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Thread: Problem with starship travel

  1. #1 Problem with starship travel 
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    Starships need plenty of fuel to go from one star to another right, Using methods like antimatter,hydrogen etc a massive storage unit is needed and i agree with that but why would a big storage unit would hamper the progress of the ship given there is not friction. Could someone please explain.


    just wondering
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  3. #2  
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    Inertia.


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  4. #3  
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    Fuel storage means extra mass, and even without friction it takes energy to accelerate a mass.

    It doesn't really take a lot of fuel to travel from star to star, it just takes a lot to do it in a reasonable amount of time.

    Say it takes 1 kg of fuel to accelerate a 1 kg payload to 100 m/s. To what speed can the same payload be accelerated to with 2 kg of fuel? 158 m/s.

    You doubling the fuel only increases the final velocity by less than 60%

    Tripling the fuel gets you to about 200 m/s

    The reason for this is that you have to burn fuel to accelerate the fuel you haven't burned yet. More and more fuel is being used just to accelerate fuel.
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  5. #4  
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    The correct way to do it is first stream out packets of fuel toward the destination. Then your ship accelerates better because it refuels along the way.
    A pong by any other name is still a pong. -williampinn
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  6. #5  
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    Quote Originally Posted by Pong
    The correct way to do it is first stream out packets of fuel toward the destination. Then your ship accelerates better because it refuels along the way.
    It seems like you would still have momentum transfer issues with the captured fuel...
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  7. #6  
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    What if you never actually take the fuel on board? Just grab it with a powerful electromagnet, and throw it behind you as you pass by.

    The process could become even more efficient if you make sure that there is always two way traffic traveling through the area. Say it's a trip between Earth and Proxima Centari. One ship grabs each packet and throws it toward Earth, on its way to PC, the other grabs the same packets, and throws them back toward PC, on its way to Earth.
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  8. #7  
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    Quote Originally Posted by Scifor Refugee
    Quote Originally Posted by Pong
    The correct way to do it is first stream out packets of fuel toward the destination. Then your ship accelerates better because it refuels along the way.
    It seems like you would still have momentum transfer issues with the captured fuel...
    I imagined the fuel as rockets, so they would burn a large amount getting up to speed. That's wasteful of fuel, perhaps, but the priority I think is optimal acceleration of manned spacecraft not conservation of fuel.

    Anybody care to do my math for me?

    Maybe something like a ramjet, eating a continuous stream, so the relative velocity of fuel is insignificant.


    Kojax I like your idea best. The perfect embodiment would act as a ladder with trains of climbers on opposite sides. You could have regular departures - say on the minute - without bottleneck because each accelerating vehicle would always be one minute's distance between the next and last.

    Something really weird would happen if you linked those accelerating vehicles and some were getting close to light speed. An then go figure the enormous mass of track segments pushed and pulled at near-light speed... it's weird huh?
    A pong by any other name is still a pong. -williampinn
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  9. #8  
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    The best way to 'get around' these limits is to make sure that the reaction mass thrown out the back of your space vessel is tossed backwards at a very, very high velocity.

    A recent New Scientist suggested two possible methods, though each will require new physics.
    http://nextbigfuture.com/2009/11/dar...er-rocket.html

    First : The dark matter ramjet. The space vessel uses currently unknown techniques to scoop up dark matter and compress it. According to one theory, that will cause the dark matter to annihilate itself with the emission of vast amounts of energy, which is permitted to escape by the back of the craft. This provides thrust, and a very high final velocity due to the high speed of the exhaust.

    Second : The black hole spaceship. A mini black hole of one million tonnes (about the size of a nucleus of an atom) is created by the new physics. It is held somehow by the spaceship, and slowly dissolves by Hawking radiation, with its mass converted to energy in the form of particles leaving at very high velocity (almost light speed). Those particles are permitted to exist the craft via the back only, causing acceleration forwards. Again, due to the extraordinarily high speed of the exhaust, the craft can accelerate to a very high speed.

    Of course, neither technique is possible with present day physics and technology, and only time will tell if either ever becomes possible. However, both involve the emission of material at enormously high velocity to permit the spacecraft to accelerate to a high fraction of light speed.

    A technique currently in use for some space probes, though very low in potency with today's technology, is the ion drive motor. Instead of a chemical rocket, ionised particles are accelerated by an electric field and emitted out back at high speed. This gives low acceleration, due to small mass being emitted per second, but a much higher final velocity due to the high speed of the exhaust.
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  10. #9  
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    Quote Originally Posted by Pong
    I imagined the fuel as rockets, so they would burn a large amount getting up to speed. That's wasteful of fuel, perhaps, but the priority I think is optimal acceleration of manned spacecraft not conservation of fuel.
    Well, at least you could definitely use it as a breaking mechanism when you want to slow down; capturing the fuel will slow you down due to transfer of momentum, and then you burn the fuel for still more deceleration.
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  11. #10 Problem with starship travel 
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    One problem with starship travel thats seldom pointed out is the risk of colliding with a rock or large chunk of ice between stars. The odds might be small but hitting a 2kg rock when travelling at thousands of kilometers per hour must be catastrophic.


    On the fuel side, the more you can take advantage of the environment to accelerate on the way to a destination and to decelerate(you need unfortunately considerable amounts of energy just to slow down) the better. I think satelites take advantage of planets and moons to acceletate (like in the game Star Control) pass them, is there a limit to the amounts of acceleration you can get with this techniques? Besides atmospheric braking which sounds hazardous are ther other means of decelerating without using onboard energy?

    Solar sail ship (maybe as auxiliary propultion?) sound interesting.

    Maybe for braking they could make a bungee cable between two rods like a sling-shot, manouver past small asteroids so its cought in the bungee-sling-shot module anddecelarate as the asteroid pulls on the bungee cables .
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  12. #11  
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    I have always thought that solar sails would have more potential for deceleration than acceleration. As the starship enters another star system, it unfurls its solar sail so that the radiation pressure of the new sun acts on it like a parachute.
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  13. #12 Re: Problem with starship travel 
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    Quote Originally Posted by icewendigo
    I think satelites take advantage of planets and moons to acceletate (like in the game Star Control) pass them, is there a limit to the amounts of acceleration you can get with this techniques?
    It depends on how fast the planet is moving relative to you and how massive it is. Note that you can only use a planet for a boost this way if the planet is already moving in the direction you want to move. Star Control was somewhat inaccurate, because it didn't have that limitation.

    But once you're talking about speeds near the speed of light, I think you would just flash past in an instant and not get any significant course change (unless you're passing by a black hole or something).
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  14. #13  
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    Doesn't it only take the fuel to accelerate you to the desired velocity, but once at that velocity, you'd just coast to the destination? In other words, why is a constant fuel supply necessary? Is there appreciable friction along the way? The Voyager space probe is not propelled anymore... it's just coasting.
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  15. #14  
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    Quote Originally Posted by william
    Doesn't it only take the fuel to accelerate you to the desired velocity, but once at that velocity, you'd just coast to the destination? In other words, why is a constant fuel supply necessary? Is there appreciable friction along the way? The Voyager space probe is not propelled anymore... it's just coasting.
    At 17 km/sec. At that speed it would take nearly 76,000 yrs just to reach Alpha Centauri.

    Again, the problem isn't getting there, it is getting there in a reasonable amount of time.
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    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  16. #15 Re: Problem with starship travel 
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    Quote Originally Posted by icewendigo
    colliding with a rock
    A fuel stream may help clear the way. I'm thinking fuel packets tiny relative to the manned craft. If the packets themselves are thrusting, some could maneuver to sacrificially intercept debris. Imagine this in wild ballpark of packets the size of trash cans, launched every second, from the moon most likely. Most would ultimately maneuver themselves into the "ramjet" of a manned craft, which carries no fuel.
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  17. #16  
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    About ten years ago, there was an article in Scientific American about starship potential, written by two NASA scientists.

    They suggested that, assuming known technology is developed to a state of perfection, humans would be able to accelerate to between 0.1 and 0.2 c (10% or 20% of light speed). They suggest this will take 500 to 1000 years.

    A simple calculation using the assumptions of maximum speed 0.1c and taking 10 years to accelerate to that speed, plus ten to decelerate again, shows that a trip to Alpha Centauri would take 55 years.
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  18. #17  
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    Yeah, we'd have to accelerate to simulate a normal Earth gravity, so travellers can stand up, walk around, and puke on the floor like civilized people.
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  19. #18  
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    Actually, Pong, simulating gravity is the easy bit. Simply build your starship with living areas well away from the centre and rotate the entire structure.

    A much more difficult problem is radiation. The entire galaxy is filled with cosmic radiation - very energetic particles which zip through everything, and will kill if people are exposed over a period of years. We can shield a ship using an outer shell of water, but it takes a lot of water.
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  20. #19  
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    Quote Originally Posted by skeptic
    Actually, Pong, simulating gravity is the easy bit. Simply build your starship with living areas well away from the centre and rotate the entire structure.
    Maximum acceleration is going to 1g in any case, so I'd think it better just to maintain that, and use it for your simulated gravity.
    A pong by any other name is still a pong. -williampinn
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  21. #20  
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    Pong

    If you accelerated at 1 G (which is seriously unlikely even to be possible), you would reach 10% of light speed in less than 2 months. You would then coast for 42 years before decelerating. While coasting, without rotation, you would be in zero gravity. Having one gravity from acceleration/deceleration for less than 4 months, and having zero G for 42 years kind of defeats the purpose, don't you think?
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  22. #21  
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    I'm assuming the craft hauls no fuel, so 1g is easily attainable. But yeah you're right there would be a speed limit. Maybe better use fuel streams interplanetary.
    A pong by any other name is still a pong. -williampinn
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  23. #22 not much time 
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    They suggest this will take 500 to 1000 years.
    I hope you dont mean the time taken to develop this technology because we would(please correct me if I'm wrong) likely be running out of resources then and unless we had started mining places like the moon we would be looking more at bioastrotechnology(new word there).Just something to note.
    just wondering
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  24. #23  
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    there is no way we could use modern fuel or any fuel in the near future for space travel, we need to enter the plasma and fusion era before we can go deep into space.
    the more science you know, the less crap you get.
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  25. #24 Not part of topic 
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    how do you unquote
    just wondering
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  26. #25 Re: Problem with starship travel 
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    Quote Originally Posted by Pong
    Quote Originally Posted by icewendigo
    colliding with a rock
    A fuel stream may help clear the way. I'm thinking fuel packets tiny relative to the manned craft. If the packets themselves are thrusting, some could maneuver to sacrificially intercept debris. Imagine this in wild ballpark of packets the size of trash cans, launched every second, from the moon most likely. Most would ultimately maneuver themselves into the "ramjet" of a manned craft, which carries no fuel.
    Launched how? If you are using the same type rocket propulsion, I don't see any savings. If you launch them at a slower speed ahead of the ship, the ship will lose momentum so some of the fuel will be used up just to make up for the momentum loss. ( this is a draw back to the Bussard Ramjet; at a certain point, the drag from collecting the fuel equals the thrust produced by the fuel. The limiting speed has been estimated to be from 1 to 10% of c). If you launch them so that they match speed with the ship, you'll end up burning up just as much fuel as if you had carried the fuel with you in the first place.

    If you launch them by some type of electromagnetic cannon, you stil ened up wasting fuel if the fuel packets are traveling slower than the ship upon rendezvous.

    So the most efficient means would be to launch them so that they match spped with the ship at rendezvous. But that means that you will not be launching them ahead of the ship, but from behind the ship. They won't be able to clear a path. This also means that your fuel launch system needs to be nearly fool proof. If the system breaks down, your ship can be left with out fuel. The aiming would have to be very precise also. Even an error of one millionth of an arc second produces a error of 46 kilometers at 1 light year distance.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
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  27. #26 Re: Problem with starship travel 
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    Quote Originally Posted by Janus
    So the most efficient means would be to launch them so that they match speed with the ship at rendezvous. But that means that you will not be launching them ahead of the ship, but from behind the ship. They won't be able to clear a path.
    I think there's enough space, in space. :wink:

    As said, the fuel packets would be capable of small course adjustments. I was thinking they could stage out into more continuous feed as well, at very low cost. So the ship spends zero energy collecting fuel and little energy handling it. That differs crucially from the Bussard Ramjet, which draws passive fuel with a broad scoop. Conceptually the ship would be a tube on a stream. If the tube is very long, it is possible to operate more like pulsejet than ramjet (incorporates a valve).

    A better embodiment of fuel stream provides for return travel, and also multiple ships. That would be a stream orbiting between stars, or if local, a stream path not unlike comets and near the plane of planets. In this case the fuel is practically stationary, though it might have "lanes".

    I do think this is better suited to interplanetary travel, where you want round trips accelerating for 1G the entire way. One could always argue less acceleration for fuel savings, but we're an impatient species, so 1G is optimal.

    I would like the smallest division of manoeuvrable packets to be something on the scale of juice boxes or candy bars, with a simple lens-powered (laser) guidance mechanism. So you hit it with a light, and it thrusts (very very slightly) depending on how the light strikes it. Rude mechanism not computer. A nice feature would be last-minute staging of fuel down to granular stream. Maybe look at consumer packaging and dollar-store toys for inspiration.

    The energy cost of astronomically huge course change is insignificant. A stream would tend to narrow in deep space just by mutual gravity of the packets, but I dunno if that's sufficient. And a very very slight slipstream effect, but again insufficient. I imagine that a craft would project beacon "headlights" so that packets days or weeks ahead could tweak into position - then your tube may be not much wider than the packets, at the intake end.
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  28. #27  
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    This may seem a bit strange but if you only need to throw particles behind to create thrust(dark matter powered idea) then couldn't we create a type of paddle steamer idea where we throw the particle then draw it back in where it is thrown again.
    just wondering
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  29. #28  
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    zendra

    That would be like your paddle steamer rotating the paddle clockwise one turn and then anticlockwise one turn, which would neutralise the movement. Picking up mass to throw it again would reverse the thrust leaving you dead still in space.


    Pong
    The idea of throwing fuel packages to rendezvous with the craft would work well at low speed. In other words, getting the craft through its first few months of acceleration. This could, in theory, be done using a massive linear electromagnetic accelerator on the moon.

    However, we are talking of a final speed of the order of one tenth of light speed. Do you know how fast that is? To get your fuel packages to anything like that speed would require enormous accelerations, if achieved with some 'throwing' device, such as a linear electromagnetic accelerator. The accelerations would simply turn our fuel packages into one molecule thick film, or tear them to molecular shreds.

    To get to those incredible speeds using lesser accelerations would require that the packages would have to be carried on a space vehicle rather similar to the star ship that is carrying the passengers. If you are going to do that, why not avoid all the hassle and simply carry all the fuel on the one craft?

    I also have to point out that acceleration/decelerations of 1 G are almost certainly impractical. I suspect that about 1% of that would be all we could hope for. The space craft is not going to travel under rocket power, which is what gives high acceleration. Rocket power is fine for achieving orbit, but not able to achieve such high final velocities. Much more likely is a futuristic ion drive engine, firing ions backwards at close to light speed. Such an engine will not be able to achieve high accelerations, though it will -eventually- achieve very high velocity.
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  30. #29 dam 
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    what if the pull was brought back through a different medium? paddle steamers don't reverse their thrust because the top goes through the air instead of water.Couldn't we achieve a similar effect in spaceships?
    just wondering
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  31. #30  
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    You could stretch a cable and run ferries on opposite sides. That's a lot of cable.
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  32. #31  
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    i mean having the cable run through the ship in a medium that causes less reverse thrust. such as keeping water or something in a section of the ship and running the cable through there
    just wondering
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  33. #32  
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    I suggested multiple ferries running opposite directions because this balances the strain on the cable.

    Neither idea's appropriate to interstellar distances or tolerable travel times. This discussion's coming down to Earth.
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  34. #33  
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    We are talking of a starship that will travel at least 4.3 light years (distance to Alpha Centauri). A cable that long is not possible. Nor could it be used at 0.1c.

    Since the starship will be travelling through vacuum, there is nothing else to take the place of a cable.

    We do not know what will be discovered and invented in the future, but based on today's science, the only ways of possibly getting to the sort of speeds needed for interstellar travel involve throwing something backwards at enormous speed, or possibly using light in a light sail.

    It has been suggested that it might be possible to build a laser of enormous power, which will be fired at a starship leaving our solar system, so that the laser beam enters the light sail and pushes the ship on its way. If the laser beam pushed for some years, it might get the starship up to a reasonable fraction of light speed.

    However, such a laser is way beyond today's technology, and would require power inputs of gargantuan proportions. It may never be possible.

    My own view has been that the first human carrying starship will be a space habitat modified for interstellar travel. With a very large, almost self sufficient habitat, the time taken to get there is less important. However, strapping onto the habitat a giant linear accelerator, to fire ions at almost light speed out the back, might be enough to get the habitat to a reasonable proportion of light speed - say 0.1 to 0.2 c.
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  35. #34  
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    Quote Originally Posted by skeptic
    My own view has been that the first human carrying starship will be a space habitat
    My guess too. Moreover, I trust that we can blunder into interstellar travel just by having evolved large self-sufficient habitats that happen to go astray. This would take a while, but it seems inevitable.

    A problem here is evolution. On this time scale we evolve so much that colonists retain no allegiance to mission. We can't expect them to share the same values after 10,000 years of self-sufficiency. They'd be practically an alien species... collective mind... AI... cannibal... who knows? They might hate us and want to kill us. So how do we ensure they reach that star? Revisit the fuel stream. Make it a trail of breadcrumbs.
    A pong by any other name is still a pong. -williampinn
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  36. #35  
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    How long to reach a star? It all depends on cruise velocity, and to a lesser extent, degree of acceleration/deceleration.

    I suggested 55 years to reach Alpha Centauri, but that is based on 0.1 c and ten years for acceleration and for deceleration. That might well be wrong.

    However, the link with Earth will be via some communication device. Perhaps a messaging laser? And that will travel at light speed, meaning time to send a message from Alpha Centauri to Earth, and receive a reply, of 8.6 years.

    I do agree that, in the long run, humanity may change, by evolution or by genetic science, into many different forms. Perhaps in a million years, there may be a million different species of intelligent beings, all descended from us.

    However, they are far more likely to be indifferent to other human descendants than hostile. How can you wage war across light years, when getting there takes many decades each way? The equivalent of trade would be in knowledge. Sending data packages via messaging laser across the galaxy.
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  37. #36  
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    Quote Originally Posted by skeptic
    How long to reach a star? I suggested 55 years...
    That's operating in hasty-wastey Earth-time. Why not 10,000? It's not a rhetorical question.

    Okay Pong's officially thinking like a space alien now.
    A pong by any other name is still a pong. -williampinn
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  38. #37  
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    Pong

    In terms of current capability, it would be 10,000 years, if not more.

    However, I based the speed on the article I read in Scientific American by NASA scientists, who claim that 0.1 c would be possible, but probably not for 500 to 1000 years.

    Of course, to depart in a starship that will take 10,000 years, when another few hundred years of science and technology will lead to a starship able to cross in 55 years.....

    Imagine arriving 10,000 years later only to find that every lump of rock in the Alpha Centauri system is already overpopulated with humans?
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    Unless you can build some kind of hibernation or stasis chamber, humans on such long voyages would need incredible amounts of supplies, including oxygen. Possibly a hollowed out lump of rock maybe ten miles across might fit the bill for nearby interstellar travel over a century, maybe?

    I do wonder if FTL travel is possible? I don't think we can currently even imagine such an engine. Wormholes need impossible amounts of power to work so can be disregarded.

    I also wonder about even ships moving at a good fraction of light speed. Could we survive? Call it time dilation or whatever you want but as we get nearer light speed, what we call time slows down. But only for matter. Light and all forms of energy still travel at the same speed. So imagine you have been slowed down ten times. Energy is still working at the same speed so now seems ten times more powerful. What would have stimulated a nerve before may now burn it out, and kill you as your brain catches alight.
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    Quote Originally Posted by skeptic
    Pong

    In terms of current capability, it would be 10,000 years, if not more.

    However, I based the speed on the article I read in Scientific American by NASA scientists, who claim that 0.1 c would be possible, but probably not for 500 to 1000 years.

    Of course, to depart in a starship that will take 10,000 years, when another few hundred years of science and technology will lead to a starship able to cross in 55 years.....

    Imagine arriving 10,000 years later only to find that every lump of rock in the Alpha Centauri system is already overpopulated with humans?

    Marvel Comics did a story on this some 40 years ago where a man is sent on a thousand year voyage in suspended animation. FTL travel is discovered some time later and he arrives at his destination to find man reached it several centuries earlier.
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    none of these theories will work, we are no where near being willing to spend 55 years in space when we know very little about the other solar system, I believe there are planets better than earth out there, but far beyond reach, the laser theory would be so hot it would incernerate the ship, and the cable theory is really only useful for the moon, but the other 10 miles theory is not practical either, ofcourse the moon is are test base for space and a colony should be built there( it's extremes prepares us for the worse so we will be able to tolerate more when we get to the planets that are slightly milder, and we should start training people and doing experiments breathing different types of air, and stuff like that. but we definitely need speeds far faster to get anywhere out of the solar system fast, like maybe 2 million miles a second. Many years ago people that if someone traveled even near the speed of sound all humanity would be negatively effected and it was impossible, it's ashame some people still think the same about a speed exponetialy faster, the only problem is to get the government to stopping using money spying on the size of there citizens asses and on space.
    the more science you know, the less crap you get.
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    Quote Originally Posted by Cyberia
    Call it time dilation or whatever you want but as we get nearer light speed, what we call time slows down. But only for matter. Light and all forms of energy still travel at the same speed. So imagine you have been slowed down ten times. Energy is still working at the same speed so now seems ten times more powerful. What would have stimulated a nerve before may now burn it out, and kill you as your brain catches alight.
    This is absolutely wrong. The speed of light is invariant, meaning that it has the same value relative to any frame as measured from that frame. In your space ship light travels no faster relative to you than it does for someone sitting home at Earth as far as you are concerned. Everything will seem perfectly normal for you. If your ship had no windows, you wouldn't even know that you had any relative motion with respect to the stars at all.

    The only Light/energy that you will see an increase in will be that produced by objects ahead of you, which have a high relative velocity to you. (the stars in front of you) This will be due to relativistic Doppler shift. At a relative velocity that produces a time dilation rate of 10, we get a Doppler shift factor of 20. Meaning visible light from those stars will shift to the hard Ultraviolet with 20 times the energy. But since the total energy in starlight is very small, 20 times it is not significant. Pretty easy to shield against. Much less of a problem than the collision with interstellar dust and gas will cause.

    On the other hand, the light from the stars behind you will shift to 1/20 of their frequency, towards the radio waves, and will have 1/20 the energy.

    IOW, light from the stars in front of you will blue-shift, light from stars behind you will red-shift, and light produced by objects in the ship with you will be normal.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    If we assume a starship is accelerating to its cruise speed by throwing stuff out the back, such as ions at a high fraction of light speed, then we need large amounts of reaction mass for both acceleration and for deceleration.

    This puts severe limits on how fast the space vehicle can reach. If we accelerate to a very high fraction of light speed, there will be insufficient reaction mass to decelerate to zero again, and our starship will pass through the Alpha Centauri system at great speed. The thing is that the reaction mass that is destined for deceleration must also be accelerated to almost light speed.

    I am no rocket scientist, but the SciAm article implied that when the maths was done, it was discovered that the fastest practically attainable in theory was 0.1 to 0.2 C. That is, for any starship drive based on throwing mass backwards.

    The only alternative I am aware of, that has real potential, is light sails. So far, that is still theoretical only. The few efforts to try them in practise have ended in disaster. At least with ion drive motors, some have already been built and proven to be practical.
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    Quote Originally Posted by skeptic
    If we assume a starship is accelerating to its cruise speed by throwing stuff out the back, such as ions at a high fraction of light speed, then we need large amounts of reaction mass for both acceleration and for deceleration.

    This puts severe limits on how fast the space vehicle can reach. If we accelerate to a very high fraction of light speed, there will be insufficient reaction mass to decelerate to zero again, and our starship will pass through the Alpha Centauri system at great speed. The thing is that the reaction mass that is destined for deceleration must also be accelerated to almost light speed.

    I am no rocket scientist, but the SciAm article implied that when the maths was done, it was discovered that the fastest practically attainable in theory was 0.1 to 0.2 C. That is, for any starship drive based on throwing mass backwards.
    It really depends on how fast you can throw those ions out the back.

    The formula is:



    Where

    MR is the mass ratio of payload + fuel to payload.
    v is the final velocity
    Ve is the exhaust velocity.

    at a Ve of 0.01 c and a final velocity of 0.1c we get a mass ratio of 22777

    If we bump Ve up to 0.1c we get 2.73

    So by increasing the exhaust velocity by a factor of 10 we reduce the mass ratio by a factor of 8343
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    Well... If you have such a big spaceship, you would need to use that much fuel to move it. So you mind as well have a small ship that uses less fuel than a large one that globbles up fuel.

    And.... it seems that we've been thinking only about moving it. When it's time to pull the breaks, you're going to wish you had a smaller ship and curse inertia.
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    Technerd

    I suspect that a large spaceship is going to be essential. If it takes 55 years to get to Alpha Centauri, that is essentially a lifetime for the passengers. They are not going to be happy on a small ship. Nor could a small ship carry everything that is required.

    My own view of an interstellar ship would be a very large structure, rotating for gravity, and with the living area covered with a 2 metre shell of ice to shield against cosmic radiation. It will have an advanced linear accelerator running through its long axis, to accelerate ions to near light speed for acceleration/deceleration. It would also carry a vast amount of water for reaction mass. Probably thousands, or hundreds of thousands of tonnes. It would probably pick up this mass in space, since there is a lot of ice in various parts of our solar system.

    Energy would come from nuclear fusion, both for propulsion and for the life support systems. The latter would be enormous, since they would need to be close to a self sufficient mini-ecosystem.
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    Fuel and mass are ALWAYS the main issue when it comes to getting from point A to point B in a reasonable time.

    The only way to avoid at least one of those issues is if you were able to get thrust from power conversion alone (I'm talking electricity) which you can get from sunlight.

    Assuming you were somehow able to harness dark energy (the theoretical force that is causing the universe to expand) through low power solar power, then at least fuel wouldn't be a problem. If your acceleration was rocket level or above, you'd do just fine.

    But that sounds just too good to be true, and it's basically a science fiction handwave. If and when we do harness dark energy, I don't think we will do it with solar power.

    I suspect there are plenty of forces in the universe we know nothing about that haven't even been tapped yet.
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    Quote Originally Posted by zendra View Post
    Starships need plenty of fuel to go from one star to another right, Using methods like antimatter,hydrogen etc a massive storage unit is needed and i agree with that but why would a big storage unit would hamper the progress of the ship given there is not friction. Could someone please explain.
    Well that's if we ever get to the point in wich we could travel to other stars! I mean even if we achieved the speeds of light you could still hit things? I mean what if a ship traveling at 186,000mps hits an astroid? not very pretty!
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    Quote Originally Posted by Physicsforall View Post
    Quote Originally Posted by zendra View Post
    Starships need plenty of fuel to go from one star to another right, Using methods like antimatter,hydrogen etc a massive storage unit is needed and i agree with that but why would a big storage unit would hamper the progress of the ship given there is not friction. Could someone please explain.
    Well that's if we ever get to the point in wich we could travel to other stars! I mean even if we achieved the speeds of light you could still hit things? I mean what if a ship traveling at 186,000mps hits an astroid? not very pretty!
    .

    Unless you have black holes for shields or the equivalent thereof, then yeah, you die horribly. The way I see it, if we ever get that god-mode with techonology, we had better have our social issues worked out (world peace, ETC).

    Because truth be told, if you can go warp speed in a spaceship (that can take a hit or two at FTL), you don't wan't a socio-path behind the wheel. Realistically, war would be progressing the way it already is. A lot more MAD scenarios than science fiction indicates.

    War is not a matter of using the weakest strategies available, it's about using the most powerful stuff you've got.

    Either we have universal piece with FTL drives, or we blow ourselves back to the stone age not long after.
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  50. #49  
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    Quote Originally Posted by lorbo View Post
    Unless you have black holes for shields ...
    If you have black holes anywhere near your ship, interstellar travel should be the least of your concerns.
    "Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us." -Calvin
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    Quote Originally Posted by lorbo View Post
    Quote Originally Posted by Physicsforall View Post
    Quote Originally Posted by zendra View Post
    Starships need plenty of fuel to go from one star to another right, Using methods like antimatter,hydrogen etc a massive storage unit is needed and i agree with that but why would a big storage unit would hamper the progress of the ship given there is not friction. Could someone please explain.
    Well that's if we ever get to the point in wich we could travel to other stars! I mean even if we achieved the speeds of light you could still hit things? I mean what if a ship traveling at 186,000mps hits an astroid? not very pretty!
    .Unless you have black holes for shields or the equivalent thereof, then yeah, you die horribly. The way I see it, if we ever get that god-mode with techonology, we had better have our social issues worked out (world peace, ETC).Because truth be told, if you can go warp speed in a spaceship (that can take a hit or two at FTL), you don't wan't a socio-path behind the wheel. Realistically, war would be progressing the way it already is. A lot more MAD scenarios than science fiction indicates.War is not a matter of using the weakest strategies available, it's about using the most powerful stuff you've got.Either we have universal piece with FTL drives, or we blow ourselves back to the stone age not long after.
    Or we could have some sort of way to pull the object aside (using blackholes is unlikely, because there is a huge problem of the ship getting sucked into it!)... But as far as it goes,there are problems such as radiation, the shape of the craft? As far as the fuel goes (some people said this before) there are most likely plenty of undiscovered forces, and fuel.
    Last edited by Physicsforall; December 17th, 2013 at 04:45 PM. Reason: Black holes?
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