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How fast can we truly ever hope to make a spacecraft?

  1. Aug 2, 2011 #1
    OK I'm not sure if this is the proper place to post this question, but since there probably is no correct definitive answer but hypothesis ....here goes...
    What is the fastest speed in the form of percentage of light speed, that we will realistically probably ever be able to get a spacecraft going? NO warp drives,..no FTL drives like in the movies or on SciFi (not SyFy).because I understand there is No law of physics preventing those from hypothetically being possible but I have never heard even an incling of an idea how one could even begin to actually make those possible.What I mean a space craft large enough to carry a crew and everything needed to support it,or even seceral space probes.Using any one of the various different propulsion types, different engines that have been designed and tested and even some of the ones that have not quite been built because technology is not quite there yet but will realistically exist in the future. Combined with sources of energy that will realistically exist at some point. What's the fastest speed we can realistically count on being able to explore the galaxy at SOMEDAY. For example will we be able to get a craft going at 10 to 20% the speed of light?? I just wonder because if we could get a craft going to 20% the speed of light than we could send probes out to our closest neighbors in the galaxy.the alpha centauri stars. They are what 4 light years away, so at 20% Light speed it should take what?.. 20 yrs to get there approximately? And then data and pictures could be sent back at the speed of light. So in under 30 yrs we could have the answer to the question is there life around our closest neighbors.And on to each star in our neighborhood. If we could get going that fast we could realistically find out the answers to a lot of questions in just a single or just or up to a few life times...and not 100,000 yrs or whatever it would take going the speed of what is now our fastest moving space craft, the new horizons probe. just to get 4 light years away. It seems like it is a matter of power...energy... that would decide how fast we could get a craft going using one of the propulsion systems we have or have some understanding of how to actually make work. So I guess I'm just wondering if any of you have ever heard this question or something like it ever asked or discussed before by someone knowledgeable in a field relative to this..someone much smarter than myself! :confused:
     
    Last edited: Aug 2, 2011
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  3. Aug 2, 2011 #2

    Ryan_m_b

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    I don't think this question is really answerable. We have no good idea as to how to make propulsion systems with good enough performances (e.g fusion rockets, antimatter rockets) so we can't say with any certainty what we will be able to achieve in the future. It could be that within the next century breakthroughs in nuclear fusion technology allow us to make probes capable of >.1C, it's also conceivable that we'll uncover a bunch more engineering issues we didn't know about and be little better off in terms of technology than we are now.

    The best proposal I've heard for trying to make an interstellar probe is a starwisp but even that is a monumental engineering challange.

    Regarding the building of a crewed vessel not only would you have to build the relevant propulsion but you would also need to fit a stable ecosystem into the ship and an industrial complex capable of maintaining it! These are both far bigger problems than propulsion.
     
  4. Aug 2, 2011 #3
    As a Designer in "Project Icarus" I can say that achieving high percentages of the speed of light is not easy. But there are several ways of achieving near-light speeds if one has a sufficient power supply. The most promising system in terms of easy extrapolation from current knowledge is the mass-beam, which pushes a starship with a beam of small pellets/sails. In the near-term such a system might reach ~0.1-0.15c via laying a pathway of fuel for a larger vehicle to pick up or capture on the fly.

    With more beam power the pellets can push the vehicle directly - if they're reflected with the same relative velocity as the vehicle, then the energy efficiency is the highest possible for any system. But the power supply needs to be very high and the aiming system very accurate, though the pellets themselves can be made partially self-guided. Such a system can push a vehicle as close to light speed as one can fling the pellets - well a little bit slower.

    For sheer energy efficiency I think the best concepts are interstellar solar sails (which can reach ~0.12c with some tricky materials design) and the chip-sat concept of Mason Peck, which accelerates the chip-sats using the magnetic field of Jupiter. He thinks they might reach a similar speed. With the right guidance such might provide a means of sending fuel to a larger starship capable of carrying a crew. Such "free-energy" concepts have a lot of appeal.
     
  5. Aug 2, 2011 #4

    Ryan_m_b

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    Let's not get too far ahead of ourselves. Crewed missions to orbit, near Earth objects and even intrasystem travel are a world apart from the necessities of an interstellar crewed mission.
     
  6. Aug 2, 2011 #5
    Intersystem travel is like walking to the bottom of our garden and interstellar travel is like walking to the next city. At the moment we havent even gotten off our back porch!

    This is a crude analogy but I think gets the point across :biggrin:

    Unfortunately for us, the speed limit of the universe is a physical mitigating factor. Even if we get close to the upper limit the galaxy is still a big, big place. No one has yet mentioned intergalactic travel which I am very grateful for.

    Ah if only we had Geordie LaForge.....
     
  7. Aug 2, 2011 #6

    Ryan_m_b

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    To adjust the analogy I would say that interplanetary/intrasystem travel is akin to walking from the beach hut to the beach whereas interstellar travel is like going from the beach hut to the mountain on top of the continent across the sea (and we haven't yet gotten out of bed).

    I say this because whilst interplanetary and interstellar travel seem superficially similar in technical requirements in reality they fundamentally aren't. Interstellar travel requires far more than a simple larger scale version of interplanetary technology, it requires mastering of sciences that are far more complex.
     
  8. Aug 2, 2011 #7

    PAllen

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    Let's not forget protection of the crew. If you ever reached even .86c, then impact with 1 gram particle would release 1 Nagasaki fission bomb's worth of energy.
     
  9. Aug 2, 2011 #8
    ' As a Designer in "Project Icarus" '

    Wow !! I remember being at the BIS meeting when the 'Daedalus Final Report' was published. ( I collected a bunch of autographs ;- ) Unfortunately, 'productive' pulsed fusion turned out to be significantly harder than expected...

    By comparison, the dust-shielding issues were 'just engineering': An automatic dispenser would launch and replenish a cloud of talc-sized particles ahead of the craft to 'mop up' dust grains and ablate gravel. The craft itself would have a multi-layered, spaced buffer at the bow, with a modest overhang to take care of transverse velocities...
     
  10. Aug 2, 2011 #9
    Wow!! just what I thought...BIG PROJECT!! I agree with the key here is Power...right?? So are I wonder if achieving true fusion for power will ever happen. I think i heard they can do it, but it takesmore power going in than they get out or something like that.So there's no point in doing it that way. we need the Mr fusion. oh and what speed or percent of light speed does >.1c represent? I'm still learning about all this. I'm teaching myself? So do you all think we might hit 10 -20 % of LS? I' didnt get whether or not you think that will happen say in 100 yrs or so. And i agree sending people not practical..Probes are the way to go and if we find another earth...then we send em if we can
     
  11. Aug 2, 2011 #10

    DaveC426913

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    Well, .1 is one tenth of one, so .1c would be 10% of the speed light.
     
  12. Aug 3, 2011 #11

    Ryan_m_b

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    The problem isn't just power, it's propulsion. You've got to turn that power into momentum, fusion rockets could give a specific impulse of 100,000 seconds. In other words if we had an equal ratio of ship mass to fuel mass the ship will be able to accelerate at 1g for 100,000 seconds. In other words for a fusion rocket to reach 0.1C would require 30 parts fuel for every 1 part ship!!

    On top of this you now have the problem that your probe (probably massing on the order of 10s-100 of tonnes) now has the potential to be a kinetic weapon capable of releasing 5e17-5e18 joules, with pretty much no opportunity to stop it.
     
  13. Aug 3, 2011 #12
    wow, It looks like we are probably stuck here in our little corner of the galaxy, a spec on a spec, on a spec, on a spec, on a spec. for the long forseable future,. probably be lucky if we ever even get out of our solar system..it will just be too expensive.We would have to get the whole planet to cooperate and work toward the goal of sending people out to our closest neighboeing stars. Like the Apollo program was here in the US. But on a global scale. Probably would take an impending global catastrophe to make it happen.
     
  14. Aug 3, 2011 #13
    Oh i forgot NIK and qraal,.....what is or was project Icarus?
     
  15. Aug 3, 2011 #14

    Ryan_m_b

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    I doubt it. Impending disasters wont get us to act because if they are too far away they are abstract (why worry about something that will happen in thousands of years?) and if they are too close then we wont have time ("you want to design a fully functional, stable, closed ecosystem capable of supporting a closed-system industrial society....in 10 years??")

    Also if you were able to do the later and discover all the necessary science, engineer all the necessary technology and build all the necessary infrastructure to make a functional, stable, closed ecosystem capable of supporting a closed-system industrial society it would be much easier to live in stations orbiting Earth rather than trying to play space cadet.
     
  16. Aug 3, 2011 #15
    It would be easier but I think psychological reasons would always lean us to earth analogues.

    For me - to terraform a planet we need to smash it with enough comet material to create and warm an atmosphere. Then send in a few hundred thousand extremophile containing "seed pods". Then sit back for a couple million years - maybe read a book and have some lunch - hey presto!

    As a technological space-faring species - once we have intersolar capability we should try to "seed" life as much as possible in our little corner of the galaxy.
     
  17. Aug 3, 2011 #16

    Ryan_m_b

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    Earth analogues? I am highly sceptical of the idea that there are planets which have Earth like conditions and evolved life that we can co-exist with.

    I like your idea of terraforming, far more realistic than many peoples expectations. I don't particularly care about the idea of directed panspermia, seems a bit pointless.
     
  18. Aug 3, 2011 #17
    By earth "analogues" I mean planets which could be developed into earth analogues - this is assuming a long term terraforming process as I indicated above. Essentially we would need an iron core planet of roughly equivalent mass which we then could terraform.

    I did not mean earth type life we can co-exist with. Although if life did develop independently of us on an earth like analogue then it could be expected we would have similarities although I do not believe you colud ever integrate two ecologies (at least not without profound consequences.)
     
  19. Aug 6, 2011 #18
    "Project Icarus" is the sequel to "Project Daedalus", which was a design study of a fusion propelled interstellar probe, conducted from 1973-1978. Our webpage is here...

    http://icarusinterstellar.org/" [Broken]

    We have the goal of slowing down the vehicle, rather than specifying a flyby mission like "Daedalus" and the maximum mission duration has been expanded to 100 years. We're also investigating non rocket concepts to enhance the speed, though still fusion powered/propelled for part of the mission, most likely the boost phase.
     
    Last edited by a moderator: May 5, 2017
  20. Aug 17, 2011 #19

    The fastest interstellar probe velocity that I can calculate is using a Mercury gravity assist:
    [tex]v_t = \sqrt{\frac{2GM_e}{r_e}} + 2 \sqrt{\frac{G M_{\odot}}{r_1}}[/tex]
    [tex]\boxed{v_t = 106.938 \; \frac{\text{km}}{\text{s}}}[/tex]
    It is possible to increase this velocity by using booster rockets at Mercury periapsis, however this would only contribute to a fraction of this velocity.

    Even at this velocity it would still require 11.763 thousand years to reach the nearest star Proxima Centauri.

    Key:
    M_o - Sun total mass
    M_e - Earth total mass
    r_1 - Mercury semi-major axis
    r_e - Earth radius

    Reference:
    http://en.wikipedia.org/wiki/Gravity_assist" [Broken]
     
    Last edited by a moderator: May 5, 2017
  21. Aug 17, 2011 #20

    DaveC426913

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    I told them five years ago they should have started this journey!

    All that time wasted...
     
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