Practical space travel

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Norsefire, Aug 31, 2008.

  1. Norsefire Salam Shalom Salom Registered Senior Member

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    What are our real options for practical space travel? By "practical", I mean someone can arrive at their destination before they are old or dead.

    I think we really need to think outside the box; not just improving rockets, but entirely new, unique approaches to travel.


    However, ion engines and the anti matter engine ideas are pretty good IMO. Even then, they won't be taking us any significant galactic distances in a practical amount of time, however. What would it take to actually be able to travel from Earth to, say, the other side of the galaxy within one life time?
     
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  3. Fraggle Rocker Staff Member

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    Based upon what we have discovered about the laws that govern the natural universe, we have no "options." The speed of light is an absolute limit and at the speed of light it takes one year to travel one-light year. In addition, we're limited by the gee-force our bodies can withstand. So, at constant one-gravity acceleration, it takes a year to reach the speed of light. Of course objects with non-zero mass cannot attain the speed of light, but the same principles apply just to get close to it.
    The galaxy is a hundred thousand light-years across. That means that it takes light itself a hundred thousand years to traverse that distance. Unless we're completely wrong about relativity, we'll never be able to travel faster than that.

    People speculate about "wormholes." But the whole concept of wormholes assumes that if and when we discover a fourth spatial dimension, we'll also discover that the natural universe as we know it is actually folded over on itself like a sheet of paper. So an insect (or a human with a ray gun) can chew a hole in it and come out on the other side of the fold.

    Unfortunately the natural universe is indifferent to our yearnings.
     
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  5. kaneda Actual Cynic Registered Senior Member

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    Star travel is way beyond our present capabilities. It will probably be accomplished by a means we at present cannot imagine. There is enough to keep us busy in the solar system for the next century.

    Our big problem is fuel. Watch an episode of Lost in Space and you see John Robinson flying with a jet pack on his back. It was thought that everyone might use them one day but it never happened because we never developed a better fuel so they had strictly limited use. We have the same problem with rockets in that the fuel we use is rubbish. It is weighty and burns out too quick. We need a better fuel.

    Manned exploration is hugely expensive so for now, unmanned probes is the way ahead. Possibly even putting a probe on a lump of rock we know will spend much of it's time outside of the solar system and has a useful orbit, and let it take pictures over the following decades.

    It takes fuel and time to build up speed in a rocket. We could launch a rocket which will slowly build up speed over years (by slingshots around the sun, etc) without using it's fuel payload. Finally when moving sufficiently fast and coming near us, we use a rocket with hard acceleration which will use much of it's fuel catching up to it and matching speeds. Then it will transfer a crew across to the other rocket with it's full load of fuel and add speed to reach Jupiter's moons or whatever. Possibly then the chemicals needed for the fuel for the return trip would be synthesised using the hydrogen, etc on Jupiter's moons. Going sunward, it would fairly easily build up speed. The crew could be taken off when near the Earth's orbit.

    Scientists are working on suspended animation which would save a huge amount of weight on food, water and even oxygen. It is possible that we may have stop off points in the asteroid belt in the future, and further points to reach the outer solar system. Ceres has more fresh water than the Earth and at 560 miles across would be ideal.

    We could put a probe (with lots of instruments) on lumps of rock which spend much of their time out of the solar system. A free ride.
     
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  7. cosmictraveler Be kind to yourself always. Valued Senior Member

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    And go where? If there's nothing to eat, use for fuel or water wherever humans travel would it be worth sending them into the unknown without knowing what's there first?That's why robotic spacecraft should always be sent way ahead of humans to see what lies out there and to determine the best places to visit that would be worthwhile. Putting humans into a sleep mode for long periods of time asks for troubles because if something happens to the ship, either a glitch in the electronics or navigation system or it gets hit with a micrometeorite which causes loss of air then many humans will be lost in space forever.
     
  8. Janus58 Valued Senior Member

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    Its weight and how fast it "burns out" is not the problem. The problem is how "hot they burn". The hotter a fuel burns, the higher the exhaust velocity, and it is the exhaust velocity that determines the efficiency of the rocket. High exhaust velocity equals high efficiency, which equals a greater delta V for the same mass of fuel.
    You can't slingshot around the Sun, you can only gain delta V by doing a slingshot around a planet orbiting the Sun. While this method has been used for probes, one disadvantage is that you have to wait until all the planets involved are in the correct relative positions. If you miss your launch window for any reason you have to wait for a new alignment.
    Not a free ride, as it takes just as much delta V to match velocities with that rock in order to put the instruments on it as it would to just put the probe itself into the same orbit as the rock.
     
  9. orcot Valued Senior Member

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    within 50 years or so we might be able to hollow out a comet and build a city in it to travel to the alpha centauri in 20 000 years or so. Or send a unmanend starwisp (weigting around a kg) at 10%the speed of light.
    Or watch it's planet's with a 4,3 year delay.
    These are our options for the near future.

    On the other hand right now we have none worth mentioning
     
  10. Nasor Valued Senior Member

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    If it's going to take tens of thousands of years, you're probably better off waiting for someone to invent a better technology. Your 20k year city-ship would probably arrive to find the entire system already populated by the descendants of people who left earth a few hundreds of years after the comet ship and arrived at alpha centauri 19500 years ago.

    Our best current bet would probably be a nuclear saltwater rocket, which has a theoretical exhaust velocity of 4700 km/sec. If your ship was 99% fuel and 1% everything else, that would let you get up to about 3.6% of light speed and then slow back down, which would have you in alpha centauri in "only" about 120 years.
     
  11. kaneda Actual Cynic Registered Senior Member

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    We know the orbits of objects like Halley's comet. With such a probe, it is not necessary that it come back into the solar system again. It would of course be unmanned since it's voyage would last for decades at least.

    A suspended animation craft would have various warning systems on in case of any major problems where designated members of the crew could be revived. Micrometeors and larger are always a problem and it would be hoped that some system of sealant could be devised, maybe self sealing.

    Whatever system we use for "long distance" space travel, it is probable that crews will be lost for any number of reasons.
     
  12. kaneda Actual Cynic Registered Senior Member

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    Magnetically accelerate the expelled gases.

    Of course you can. It's a gravitational source. Since it is unmanned, it can be shielded against heat with a literal shield since heat does not conduct in the vacuum of space.

    Match speeds on the way in so we have an assist from the sun.
     
  13. losfomoT Unregistered User Registered Senior Member

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    This is true for an observer on Earth, but it is theoretically possible for the traveler to complete the journey in his lifetime. It is just not yet technologically possible.
     
  14. Nasor Valued Senior Member

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    Simply being a gravitational source isn't enough; the gravity source has to be moving relative to you in the direction that you want to accelerate. This sort of "gravity assist" scheme works because the massive object will "pull you along" in the direction that it's traveling as you pass it. If the massive object is sitting stationary relative to you, it can't be used in this way.

    I think the point was that you can't get a "free ride" from the comet, since you have to match orbits with it anyway - meaning you would go wherever the comet went even if the comet weren't there.
     
    Last edited: Sep 3, 2008
  15. orcot Valued Senior Member

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    You could harpoon it and wield yourself in a a multi km tether
     
  16. Dinosaur Rational Skeptic Valued Senior Member

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    Current thoughts indicate that only a generation ship or a stasis field would allow interstelar travel.

    There have some (many?) SciFi stories about both of these ideas.
     
  17. orcot Valued Senior Member

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    Like stasis fields?
     
  18. Dinosaur Rational Skeptic Valued Senior Member

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    Orcot: I assume you are asking about the statis field concept.
    A stasis field stops time for anything or anybody inside of it.

    Larry Niven wrote a delightful novel about an alien found to be in a stasis field. When released, it was discovered that he had psychic powers that enabled him to control other animals, including humans. His culture used the stasis field as a life boat for use in the event of a starship catastrophe.

    The idea was that a person in the field required no food, water, oxygen. Time was suspended for him until he could be rescued. In the Niven novel, the alien had been in the field for perhaps a billion years. His kind had once ruled the galaxy due to their psychic powers, but had been overthrown. The alien was incredibly stupid. Intelligence was not an evolutionary goal for that race due to the psychic powers.

    In other novels, the stasis field was used to allow astronauts to take interstellar trips requiring thousands/millions of years. In one novel those in such a field arrived at their destination hoping to colonize a virgin planet. Their trip had taken 500,000 years. While in transit, Earth science had discovered FTL technology. The planet had been colonized for 400,000 years and the culture was similar to one they had found intolerable.
     
  19. Nasor Valued Senior Member

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    It's also entirely possible that in the future technology might greatly extend normal human lifespans, in which case people might not mind spending 40 years (or whatever) waiting to get to where they're going.
     
  20. draqon Banned Banned

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    exactly, ion drives sure are efficient and do the job. However they have extremele low thrust.
    Utilization of the Lorentz Force is the key, however much more energy is needed.

    The way I see it, we need to combine nuclear energy and ion drives and use that for space travel.
    The problems I see with it are: cooling issues.

    From Wiki, these used ion drives:

    SERT
    Deep Space 1
    Artemis
    Hayabusa
    Smart 1
    Dawn
    LISA Pathfinder
     
  21. Syzygys As a mother, I am telling you Valued Senior Member

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    Let's face it kiddos, spceatravel wasn't made for humanity, there is no really point in it, we don't have the resource,technology or lifespan...

    End of story...

    P.S.: Did I scew up the party?
     
  22. Asguard Kiss my dark side Valued Senior Member

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    FR i thought worm holes were possable.

    dont they alow a theoretical shortcut?
    futher more if its age rather than time your worried about there is always the possablity of suspended animation
     
  23. Letticia Registered Senior Member

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    In mostof solar system, it is already possible to arrive at their destination before they are old or dead -- just very very expensive.

    Assuming you are talking about interstellar travel, the only "real option" I see (and it is not THAT real) is radical life extension. (Suspended animation is a variation on that.)
     

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