Astronomy and space exploration

Discussion in 'General Discussion' started by eloyc, Apr 10, 2017.

  1. KimB

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    Her.
     
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  2. KimB

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    Many links have been posted. Which one are you referring to, specifically?

    Note that I'm not promising to look into it in any amount of detail. I'm not sure how much time I'd want to dedicate to this. But the short of it is that space travel is monstrously difficult. Rockets are incredibly inefficient, and as a result can't get us very far. Our best bet for long-distance propulsion is probably either a light sail or ion drive, both of which have exceedingly low rates of acceleration. The other main alternatives we currently know of are probably impossible.
     
  3. eloyc

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    Page: https://www.spacewarpdynamicsllc.com/
    Paper (from the documents section on their site): https://docs.wixstatic.com/ugd/0679fd_04fb60d906f14a60acef9e6fa41d6384.pdf
    ;-)
    I think we all know that, but I would like to know the whys in more detail, and specifically what other scientists think of this experiment.
     
  4. KimB

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    Ah, no. That one is complete bullshit. The criticisms of others are correct: it requires violation of conservation of momentum. That isn't happening.

    The idea that it's a "space warp" drive is complete, unadulterated nonsense.
     
  5. vjPiedPiper

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    I still hold out hope that VISIMR tech will eventually become useful. It's high impulse but low thrust, so it still works for unmanned long journey space travel.
    If they can manage to get the thrust up a bit more it becomes a lot more useful.

    Really i think that issue of energy generation in space is going to be the next big frontier, solar aint gonna cut it for anything serious.
    We will probably need some form of nuclear energy generation for both planet based and long time in space missions.
     
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  6. KimB

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    Yeah, ion drives are definitely viable.
     
  7. pcchen

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    Solar is probably good enough for missions to inner planets. You'll probably want to use nuclear for anything beyond Mars. Almost all deep space probes use nuclear batteries (RTG) as main power source (one notable exception being Juno, with very large solar arrays).
    Nuclear reactors are even more efficient than RTG, but the complexity of running a nuclear reactor makes it less ideal in space.
    Something like project Orion (the idea of exploding nuclear bombs behind a spacecraft to push the craft forward) is probably required to accelerate fast enough to visit another star system.
     
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  8. zed

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    no probably about it. I heard in a podcast (maybe ted talk) but to get a spaceship the size of a box of matches to alpha centauri using conventional propulsion methods in a reasonable amount of time requires more fuel than exists in the universe.
    Which to me sounds pretty unbelievable but IIRC the guy saying this knew his stuff (from nasa IIRC or soemthing)
     
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  9. cheapchips

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    Breakthrough Starshot are proposing a swarm of nanoprobes propelled via lightsails. You push them on their way with giant lasers. Crazy amount of power required but it's not impossible.

    https://breakthroughinitiatives.org/initiative/3

    In principle I think this idea scales up to human scaled craft and you can have a laser highway between the stars. The excellent Isaac Arther has a video about them, but haven't watch that particular one.
     
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  10. Arnold Beckenbauer

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  11. eloyc

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  12. zed

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    Thats the one bill nigh the science guy is the face on I assume?
    https://blogs.scientificamerican.co...cal-rockets-and-interstellar-travel-dont-mix/

    Thus impossible to get a toothpick sized spaceship to the nearest star in a reasonable time frame!
     
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  13. hoom

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    Depends on your definition of 'reasonable'.
    But probably is referring to specific impulse: conventional chemical rockets can only hit a low % of C due to relatively low exhaust velocity.
    And as you approach that velocity you get law of diminishing returns -> need stupid amounts of fuel if running a constant burn interstellar trip with a chemical rocket.

    Thats why most Sci-fi uses variants of stuff like ion-thrusters, matter-antimatter annihilation, fusion exhaust & small blackholes that can produce much faster exhausts.
    Mostly using a lot of handwavium (or not much but super-vague) to make whatever method small, cheap, extremely efficient & safe.

    Long ago I ran into a description of a relativity limited Type III Kardashev civilisation using a network of Dyson spheres dedicated to stellar-scale lasers to enable high % of C 'solar sail' travel around the galaxy.
     
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  14. cheapchips

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    Lightsail 2 is a different thing, from the Planetary Society. Bill Nye's their CEO.

    It's to demonstrate that cubesats can sail on light particles from the Sun. It's for in solar system applications rather than interstellar travel. No giant lasers involved (pity!).

    It's due to deploy it's sails on Sunday, at the earliest.

    http://www.planetary.org/explore/projects/lightsail-solar-sailing/
     
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  15. KimB

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    To be clear, it's impossible to get a toothpick-sized rocket-powered spaceship to the nearest star. The reason why rockets are so inefficient is that the velocity of their exhaust is relatively low, and as a result they end up expending most of their energy just accelerating the fuel they carry.

    This is why ion drives are potentially viable: they can, in principle at least, expel charged particles at relativistic velocities. They lose a good amount of energy accelerating the particles to such high speeds, but they no longer need to carry a lot of stuff to expel. To get the relevant efficiency for an ion drive, you'd need to re-derive the formula there to include relativistic effects, including the radiation reaction that results from accelerating charged particles to relativistic speeds.

    A solar sail also doesn't have this issue because it doesn't need to carry any propellant. It just needs an initial kick, and a long-lasting power source that will allow it to manipulate its sails so as to take advantage of the local photon environment as it travels.

    Either of these will take an extremely long time because they are such low-acceleration propulsion systems. But they actually can accelerate for a long time without running into the problems of chemical rockets.

    Another solution that has been proposed is the Bussard Ramjet. The idea here is similar to the ion drive, but instead of carrying its reactor and the material to make expelled ions, it uses a magnetic field to funnel interstellar particles into a nuclear reaction, and uses that nuclear reaction to power the ship. Such a ship would need a tremendous initial boost, and some way to stop when it reaches its destination (such as a big rocket), but if it could get up to speed, it could potentially get to a point where it is self-sustaining. However, nobody has yet come up with a design that comes close to being feasible. Crucially, the amount of energy they could theoretically extract from the thin interstellar plasma is too small to counteract the drag such a ship would experience moving through said plasma. However, perhaps it's possible to use the concept of this ramjet to improve the efficiency of an ion drive: instead of carrying the material to ionize, it would just accelerate the interstellar plasma.
     
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  16. Davros

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    My money is on The Infinite Improbability Drive
     
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  17. hoom

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    So not only the front fell off, its leaked 50,000 tons of fuel & caught on fire

    Probably about time to tow it outside the environment :runaway:

    Edit: longer version, things start happening about 47:00
     
    #497 hoom, Jul 18, 2019
    Last edited: Jul 18, 2019
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  18. cheapchips

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    According to NasaSpaceFlight the static fire itself was fine. The Hopper doesn't show any visible signs of damage. You wouldn't know it was in the middle of that 30m? high fireball.

    No more testing this week but wouldn't expect it to be that long before they have a crack at the hover.

    Edit: Hop confirmed for next week.
     
    #498 cheapchips, Jul 18, 2019
    Last edited: Jul 18, 2019
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  19. KimB

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    I hope they checked very carefully, because really subtle structural flaws can cause complete failure of a rocket.
     
  20. cheapchips

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    I assume they're not winging it too much!

    The steel on the Hopper is much thicker than the drinking can thinness of orbital rockets (or the prototype Starships they're building)

    Presumably it's in part to survive hiccups like this fuel leak. It also needs as much dry mass as a final Starship three times it's height. The Raptor engine can only throttle down to 100 tons of thrust. It couldn't hover if it was too light.
     
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