1. Attachments are working again! Check out this thread for more details and to report any other bugs.

interesting stories on China discussion

Discussion in 'Fred's House of Pancakes' started by cwerdna, Jan 31, 2013.

  1. Trollbait

    Trollbait It's a D&D thing

    Joined:
    Feb 7, 2006
    21,595
    11,220
    0
    Location:
    eastern Pennsylvania
    Vehicle:
    Other Non-Hybrid
    People have eaten mammoth dug out of the permafrost.
    As long as the meat was frozen fresh and kept frozen for all that time, it should be safe to eat. Safe doesn't mean it will taste good though.
    Doesn't sound like that was the case above.
     
  2. tochatihu

    tochatihu Senior Member

    Joined:
    Apr 10, 2004
    8,972
    3,501
    0
    Location:
    Kunming Yunnan China
    Vehicle:
    2001 Prius
    A large radio telescope

    China is Building an Absolutely Massive Radio Telescope

    Arecibo 300 m this one 500. This one not built in hurricane zone, which is a good plan.

    So, why does one built these things in limestone pits? An underlying support structure of this scale costs too much.

    It will be aim-able by moving the triangular reflectors to create local parabolas. Thus a technical step beyond Aercibo.

    Radar transmit power is essentially limited by how many capacitors you want to buy. Has anyone here visited the Arecibo capacitor room?
     
    bwilson4web likes this.
  3. hkmb

    hkmb Senior Member

    Joined:
    Sep 27, 2010
    279
    1,855
    0
    Location:
    Sydney, Australia
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    This looks like a fantastic thing.

    I've never been to Guizhou, and I know it's sparsely-populated by Chinese standards. But I'm still kind of surprised that they'd put this anywhere in Eastern China when there's so much artificial radio noise around. I know there are practical issues around construction, but a good valley in Tibet, Qinghai or Xinjiang would have had to deal with far less ground-based interference. Unless a very small separation from a population centre is enough: I really don't know.

    Fox Mulder did, if I recall correctly. It didn't end well.
     
  4. tochatihu

    tochatihu Senior Member

    Joined:
    Apr 10, 2004
    8,972
    3,501
    0
    Location:
    Kunming Yunnan China
    Vehicle:
    2001 Prius
    This spot at about 105 oE is not what I would call 'eastern'. The provinces hkmb mentioned are short on limestone -> karst sinkholes -> simple construction.

    How large radio quiet zone needed might be inferred from Greenbank (Virginia US), which has about a 20 kn hole I think. Perhaps the local bosses could double that without great travail.

    This larger 'dish' will get sensitivity (depth) and only a little better angular resolution than Arecibo. Angular resolution is (now) VLA in New Mexico, and I think a couple of other projects are trying to improve that.

    I need to know more about x-files as above! Apparently have missed a lot of TV.
     
  5. hkmb

    hkmb Senior Member

    Joined:
    Sep 27, 2010
    279
    1,855
    0
    Location:
    Sydney, Australia
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    It's not Eastern Eastern. But it's closer to highly-populated parts of Sichuan, Chongqing and Hunan than to the wide-open spaces of Qinghai. But yes, the karst landscape would make construction a lot easier in Guizhou.

    Australia has a set of radio telescopes that are only about 20km from Canberra - we went to visit it a few weeks ago, and it was brilliant. But in spite of being the capital, Canberra isn't much of a population centre. On the plus side, I was thrilled to note that there were all these really good, empty, country roads nearby, and that the police weren't allowed to use radar guns in case they interfered with the system. This facility is also separated from Canberra by a mountain range, which helps. The pictures suggest that FAST is in a very mountainous area too, so it's probably OK.

    This was a very early X-Files - Season 1, I think - so it would have been early 90s. Mulder ends up at Arecibo while searching for evidence of alien contact.

    There's a new X-Files season coming out at the end of this year, I think.
     
  6. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,068
    15,372
    0
    Location:
    Huntsville AL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Dark Side of the moon anyone?

    I remember someone once suggested Lagrange points based radio telescope. The widely space receivers, coupled would have incredible resolution.

    Bob Wilson
     
    #46 bwilson4web, Jul 26, 2015
    Last edited: Jul 26, 2015
  7. FL_Prius_Driver

    FL_Prius_Driver Senior Member

    Joined:
    Jun 17, 2007
    4,319
    1,527
    0
    Location:
    Tampa Bay
    Vehicle:
    2010 Prius
    Model:
    I

    I fail to see the big selling point of a Lagrange point location for a radio telescope, much less a space based advantage. There would be no isolation from Earth radio noise. In fact, you might get more space noise than a earthbound remote site location. Likewise, the bandwidth and geometry would be much less than what the same money can buy for earth. Right now the radio telescope resolution is limited by the size of the planet. The really big baseline arrays digitally reconstruct the beamformed signals from space from the dishes on different continents I don't think we could get something that big in space.
     
  8. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,068
    15,372
    0
    Location:
    Huntsville AL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Sorry, I meant a radio telescope consisting of receivers at the Lagrange points:
    NASA - Thinking Big About Space Telescopes

    I would be OK with construction of a huge, single radio telescope in orbit . . . say at the space station. Integration and test then boost it to a Lagrange point. But I prefer separate receivers. With accurate emphermis, the signals can be integrated to see small things a very long away with high fidelity.

    Bob Wilson
     
  9. FL_Prius_Driver

    FL_Prius_Driver Senior Member

    Joined:
    Jun 17, 2007
    4,319
    1,527
    0
    Location:
    Tampa Bay
    Vehicle:
    2010 Prius
    Model:
    I
    OK, I can see the possibilities of coordinated RF direction finding satellites. One limitation is all the Lagrangian points are on one plane, but still good enough to try out.
     
  10. tochatihu

    tochatihu Senior Member

    Joined:
    Apr 10, 2004
    8,972
    3,501
    0
    Location:
    Kunming Yunnan China
    Vehicle:
    2001 Prius
    I think this

    Square Kilometre Array - Wikipedia, the free encyclopedia

    is poised to get the highest spatial resolution. Inferometry is all about getting your clocks lined up. Probably very doable on earth. Maybe much harder with satellites flinging themselves about. A nanosecond (for light) is a foot. How far are two satellites apart? I do not know.

    A single big reflector on the ground is all about digging down into the decibels. Remains to be seen how deep they can dig. But spatial resolution? Nah. VLA in New Mexico is already much better, and the SKA can (will, might) bump that way up.
     
  11. FL_Prius_Driver

    FL_Prius_Driver Senior Member

    Joined:
    Jun 17, 2007
    4,319
    1,527
    0
    Location:
    Tampa Bay
    Vehicle:
    2010 Prius
    Model:
    I
    Using GPS satellite signals alone, sub centimeter resolution is possible with GPS satellites, so that problem has been solved. One very important aspect of the sub-cm resolution is the angular signal processing can be figured out after the fact using data over months of averaging and integrating to figure out all the error contributions. I personally worked on the GPS receivers on the ground that were used to figure out exactly where the satellites were. Knowing where they were are in real time is sporty. Figuring out where they were exactly after days of error removal processing was routine. The key assumption is the reference locations don't move.
     
    bwilson4web likes this.
  12. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    27,068
    15,372
    0
    Location:
    Huntsville AL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Places I'd like to see examined:
    • areas around black holes
    • background radiation anomalies
    Bob Wilson
     
  13. tochatihu

    tochatihu Senior Member

    Joined:
    Apr 10, 2004
    8,972
    3,501
    0
    Location:
    Kunming Yunnan China
    Vehicle:
    2001 Prius
    FL_Prius_Driver is certainly correct about locations on the earth's surface. For orbiting satellites, I don't think GPS is an option.
     
  14. FL_Prius_Driver

    FL_Prius_Driver Senior Member

    Joined:
    Jun 17, 2007
    4,319
    1,527
    0
    Location:
    Tampa Bay
    Vehicle:
    2010 Prius
    Model:
    I
    But the same math and techniques apply using pulsars as reference sources.
     
  15. hkmb

    hkmb Senior Member

    Joined:
    Sep 27, 2010
    279
    1,855
    0
    Location:
    Sydney, Australia
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    My understanding is that, because of the speed that they travel or the lower levels of gravity or something, the GPS satellites travel more slowly through time than we do, and that the GPS system constantly has to compensate for that. Is this right? It sounds like it's something you'd have dealt with.

    Would this further complicate an array-based radio telescope in space? Would it be possible to compensate as easily as with GPS, or would the problem get more complicated?
     
  16. tochatihu

    tochatihu Senior Member

    Joined:
    Apr 10, 2004
    8,972
    3,501
    0
    Location:
    Kunming Yunnan China
    Vehicle:
    2001 Prius
    @54, orbiting radio telescopes calculating their position by triangulating pulsars? It that what you suggest? What accuracy would result?

    One reason I doubt that radio telescopes could be useful 'above the atmosphere' is cosmic ray flux. Those detectors are operating right at the noise floor. Some hot protons come sailing through, and I would expect to hear snap crackle pop.

    Atmosphere above ya has many benefits.
     
  17. tochatihu

    tochatihu Senior Member

    Joined:
    Apr 10, 2004
    8,972
    3,501
    0
    Location:
    Kunming Yunnan China
    Vehicle:
    2001 Prius
    hkmb, LEO satellites really zip around by our standards, but if I did the math right they are 42 millionths of the speed of light. So yeah, they experience time dilation, and that does get corrected for.

    The few astronauts who've spent a year on orbit aged less as a consequence. But I haven't read the effect size.

    Is this right? T / To = sqrt (1-(V^2/C^2))
     
    hkmb likes this.
  18. FL_Prius_Driver

    FL_Prius_Driver Senior Member

    Joined:
    Jun 17, 2007
    4,319
    1,527
    0
    Location:
    Tampa Bay
    Vehicle:
    2010 Prius
    Model:
    I
    Actually both velocity effects (special relativity) and gravity effects (general relativity) are separate corrections incorporated into the GPS system. The velocity effects are incorporated in the positioning calculations and the general relativity effects are incorporated by making the cesium and rubidium time standards in the satellite a little slower. That way, as the GPS signals "fall" to earth, they actually speed up to the frequency expected.

    All of these factors are involved in any space communication or navigation engineering. The precisions get quite high. For example, one would think the gravity exerted by the earth would be the same around the entire orbit of the satellite, but in reality, mountain ranges and rock/water density changes actually cause gravity wiggles in every satellite orbit. Even these wiggles must be compensated out. Some time ago, all this "wiggle" data was classified since it is used to correct the trajectories of ballistic missiles. Now this wiggle data is measured for figuring out changes in the ocean floor due to tsunamis and other large earth changes.
     
    hkmb and bwilson4web like this.
  19. hkmb

    hkmb Senior Member

    Joined:
    Sep 27, 2010
    279
    1,855
    0
    Location:
    Sydney, Australia
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
     
  20. tochatihu

    tochatihu Senior Member

    Joined:
    Apr 10, 2004
    8,972
    3,501
    0
    Location:
    Kunming Yunnan China
    Vehicle:
    2001 Prius