# Alpha Centauri Explorer II

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#### keermalec

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'><font size="3">What about using ION engines in stages?</font></DIV><br /><br />Dryson, using four stages will not multiply the final velocity by four.</p><p>If&nbsp;V is the change in velocity of a single stage, and P is the&nbsp;wet mass to&nbsp;dry mass ratio, the final speed is&nbsp;V1 + V2 + Vn&nbsp;and the necessary initial mass is P1 * P2 * Pn.</p><p>Example</p><p>Stage 1:<br />V1 = 3 km/s<br />P1 =&nbsp;10 (including mass of stage 2 + payload)</p><p>Stage 2:<br />V2 = 3 km/s<br />P2 =&nbsp;5 (including payload)</p><p>Stage 3 (payload)<br />V3 = 0<br />P3 = 1</p><p>Total change in velocity = 3 + 3 + 0 = 6 km/s<br />Total initial mass =&nbsp;10x5x1 = 50 x payload mass</p><p>Concerning the laser beam pointing at the destination star, this cannot be of use in any way. If you want to thrust to Alpha Centauri, simply point your vehicle in the right direction and thrust away.</p><p>Concerning the original post on this thread, if you're interested in what nuclear fusion could do for us in something like a century from now, check out Borowski's 2005 Piloted Spherical Torus Nuclear Fusion Propulsion. To summarize, this manned ship to Jupiter and Saturn attains a peak velocity of "only" 156 km/s on the Saturn scenario. This is 0.05% of light speed. Such a ship could get to Alpha Centauri in just over 8,000 years...</p><p>Adding many more fuel tanks and dropping them off as the ship accelerated could probably reduce trip duration to 1,000 or 2,000 years but anything less would require more advanced fusion or antimatter.&nbsp;</p><p>I would say anything beyond that is unfortunately pure science fiction, today.</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

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#### dryson

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Dryson, using four stages will not multiply the final velocity by four.If&nbsp;V is the change in velocity of a single stage, and P is the&nbsp;wet mass to&nbsp;dry mass ratio, the final speed is&nbsp;V1 + V2 + Vn&nbsp;and the necessary initial mass is P1 * P2 * Pn.ExampleStage 1:V1 = 3 km/sP1 =&nbsp;10 (including mass of stage 2 + payload)Stage 2:V2 = 3 km/sP2 =&nbsp;5 (including payload)Stage 3 (payload)V3 = 0P3 = 1Total change in velocity = 3 + 3 + 0 = 6 km/sTotal initial mass =&nbsp;10x5x1 = 50 x payload massConcerning the laser beam pointing at the destination star, this cannot be of use in any way. If you want to thrust to Alpha Centauri, simply point your vehicle in the right direction and thrust away.Concerning the original post on this thread, if you're interested in what nuclear fusion could do for us in something like a century from now, check out Borowski's 2005 Piloted Spherical Torus Nuclear Fusion Propulsion. To summarize, this manned ship to Jupiter and Saturn attains a peak velocity of "only" 156 km/s on the Saturn scenario. This is 0.05% of light speed. Such a ship could get to Alpha Centauri in just over 8,000 years...Adding many more fuel tanks and dropping them off as the ship accelerated could probably reduce trip duration to 1,000 or 2,000 years but anything less would require more advanced fusion or antimatter.&nbsp;I would say anything beyond that is unfortunately pure science fiction, today.&nbsp;&nbsp; <br />Posted by keermalec</DIV></p><p>&nbsp;</p><p>I wasn't speaking about stages, in the ship itself but 8 total ION engines. Two would fire to max velocity, once achieved the engines would decrease&nbsp;to 25%&nbsp;thrust as two more engines fired to max thrust, once these two engines achieved max velocity they would decrease to half thrust, the next would fire to max velocity. When max velocity has been achieved the engines would decrease to 75% velocity. The final two engines would fire to max velocity. In theory each time an engine decrease's velocity the ship would coast at the current speed of velocity as the first set of engines, slightly decreasing forward momentum. When the second set of engines fired to max velocity the ship should be propelled slighty faster then the first set of engines achieved and so forth.<br /></p>

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#### scottb50

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I wasn't speaking about stages, in the ship itself but 8 total ION engines. Two would fire to max velocity, once achieved the engines would decrease&nbsp;to 25%&nbsp;thrust as two more engines fired to max thrust, once these two engines achieved max velocity they would decrease to half thrust, the next would fire to max velocity. When max velocity has been achieved the engines would decrease to 75% velocity. The final two engines would fire to max velocity. In theory each time an engine decrease's velocity the ship would coast at the current speed of velocity as the first set of engines, slightly decreasing forward momentum. When the second set of engines fired to max velocity the ship should be propelled slighty faster then the first set of engines achieved and so forth. <br /> Posted by dryson</DIV></p><p>You would have to consider the total mass required to do this. The thrust of an ion engine is infantisimal. It's the steady push that builds speed over time, but to build speeds to the realm you are interested in would take thousands of years and many thousand pounds or reactant. The Bussard collector is a prime example, it collects the ions needed as it goes, the problem then becomes how do you inonize the Hydrogen and various atomic particals scooped in? Solar would work out to the heliopause, though how well outside the major Planets is a question. A scoop the size of&nbsp; Earth and solar panels the size of Jupiter might work, but you still have to get them into Space to begin with.</p><p>I see no reason a Solar collector can't also act as a sail, but the scale required to get to even a relatively close system is beyond reason. What we need is a leap in technolgy akin to the Spanish introducing horses to the Americas. That they failed to introduce the wheel at the same time is another thing.</p> <div class="Discussion_UserSignature"> </div>

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#### vidargander

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>In your "electromagnetic pulse" idea, it wouldn't work because the pulses woudl be reflected, then hit the rear of the ship and the ship would move back.&nbsp; Unless the back was open, but if it was, then you'd have the same effect if you just turned the generator around and fired the pulses out the rear.<br />Posted by baulten</DIV><br /><br /><span><font face="Times New Roman"><font size="2">There will not be any magnetic plate at the back, - only at the front. Therefore the electromagnetic pulse will have an effect forwards, not backwards.</font></font></span><span><font face="Times New Roman" size="2">&nbsp;<span><font face="Times New Roman"><font size="2">Anyway, if the electromagnetic idea appeals, it is still possible to make a mechanical proto-type.</font></font></span></font></span></p><p><span><font face="Times New Roman"><font size="2">Just like hammering at the back of a cart makes it move forward, hammering at a front panel will cause the same. Physical pulses at 1KHz at the front panel will cause a steady acceleration of the cart.</font></font></span></p> <div class="Discussion_UserSignature"> </div>

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#### vidargander

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> On the topic of the Partial Ban Test Treaty, it bans nuclear explosions in space.&nbsp; I'm pretty sure there is another treaty that bans the stationing of nuclear weapons in space (such as an orbital nuclear platform).&nbsp; Nothing bans nuclear reactions such a would be used in "confined" nuclear propulsion systems (salt water, gas core, etc.).&nbsp; They'd have to go take care of the Sun if that were the case, and all the stars! "</DIV></p><span><font face="Times New Roman"><font size="2">That&rsquo;s good news to me. I thought there was a total ban of nukes in space.</font></font></span> <p style="margin-top:0cm;margin-left:0cm;margin-right:0cm" class="MsoNormal"><span><font face="Times New Roman" size="2" color="#800080">http://en.wikipedia.org/wiki/Partial_Test_Ban_Treaty</font></span></p><p>&nbsp;<span><font face="Times New Roman" size="2">The ban does obviously not apply for RTG because it&rsquo;s used on several spaceships already. </font><font face="Times New Roman" size="2">http://en.wikipedia.org/wiki/Radioisotopic_Thermoelectric_Generator#RTG_models</font></span><span><font face="Times New Roman" size="2">&nbsp;</font></span></p><p><span><font face="Times New Roman" size="2">It seems that a reason to the ban was to shut down projects like &ldquo;Project Orion&ldquo;. </font><font face="Times New Roman" size="2" color="#800080">http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29</font></span></p><p><span><font size="3"><font face="Times New Roman"><font size="2">The nuclear (blast) pulse propulsion technology is still banned. There are alternatives by using RTG though.</font> </font></font></span></p><p><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### qso1

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<p>http://en.wikipedia.org/wiki/Partial_Test_Ban_Treaty</p><p>The partial test ban treaty came into existence not as a tool to shut down Orion. But as a treaty to slow down the arms race. There had been hundreds of atmospheric nuclear tests by both the U.S. and Soviets when the treaty was signed. Not to mention noticeable increases in radioactive fallout present in the atmosphere.</p><p>The Orion project simply became collateral damage.</p><p><font color="#800080"><span><font size="3"><font face="Times New Roman"><font size="2">The nuclear (blast) pulse propulsion technology is still banned. There are alternatives by using RTG though.</font></font></font></span></font></p><p>RTGs are power production devices and would not be a viable propulsion alternative for any current or planned propulsion system.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### baulten

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<p>"RTGs are power production devices and would not be a viable propulsion alternative for any current or planned propulsion system. "</p><p>Actually, one idea for propulsion is known as the "fission sail".&nbsp; It's a large sail that is coated in a radio active isotope.&nbsp; As it decays, the released neutrons either exit the rear or reflect off the front, resulting in thrust.&nbsp; Same idea as the RTG.</p><p>Of course, the thrust from this would be absolutely miniscule, but with nigh perfect efficiency.</p><p>On a similar note, I had an idea a while back of building on the fission sail design and adding positron emission isotopes such as carbon-11 to the radioactive isotope used to coat the sail.&nbsp; When positron emission occured, there'd be a small chance it'd encounter an electron before leaving, and, if it did, they would annihilate and release energy, possibly triggering a small amount of fission.&nbsp; It'd just increase the thrust.</p><p>Anyone have an opinion on that? </p>

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#### qso1

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<p>Haven't heard of the fission sail, gotta link so I can update myself?</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>"RTGs are power production devices and would not be a viable propulsion alternative for any current or planned propulsion system. "Actually, one idea for propulsion is known as the "fission sail".&nbsp; It's a large sail that is coated in a radio active isotope.&nbsp; As it decays, the released neutrons either exit the rear or reflect off the front, resulting in thrust.&nbsp; Same idea as the RTG.Of course, the thrust from this would be absolutely miniscule, but with nigh perfect efficiency.On a similar note, I had an idea a while back of building on the fission sail design and adding positron emission isotopes such as carbon-11 to the radioactive isotope used to coat the sail.&nbsp; When positron emission occured, there'd be a small chance it'd encounter an electron before leaving, and, if it did, they would annihilate and release energy, possibly triggering a small amount of fission.&nbsp; It'd just increase the thrust.Anyone have an opinion on that? <br />Posted by baulten</DIV></p><p>One might use an RTG as the energy source for an electric propulsion system -- arc jet, ion.&nbsp; But you still have to deal with the low thrust of such systems.&nbsp; It seems to me that&nbsp;the concern over thrust levels applies in spades to the fission sail.&nbsp; I don't see how to get useful propulsion from something with near maximum Isp but near zero thrust.&nbsp; You need to accelerate a macroscopic payload.&nbsp; To get any significant thrust at all the sail would have to be immense, and stabilizing a large membrane in a vacuum (no damping from an atmosphere) is a challenge all by itself.<br /></p> <div class="Discussion_UserSignature"> </div>

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#### baulten

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<p>"Haven't heard of the fission sail, gotta link so I can update myself?"</p><p>http://en.wikipedia.org/wiki/Fission_sail</p><p>Best I've got.&nbsp; I mean, it makes sense and seems like it would work, but it just doesn't seem realistic since it would have, as DrRocket said, virtually no thrust. </p>

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#### qso1

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<p><font color="#800080">"http://en.wikipedia.org/wiki/Fission_sailBest I've got.&nbsp; I mean, it makes sense and seems like it would work, but it just doesn't seem realistic since it would have, as DrRocket said, virtually no thrust. Posted by baulten</font></p><p>Thanks for the link. I couldn't really comment on it without knowing what it was. But looks like DrRocket explained it as well.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### baulten

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Yeah, I was just saying it was (basically) the same idea as radioisotope generators, but harnassed for propulsion.&nbsp;

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#### qso1

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<p>I tend to think we will just about have to find a means of propulsion that we are not yet aware of today before we go setting off to the stars.</p><p>I'd mentioned somewhere else that we are more or less at a point in time where star travel is concerned that Jules Verne was where travel to the moon was concerned. Verne was the visionary of his day who proposed through his book, "From The Earth To The Moon" a trip to the moon. The trip being a little bit based in reality.</p><p>Part of that being the idea of being fired from a cannon which is actually not practical at the very least and probably impossible. The cannon idea could be the nuclear pulse, light sail, or Bussard ramjet of its day. Few people really thought rockets would propel us into space including the Russian father of rocketry who was just a child in Vernes day.</p><p>Konstantin Tsiolkovsky and later Robert Goddard provided the means to reach the moon by detailing how it could be done using rockets. Bussard, Robert Forward, Freeman Dyson may be the Goddards of today...or we may still have yet to see such a person come about.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### keermalec

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I wasn't speaking about stages, in the ship itself but 8 total ION engines. Two would fire to max velocity, once achieved the engines would decrease&nbsp;to 25%&nbsp;thrust as two more engines fired to max thrust, once these two engines achieved max velocity they would decrease to half thrust, the next would fire to max velocity. When max velocity has been achieved the engines would decrease to 75% velocity. The final two engines would fire to max velocity. In theory each time an engine decrease's velocity the ship would coast at the current speed of velocity as the first set of engines, slightly decreasing forward momentum. When the second set of engines fired to max velocity the ship should be propelled slighty faster then the first set of engines achieved and so forth. <br />Posted by dryson</DIV><br /><br />I think you misunderstand the physics involved in&nbsp;space propulsion. No offence, it took me some time to get it too. The highest speed will be obtained by firing all eight engines at maximum thrust: no use throttling them.</p><p>The final speed depends on the speed of the exhaust gasses, this is measured in terms of isp. A good&nbsp;ion drive has an ISP of&nbsp;4,000 seconds, which means the exhaust gasses have a speed of 40,000 meters per second. To calculate the final speed of the vehicle you need to know its initial and final mass (the difference is propellant mass) and use the Rocket Equation.</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

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#### baulten

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<p>"I tend to think we will just about have to find a means of propulsion that we are not yet aware of today before we go setting off to the stars."</p><p>I agree to some degree.&nbsp; I guess it depends what breakthroughs we have in physics.&nbsp; Maybe there is something like a warp drive out there, or maybe there is some exotic form of propulsion that can provide the infinite energy to accelerate past C.&nbsp; Only time will tell.</p><p>However, even if there isn't, I do ultimately think that, baring us destroying ourselves, we'll set out in generation ships.&nbsp; It may not be for a long time, but I imagine it happening.&nbsp; Either nuclear driven or antimatter driven, if we never discover new energy sources. </p>

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#### qso1

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<p><font color="#800080">I agree to some degree.&nbsp; I guess it depends what breakthroughs we have in physics.&nbsp; Maybe there is something like a warp drive out there, or maybe there is some exotic form of propulsion that can provide the infinite energy to accelerate past C.&nbsp; Only time will tell.However, even if there isn't, I do ultimately think that, baring us destroying ourselves, we'll set out in generation ships.&nbsp; It may not be for a long time, but I imagine it happening.&nbsp; Either nuclear driven or antimatter driven, if we never discover new energy sources. <br /> Posted by baulten</font></p><p>I agree as well that will probably figure out some way to do interstellar, be it exotic propulsion or generational spacecraft. It may even be that generational spacecraft will be the way to go for a few centuries. Then towards the maturing of the generational ship era, a breakthrough in exotic propulsion occurs that allows travel to very distant stars or in the case of wormholes, maybe Galaxies.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### hal9891

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I agree to some degree.&nbsp; I guess it depends what breakthroughs we have in physics.&nbsp; Maybe there is something like a warp drive out there, or maybe there is some exotic form of propulsion that can provide the infinite energy to accelerate past C.&nbsp; Only time will tell.However, even if there isn't, I do ultimately think that, baring us destroying ourselves, we'll set out in generation ships.&nbsp; It may not be for a long time, but I imagine it happening.&nbsp; Either nuclear driven or antimatter driven, if we never discover new energy sources. Posted by baultenI agree as well that will probably figure out some way to do interstellar, be it exotic propulsion or generational spacecraft. It may even be that generational spacecraft will be the way to go for a few centuries. Then towards the maturing of the generational ship era, a breakthrough in exotic propulsion occurs that allows travel to very distant stars or in the case of wormholes, maybe Galaxies.&nbsp; <br /> Posted by qso1</DIV></p><p>&nbsp;</p><p>I think that by the time we will be able to build generational ships the concept of generational ships won't make much sense because even those who will choose to stay (mostly) biological will be able to extend their lives almost infinitely, so even if trip would take thousands of years the same individuals could reach the destination.</p><p>Also I believe the whole problem of traveling in subluminal speeds exist only because of our short lifetimes and inability to hibernate for long periods, neither of which will be much of a problem in the future. </p> <div class="Discussion_UserSignature"> <div style="text-align:center"><font style="color:#808080" color="#999999"><font size="1">"I predict that within 100 years computers will be twice as powerful, 10000 times larger, and so expensive that only the five richest kings of Europe will own them"</font></font><br /></div> </div>

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#### tanstaafl76

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<p>&nbsp;</p><p>Just need a gravity drive so we can go to hell and back!</p><p>With the laser sail, did I read right the first post talked about a constant rate of acceleration of 10G?&nbsp; Wouldn't that require an extremely powerful laser capable of operating for a significant amount of time with a very small degree of error?&nbsp; I assume this laser would have to be in orbit?&nbsp; Wouldn't it need to be constantly adjusting its aim since we are moving relative to Alpha Centauri?</p><p>Also, even if it were possible to get anywhere near the speed of light, this would seem problematic when it comes to a pre-programmed spacecraft due to time distortion.&nbsp; Also I don't know how valuable the data sent back from Alpha Centauri would be if our spacecraft goes smoking by at the speed of light?&nbsp; Seems like it would be like trying to get a snapshot of a bug before it hits your windshield on the freeway!</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### vidargander

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Also, even if it were possible to get anywhere near the speed of light, this would seem problematic when it comes to a pre-programmed spacecraft due to time distortion.&nbsp; Also I don't know how valuable the data sent back from Alpha Centauri would be if our spacecraft goes smoking by at the speed of light?&nbsp; Seems like it would be like trying to get a snapshot of a bug before it hits your windshield on the freeway!&nbsp; <br />Posted by tanstaafl76</DIV><br /><br /><p style="margin:0cm0cm0pt" class="MsoNormal"><span><font face="Times New Roman"><font size="2">I don&rsquo;t believe there is a speed barrier for superluminal travelling. </font></font></span><span><font face="Times New Roman"><font size="2">However, I think there are two other reasons why first ACEs won&rsquo;t do.</font></font></span></p><span><font face="Times New Roman"><font size="2"></font></font></span>&nbsp;<span><font face="Times New Roman"><font size="2">Firstly, we don&rsquo;t have the power to get it passed C.</font></font></span> <p style="margin:0cm0cm0pt" class="MsoNormal"><span><font face="Times New Roman"></font></span></p><span><font face="Times New Roman"><font size="2">Secondly, if we did pass C, we wouldn&rsquo;t be able to communicate&nbsp;and remote control it.</font></font></span> <div class="Discussion_UserSignature"> </div>

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#### vidargander

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>A cart will move forward if you sit on it and hit it hard on the back. That&rsquo;s a fact that can be proved. That fact&nbsp;can be used for propulsion.&nbsp;I suggest that an interior generator, making electromagnetic pulses directed to a magnetic front (of the same polarity) will make a vessel move forwards. A thousand pulses per second will provide a steady forward motion. That should be possible to test on a ship. <br />Posted by vidargander</DIV></p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>This works on Earth because gravity causes us to press against the ground.&nbsp; So when you throw hard enough forward, the whole thing slides.&nbsp; It can't slide back when you recoil slower because of friction.&nbsp; In space there is virtually no friction, so every time you swung back, the entire, ship would move back a little.In your "electromagnetic pulse" idea, it wouldn't work because the pulses woudl be reflected, then hit the rear of the ship and the ship would move back.&nbsp; Unless the back was open, but if it was, then you'd have the same effect if you just turned the generator around and fired the pulses out the rear.&nbsp; It'd be really low thrust because photons have 0 rest mass.&nbsp; I'm not sure how you'd calculate it.http://en.wikipedia.org/wiki/Reactionless_drive explains it better than I can. <br />Posted by baulten</DIV></p><p><span><font face="Times New Roman"><font size="2">Now I have read some about that reactionless drives. They are violating the Newton's Third Law of Motion. I think that what upsets scientists the most &ndash; they can&rsquo;t stand lawbreakers <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" />. There are several lawbreakers out there, though, http://en.wikipedia.org/wiki/Reactionless_drive#See_also</font></font></span><span><font face="Times New Roman" size="2">&nbsp;</font></span> </p><p><font size="2"><span><font face="Times New Roman">I don&rsquo;t think I propose reactionless drive. The proposed principle is accepted even by Newton. However, it&rsquo;s explained due to gravitational friction and is therefore believed not to work in the frictionless space. I am not convinced, because I don&rsquo;t think the cart moves forward due to friction, but due to the&nbsp;internal pulses.</font></span><br /></font></p> <div class="Discussion_UserSignature"> </div>

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#### qso1

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<p><font color="#800080">I think that by the time we will be able to build generational ships the concept of generational ships won't make much sense because even those who will choose to stay (mostly) biological will be able to extend their lives almost infinitely, so even if trip would take thousands of years the same individuals could reach the destination.</font></p><p>If future progress is anything like past progress, we'll see interstellar travel develop in stages. The first being generational ships more than likely because of the speed limitations. The only practical two way trip destinations at sublight speed are stars within 20 light years.</p><p>The second stage of interstellar travel may either be some as yet unforseen breakthrough that allows superluminal travel...or generational ships to extreme distant destinations while round trip ships would operate closer to home with people that have longer life spans.&nbsp;</p><p><font color="#800080">Also I believe the whole problem of traveling in subluminal speeds exist only because of our short lifetimes and inability to hibernate for long periods, neither of which will be much of a problem in the future. Posted by hal9891</font></p><p>Thats certainly a big part of it and more than likely, it'll be a problem for future generations to overcome and I imagine they will barring some catastrophe man made or otherwise destroying the human race. Subluminal at near light speed, say .75C, with humans that live for say 200 years...there would be quite a few stars within reach.</p><p>The main sun like stars being Alpha Centauri, Tau Ceti, Delta Pavonis. Of course, we'd probably have to have a really good reason to go and by the time were capable, there will hopefully be a really good reason in the form of an earthlike world orbiting one of those stars or some other star nearby.&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### scottb50

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I think that by the time we will be able to build generational ships the concept of generational ships won't make much sense because even those who will choose to stay (mostly) biological will be able to extend their lives almost infinitely, so even if trip would take thousands of years the same individuals could reach the destination.If future progress is anything like past progress, we'll see interstellar travel develop in stages. The first being generational ships more than likely because of the speed limitations. The only practical two way trip destinations at sublight speed are stars within 20 light years.<br /> Posted by qso1</DIV></p><p>&nbsp;</p><p>Scientists have discovered a warm and rocky "second Earth" circling a star, a find they believe dramatically boosts the prospects that we are not alone.</p><p>The planet is the most Earth-like ever spotted and is thought to have perfect conditions for water, an essential ingredient for life. Researchers detected the planet orbiting one of Earth's nearest stars, a cool red dwarf called Gliese 581, 20 light years away in the constellation of Libra.</p><p>http://www.guardian.co.uk/science/2007/apr/25/starsgalaxiesandplanets.spaceexploration</p><p>The only problem&nbsp; is has it developed life and what kind has it developed. According to the definition Red Dwarfs use their fuel slowly and can be tens to hundreds of billion years old. If advanced life exists there I would think we would have heard something by now. To set of on such a journey with no idea what you will find at the destination seems pretty risky to me. From what I see Gliese 581 is a prime candidate, but if there was higher life we would know about it by now. If there was at one time is another question</p> <div class="Discussion_UserSignature"> </div>

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#### qso1

##### Guest
<p><font color="#800080">Scientists have discovered a warm and rocky "second Earth" circling a star, a find they believe dramatically boosts the prospects that we are not alone.The planet is the most Earth-like ever spotted and is thought to have perfect conditions for water, an essential ingredient for life.</font></p><p>That was the planet discovered a few months back. IMO, the announcement put too much emphasis on the planet being earthlike simply because its rocky. I don't recall much about water actually being detected. At this point, I'm not sure astronomers can really detect water on any of these worlds. Just the chemical traces of water vapor AFAIK.</p><p>I'm hoping a world more earthlike than mars or venus will be discovered around a sun like star before too long. Thats the kind of world that will really get attention and possibly ignite a drive to develop interstellar technology in less than 500 years as opposed to the 500 or more years it would probably take otherwise.&nbsp;</p><p><font color="#800080">To set of on such a journey with no idea what you will find at the destination seems pretty risky to me. From what I see Gliese 581 is a prime candidate, but if there was higher life we would know about it by now. If there was at one time is another question Posted by scottb50</font></p><p>I would expect that by the time we have the technology to set off on such a journey, we will have a wealth of information from advanced ground and space based observatories that will allow humanity to set off on a destination already fairly well known.&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

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#### vidargander

##### Guest
<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> I don&rsquo;t think I propose reactionless drive. The proposed principle is accepted even by Newton. However, it&rsquo;s explained due to gravitational friction and is therefore believed not to work in the frictionless space. I am not convinced, because I don&rsquo;t think the cart moves forward due to friction, but due to the&nbsp;internal pulses. <br />Posted by vidargander</DIV><br /><br /><span><font face="Times New Roman"><font size="2">I found an image that might explain a similar mechanical impulse effect that cause forward motion. </font></font></span><span style="font-size:10pt"><font face="Times New Roman">It&rsquo;s called the &ldquo;Henry Bull&rsquo;s Impulse Engine of 1935&rdquo; </font><font face="Times New Roman" color="#800080">http://jnaudin.free.fr/html/hbimp35.htm</font></span><span style="font-size:10pt"><font face="Times New Roman">&nbsp;</font></span></p><p><span style="font-size:10pt"><font face="Times New Roman">In the ElectroMagnetic propulsion I propose, the magnet in the front should be attached to several springs, or elastic material, that will compress by the trust. That should make a net forward thrust that will move the ship forwards. </font></span></p><span style="font-size:10pt"><font face="Times New Roman">Can anyone argue with that<span style="font-size:10pt">?</span></font></span><span style="font-size:10pt"></span> <div class="Discussion_UserSignature"> </div>

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#### Mee_n_Mac

##### Guest
<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> Can anyone argue with that? <br />Posted by <strong>vidargander</strong></DIV><br /><br />I can.&nbsp; In step 3 it says "Here's the magic".&nbsp; That is correct, it is magic and not true physics.&nbsp; The spring is 3x as efficient in transmitting the force ?&nbsp; Nope.&nbsp; Assuming the mass of the tube setup is />> larger than any one of the moving weights. When one weight (#1)&nbsp;hits the spring near it's end, it'll start to force the tube to move. The spring will arrive at some point of compression and then send the weight moving back. So right here not all the energy in that moving weight is transmitted to the tube. At the the other end the weight smacks the tube and let's say imparts all it's energy. This will stop the tube and start it moving back the other way. Thus it comes to a stop, like a billiard ball hitting another. The tube is now in motion as the forces weren't balanced. However the weight is still stuck at the far end of the tube. The energy and forces needed to get both weights back to the center and recompress the spring aren't equal as one is moving and one isn't.&nbsp; There will be a net force that will cancel the motion as the weights are brought back to center. </p><p>But let me tease you with one, similar in nature, that's not so easily disproven.&nbsp; I think I saw it on the old Uplink.&nbsp; Let's have 2 spaceships separated by some fair distance, a few light seconds at least. Each one has a magnetic feild generator that can turn the ship into the equivalent of a bar magnet with north and south poles. We line the ships up nose to tail and have the trailing ship turn on it's electromagnet for 2 seconds.&nbsp; The feild propagates out towards the lead ship who, just a microsecond before the feild arrives, turns on his electromagnet (for 2 secs) such that he gets a push for the 2 seconds the feild exists (he makes his tail south to oppose the north side of the trailing ship). The lead ship moves forward.&nbsp;Now that 2'nd feild propagates back towards the trailing ship but his electromagnet switches polarity so instead of getting pushed, he gets a pull. This new, reversed feild propagates towards the lead ship again &nbsp;and catches it. But just before it does, he switched polarty as well and gets a push, not a pull.&nbsp; This goes on ad nasuem turning electricity into motion w/o expelling mass.&nbsp; Violates conservation of momentum but why won't it work .....</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>

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