprocal of the square root of 1 minus the speed (as a fraction of the speed of light) squared. So if you are going at .9999c then gamma is calculated as:

    1/√(1-0.99992) = 1/√(1-0.9998) = 1/√0.0002 = 1/0.1414 = 70.7

    This means that if 200 years passed on the ship, 14140 years passed on earth. Not only that, but the ship will have traveled just under 14140 light-years away during that period of time.

    So if you are suggesting that their destination is 200 to 500 light-years away, as long as the ship is approaching light speed, the inhabitants only have to survive for a few years to get there. Of course, they will also have to survive an unrealistically high g-force to get to that speed and to slow down when they get there, but that's another story. If you really want to make it realistic, in terms of the forces, you can have the ship constantly accelerate at 1 g for the first half of the trip, then turn around while decelerating at 1 g so the inhabitants will have the same experience they have on earth. The Relativistic Rocket website shows you some numbers to achieve this. For example, you could land on a planet that was double 1839 light-years away (3678 ly) in only 16 years for the travelers but 3680 earth years.
  4. Aug 24, 2012 #3
    Oh goodness! Thank you so much! Very helpful answer.

    Two things:
    1. The ship itself is meant to be generational, so people will have kids to have kids to have kids ect so that whenever the ship were to arrive at the planet a fresh group of colonists were ready to go forth onto the planet. Since that is their goal, you mentioned a more realistic option. But wouldn't that entail them having to turn around again away from their destination?
    2. Your equation used .9999c, which seems higher than I had in mind. Also, to travel at 1g there needs to be constant acceleration. Is there not an adequate speed that would allow the ship to spend 200 years travelling and arrive while 10,000 to 14,000 years were spent on Earth? Or perhaps it might go in bursts of acceleration and cruise the in bursts...?

    And George, I really am very appreciative of your amazing answer. I have spent some stressful time contacting meetup.com people in my area, as well as professors at the local university, but nobody responds to me. So your answer really made today a happy day for me. Thank you
  5. Aug 24, 2012 #4


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    This may be helpful: http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html [Broken]
    Last edited by a moderator: May 6, 2017
  6. Aug 25, 2012 #5
    When one says constant acceleration in SR, it is meant proper acceleration, as measured by an inertial frame moving with the same velocity as the ship. These frames change from an instant to an instant as the velocity of the ship changes.
  7. Aug 25, 2012 #6


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    By more realistic option, I was referring to the way your ship would achieve a speed close to lightspeed. If you don't spread the acceleration out over a long time, it becomes higher than most people would want to endure. And since you have rivers and lakes, it seemed to me that 1g would be best. You don't want your people to drown while swimming because they weigh many times their Earth weight but if they were weightless, the water wouldn't stay in the river bed or lake bed.
    I'm confused, I just said that a speed of 0.9999c provides a ratio close to what you just asked for.

    Since you mentioned alluding to a large nuclear source, I assumed energy was no problem, because, of course, that is the single biggest problem. So since any valid scientific solution is out of the question, you get to use the excuse that it is science fiction and now you can eliminate that problem. But there is no need to violate science in other areas.

    But traveling to a planet that is many thousands of light-years away presents another problem in that when we view the planet from Earth, we are seeing the planet as it was many thousands of years ago. There's no guarantee that as you approach the planet, it will still be hospitable. In fact, the planet will age more than double the time that we see it in the past. So if it is 14,140 light-years away and you travel to it at near light speed, it will age 28,280 years by the time you get there.

    Of course, you could use this to advantage in your story. NASA could have spotted a hospitable planet that was only 82.7 light years away but during the trip, in which the travelers were supposed to age only 5 years, they see to their horror that the atmosphere of the planet is destroyed by a wayward asteroid and so they have to search out and travel towards another candidate. This could be where they develop their newer and faster technologies and where the travelers are forced to become generational.
    You're welcome. Sounds like fun. I can't wait for the movie.
  8. Aug 25, 2012 #7

    Filip Larsen

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    From the perspective of a science fiction writer you may also find some of the following useful:

    The Starflight Handbook: A Pioneer's Guide to Interstellar Travel, by Mallove and Matloff, Wiley 1989.
    Centauri Dreams: Imagining and Planning Interstellar Exploration by Paul Glister, Spring 2004.
    Deep Space Propulsion: A Roadmap to Interstellar Flight by Long, Spring 2011.
    Space Travel: A Writer's Guide to the Science of Interplanetary and Interstellar Travel by Ben Bova, Writer's Digest Books 1997.
    How to Write Science Fiction & Fantasy by Orson Scott Card, Writer's Digest Books 2001.
  9. Aug 28, 2012 #8


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    Quick question, why exactly are they spending so much energy travelling to another system? Why can't they just populate our current system? Also if the US is at war yet capable of such massive industrial presence in space why can't it use that to achieve military dominance in space?

    With regard to the craft itself how fast do you intend it to go? Something that huge would take ridiculous amounts of fuel even with speculative technologies (just try running an asteroid mass through the ideal rocket equation!). In the meantime how do you intend the colonists to survive? Is there enough of them to maintain a technological society? How do they maintain their ecosystem? What social, political and economic models will they use (this one is particularly of issue if your aim is to survive societal collapse)?

    These aren't intended as negative criticisms, just curious as to what you may have already thought of to address these and to point them out if you haven't realised. Depending on the story you could avoid giving away to much detail for the original reason but some readers will still wonder why what exactly prompted this course of action rather than using similar industrial/technological capability to solve the problem.
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