Thanks, Ed, this is a really nice explanation.

]]>https://ned.ipac.caltech.edu/level5/March02/Sahni/Sahni4_5.html

including how the minimum in apparent size depends on both the mass density and dark energy density of the universe. ]]>

Ah, thanks for correcting me on that Shawn. Sorry about that. I changed my original comment to reflect that 1 kg of uranium has 17,000 metric tons and not 17 metric tons of TNT energy.

]]>Hi David, thanks for doing the math, 1 kg of uranium has 17 kilotones not metric tonnes on TNT energy. I think relativistic changes to the ship would all be from the vantage point of an outside/stationary observer. I think no matter how fast the ship goes a cup of tea would weigh exactly the same. There is nothing special about any velocity, we are all traveling at the speed of light. There does seem to be a difference of opinion on this subject. In the future I plan to research everything Einstein had to say on this matter.

]]>Hi Shawn, Unless something is horribly wrong with my calculations, I have bad news. The energy needed per kg of payload to reach the Alpha Centauri system at 1g acceleration for the first half of the journey and 1g deceleration for the second half of the journey is 4.0702 × 10^{17} J/kg. So traveling there with a 10 metric ton ship would require 4.0702 × 10^{21} joules of energy.

If a metric ton of TNT releases 4.184 terajoules (4.184 × 10^{12} J), then dividing this into 4.0702 × 10^{21} gives us 9.728 × 10^{8} metric tons of TNT.

If every kg of uranium releases the energy equivalent of 17 metric kilotons of TNT, then dividing 9.728 × 10^{8} by 17,000 we get 57,220 kg of uranium needed. This is so much more than the mass of the ship that I would need to use calculus to account for the change in ship + fuel mass as a function of time. But this is so much uranium that I don’t think it would be feasible for interstellar travel. But for travel within our solar system, it would probably work fine.

The problem, of course, is relativity. As we reach relativistic velocities, the faster we go, the more energy it takes just to go a little faster. On this journey, we would reach 0.95*c* at the halfway point to the Alpha Centauri system.

Do my calculations make sense? I used the equations shown in the article above.

]]>Hi David, I would like to calculate how many kilotones of energy would be required to propel a 10 ton ship at a constant 1g acceleration rate for 3.6 years. I have a feeling you know how to do the math. Every kilogram of uranium contains the same energy as about 17 kilotones of TNT. A rough guess of mine would be about a half a pound of uranium would be enough to get to the Centauri system.

]]>I realize I made a mistake in my above comment. When I said “right above the threshold of jumping from one electrode to the other” I should have said right below the threshold.

It may be possible to use laser energy to get uranium or plutonium to fission in a linear fashion. What would happen if a powerful laser hit a piece of uranium or plutonium sheet? Given the fact that they are jittery, on the verge of fissioning atoms anyway I think fission would be likely. This too could be the basis for a simple fission rocket.

The clock is ticking till the day the human race starts to explore/colonize our galaxy. Whatever machine we make to do that will be made from the periodic table of elements, its our toolkit. In a million years from now its going to be the same toolkit.

I agree with you 100% on your supergovernment comments.

Thanks for the explanation, Shawn. I am looking forward to your future videos on this subject. Feel free to post them here.

Dave

]]>I would bet my left arm that the processes in my video’s would work. The uranium or plutonium atoms will probably have to head towards each other single file however which would be the main technical hurdle. I also want to point out that these would be low output engines compared to chemical rockets. There is many other potential ways of using an electrical current to trigger fission, I plan to make more video’s in the future. The next one will be called “alternating current fission rocket”. Imagine 2 iridium electrodes with a narrow specific gap in between with a specific current that is right above the threshold of jumping from one electrode to the other in a vacuum, precisely so that all it takes is one metallic atom to cause the current to jump from one electrode to the other. The idea being to “pop” a uranium or plutonium atom like a fuse, being the jittery atoms they are I cant image that fission would not occur.

Another idea is “metallic hydrogen fusion rocket”. If you pass an overcurrent to 2 electromagnets they will destroy themselves with the impact. Imagine the same concept but with individual polarized metallic hydrogen atoms. I dont think this will ever be technically possible but it something to think about.

Thanks, Shawn! Wanted to post the two YouTube videos you made here so that others can watch them, too. I found them interesting and thought-provoking. Well worth the time to watch!

Best Method for Interstellar Travel

I agree with you that we need an international weapons ban. Globally, we must work toward establishing a global “supergovernment” that enacts and enforces binding international laws that are in the best interest of all the world’s peoples. Individual nations will have to give up some sovereignty in order to effectively address global threats such as nuclear weapons, warfare, human rights violations, pandemics, climate change, pollution, environmental degradation, and loss of biodiversity. Whether the United Nations can be strengthened to serve in this role or a new organization created will need to be explored.

Shawn, I have one question about fission. I thought that the only way to induce fission is through the introduction of neutrons. How do you do it with an electrical current?

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