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A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

• comboy 10y ago
  How is such thing able to communicate back with earth? Doesn't it require a lot of energy to create signal that we will be able to receive on earth (or satelite)?
  • rm_-rf_slash 10y ago
    Not a scientist but I first read this on The Economist and they summed it up pretty well: "At its destination it would beam back pictures of the star’s planets with its on-board laser. No current observatory could possibly pick up such a signal—but the kilometre-wide launch array should be able to. The optical systems used to meld the output of the lasers could be used in reverse as a vast and sensitive telescope." http://www.economist.com/news/science-and-technology/21696876-interstellar-travel-means-thinking-both-very-big-and-very-small-new-plan http://www.economist.com/news/science-and-technology/2169687...
    • slg 10y ago
      This might be a stupid question, but if we have the technology to see a blinking light the size of a postage stamp trillions of miles away, why would we need to send a probe with a camera all the way out there in the first place?
      • Carrok 10y ago
        Because while all we can see is the blinking light, the probe can see the things close to it far more clearly. As the above quote says the probe will "beam back pictures of the star’s planets." We can receive these pictures through the data received from that blinking light, but we can't see the planets in question. Now we can.
        • slg 10y ago
          But why would we be unable to see the star's planets if we are able to see a probe that small?
          • dysfunction 10y ago
            We wouldn't be able to see the probe itself, rather we'd see its laser. The planet outputs (or reflects) vastly more total light than the laser, but the laser is pointed directly at the receiver and can output more light in that specific direction than the planet does. Plus, to get interesting data about the planet we need to get quite a lot of light from it, whereas we can get data from the laser over time by pulsing it so long as we can get any light from it at all.
            • slg 10y ago
              >The planet outputs (or reflects) vastly more total light than the laser, but the laser is pointed directly at the receiver and can output more light in that specific direction than the planet does. So then the problem is that you need a laser than can hit a 1 km^2 target from 40 trillion km away?
              • drdrey 10y ago
                No, the laser would point in the general direction of the sun and as long as Earth is within the cone it has the potential to detect the signal. The laser just happens to focus all of its energy in one narrow cone as opposed to all directions.
          • cb18 10y ago
            'Seeing' the probe is like being connected to the internet. Your friend in Japan can take a picture of an apple and email it to you in the US. Your friend's camera is like the camera on the probe. You can't see the apple from where you are, but your computer can 'see' the internet. Your friend uses the internet to send you a digital code that your computer turns into a picture of an apple. The optical systems used to meld the output of the lasers could be used in reverse as a vast and sensitive telescope. But why would we be unable to see the star's planets if we are able to see a probe that small? The laser receiver might be able to see the planets in question, but a probe with an interstellar worthy camera in the direct vicinity of the planets would obviously be able to capture a much higher resolution image.
      • jperras 10y ago
        To answer that question, you need to know a little bit about diffraction-limited systems in optics and the Rayleigh criterion. Essentially, point-like sources (the laser emitter array and the target can be considered point sources when on the scale of lightyears) separated by an angle smaller than the angular resolution of the device in question cannot be resolved.
    • david-given 10y ago
      I'd be kinda hesitant about relying on a ground-based receiving station. How stupid would you feel if after 40 years flight, you missed the return signal because your receiving station happened to be on the wrong side of the Earth?
  • lunchTime42 10y ago
    Same way it got there? Laser focused on earth? Needs good aiming though.
    • Cerium 10y ago
      Modulated retro-reflector. We pulse firing a lower power laser at it and it reconfigured the mirror to modulate the returned signal. Essentially an interstellar DLP projector.
• RIMR 10y ago
  So, how is a tiny smartphone-sized probe supposed to transmit data back to Earth from 4.37ly away?
  • derrickdirge 10y ago
    Slowly and very carefully.
  • guelo 10y ago
    Thinking out loud: You need an ingenious design that allows the laser sail to double as a directional antenna. And you pick a frequency which is not radiated by many other objects in space so it's easier to pick up the dim signal. And then you build a ginormous radio telescope bigger than any ever built before. Luckily you have a decade or two to build the telescope after the probes are launched.
    • Jtsummers 10y ago
      And/or establish a chain of these spanning the distance between here and Alpha Centauri. They don't need to actually stop, but if enough are traveling at lower speeds or depart sufficiently late in the program then they'll be in position to act as repeaters. Possibly larger probes (which would travel slower) that have more power available for reception and retransmission.
    • paulmd 10y ago
      Planar directional antennas have been done before, in EHF-type frequencies (most research has focused on 2.4 GHz and 5 GHz for obvious reasons). Lower-frequency signals would probably be harder. No idea what a nice clear frequency might be though, particularly out in the interstellar medium. Depending on what maneuvering profile these things will have, it might be desirable to have a "semi-phased" design that can be steered to a limited degree without physically moving the spacecraft. And, it also goes without saying that this antenna probably needs to be flexible or at least articulated in order to deploy. NASA has previously done some really interesting antenna designs with genetic algorithms. You just need to figure out what the goodness function here should be. https://ti.arc.nasa.gov/m/pub-archive/1244h/1244%20(Hornby).pdf https://ti.arc.nasa.gov/m/pub-archive/1244h/1244%20(Hornby)....
• sravfeyn 10y ago
  How significant are the relativistic effects at 0.2c (the probe speed they are aiming for)?
  • mabbo 10y ago
    Not enormous, but noticeable. Around 2% time lost relative to earth, I believe.
  • cwkoss 10y ago
    To the probes, wouldn't the 20-year flight 'feel' like 16?
    • mikeash 10y ago
      Not that much. Time dilation due to speed is sqrt(1 - v^2/c^2). At 0.2c, that's 98%, so 20 years would "feel like" 19.6 years.
      • gus_massa 10y ago
        (I Agree.) As a rule of thumb, you can approximate sqrt(1 - v^2/c^2) = 1 - 1/2 (v/c)^2. So if v/c = 2, then the correction is approximately 1 - 1/2 .2^2 = 98% as you said. This formula is easier for back of the envelope calculations and the important point is that it's quadratic. (I always forget the 1/2 :(. ) The GP comment used the wrong correction of 1 - v/c, that is not quadratic so the correction is much bigger.
        • mikeash 10y ago
          Cool trick. It starts to fall apart at higher speeds (at c, the approximation produces 1/2, when it should be 0), but it looks like up to 0.5 or 0.5 it's decent.
          • gus_massa 10y ago
            Yes, this is the first two terms of the Taylor series near 0, so it works only at "low" speed. For speeds that are close to c, you have to use another "Taylor" series to get a good approximation. If v is close to c, then the approximation of the correction is sqrt(2(c-v)/c). So at 99%c you get 4.5%.
• ColinCochrane 10y ago
  This is quite an interesting proposal, although there are some major technological challenges to address: To achieve that energy would require an array about a mile across combining thousands of lasers firing in perfect unison.
• ck2 10y ago
  I thought very strange things start to happen at even 10% the speed of light (mass increase, etc.) so 20% sounds impossibly ambitious? Also the fastest physical object we've ever observed is only 1000 miles per second. A far cry from even 10% of c Then there is that pesky problem of deceleration.
  • mabbo 10y ago
    At 20% the speed of light, time would dilate by around 2%, but that's about the extent of the effects, afaik. Also: why bother decelerating at all? Take a picture as you fly by.
    • zdkl 10y ago
      Wouldn't want to program that particular timer. Talk about hard real time requirements!
      • saalweachter 10y ago
        It'd be hilarious to have a bonus tied to the successful completion of that project. "In twenty years, I may get an $X bonus!"
    • onesun 10y ago
      Have you ever tried to take a picture from a moving car? They never turn out.
      • fsloth 10y ago
        The sun is 8 light minutes away from earth. These babies would span that distance in 40 minutes. If the plan is to take planetary images I would call that basically crawling speed in terms of angular velocity (unless they are on actual collision course).
    • deleted 10y ago
      [deleted]
  • 10y ago
• 0x74696d 10y ago
  Sending a swarm of unguided relativistic projectiles across the universe seems profoundly rude.
  • nkrisc 10y ago
    Ten thousand years from then, some alien on some planet somewhere might have a very bad day.
    • clem 10y ago
      "That is why, Serviceman Chung, we do not eyeball it!" https://www.youtube.com/watch?v=4tIk-vUtLBs https://www.youtube.com/watch?v=4tIk-vUtLBs
    • a3n 10y ago
      "Cool, an iPhone."
  • NoGravitas 10y ago
    It would be nice if they could use solar wind to decelerate as they approached. I know there's not enough energy there to insert them into an orbit, but they might get time for a few more pictures?
    • 1812Overture 10y ago
      Just flip the battery in the laser around and it will pull instead of pushing.
      • LyndsySimon 10y ago
        You mean we should... reverse the polarity?
        • rotexo 10y ago
          excuse me, but I think you forgot to take the opportunity provided by that ellipsis to put on your visor.
• NoGravitas 10y ago
  Moreover, to keep the beam tightly focused on one probe at a time would require an adaptive optics system that compensated for atmospheric turbulence — something astronomers know how to do over a span of 10 meters, the size of a big telescope mirror now, but not over a mile. Would it be easier just to put the lasers on the moon?
  • oabm 10y ago
    It might be easier to fire the lasers from the moon, but getting the lasers to the moon would be a huge pain.
    • stdgy 10y ago
      Not to mention supplying these hypothetical moon lasers with enough power to blast these mini-probes into another star system.
      • Zikes 10y ago
        https://en.wikipedia.org/wiki/Helium-3 https://en.wikipedia.org/wiki/Helium-3 ought to do the trick.
        • Zikes 10y ago
          I'm a bit surprised at the downvotes. I'm no scientist, but I meant this suggestion in earnest. As far as my layman's knowledge goes, I've always understood the Moon's He-3 reserves to be a "vast, as-yet-untapped power resource".
          • marcosdumay 10y ago
            People have to learn how to harvest power from fusion before.
            • ars 10y ago
              You know how they have chemically pumped lasers? So it would be awesome to directly pump the laser from H3 fusion. H3 fusion is actually very easy - I think we could do it today. We just don't have a readily available source of H3 for fuel.
• AnthonyAguirre 10y ago
  This is a pretty cool initiative — I looked into beamed propulsion a bit while teaching a course this past fall, and it seems to me that if we (or human technologies) are going to reach a star in our lifetimes, this is by far the most likely way. Still very challenging though. For a quite detailed recent treatment of optical/IR propulsion see this paper by Philip Lubim:(http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-Roadmap-to-Interstellar-Flight-15-h.pdf http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-R...) For a thorough, if somewhat outdated, treatment of the “starwisp” idea using microwaves rather than optical/IR lasers, see this paper: http://path-2.narod.ru/design/base_e/starwisp.pdf http://path-2.narod.ru/design/base_e/starwisp.pdf by Robert Forward. To poll the success of this overall endeavor, as well as start to make predictions about which components will/won’t work, Metaculus is launching a series of questions —check it out if you have expertise or opinion: http://www.metaculus.com/questions/#/?order_by=-publish_time http://www.metaculus.com/questions/#/?order_by=-publish_time
  • stcredzero 10y ago
    I'm disappointed that more people don't mention Robert Forward when this idea is being covered in the media. (Probably because his Usenet posts, papers, and books predate the World Wide Web.)
    • AnthonyAguirre 10y ago
      agreed! The starwisp paper is really very nice.
• yongjik 10y ago
  So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will instantly vaporize) while maintaining structural integrity under the acceleration of 60,000g for two minutes? And whatever laser sources we're using must track this smartphone-sized object during these two minutes across several million kilometers. Perfectly. (It also means that whatever course deviation the object experiences must be anticipated seconds before it happens, because at the end of the two minutes the object will be ~10 light-seconds away.) If they could pull this off it will be the next Apollo, but I'm skeptical. Edit: Just realized we have even more problems, about the reflective coatings. If the laser is green, by the time it's flying away at 0.2c, the laser won't be green any more thanks to the Doppler effect! I'm too lazy to calculate, but it will definitely shift toward the red. So whatever reflective coating we use must be able to work near-perfectly over a wide range of spectrum.
  • AnthonyAguirre 10y ago
    The plan calls for ultra-reflective coatings that are tuned to the wavelength of the laser. Apparently these exist, though I have not checked the numbers. In my class I abandoned laser propulsion quickly for just this reason (incinerated the target), but with these coatings it might work.
  • tachyonbeam 10y ago
    Setting incredibly ambitious goals has definitely lead to impressive achievements in the past. I think it's definitely worth studying. Worst case, we'll learn something.
    • a_imho 10y ago
      >Worst case, we'll learn something we might learn something, but we have to use resources for studying and there might just be better and/or more useful alternatives
      • bbcbasic 10y ago
        Side effects of these projects, even if they fail, may be massively valuable. Sometimes solving problem X that isn't a big concern for society will solve problem Y down the track. History of maths is littered with things that were useless when they where first invented, such as imaginary numbers.
• PaulHoule 10y ago
  Oddly the most practical use for this is as an interstellar weapon. You don't need to solve the problem of communicating back to Earth, you just need a little terminal guidance. If an iPhone weighs 100 g and we use a non-relativistic formula for energy at 1/4c, that is 2.8 x 10^14 joules, a ton of TNT equivalent is about 4.1 x 10^9 joules, so that is a cool 70kT -- The impact velocity would be high enough to break the Columb barrier as well, so you might get a nuclear boost to the yield as well.
  • jim-greer 10y ago
    The probes would be 1g, not 100g. They're sending the "guts" of an iPhone. 7kT is half of the Hiroshima bomb. Still destructive, especially if you've got a bunch of them.
    • amiralul 10y ago
      According to a screenshot I took during the presentation (http://i.imgur.com/pncUg0Q.png http://i.imgur.com/pncUg0Q.png), the probes are estimated to have around 200 grams. There's no way you could fit a battery, a RTG, a camera and propulsion system within 1 gram.
  • zeveb 10y ago
    > Oddly the most practical use for this is as an interstellar weapon. I completely don't advocate this, but the 9-year-old-boy part of my brain thinks it'd be pretty awesome to announce our presence to the universe by attacking a star system.
    • dsr_ 10y ago
      A Nicoll-Dyson laser has much the same effect, but you can fire it again and again as long as you still have a sun.
    • PaulHoule 10y ago
      One of the explanations of why we are not seeing evidence of ETs is that everybody is hiding and afraid they might get bombed by their neighbors; that's because bombing your neighbors is orders of magnitude easier to do than visiting them -- you don't need to solve the problem of decelerating on the other end for one thing.
• ant6n 10y ago
  Let's build a mass driver around the circumference of the Moon. Like a cannon in a particle accelerator shape.
• guelo 10y ago
  It seems to me that the accuracy required to aim an unguided projectile anywhere near the target stars will be impossible. They'll fly by pretty far. At what distance to Alpha Centauri does an iPhone quality camera outmatch the Hubble's photos?
  • Eyght 10y ago
    "It's not impossible. I used to bullseye womp rats from my T-16 back home." It's a serious point though. Perhaps the gravity of the star will be enough to help them right?
  • nilstycho 10y ago
    “The light beamer must focus a spot smaller than the sail onto the sail, as it orbits 60,000km above the Earth’s surface. This alignment must be produced when the target star system (Alpha Centauri) has the correct configuration with respect to all planetary and stellar bodies in the intervening space, such that the flyby occurs within 2 AU of the target planet. Using on-board photon or others thrusters, the nanocraft will have the ability to make some modest mid-course corrections, on the order of 1-2 AU. “The task of pointing the array is dominated by the problem of keeping the sail on the beam. This problem is defined by the width of the sail and the distance to it. As an example, for meter-scale sail size the launch distance is on the order of a few million km. The pointing accuracy required for beam stability at this distance is on the order of a milliarcsecond. There are several mitigation approaches that could be used to counter these effects. A model of the atmosphere, calibrated with radar, laser beam, and optical measurements in real time, would enable the required beam precision to be achieved. Targets such as Alpha Centauri are bright star systems that will inform pointing requirements. “Monitoring the laser beam output provides the information needed to form the beam. The Starshot system would be very different than a conventional telescope, and specialized to its purpose. For example, most ground-based telescopes, such as the Keck telescope, point to within a few arcseconds and can track in a closed loop mode to better than 100 milliarcseconds. For the purposes of Starshot, a significant improvement on this precision is required. However, the beam synthesis inherent in the phased array system provides considerable fine-pointing capability, supplemented by closed loop tracking of the beacon on the spacecraft.” http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=2&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru...
• jgianakopoulos 10y ago
  Zuck to fund interstellar travel w/in decades? 2040 Breaking News: Alpha Centauri Rejects Facebook's 'Free' Internet
• avian 10y ago
  I wonder what plans they have for communicating with a probe light-years away. Consider New Horizons. It has a power budget and antenna gain way beyond something that can be crammed into a few grams. Yet, the bit rate is so low it's still sending back data it gathered in 2015 from an encounter mere light-hours away. Even if the laser propulsion aspect of this works out, I think communicating with something that far away is fantastically beyond state-of-the-art in wireless communications.
  • nilstycho 10y ago
    “Images of the target planet could be transmitted by a 1Watt laser onboard the nanocraft, in a ‘burst mode’ which uses the energy storage unit to rapidly draw power for the power-intensive laser communications mode. Upon approach to the target, the sail would be used to focus the laser communication signal. “For a 4m sail, for example, the diffraction limit spot size on Earth would be on order of 1000m. A kilometer-scale receiving array would intercept 10-14 of the transmitted signal. The main challenge is to use the sail as diffraction limited optics for the laser communication system. This would be achieved by shaping the sail into a ‘Fresnel lens’ upon approach to the target. The sail structure could be different at the launch and communication phases. In order to maintain a high transmission through the Earth’s atmosphere, the communication would need to operate at a wavelength shorter than that used by the launch laser system, due to the Doppler shift of the nanocraft relative to the Earth.” http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=13&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru...
    • throwaway_yy2Di 10y ago
      "For a 4m sail, for example, the diffraction limit spot size on Earth would be on order of 1000m." That must be a misprint; the diffraction-limited spot size would be on the order of 10 million kilometers. It's correct when it says a 1 km^2 collector would intercept ~10^{-14} of the transmitted signal. https://www.google.com/search?q=4+light+years+*+1+micron+%2F+4+meters https://www.google.com/search?q=4+light+years+*+1+micron+%2F... https://en.wikipedia.org/wiki/Airy_disk#Size https://en.wikipedia.org/wiki/Airy_disk#Size
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• sna1l 10y ago
  I know we don't currently have the technology for this, but it makes complete sense. Get small things moving really fast instead of big things moving slow.
• outworlder 10y ago
  Does that mean that the US will be the winning civilization?
  • mikro2nd 10y ago
    "civilization"? You mean like when Ghandi was (allegedly) asked what he thought of Western Civilization, and replied, "I think it would be a good idea!"
    • itsnotlupus 10y ago
      You have mistaken our love of peace for weakness. You shall regret this!
    • yaacov 10y ago
      I think they meant the video game. Space race victory
      • outworlder 10y ago
        Precisely.
      • labster 10y ago
        Unlikely. I think these spacecraft won't fare so well against the mind-worms.
• valarauca1 10y ago
  The project estimates are completely off. Building a 1gigawatt power plant costs 10billion. Let alone building 100 of them. Also making the laser array. Also you can't have reflection without absorption. Also we don't have solar sails that fit the bill. This project is barely physically and economically plausible. Its not a question of scaling, or engineering. The physics just don't work. We have a way to get a space craft to 20% of C. Its called Project Orion. https://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29 https://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propu...
  • gene-h 10y ago
    You are putting out 100 gigawatts for 2 minutes. One does not need 100 one gigawatt powerplants, just some way to store and release a lot of energy really fast. Second, we have mirrors that can reflect up to 99.999% of a single wavelength of light(such as that emitted by a laser)[0]. There is a detailed analysis of the concept in [0] and the Breakthrough Foundation has a detailed list of challenges associated with this project at [1]. Getting the laser out of the atmosphere is probably one of the biggest challenges with this. [0] http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-Roadmap-to-Interstellar-Flight-15-u.pdf http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-R... [1] http://breakthroughinitiatives.org/Challenges/3 http://breakthroughinitiatives.org/Challenges/3
  • onion2k 10y ago
    I realise this is an appeal to authority, which is bad and wrong in any argument, but I trust Stephen Hawking wouldn't back a project that falls down on the physics.
  • drx 10y ago
    100 GW over 2 minutes is 3 1/3 GWh, or the equivalent of 37037 Tesla Model S 90 kWh batteries, or about $500M in batteries (in 2016).
  • Ankaios 10y ago
    Do you seriously think these guys haven't heard of Project Orion or wouldn't use Orion's approach if they thought it was best? In case you didn't notice, Freeman Dyson is involved with Starshot. Freeman Dyson co-led Project Orion.
• a3n 10y ago
  > Estimating that the project could cost $5 billion to $10 billion, Mr. Milner is initially investing $100 million for research and development. He said he was hoping to lure other investors, especially from international sources. It would be cool if there was one or more endowments for this sort of thing, to perpetuate the mission(s), similar to how schools have endowments.
• LockandByte 10y ago
  I am a self-proclaimed 'newbie' when it comes to understanding energy, astronomy, and physics in general, but I have a few questions and any answers or opinions would be appreciated: 1.) Why in the world does the 'Light / Laser Beamer' need to be physically located on earth? Why not in space? 2.) Is building 'check-points' for both data and power atop the planets not a possibility? (Solar, chemical, etc).
  • drabiega 10y ago
    As for #1 it's just a matter of logistics. It would actually be a little easier to do from space because you don't have to worry about the effects of the atmosphere, but it would be a pretty massive piece of infrastructure and it's likely that within this time frame it would be vastly simpler and cheaper to build it on earth.
    • Zikes 10y ago
      For a laser of the proposed magnitude surely a little bit of air isn't going to make a significant difference. From what I can gather the thing would be classified as a WMD and capable of carving a smiley face on Pluto.
      • david-given 10y ago
        Heat air up enough and it turns into plasma. Plasma's opaque. That's going to do terrible things to your beam focus. I remember hearing that this is a problem with high-energy laser weaponry, which is why it tends to be pulsed, to give the hot air time to dissipate. But I can't find a reference now.
  • civilian 10y ago
    For #2: What do you mean by check points? Which planets would you build the checkpoints at? When you say "atop", do you mean on the planet's surface, or in a polar orbit, or in orbit generally?
• rm_-rf_slash 10y ago
  Why don't we focus and reflect the sun's rays instead? Or even combine this and the traditional rocket method by putting the emitters in space to catch the sun and push these tiny craft after they've been shot from the Earth by the zillions in a single satellite. That way we deal with two big problems at once: generating laser energy sufficient for escape velocity, and focusing lasers through an atmosphere layer. Better yet, we can use SpaceX's reusable rockets and save even more on launch costs.
  • eanzenberg 10y ago
    My guess is the sunlight reaching the earth's atmosphere is already too diffuse. This could maybe work if the collector + launchpad were closer to the sun.
  • david-given 10y ago
    Apparently you can't collimate sunlight because it's not a point source. But I've been unable to find an explanation as to exactly why which I can understand, because this aspect of optics is deeply unintuitive, but the magic phrase to search for is 'conservation of éntendue'. If you find one, let me know.
    • vilhelm_s 10y ago
      Also, it's easier to make mirrors to reflect monochromatic laser light than broad-spectrum sunlight. You don't want to vaporise your probe.
    • XaspR8d 10y ago
      Have you seen the XKCD What If on this topic? [1] It doesn't get into the details of éntendue, and even makes a joke about the topic's complexity, so it probably won't satisfy your technical demands. But I've found the arguments about reversibility (light paths through lenses are reversible, so how could one point map back to multiple points?) and area increase (lenses do not intensify image values but can change the overall image size) intuitive enough to help quell myself and my friend's arguments about the matter. [1] - https://what-if.xkcd.com/145/ https://what-if.xkcd.com/145/
• lunchTime42 10y ago
  Ahem.. why does the object have to be behind the solar sail? Cant it be, one object hanging between two solar sails? Or Three? Is there something i dont get here?
  • amdavidson 10y ago
    The spot size of the laser will presumably be considerable after 10 light-seconds and we wouldn't want to irradiate the nano satellite.
• deleted 10y ago
  [deleted]
• maxxxxx 10y ago
  Would they slow down when they reach another star? What kind of observations can you do if you move at that speed?
  • chm 10y ago
    From my poor understanding of GR, there will be no limit on the measurements. You just have to take relative motion into consideration when interpreting them.
    • maxxxxx 10y ago
      You move the earth-sun distance in 8 minutes. I am not sure how well you can track with a camera at that speed to get any decent pictures.
      • rm_-rf_slash 10y ago
        These projections seem to point to a tenth of the speed of light. 80 minutes is a lot of time, but it probably won't be that much easier.
      • GavinMcG 10y ago
        > earth-sun distance Also known as an Astronomical Unit (AU).
      • chm 10y ago
        Doesn't it depend on how far the object is from you and at what speed you're moving relative to it? And they plan on moving at 0.2c, not 1c.
• david-given 10y ago
  This is a variation of the old Starwisp idea from 1985: https://en.wikipedia.org/wiki/Starwisp https://en.wikipedia.org/wiki/Starwisp tl;dr: a lightweight (about 1kg) vehicle made out of carbon wire mesh. It acts as a microwave mirror. You both use this for propulsion, by blasting it with microwaves from a Sol-system maser cannon, and for data recovery; its sensors cause the reflected microwave signal to be perturbed based on what its sensors see. So, you accelerate them (in bulk) at about 2G up to .1c. You ignore it until it's about 80% of the way there, and then for fire the maser at it again; the beam reaches the starwisp as it passes through the target system and powers the sensors. A few years later you read back the return signal. There were a whole bunch of technical problems with it, not least how to build a microwave lens 560km across, but it's still vastly more plausible than trying to push steel cans across the interstellar gulf. I'd be really interested to see if this version works.
• sneezeplease 10y ago
  This is swindling investors, there is no such star at such distance. This is because the earth is flat with a dome overhead. Watch a video from a high definition zoom camera on the planets and stars in the sky, they are revealed to be much closer and not at all what you think. Take a look, youll be amazed.
• WalterBright 10y ago
  A step towards such a project is to send such probes to every object in the solar system.
• deleted 10y ago
  [deleted]
• llomlup 10y ago
  Mr. Ha
• vilhelm_s 10y ago
  A quite similar proposal was discussed on Hacker News two months ago: https://news.ycombinator.com/item?id=11151497 https://news.ycombinator.com/item?id=11151497
• pklausler 10y ago
  How close does a tiny cell-phone camera objective lens have to get to an interstellar object before it can resolve detail better than the High-Def Space Telescope will?
  • antognini 10y ago
    A cell phone camera probably has a resolution of ~1 arcminute (about the resolution of the human eye). The Hubble has a resolution of ~0.05 arcseconds. The HDST would have a resolution of ~0.002 arcseconds. So to get comparable resolution to Hubble the probe would have to be at a distance of (.05 / 60) * 270,000 AU ~ 225 AU and a distance of (.002 / 60) * 270,000 AU ~ 9 AU to beat HDST. A camera on such a telescope would probably be of somewhat higher resolution, however. In fact, it would probably be at the diffraction limit, which for a ~1 cm aperture in visible light would be closer to ~10". This would increase the distances above by a factor of 6 or so. Resolution isn't the only thing, though. The contrast is extremely important. A little probe in the Alpha Centauri system would be able to take clean images of any planets in the system. A telescope in our solar system trying to directly image these planets has to contend with contamination of light from the stars.
• dang 10y ago
  Related article at https://news.ycombinator.com/item?id=11481351 https://news.ycombinator.com/item?id=11481351 (but comments moved here).
• ridgeguy 10y ago
  What about the energy dissipated by collision with the interstellar medium? Won't that slow the probe considerably? Apologies for significant errors and appreciation for corrections in the following hasty and unchecked calcs. Wikipedia [1] says the ISM density ranges from as little as 1e-4/cm^3 for hot, ionized regions to 1e6/cm^3 for cool, dense regions. Let's say it's all neutral hydrogen, which conveniently masses 1g/mole. A mole is 6.02e23 particles. A single H atom masses about 1.66e-27kg. And let's say the ISM has a hydrogen atom density kind of midway between the extremes: 10/cm^3 (=1e7/m^3). Let's say the spacecraft presents 2.54cm x 2.54cm (1 square inch) = 6.45e-4 m^2 to the ISM as it moves. I think this is small compared with what the project is proposing, but we can scale as needed. At 20% of C, the spacecraft sweeps out a volume of [(3e8.2)m/sec](6.45e-4m^2) = about 3.9e4m^3 every second, which contains about 3.9e11 hydrogen atoms, or a mass of about 6e-16kg/sec. If all those atoms hit and stick to the spacecraft, they all get accelerated to the spacecraft's velocity. At 20%C, relativistic mass increase should be small, so let's ignore it. The energy needed to accelerate one hydrogen atom to 20%C is about 3e12J/atom. If the spacecraft is hitting 3.9e11 atoms/sec and spending 3e-12J/atom accelerating impacting atoms to 20%C, that's slightly over 1 Watt that's decelerating the spacecraft. Over a 20-year trip (6.31e8 seconds and assuming no deceleration), that's 6.31e8 W-sec, or 631 megaJoules of energy needed to sustain 20%C because of collisions with the interstellar medium. A Watt isn't much, but over a 20 year trip, it integrates to a pretty big energy requirement, or a significant deceleration of an unpowered, very low mass spacecraft. It looks to me like small, light probes won't maintain their high initial velocity very long into the cruise phase without ongoing propulsion. [1] https://en.wikipedia.org/wiki/Interstellar_medium https://en.wikipedia.org/wiki/Interstellar_medium
  • igravious 10y ago
    So you're saying they'll slow down significantly due to the friction of the interstellar medium so they'll need some form of propulsion of their own?
    • ridgeguy 10y ago
      Yes, but yk's note that the friction load is a small fraction of the craft's kinetic energy makes me rethink whether the effect will matter much.
• trhway 10y ago
  to me the most intimidating problem is to make sure that the the beam is symmetric and sail is perfectly symmetrical reflecting the beam, otherwise it will go in very different direction than intended. Given the high acceleration during the short time period, i don't see how it can be sufficiently corrected for the beam and sail asymmetries. It is like kicking a soccer ball - you'd like to hit a perfect "9" ("upper 90" in US), yet ...
• KKKKkkkk1 10y ago
  Messrs Milner and Zuckerberg are surely aware that their business is perceived as an occasionally creepy timesink that made them enormously rich while adding little value to society. I'm sure they're not happy about this and would want to change this perception. One way to accomplish this is to pay a team of celebrity scientists for the privilege of associating your names with theirs.
• JoeAltmaier 10y ago
  Why not accelerate slower with smaller lasers? What harm in taking 2 days? 2 months? to get to speed.
  • tim333 10y ago
    The longer you take the further away it will be and the range of the lasers is only so far. The average speed during acceleration is 0.1c so if you take 2 days it would be 51 billion km away which is out of range.
    • JoeAltmaier 10y ago
      Ok. 10 minutes then.
• georgehm 10y ago
  Did this remind anyone of the Polis' spreading and searching the stars in Diaspora (by Greg Egan)
• deleted 10y ago
  [deleted]
• ryao 10y ago
  Is it going to just do a fly by or will it somehow enter orbit once it reaches Alpha Centauri? How is it going to transmit data back to earth in a manner that would overcome the signal to noise ratio? Will power be solar or nuclear? How would it know when it is there to begin operating, especially if it uses solar power?
  • ars 10y ago
    Answers to your questions are mostly in the article. Did you read it? Fly by. Laser. Nuclear.
• eva1984 10y ago
  So basically project something that we are never going to know or measure whether or not it has succeeded？
  • simonh 10y ago
    They describe a plan for sending a signal back.
• a_imho 10y ago
  Why do we need thousands of theses things, not just a couple of big ones? There seems to be some concern over the size constraints, but don't really see the advantage of having many of them?
• digsmahler 10y ago
  We should send even smaller nano-probes that would be even easier to accelerate and would have the capability to collect dust and build it into larger probes that would talk back to us when they come online!
• lholden 10y ago
  I wonder how they intend for the probe to actually communicate back to earth. Flying by Jupiter... The data downlink feed from New Horizons was about 38 kilobits per second. After the Pluto flyby... it was down to 2 kilobits per second and has been decreasing the further away it gets. Perhaps it could be done with laser? Having said that, I'd think the beams focus would be quite wide by the time it reaches earth. It would have to be both perfectly formed and aimed with absolute accuracy. (I don't work with lasers and may be off on this, so take this paragraph on principle rather than factual). Maybe with some form of quantum entanglement? Current forms of usable quantum communication still require mediums like fiber optics as far as I understand. Ex: http://www.nature.com/news/quantum-communications-leap-out-of-the-lab-1.15093 http://www.nature.com/news/quantum-communications-leap-out-o... And how to keep this iphone sized device powered?
  • firethief 10y ago
    > Maybe with some form of quantum entanglement? https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem Your other questions are all addressed in an article in The Atlantic: http://www.theatlantic.com/science/archive/2016/04/yuri-milner-zuckerberg-starshot-interstellar-centauri/477669/?single_page=true http://www.theatlantic.com/science/archive/2016/04/yuri-miln...
• andreapaiola 10y ago
  Bah... I think that it's better to make a magnetic luncher on the Moon.
• jondiggsit 10y ago
  Here's my big question: How do you slow down? 4.37 light years does not take into account all the time required to slow the hell down. Am I missing something? Isn't this the biggest fundamental issue with long range space travel?
  • hughes 10y ago
    You don't. You get a few hours (tops) to look around at anything interesting in Alpha Centauri before zooming out of the target system and off into really deep space. Kind of like the New Horizons mission, which never stopped at Pluto. It just flew right on by, but still got a ton of useful scientific data.
• ryao 10y ago
  If this works, it would probably be more useful for probing objects in our solar system. You could send a probe to Jupiter and hear back in ~4 hours. Waiting ~25 years for results from Alpha Centauri would be rather painful in comparison. Getting anything interesting back would be a long shot as the instruments would be rather limited and solar systems tend to be rather large. I imagine/hope that they would probably do tests in the solar system before trying to send them to Allha Centauri.
• appelza1 10y ago
  Bunch of javascript monkeys trying to be arm chair scientists. Go drink some coffee at your overpriced hipster cafe, and leave the real science to the pros.
• 1024core 10y ago
  I'll join the skeptics line with this observation: even if we are able to put this little device near Alpha Centauri, how the heck will we get a signal back from it? Will it have the juice to beam a picture back to Earth?
• retrogradeorbit 10y ago
  Why not go to Proxima Centauri? It's closer! https://en.wikipedia.org/wiki/Proxima_Centauri https://en.wikipedia.org/wiki/Proxima_Centauri
• mikepalmer 10y ago
  Say you could accelerate a ~1g camera to 0.2c. I don't know how to do general (hard) AI, but if I did, I can't think of a fundamental reason I couldn't shrink the AIs down to ~1g and make them able to survive 60,000G. So you could send a bunch of AIs on a 20 year trip to Alpha Centauri. I would imagine Stephen Hawking has already put two and two together in this way; he often warns that humans should leave Earth to avoid extinction. Even if we can't colonize other stars with people within this century, AIs could be thriving there within that timeframe. At least our "descendants" (the AIs) would be protected from extinction (by redundancy across stars).