Easier way to get to Mars and back to moon...

Discussion in 'General Science & Technology' started by cosmictotem, Feb 3, 2016.

  1. DaveC426913 Valued Senior Member

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    Yes. In Earth orbit. Very small delta-v, especially since we can strategically time the launches to minimize it.

    You're talking solar orbit. Order of magnitude larger delta-v, and your colonies will always be in a bad spot for docking because of it.

    Where will you keep all this fuel? Your rockets iwll be the size of mountains. We can't build those.
     
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  3. billvon Valued Senior Member

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    Then they would be moving at 30km/sec.

    The SLOWEST a craft going from Earth to Mars can go is 31km/sec. That's 1km/sec speed differential, and that delta-V requirement is one of the hardest part of any Earth to Mars mission. To speed up by that amount (about 2300 miles per hour) take a tremendous amount of fuel, and it has to be done at least twice during an Earth to Mars mission. So you have several problems with your idea.

    1) If you have a problem, a habitat has to just happen to be nearby. Since they will be whizzing by at 2200 mph relative speed, and Earth's orbit is a very big place (roughly a circle over 500 million miles long) either you need thousands of habitats, or there will never be one nearby.

    2) If one happens to be nearby, you have to decelerate to match speeds with it. 2200 miles an hour would be over a minute of acceleration at 2G's. That is a large spacecraft with a lot of fuel. (And if you can achieve that delta-V you can get back to Earth anyway.)

    3) Even if you do get to the habitat, if there's a big problem (i.e. medical) then the whole habitat has to change course and head back to Earth anyway (or launch an equally capable spacecraft.)

    It just doesn't make sense.
     
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  5. cosmictotem Registered Senior Member

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    Because all life on a planet or moon can be extinguished by one unlucky comet strike. But a human population spread throughout the inner solar system ( and eventually multiple solar systems) on biospheres is not going to be easily extinguished. Stephen Hawking has warned us about about planets in the sense that, just being on one, can subject a population to extinction in one shot.
     
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  7. DaveC426913 Valued Senior Member

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    To address the thread title, it is safe to say that it is without question, not "easier" to get to Mars this way - though it might fulfill other motives.

    Maybe you could rephrase the question now to address a different motivation for going the waypoint method.
     
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  8. DaveC426913 Valued Senior Member

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    Ah well. That's a very different argument than "An easier way to get to Mars".
     
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  9. billvon Valued Senior Member

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    Ah, so you don't want to go to Mars, you want to build space stations! That's fine. If you want to build space stations, build space stations. If you want to go to Mars, go to Mars. Don't try to conflate the two.
     
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  10. cosmictotem Registered Senior Member

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    I think I'm following you now. Not sure why I didn't see that before. There's a little more involved than I anticipated. But this is all good to know. I can ponder this for a while and reexamine my proposal and either change it or scrap it.

    So you're saying even craft sent from stations in adjacent orbits with other stations would have trouble catching up to those other stations and docking with them?
     
  11. cosmictotem Registered Senior Member

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    True. But yours and billvon's and Billt T's points are starting to make sense to me.
     
  12. DaveC426913 Valued Senior Member

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    And yours are starting to make sense to me.

    Please Register or Log in to view the hidden image!

     
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  13. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Hey, I want to do it too! Just like my other fantasies: winning the lottery, winning the Super Bowl and marrying Jennifer Garner. But unlike cosmictotem's fantasy, at least mine are possible with existing technology and global budget constraints!
     
  14. Russ_Watters Not a Trump supporter... Valued Senior Member

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    So then that's more like your previous suggestion of just sending two spaceships on the same voyage -- a spare. But as you say, it wouldn't be possible for such a ship to dock at a waypoint without it being substantially larger than the primary spacecraft -- bigger engines and more fuel. Nor would there be any reason to dock at such a waypoint anyway.

    Yeah, I guess I'm seeing too that this is all just a convoluted and bad excuse to build space stations. Perhaps an acknowledgement that there's no good reason to build them, so he has to make one up.
     
  15. cosmictotem Registered Senior Member

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    Why does every proposal on the internet get interpreted as an intentional attempt to deceive?
     
  16. billvon Valued Senior Member

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    Well, craft sent from the SAME orbits (i.e. two craft on the same orbit, just at different locations along that orbit) can reach each other pretty easily. But if those orbits differ then it becomes progressively more difficult to make the change.

    For example, one of the most difficult orbital maneuvers to accomplish is a plane change. Let's say you are in an equatorial orbit around the Earth and another satellite is in a polar orbit. You pass each other twice per orbit, perhaps within a few hundred meters. It would be nearly impossible (with today's technology) to change your orbit enough to reach the other satellite.
     
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  17. brucep Valued Senior Member

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    If we were trying to colonize the entire solar system we might end up with a string of bases similar to what you imagine. How long would it take to achieve that? At least 200 years. Making stepping stone bases to eventually put somebody on Mars doesn't make any sense. Like billvon said. The first step is ..........? You decide. If I could choose I would choose the Mission to Mars. Do everything to make it successful and hope the success would inspire humans to want to continue. Depending on that I would consider a project to put a science station in near earth orbit to investigate all the science associated with manned space flight. Including interstellar space flight. Which would require a completely self sustaining environment. Personally I don't believe the human race will ever have the will to do something like that. Even if we could. Regardless I don't think spending money on such projects would lead to economic ruin. I think it would be just the opposite.
     
    Last edited: Feb 5, 2016
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  18. Russ_Watters Not a Trump supporter... Valued Senior Member

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    I can't be certain, but there aren't a lot of options here. It's a bad idea, with a bad motivation that isn't well defined and is backwards.
     
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  19. cosmictotem Registered Senior Member

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    Ok so progressively more difficult if they are adjacent, not impossibly more difficult?

    In other words, if the biosphere stations are in close adjacent orbits and on the same Equatorial plane, it is only slightly more difficult to jump from one nearby orbiting station to the next?

    If that's the case, does that resurrect my idea of using a station supply line -- provided craft move from one nearby orbiting station to another nearby orbiting station without trying to skip orbits--- and don't try to stop at stations with vastly different orbiting velocities?

    Because, essentially, that was my original point...to just move along the "line" from one nearby station to the next.
     
  20. billvon Valued Senior Member

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    If they have similar orbital parameters - yes.
    Because:

    1) To get to every orbit you have to accelerate to go to the next higher orbit then decelerate to match speeds with the higher orbiting vehicle; that takes insane amounts of fuel

    2) At some point you leave the vicinity of stable Earth orbits and then you are back to the problem that you need thousands of vehicles in solar orbit to make that work

    As I said before, if you want to build space habitats, build space habitats. If you want to go to Mars, go to Mars. Your desire to "game the system" to get people to build cool space habitats is nonsensical. Imagine where we would be today if Columbus had claimed that he couldn't go exploring unless the Spanish government built dozens of seafaring villages between Spain and the East Indies that he and his men could visit "just in case."
     
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  21. cosmictotem Registered Senior Member

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    Okay, so I shouldn't have equated getting to Mars with the idea of a space colony. Although, my poor grasp of the intricacies of different orbit parameters gave me the impression there wouldn't be any problem with that.

    What's so perplexing is that I instinctively should know that the orbit velocities of planets are different. I know that from grade school but I completely brushed over the effect that would have for traversing through different orbits to destination...probably because I'm not a scientist (or avid space travel reader) who plans space missions and is continually confronted with that consideration.

    Thanks for sticking with me.
     
  22. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    In post 41, you suggest 40,000 biospheres in the first circular orbit, at about 1AU from the sun. You have also suggested that they each house 100,000 people and be sized like there largest stadiums.

    These "stadiums" will need to be enclosed in spherical mass shells, for protections from cosmic rays. For life time long protection these shells will need to be at least 30 meters (40 feet) thick. So my most important "remaining objection" is the one i've already asked at least 4 times now:

    Where does all this mass come from?

    Here is how to estimate it:

    If R is the mean radius of the 40 foot thick spheres and we call pi = 3.14 then the surface Area of the spherical shells is A= 4x3.14R^2 and the Volume of mass in each is V = TxA, where T is the Thickness of the mass shell.

    For good shielding, the average density of the mass should be more than that of water. You would want the outer most layers to be lead, to convert each high energy cosmic ray into a dozen or more "daughters" of lesser energy, which could be converted into more than 100 still lesser energy "grand-daughters." The material doing this could be only half as dense as lead. Finally, the two innermost layers should be even lower density. Innermost is mainly carbon as the 10,000 great, great grand daughters of each primary ray need to collide with modest weight atoms - best for "sucking" energy out of them with the struck atom's recoil. The layer next to the carbon layer should have about twice the density of water. The overall density of the shell, averaged, would be more than 3 times that of water, but I'll call it 3. If we work in feet (water is 64 pounds/ ft^3)

    So the mass of your 40,000 bioshells is 40,000x3x64x4x3.14xT(R^2) =32,153,600T(R^2) pounds where both T & R are given in feet. If T = ~31 feet (probably to little, but makes for nice round number.) I. e. 1,000,000,000R^2 pounds. I think R must be at least 1000 (length of 10 foot ball fields is very small to cram 100,000 people inside) then here it the weight, of just the innermost of a set of rings between Earth and Mars: 1,000,000,000x1000x1000 pounds or in scientific notation: 1E15 pounds. That is about equal to taking the top layer half a mile deep from all the dry land parts of the earth. Doing that might reduce the dry land to only 80% of the present area.

    So again, for the fifth time, where will you get all the needed mass, just for the cosmic ray shield? (and then more for the rest of the biosphere)?

    Also, note that the area growing food for 100,000 people can't be inside the opaque (no sunlight) bioshield. Perhaps some fungus growing outside on its surface can survive bombardment by cosmic rays, but I doubt it. This is the 2nd problem I would raise. The impossible cost is about 4th or 5th, of my objections, but perhaps "doable" if more than 500 years are used to build each biosphere. 40,000x500 = 20 million years to complete first ring.

    Facts are very ugly enemies to foolish dreamers, arn't they.
     
    Last edited: Feb 5, 2016
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  23. cosmictotem Registered Senior Member

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    So are you saying most docking in science fiction is highly oversimplified or the true physics involved is generally ignored?
     

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