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jmlloren

The artificial skylight that you won't believe isn't real - 9 views

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    Nautral Light for Human Space Exploration
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    wow, that looks pretty real to me! I remember a presentation some time ago on difficulties with large scale LED lights for making directed light sources. I guess we can cross that off the list :)
Thijs Versloot

Is Westeros orbiting a binary star system? #ArXiv - 5 views

shared by Thijs Versloot on 21 May 14 - No Cached
Nicholas Lan liked it
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    To right that appalling wrong, here we attempt to explain the apparently erratic seasonal changes in the world of G.R.R.M. A natural explanation for such phenomena is the unique behavior of a circumbinary planet. Thus, by speculating that the planet under scrutiny is orbiting a pair of stars, we utilize the power of numerical three-body dynamics to predict that, unfortunately, it is not possible to predict either the length, or the severity of any coming winter.
jmlloren

Scientists discover how to turn light into matter after 80-year quest - 5 views

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    Theoretized 80 years ago was Breit-Wheeler pair production in which two photons result in an electron-positron pair (via a virtual electron). It is a relatively simple Feynmann diagram, but the problem is/was how to produce in practice a high energy photon-photon collider...

    The collider experiment that the scientists have proposed involves two key steps. First, the scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than visible light. The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field, generating light similar to the light emitted by stars. They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can.

    Now this is a good experiment... :)
  • ...6 more comments...
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    The solution of thrusting in space.
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    Thrusting in space is solved already. Maybe you wanted to say something different?
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    Thrusting until your fuel runs out is solved, in this way one can produce mass from, among others, solar/star energy directly.

    What I like about this experiment is that we have the technology already to do it, many parts have been designed for inertial confinement fusion.
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    I am quite certain that it would be more efficient to use the photons directly for thrust instead of converting them into matter.
    Also, I am a bit puzzled at the asymmetric layout for photon creation. Typically, colliders use two beam of particle with equal but opposite momentum. Because the total momentum for two colliding particles is zero the reaction products are produced more efficiently as a minimum of collision energy is waisted on accelerating the products. I guess in this case the thermal radiation in the cavity is chosen instead of an opposing gamma ray beam to increase the photon density and increase the number of collisions (even if the efficiency decreases because of the asymmetry). However, a danger from using a high temperature cavity might be that a lot of thermionic emission creates lots of free electrons with the cavity. This could reduce the positron yield through recombination and would allow the high energetic photons to loose energy through Compton scattering instead of the Breit-Wheeler pair production.
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    Well, the main benefit from e-p pair creation might be that one can accelerate these subsequently to higher energies again. I think the photon-photon cross-section is extremely low, such that direct beam-beam interactions are basically not happening (below 1/20.. so basically 0 according to quantum probability :P), in this way, the central line of the hohlraum actually has a very high photon density and if timed correctly maximizes the reaction yield such that it could be measured.
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    I agree about the reason for the hohlraum - but I also keep my reservations about the drawbacks.
    About the pair production as fuel: I pretty sure that your energy would be used smarter in using photon (not necessarily high energy photons) for thrust directly instead of putting tons of energy in creating a rest-mass and then accelerating that. If you look at E² = (p c)²+(m0 c)² then putting energy into the mass term will always reduce your maximum value of p.
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    True, but isnt it E2=(pc)^2 + (m0c^2)^2 such that for photons E\propto{pc} and for mass E\propto{mc^2}. I agree it will take a lot of energy, but this assumes that that wont be the problem at least. The question therefore is whether the mass flow of the photon rocket (fuel consumed to create photons, eg fission/fusion) is higher/lower than the mass flow for e-p creation. You are probably right that the low e-p cross-section will favour direct use of photons to create low thrust for long periods of time, but with significant power available the ISP might be higher for e-p pair creation.
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    In essence the equation tells you that for photons with zero rest mass m0 all the energy will be converted to momentum of the particles. If you want to accelerate e-p then you first spend part of the energy on creating them (~511 keV each) and you can only use the remaining energy to accelerate them. In this case the equation gives you a lower particle momentum which leads to lower thrust (even when assuming 100% acceleration efficiency). ISP is a tricky concept in this case because there are different definitions which clash in the relativistic context (due to the concept of mass flow). R. Tinder gets to a I_SP = c (speed of light) for a photon rocket (using the relativistic mass of the photons) which is the maximum possible relativistic I_SP:
    http://goo.gl/Zz5gyC .
Dario Izzo

Back to Earth with a splash! Fisherman finds car-sized fragment of a SPACE ROCKET in a ... - 4 views

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    ooops ....
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    Where is the sticker saying "if found, please post this item unstamped to the following address"?
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    Yup, it's ours...

    Still, better take it out of the river than in the face. Such a big one especially.
Luís F. Simões

Evolution of AI Interplanetary Trajectories Reaches Human-Competitive Levels - Slashdot - 4 views

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    We made it to Slashdot's frontpage !!! :)
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    Congratulations, gentlemen!
jmlloren

Shark Wheel - the SQUARE skateboarding wheel that shreds! by SharkWheel.com and SharkWh... - 2 views

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    The square wheel!
jmlloren

COPENHAGEN SUBORBITALS - OPEN SOURCE AND NON PROFIT SPACE - 1 views

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    Our mission is very simple. We are working towards launching a human being into space. 
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    Nicholas this is project I mentioned while G&T-ing in Madrid.
Luís F. Simões

Physicists Discover a Whopping 13 New Solutions to Three-Body Problem - ScienceNOW - 1 views

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    They search numerically for initial conditions resulting in periodic orbits. Reminds to me the methods we employed for the "search for invariant relative motion" and which brought us to discover the magic inclinations (47.9 degrees).

    I wonder what are the implications. In any case nice plots :)
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    Haven't read in detail, but it's not clear to me what it means exactly. If they were discovered numerically (I assume it means via numerical integration), how can they be sure the orbits are truly periodic?
Joris _

NASA International Space Station Longeron Marathon Challenge - 1 views

shared by Joris _ on 18 Jan 13 - No Cached
LeopoldS liked it
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    nice - did not know about it. GTOC on steroids and with loads of cash. concerning this specific challenge and especially the last condition: doesn't this hint towards a flawed design?

    In addition to maximizing the total power output there are some constraints on the possible movements:
    Each SARJ and BGA is limited to a maximum angular velocity and to a maximum angular acceleration.
    Each SAW must produce at least some minimum average power over the orbit (which is different for each SAW).
    The sequence of positions must be cyclic, so it can be repeated on the next orbit.
    The maximum amount of BGA rotation is not limited, but exceeding a threshold will result in a score penalty.
    Some structural members of the SAW mast (called Longerons) have restrictions on how they can be shadowed.
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    The longerons will expand and contract with exposition to sun (I think whatever the material they are made of). Because you have 4 longerons in a mast, you just need to be carefull that the mast is well balanced, and that the 4 longerons support each other, basically, you need an even number of shadowed longerons, possibly 0 too. I would call this an operational constraint.
Joris _

SpaceCamera on Apophis - 1 views

shared by Joris _ on 09 Jan 13 - No Cached
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    Apophis is back! You can watch its close approach live.
    Announcement: http://images.slooh.com/files/press_release/asteroid_apophis2013.pdf
Joris _

Out of this world! Student takes stunning snaps of space using only a £30 sec... - 2 views

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    Boh....
Dario Izzo

TETRIS - 5 views

shared by Dario Izzo on 27 May 12 - No Cached
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    Connected to asteroid deflection? :)
Joris _

video of the short hop test flight - 4 views

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    Have you seen this?!
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    no! quite impressive indeed!
    thanks for sharing it here
Joris _

ATV docks with the ISS | Bad Astronomy | Discover Magazine - 4 views

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    On March 28, ATV-3, named Edoardo Amaldi, docked with the ISS. Astronauts on the station took this unbelievable picture of it as it approached
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    More pics here: http://www.flickr.com/photos/europeanspaceagency/
    ATV docking is a bit further down the photostream.
Joris _

New DARPA challenge wants unique algorithms for space applications - 4 views

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    "On March 28, the Defense Advanced Research Projects Agency will kick of another one of its highly successful challenges this time looking for teams or individuals to develop unique algorithms to control small satellites on-board the International Space Station. "

    Will the ACT participate?
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    That would be wrong on so many levels...
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    Could not find out what the prize money is? Also does not seem clear to me how three cubes can catch an object "flying" in the opposite direction... But the approach is nice to see
jmlloren

A Swarm of Nano Quadrotors - YouTube - 3 views

shared by jmlloren on 01 Feb 12 - No Cached
LeopoldS liked it
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    Nice formation flying, though I still prefer Dario's 3D animation
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    very nice indeed!!
Joris _

DARPA Aims to Repurpose Retired Satellites - 2 views

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    Agency wants to send mini robots into space to recycle and reuse antennas from more than 1,300 dormant satellites in geostationary orbit above the earth.
Joris _

Domino's plans pizza on the Moon - Telegraph - 0 views

jmlloren

Designer lattices - 5 views

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    Perhaps interesting for the SPS self-assembling
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    nice, read only the abstract so far but looks to me like a bit of 19th century crystallography reinvented ...
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