Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Amount of nuclear power need to propel a shuttle at the speed of light!

  1. Nov 8, 2011 #1
    hello, my name is Zachary. i have little to no experience in astrophysics but i must say it is the most intriguing subject of discussion for me. what i believe i have worked out is the amount of nuclear energy (MeV) in megaelctronvolts, to propel a space shuttle (for a general number for M) at the speed of light. granted we haven't engineered a reactor capable to touch the number i have came up with but if there are any of you smart astrophysicists feel free to critique or correct my work.

    J = joules
    MeV = megaelectronvolts
    KE = kinetic energy
    M = mass
    C = speed

    easiest way to calculate energy in motion is KE= 1/2(m*v^2)
    shuttle in mass = 2,030,000 kg
    speed of light = C = 299,792,458 m/s

    long story short the KE in joules = 9.12236506x10^38 J

    nuclear power is measured in MegaElectronVolts (MeV)
    1 MeV = 1.60217653x10^-13 J

    then you have to convert our KE in joules to MeV's
    9.12236506x10^38 J = 7.8018829506x10^14 MeV's

    so in theory you would need to build a nuclear propelled rocket/shuttle/ship that could produce 7.8018829506x10^14 MegaElectronVolts at any given time to continuously propel the ship at the speed of light. currently our nuclear power plants cannot even come close to 0.000000001 of that amount as far as i've read. but mathematically it is possible and the next thing to do would be to find a way to increase the amount of MeV's we can produce at any given moment without losing the control of that kind of power. it's because of how powerful this could be that makes it a safety issue, which is a red flag raised by anything with the word nuclear in it. but to me i think this is the future of propulsion along with electromagnetic propulsion (i.e. rail gun) please feel free to leave any thoughts.

    - Zachary
     
  2. jcsd
  3. Nov 8, 2011 #2

    Drakkith

    User Avatar

    Staff: Mentor

  4. Nov 8, 2011 #3

    Pengwuino

    User Avatar
    Gold Member

    There are several things wrong here. For one, you didn't do the calculation correctly, try again. The right answer, in MeV (which is an absurdly useless way of talking about macroscopic object energies) is 5.62x10^35 MeV.

    Second, objects can never reach the speed of light.

    Third, the kinetic energy of an object near the speed of light is not [itex]{{1}\over{2}} mv^2[/itex]. It is given by [itex]KE = (\gamma - 1)mc^2[/itex] where [itex]\gamma = {{1}\over{\sqrt{1-{{v^2}\over{c^2}}}}}[/itex]. Use that and use some sufficiently fast speed such as 0.5c or 0.75 (letting v = c will give you a 0 in the denominator and not work).

    Also, you don't need a reactor that can generate huge amounts of energy "at any given time". Just like a car engine doesn't need to produce a massive amount of energy to propel a car to 150mph at any given time, neither would a spaceship. In fact, our fastest probes work on the concept of having an extremely weak "engine" that propels the object for very very long times and eventually achieves extremely fast speeds. See: http://en.wikipedia.org/wiki/Ion_drive
     
  5. Nov 8, 2011 #4
    thank you both i really apreciate the help, again i am only 19 and the most experience i have is watching through the wormhole with morgan freeman and high school physics. i am highly interested in learning more and perhaps someday help make an impact on the astrophysics world. also i believe that traveling by propulsion will be obsolete as far as exoplanetary exploration (which is of my utmost interest), i feel as tho the distances are so vast that we would need to develop a way to travel outside of normal means for example 4th dimension and beyond.
     
  6. Nov 8, 2011 #5
    also looking back on my work i saw where i messed up and 5.62x10^35 was one of the first numbers i came up with, i have a tendency to over think things.
     
  7. Nov 8, 2011 #6

    Drakkith

    User Avatar

    Staff: Mentor

    If you are truly interested in learning then start with the basics and go from there. Many popular shows on science are horribly inaccurate, so don't get too taken in by things like wormholes and extra dimensions. (At least not the way they are usually portrayed)
     
  8. Nov 9, 2011 #7
    Through the wormhole is just the name, hosted by morgan freeman it discusses the most intriguing topics in a documentary format with some of the more well know scientists. But where should i start?
     
  9. Nov 9, 2011 #8

    Drakkith

    User Avatar

    Staff: Mentor

    Hit up the academic guidance forum. :biggrin:
     
  10. Nov 15, 2011 #9
    well we currently can not use nuclear power to push something at 'C',
    But is it possible to convert something into 'Photons' itself , and then back to itself from 'Photons' , as energy is reversible in nature ????...this is totally fantasy question...but I wonder if that is possible .......
     
  11. Nov 15, 2011 #10

    Ryan_m_b

    User Avatar

    Staff: Mentor

    Nothing with mass can travel at c. To convert mass into photons you would need to annihilate it (By antimatter bombardment for example). No idea how you would turn it back. Either way that doesn't really solve how to travel because all you've managed to do is destroy the original object. You'll never be able to reassemble it from the light you've produced.
     
  12. Nov 15, 2011 #11
    The problem with reaching c is that as an object with rest mass approaches the speed of light, the mass approaches infinity. So the faster you go, the more energy you need to increase your speed.
     
  13. Nov 16, 2011 #12
    Hi Zachary
    You can't travel at light speed via rocket propulsion and exotic options, like warp drives and wormholes, take immense amounts of negative energy which is hard to make, to say the least.

    So what options are available? Rockets require carrying along all the fuel and propellant you intend to use, and if you're planning on stopping, the fuel+propellant required multiplies.

    What if you don't need to carry fuel or propellant? Using lasers, particle beams or accelerators, one can send fuel and propellant to a starship. This bypasses the limitations inherent in carrying all one's fuel and propellant. Several different designs exist - Google Jordin Kare and Sail-beam or Dana Andrews Roger Lenard and magnetic-sails or Gerald Nordley and mass-beams for some examples. Such systems, given sufficient pointing accuracy and/or particle steering, can accelerate a starship to near light speed for a much lower fuel and energy budget than a pure rocket alone.
     
  14. Nov 17, 2011 #13
    I think the original question has been answered:

    No amount of fuel or the energy we derive from it can accelerate an object with rest mass to C. As you approach C you need more and more energy to keep increasing speed until eventually you would need infinite energy to accelerate any faster (The energy requirements at the higher end of the scale would be horrendous)

    Lets also remember that if you get to even 0.1c, then impacting with stellar dust would release huge amounts of energy akin to nuclear explosions!

    I would disregard talks of exotic matter and Alcubierre "warp" drives and deal with proven/tested technologies for a greater understanding.

    Cosmo
     
  15. Nov 17, 2011 #14
    yes i understand no resting mass can reach c, to be repeatedly told i am wrong. my whole scenario was supposed to be hypothetical and i jus wanted to check my answer. tho i do appreciate everyones insight!! thanks!!!!
     
  16. Nov 17, 2011 #15

    PAllen

    User Avatar
    Science Advisor
    Gold Member

    The figure I've calculate and like to use is that impact with one gram at .9c will release the energy of the Nagasaki atom bomb. For dust to be that dangerous, you would have to be a lot closer to c. The ultimate limit (short of the exotics you mention) is when CMB radiation has become blueshifted to ultra-hard gamma rays with energy sufficient to disassemble even atomic nuclei.
     
  17. Nov 22, 2011 #16
    Sorry to spoil but traveling at the speed of light is impossible. The universe does everything to prevent you from traveling as fast. Increasing mass, reducing time and another which i sadly can't recall atm. Interesting fact: I have done some research on this and moving at 99.9999999% of the speed of light will move you in the future 100 years if you traveled at the speed for a week. That's 1 hour 40 minutes and 47.5 seconds (all my work :))
     
  18. Nov 22, 2011 #17
    Thankyou very much for this information; I knew I was on roughly the right track I just didnt have the exact numbers. I never considered extreme blueshifting of the CMB as a danger but obviously I should have wrt near light speeds.


    Is this a joke? Can you show your reasoning for this?
     
  19. Nov 22, 2011 #18
    @ Cosmo Novice, this is from a Stephen Hawking Documentary actually, pretty cool, it's about time travel. Strongly recommend some really interesting facts on it.
     
  20. Nov 22, 2011 #19
    Ah ok, my apologies.

    When you say time travel i thought you actually meant backwards - you are talking about accelerated reference frames due to relatavistic speeds. This is not time travel as such but you are correct in that using an accelerated reference frame you could "slow" time from another frame of reference. You do not "move" into the future, you just experience the passage of time slower than the person in a non accelerated reference frame - both frames of rerference are equally valid.

    I think I have seen the documentary you are reffering to and it was a nice thought experiment from my recollection and on a similar thought to the twin paradox.
     
  21. Nov 22, 2011 #20
    Dw, sounded a bit hazy at first, traveling backwards is impossible.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Amount of nuclear power need to propel a shuttle at the speed of light!
  1. Speed of light. (Replies: 32)

  2. Speed of light (Replies: 17)

  3. Speed of light (Replies: 16)

Loading...