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Scifi Author Needs Answer to Question

  1. Jan 14, 2013 #1
    !Hi. I am currently writing a short story and need a few questions answered.

    1. How could a spacecraft travelling at 10% the speed of light be slowed down?

    2. Is such a high velocity practical for a spacecraft staying within the same solar system? My story is set within a colonized solar system. Suppose a spacecraft were to launch from earth to a colony near Saturn. Is a craft this fast a problem?

    I write "soft" scifi (which focuses primarily on character-driven plot, as opposed to "hard" scifi, which often integrates real science as a major component of the storytelling), so it doesn't have to be a well thought out reply. It's only a brief scene in the beginning, but the last thing I want to do is throw a scientifically-mimded reader off!

    Thanks for reading my post.
  2. jcsd
  3. Jan 14, 2013 #2


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    A. Fire thrusters/engines to slow it down.
    b. Hit something. (If by slow down you mean "turned into a world-ending nuke".)

    That depends entirely of how you accelerate it to 10% c. Using standard propulsion methods and not invoking any crazy technology that doesn't exist and probably won't exist, such as inertial dampeners, antimatter reactors, etc, it would take you a long time to reach 10% c. Far longer than it would take you to actually travel from Earth to Saturn at that velocity.

    You're best bet is to not even mention anything about the technology then. Assume you can accelerate to 10% c in mere minutes with no detrimental effects to the ship or crew. If you don't mention it, people can't complain about it. (As long as you write a good story and don't make a critical research failure)
  4. Jan 14, 2013 #3
    Welcome to physics forums, Kam. I think there's a Sci-fi thread in this forum, probalby best to post there.
  5. Jan 15, 2013 #4
    Use a "Casimir Dark Boundary Drive". This system modifies a "Drive Plate" so that there is a nano-scale gap between it and the "Dark Energy Field" that pervades the Galaxy. This produces thrust via a repulsive Casimir Effect. You could also include enhanced thrust via amplification of Dark Energy negative acceleration described by the Einstein-Korobov String Rotation theorem (no such thing, AFAIA, but SF is full of invented theories so no worries there). You haven't got just deceleration to worry about, there is manoeuvring as well, but fortunately, you can place Drive Plates at various points around the vessel. However, you appear to have another problem in that to achieve 0.1 c at around the (Earth-Saturn) half-way point then I estimate you'll need to be pulling around 58 g for a total duration of ~ 42 hrs, which means you'll need "inertial compensators" to avoid squashing the crew (standard SF equipment, so you're OK there - none in reality yet) unless you keep it slightly more real and restrict acceleration to around 1 g, which gives a top speed of around 0.0125 c and about 14 days travel time. (Get somebody to check the figures ... I'm fond of missing out the odd power of 10 here and there.)

    ... that was just a top-of-the-head idea and was immediately followed by my recalling the last part of Ecclesiastes 1:9 (Нет ничего нового под солнцем or je pa' ghaH ghobe' chu' Doch bIng the pemHov in the original Klingon) and, sure enough, there are Casimir drives out there according to Google - although the ones I glanced at appear to use the Casimir effect for warp drives not standard inertial in-system drives ... you may be in luck for using a side-effect of the drive for inertial compensation as well!
  6. Jan 15, 2013 #5


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    If its soft science fiction just use a technobabble explanation like nemo has above, it's nonsense but its not the focus so it doesn't matter. However bare in mind what Drakkith said about how long it would take to get to said speed, I think at 1G acceleration it would take around a month to get to 0.1c and in that time you would cover about 45 trillion kilometres, around 6500 times the distance between Pluto and the sun. If you want to lower that distance you'll have to up the acceleration but to get to anything useful (I.e. less than solar system sizes) you're probably going to have to up it to hundreds/thousands of G.

    As with all SF, very hard or very soft, you should explore the full ramifications of your speculative plot devices to make sure they are consistent and don't break the story. Anything above 20gs for a significant amount of time is deadly to a human so you're going to need to throw in a workaround for that acceleration like inertial negation or crew uploaded to computers.

    Other things you're going to have to consider is Jon's Law/Burnside's Advice. The technology to propel spacecraft at significant fractions of the speed of light means that doomsday devices are now common place. Consider that a 1000 tonne spacecraft (just over twice the mass of the international space station) travelling at 0.1c has a kinetic energy of 4.5e20 joules which is 2000 times more powerful than the most powerful nuclear bomb ever built. Crank it up a bit and instead of a ship bolt one of these SuperDrives to a 100m3 block of ice and you've got a weapon more powerful than the asteroid that wiped out the dinosaurs. The implications here are problematic, let in super propulsion to your setting and suddenly every spacecraft is a potential weapon of mass destruction. That poses serious problems for any science fiction setting with mass civilian space travel.

    Lastly the problem of energy rears its head: if your 1000 tonne ship can gain 4.5e20 joules of kinetic energy where did that energy come from? Assuming an impossible near perfect energy to momentum device you'd have to plug in at least those 4.5e20 joules which is the mass-energy equivalent of 100 tonnes. Now your hypothetical reactor is a weapon of ultra mass destruction as well...

    You could just ignore all this and focus and hope that readers won't pick up on it but in my experience science fiction readers are quite voracious in how they pick apart settings. That doesn't mean don't do it by all means but it might be good to carefully put in place reasonable limitations to the plot devices you use.
    Last edited: Jan 19, 2013
  7. Jan 19, 2013 #6
    1. You can take a "ripped from the headlines" approach and assume that the White-Juday warp-field interferometer experiment is a success and a fully functional White-Juday-Alcubierre warp field generator was eventually built into most starships, allowing for quick travel between locations without even worrying about acceleration issues. The original paper has good descriptions of theoretical future trips. Since it is soft SF, you can assume that all the other issues are fixed as well without explanation.

    2. There aren't many issues with using the warp bubble at subluminal "velocities", since the travelers experience the same proper time and distance inside the bubble as the original reference frame before the bubble was initiated. They don't even experience acceleration.
  8. Jan 19, 2013 #7
    That rather depends upon how you define soft v hard SF and what role "technobabble" necessarily plays in SF. As we have no supporting FTL theories at the moment, anything that involves FTL necessarily uses "technobabble" as an explanation unless it ignores theory all together - however, a lot of authors do speculate and in some instances their stories actions can hinge around particular aspects of their hypothetical drives. With regard to the "Casimir Dark Boundary Drive" and looking at the SF Grading criteria given below ...

    The Casimir Effect itself is "Present Day" theory and includes repulsive as well as attractive forces.

    Dark Energy is currently thought to represent ~73% of the total mass-energy in the Universe and also falls into the "Present Day" category.

    Nano-scale technology is real and in use.

    The speculative element of the drive is the existence of device that allows the Casimir effect to take place at some boundary between our normal mass-energy dimension and the dark energy field. Many SF stories explicitly name the underlying future theories that allow the technology / effect they are using; the "Einstein-Korobov String Rotation" theorem is such a story device and hints at both general relativity and string theory, with the drive name perhaps implying a Domain Wall involvement.

    As also mentioned, the Casimir effect is also a mechanism that has been looked at in relation to wormholes (eg, http://arxiv.org/pdf/hep-th/0510232v2.pdf ). See this paper from NASA's Eagleworks ... http://ntrs.nasa.gov/search.jsp?R=20110023492 which links to http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023492_2011024705.pdf for some other, less speculative, ways of using quantum vacuum effects (the paper specifically mentions Earth-Saturn transit times of 70 days).

    Consequently, using the criteria and examples given below, I estimate that the Casimir Dark Boundary Drive falls into the Plausibly Hard category.

    The other thing to bear in mind that a story is not limited to being totally hard or soft; for example, the plot may hinge upon quite realistic biology but not be too fussed about how people get between planets or stars (everybody knows about warp drives so no need to explain (Murray Leinster springs to mind, or many of Niven's Known Space stories and the Banks' Culture). The Medium category is where a lot of my favourite stories lie. A device need not be overly plausible under current technology if it captures the imagination and makes one think "what if ..?"

    I think about 10 times Pluto's orbital radius to get to 0.1 c at 1 g, and just under 1 day at roughly 80 g to get to Saturn at nearest approach (allowing for a brief "cruise" phase at 0.1 c). A 1 g trip to Saturn should take about 8 days and get up to ~ 0.01 c.

    Consistency's good, but working out the full ramifications of real devices and theories is daunting enough, let alone fictional ones. Getting rid of the 'obvious' (undergrad level) errors may be a reasonable level to aim for ...
    'crew upload' introduces the philosophical subject of identity plus the subject of 'crew download' (eg, what is being downloaded into what and how?).

    It only poses problems for a setting which involves it - some SF tackles it head on and describes the defences (or lack of them), some SF notes the threat but just states the existence of defences whilst the majority of (good) SF I've read gets on quite well with the assumption that nobody does that kind of thing (by analogy, a heavy goods vehicle or tank can do a lot of damage in the wrong hands, but the overwhelming majority of us drive along the roads without the slightest concern that the lorry in the other lane is going to deliberately or accidentally slam into our lane).

    Or you could use one of a number of "Medium" devices which either tap into some external power source (eg, quantum vacuum energy) whilst using the on-board systems as exciters/catalysts.

    Agreed. It's worth asking, however, how many people have some knowledge of the Soft Star Wars and Star Trek and compare that figure to the number who've can tell you anything about some of the Hard SF ...

  9. Feb 16, 2013 #8
    1. How could a spacecraft travelling at 10% the speed of light be slo

    The same way you speeded it up to 0.1c in the first place.

    For any plausible high-speed* propulsion system you need to allow the same time to decelerate at the end of the journey as to accelerate at the beginning.

    If you want to get there as fast as possible (and have enough energy available) you would accelerate for the first half of the journey, then turn around the spacecraft around so the thrusters face forwards and decelerate for the second half of the journey.

    * By high speed I mean that the spacecraft is travelling much faster than the speeds of the planets it is travelling between. This would not be true for example for a minimum energy transfer from Earth to Mars. In that case you would accelerate at the start to get into the transfer orbit, coast until you reach the orbit of Mars, then accelerate again to match your speed with Mars.
    Last edited: Feb 16, 2013
  10. Feb 16, 2013 #9
    At 0.1c you could travel to Saturn in about 12 hours. Do you need travel in your solar system to be that fast? If you are happy for the journey to take days or weeks then a much slower (and more plausible) propulsion system would do. (Though still much faster than anything we have today).
  11. Feb 20, 2013 #10
    A bit of personal taste-

    If the propulsion system is a key plot element you must worry about.
    If it isn't you just need to say they travelled. Elaborate "travelled" as much as you
    like but it isn't any interest in a story not about space flight so keep it brief.
    Call it warp drive - then move on. We all know what warp drive is - and isn't.

    I really hate all these huge tombs of irrelevant fatuous waffle that appear to abound these days. (starting a few years ago maybe) - I stopped buying so many books because of them. I now select paperbacks on the basis of author name and thickness.
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