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The Odds on Starshot

Yesterday’s announcement of Breakthrough Starshot brought an email from exoplanet hunter Greg Laughlin (UC-Santa Cruz), whose work has been an inspiration to me since the early days of Centauri Dreams. One of Greg’s new projects, working with Anthony Aguirre (Foundational Questions Institute) and several other colleagues, is a website called Metaculus, which bills itself as “a community dedicated to generating accurate predictions about future real-world events by aggregating the collective wisdom, insight, and intelligence of its participants.” In other words, this is a kind of prediction market space for science and tech issues.

Breakthrough Starshot fits the bill here exactly, because Metaculus is all about the probability of future events, some of which can be predicted to a high degree, while others are purely a matter of calculated odds. The site is open to all and contains the basic information about its methods, and any logged in user can propose a question for consideration. Starshot comes into play through a series of four questions now available under the category ‘To the stars!’:

  • Will the private investment in laser-sail extra-solar travel be matched by a comparable amount within 5 years?
  • Mountaintop lasers, rockets, optics and wafers? Or something else?
  • Will a first test of a high-power phased array laser system occur by 2018?
  • Do potentially habitable planets exist in orbit around Alpha Centauri A or B?

The questions are now active on the site, and I think you’ll enjoy having a look and perhaps getting involved with your own predictions. It’s interesting to cull through the other questions as well ranging from discoveries at the LHC to the Turing Test. As the site notes:

Like many mental capabilities, prediction is a talent that persists over time and is a skill that can be developed. By giving steady quantitative feedback and assessment, predictors can improve their skill and accuracy, as well as develop a quantified track record. Then, probabilities of future events can be reliably drawn by optimally aggregating predictions — counting more heavily those with domain expertise and a strong prediction track record.

An Interstellar Swarm

Dennis Overbye is one of our most incisive science writers. I’ve profited from his work ever since his Lonely Hearts of the Cosmos (HarperCollins, 1991) and continue to read him in the New York Times. And it doesn’t surprise me at all to find that Breakthrough Starshot has triggered his usual elegance in the essay Reaching for the Stars, Across 4.37 Light-Years:

If it all worked out — a cosmically big “if” that would occur decades and perhaps $10 billion from now — a rocket would deliver a “mother ship” carrying a thousand or so small probes to space. Once in orbit, the probes would unfold thin sails and then, propelled by powerful laser beams from Earth, set off one by one like a flock of migrating butterflies across the universe.

That lovely image reinforces what some of us believe, that swarms of spacecraft, offering crucial redundancy and working at the far edge of miniaturization, are the most promising technology for deep space exploration at this level of our development. Milner’s advisers, who include Avi Loeb (Harvard), Pete Worden (former director of NASA Ames), Saul Perlmutter (UC-Berkeley), Freeman Dyson (IAS, Princeton) and Ann Druyan (producer of Cosmos), clearly agree, despite costs that will eventually reach $5 billion to $10 billion.

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Image: A phased laser array, perhaps in the high desert of Chile, propels sails on their journey. Credit: Breakthrough Initiatives.

Given that the phased laser array Milner contemplates would have to generate 100 gigawatts of power for the crucial two minutes of acceleration on the sails, the task ahead is daunting. Thousands of lasers, as Overbye notes, will have to fire in perfect unison, and because this is a beamer built on the Earth, adaptive optics will have to compensate for atmospheric distortion. Moreover, we have to design a sail that will ‘ride’ the beam rather than be blown off it, and one that will be so highly reflective that it will absorb less than 1/100,000th of the energy applied to it.

These are problems that Robert Forward faced with his Starwisp design, a kilometer-wide ‘spider web’ of a sail driven by microwaves, with sensors scattered throughout the sail itself. It was Geoffrey Landis who would go on to show that as described, Starwisp would likely vaporize under the powerful beam meant to drive it to Alpha Centauri, causing a flurry of re-thinking of sail materials and design. But leaving the fuel at home is a powerful technique, and advances in technology may get us to the kind of materials that can withstand the photon torrent.

Writing for The Atlantic, Ross Andersen describes the sail this way in Inside a Billionaire’s New Interstellar Mission:

Picture a thin disc about the size of a round picnic tabletop. It would have miniaturized electronics onboard, including a power source, cameras, photon thrusters for navigation, and a laser for communication. Some of this kit would be bundled into the disc’s center, and some would be distributed through the rest of the sail. But it would all be a single unit: If you saw it streaking by, it would look like a flat, round sheet of reflective material.

We’ve also got a problem in that concept, because Jim Benford has pointed out that a flat sail is not a good ‘beam-rider’ — we’ll likely have to look at the kind of curved sail designs both Jim and brother Gregory Benford have studied in lab work at the Jet Propulsion Laboratory. But get a sail under that beam successfully and it reaches Pluto the day after launch, as Andersen notes. Another 20 years and it’s streaking through the Alpha Centauri system.

In any case, these are among the host of questions that the $100 million investment Milner is putting into the project will hope to answer, research extensive enough to offer proof of concept and finalize the design for a system that will eventually cost as much as the largest scientific projects we have built up to this time. A reusable facility may grow out of all this, one capable of sending fleets of small sails to our choice of nearby stars and returning imagery (the latter — data transmission at interstellar distances with craft this small — is another of the challenges that will have to be addressed. In a time of scaled-back thinking and low expectations, Breakthrough Starshot offers a sudden jolt of optimism that a new wave of research is on the horizon.

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Comments on this entry are closed.

  • Horatio Trobinson April 13, 2016, 11:17

    Beaming sails with powerful lasers from Earth is a bad idea, yet another hazard apart from orbital debris, and a series of other problems.

    I think all interstellar beaming should be done from a vantage point further out in the Solar System where we have an inordinate amount of energy resources to power the lasers.

    As far as we know, the only such place in the Solar System is Titan.

    • Harry R Ray April 14, 2016, 9:38

      Why not OUR moon. What a PERFECT mission to JUSTIFY the building of a PERMANENT moon base! If you need 100 nuclear reacters to power the array, build them on the moon and launch enriched uranium or plutonium from earth. We may even have FUSION reactors BEFORE the mission launches!

      • Michael April 15, 2016, 8:04

        The moon will offer unparalleled access to space, to ignore its wealth not only in materials but as a scientific observation platform would be mankind’s greatest folly.

        It also offers a place to test out multiple solar focus telescopes at the L2 point as orbiting around it (L2). Craft will intercept the solar focus light cone and give great angular resolution but reduced light gathering power when they are combined at say a central control craft.

      • Eniac April 15, 2016, 13:26

        The problem is putting the giant lasers on the moon. We just can’t do it, at this time, or even 50 years from now.

        • Horatio Trobinson April 24, 2016, 20:53

          Also, not many renewable energy resources on the Moon, only solar energy, with interruptions when the moon is eclipsed by Earth.

          We don’t need as many lasers, and energy is not a problem in Titan. We only have to figure how to put one there.

          • Michael April 25, 2016, 10:28

            Mercury is much better than Titan for energy, even Venus offers a huge amount energy in the form of deuterium for fusion at over 120 times the concentration of the Earths. Titan should be dismantled, literally, for colony and worldships on the great outward migration.

          • Eniac April 25, 2016, 11:12

            Energy is very much of a problem at Titan. There is very little of it. Remember that all the hydrocarbons are worth nothing in energy without free oxygen to burn them with.

  • superkuh April 13, 2016, 11:29

    Would a sparse phased array of lasers suffer the problem of power lost to sidelobes, ie, https://en.wikipedia.org/wiki/Thinned-array_curse? Or are the sidelobes of such large dishes with such a small wavelength light negligible?

  • Joe Morris April 13, 2016, 11:34

    Yes, there are shortcoming and design details that need to be addressed, as there is with any advanced concept. The fact that it is even being suggested is the news. Looking at the new commercial space industry news of the past few months, i.e., the successful recovery of reusable spacecraft by Space-X and Blue Origin. the testing of a Bigelow module on the space station, Bigelow and ULA’s teaming on a module launch in 2020,. and others, we are seeing an indication that the space industry is about to blossom. I believe the industry is about where the US was in 1840 in relation to the opening of the West. Now all we need is an equivalent of a Gold Rush and the transcontinental railroad. It’s a shame our political leaders can’t look up and see the potential. Maybe if we have successful space tourist flights next year or in 2018, then some eyes might be opened.

  • Leonard Hunter April 13, 2016, 11:42

    @Horatio Trobinson, to be honest, if the source of energy is solar it would not be a good idea to use Titan, Mercury would be ideal. From the perspective of actually maintaining the laser array though, it would be better to be where the mans reside and that Earth. If we wait to colonize the solar system to actually do this interstellar mission we would have to wait centuries.

    • Horatio Trobinson April 13, 2016, 13:55

      I’m not thinking solar, but methane as fuel.

      Titan is a gas station.

      • Adam April 13, 2016, 19:39

        Horatio, methane doesn’t burn without oxygen and there is no oxygen in the atmosphere of Titan to burn it.

      • lionel doolan April 13, 2016, 20:34

        Methane is only a fuel when you also have oxygen

      • Michael April 14, 2016, 16:02

        Acetylene is produced on Titan as well which is explosive and requires no oxygen, but Mercury would be much better to gather energy, even allows substantial Para-forming.

  • Leonard Hunter April 13, 2016, 12:02

    “But get a sail under that beam successfully and it reaches Pluto the day after launch, as Andersen notes. Another 20 years and it’s streaking through the Alpha Centauri system.”

    I would even suggest breaking the Starshot program up into milestones, first sending a probe to Pluto and getting useful data back. Then the next milestone would be planet 9 or Sedna.
    What is the best approach to this is that once we have the phased laser array in place we can then use it to launch more probes. The first probe would cost the most the rest would be cheap.

    • Jens Knudsen April 14, 2016, 14:37

      Yes. Something like that.

    • Michael T April 16, 2016, 22:46

      That certainly seems the way to go. I suppose the solar system probes could be larger if a little slower, and would be stepping stepping stones towards miniaturisation as well as greater distances. Geeting some to Planet 9/Tellisto or the Solar Focus would be great.

  • Thomas Marks April 13, 2016, 12:11

    Any reason they’re going for such a fast period of initial acceleration, rather than spacing it out over a few hours or so? I guess the rotation of the earth would have something to do with that, but even one hour of laser thrust would be a lot more stressful on the power grid, the laser array, and the craft itself.

    • DJ Kaplan April 13, 2016, 16:38

      @Thomas Marks: Seems to me that if you want to keep the sail small and affordable, you’d want to hit it with the laser near Earth, where the beam will be smaller in diameter, and more likely to focus on the small sail.

      BTW, I am noticing in the animation, the craft is inside a barrel-like mothership. The initial boost is given while the craft is still “stationary” inside the barrel, and as it slides up the barrel, I guess that would help in aiming.

  • DJ Kaplan April 13, 2016, 12:53

    Forgive me, but I can’t resist:
    C-3PO: Sir, the possibility of successfully navigating an asteroid field is approximately 3,720 to 1.
    Han Solo: Never tell me the odds!

    At this point, there is a thundering herd of things that we don’t know we don’t know, and we are going to find out. It’s hard to guesstimate these things. We’ve just begun to experiment with sails in space. How will they behave?

    One question I have is: How will these contraptions be aimed? The image I get is of a cluster of sailships in orbit, and a laser aiming at each one, potentially at a different angle. Multiply this angle by 4-5 lightyears and you have several misses.

    • Robert April 14, 2016, 13:13

      They only have to work within a million miles or so.

  • Alex Tolley April 13, 2016, 13:20

    Is there any benefit in a hybrid where a thicker sail evaporates, generating thrust from the emitted particles before becoming a purely reflective sail?

    [In the last post it was stated that:

    (…) 30 minute laser ‘burn’ that, reaching 60,000 g’s, drives the sail to 20 percent of the speed of light.

    Doesn’t that result in a final velocity of over 10^6 km/s or 3.3c? Doesn’t the acceleration need to be closer to 6000 g’s?]

    • Moebius April 14, 2016, 4:56

      Because of special relativity, the faster you go, the greater the acceleration needs to be to increase your speed relative to the inertial frame of the Earth (and relative to Alpha Cen).

      • Moebius April 14, 2016, 4:58

        But I didn’t do the math so I can’t really say if 60,000 g is correct. I guess so. The speed can never exceed the speed of light anyway even with an infinite acceleration.

    • Moebius April 14, 2016, 5:46

      I read 2 or 10 minutes for the laser pulse on other sources. Anyway the formula you used is incorrect, special relativity formulas never allow to exceed c.

    • Eniac April 17, 2016, 19:56

      Any benefit to adding evaporating propellant will be minuscule compared to the laser acceleration. Remember, with thermal means you can never get more than a few tens of km/s of delta-V. Compared to 60,000 km/s total that is nothing. Definitely not worth the increased starting mass and complexity.

      • Alex Tolley April 18, 2016, 10:50

        @Eniac – I agree it doesn’t seem to make any sense in terms of final velocity with these energies involved. I was more thinking of the ablation being a protective of the sail material. Unlike Benford’s suggestion for ablation acceleration of microwave sails, the ablative material would just be a thicker sail that is sacrificed to save the structure. However, on reflection, a thin sail with closest to perfect reflection is the way to go, so you are right, scrub that suggestion.

  • Robert April 13, 2016, 13:31

    It may be better to invest the money into an advanced molecular nanotechnology that could manufacture an effective device at a mass in the microgram range or less that would have the capability to coordinate with other devices and build things. Then launch a huge number at a star like a beam from an accelerator. They could self organize into a huge, molecularly thin sail for deceleration at the target star. Then they could deploy looking for resources to organize and build an infrastructure for deep study of the target system. At some point, they can themselves start targeting close by systems and launch new probes repeating the process such that an entire sector of the galaxy is explored in a relatively short time

  • Alex Tolley April 13, 2016, 13:35

    As the $10bn cost is mostly the laser arrays, wouldn’t this be footed by the DoD as part of a planetary defense system (cf Lubin’s DESTAR proposal that would vaporize asteroids)?

    The use of ground based lasers has another advantage, launching dumb boosters to orbit.

    I have to say that if near perfect mirror material can be made, wouldn’t that also protect spy satellites from laser attacks and also provide a potential platform to reflect lasers back to the ground to vaporize enemy targets?

    It seems to me that there are enough military applications to get this vision funded. I just hope they actually launch starchips too.

    • Eniac April 16, 2016, 19:34

      I think the phased laser array, as envisioned, would not work for boosting to orbit. It probably works only at long distance. Besides, any scheme that relies on heating a propellant with a laser is doomed, because it does not improve much on regular rockets: You still have to take just as much propellant.

      The perfect mirror works only at a certain frequency, I am pretty sure. So it would be of little use protecting satellites. To reflect a ground laser back to Earth only requires a regular mirror. That constitutes a serious hurdle to the project, but it does not require the special mirror technology. It is a military application, but all bets are off as to whether it will get the project funded or banned.

      • Alex Tolley April 17, 2016, 0:53

        lasers have been suggested for launchers. Not sure if they need to be phased though. Their value is that the propellant can be any readily vaporized material – water, LH2, no engines needed, just a tank and a way to capture the energy to heat the propellant. Isp’s of 2x chemical rockets have been mooted.

        However you don’t have to just expel propellant. “Lightcraft” that just heat air to a plasma are propellantless for the initial part of the flight. Your could also power “lifter” technology (streaming ions dragging air molecules for thrust. I don’t know how practical this is, but a dumb water tank launcher has to be a lot simpler and cheaper to make than a rocket, a lot easier to launch, and a lot safer in the event of a malfunction.

        The point of a special mirror is that it won’t vaporize when illuminated by the lasers. Therefore I still think a mirror to redirect the laser to targets makes sense. It also makes sense for non-terrestrial targets, as it is a lot easier to rotate a mirror than the laser array. It also solves the location of the lasers. They can be situated anywhere, fire perpendicular to the Earth’s surface to minimize absorption effects, and yet the final direct of the beam can be determined by the mirror.
        It wouldn’t surprise me if this system was to be used to destroy missiles on launch and/or reentry, as well as other targets. Tanks and aircraft would be soft targets for such a weapon., as unfortunately would the laser array itself.

        We also should bear in mind that the approach to power the sail may be Lubin’s “photonic drive” which requires the laser light to continue bouncing between a fixed mirror and the sail mirror.

        • Eniac April 24, 2016, 8:42

          no engines needed, just a tank and a way to capture the energy to heat the propellant

          Of course an engine is needed, and in addition a way to capture the energy and funnel it into the engine. Conventional rockets work with the considerable advantage that the energy is already there. That is an asset, not a liability.

          a dumb water tank launcher has to be a lot simpler and cheaper to make than a rocket, a lot easier to launch, and a lot safer in the event of a malfunction.

          No, I don’t agree, see above

          You are right, the special mirrors would be useful for the military applications.

          The “photonic drive” is suspect to me, as I cannot see how you can bounce light between mirrors so far away from each other without significant losses from stray light.

          • Alex Tolley April 25, 2016, 13:05

            I should have been more precise: “No complex rocket engine required”. The engine might be as simple as a solid rocket engine – just a throat and nozzle.

            As regards efficiency, proposals have been put forward for LH2 propellant energized with microwaves resulting in an Isp of 2x chemical engines. H2O would obviously result in lower Isp, but it is certainly safer than exploding kerosone/LH2 and LOX in the event of a launch failure.

            I note that in the Lubin paper (“Roadmap…” that the use of the phased lasers for launch to LEO is mentioned.

            I agree that the photonic drive would be hard to engineer and operationalize, but we seem to handwave the issues of worldship ecosystems, fusion and antimatter drives in pursuit of possible approaches. I think it is clear that Breakthrough Starshot does not assume a photonic drive because of this issue, but rather commits to a huge phased laser array instead. This makes more sense from an engineering POV and is more in line with what the military might want as a weapon. A photonic drive is of very little value as an energy weapon unless it was based in a distant location to fire high velocity rounds at the Earth’s surface..

  • Ashley Baldwin April 13, 2016, 13:52

    I think the most significant question in the list is the one that at first glance is the most prosaic. “Will the private investment be matched within 5 years “. Because it will have to be in order to get the billions of dollars ( I suspect that $10 billion is a big underestimate ) and crucially all round momentum required to make all the interesting technology stuff to happen. Get enough momentum and this will happen, though I suspect that somewhere a long the way there is a “tipping point” when things suddenly start moving very quickly.
    Apollo is a good analogy is to go from the state of play in the early 60s to standing on the moon in just a decade took a ton of it . But it happened so Alpha Centauri can too. I saw a recent estimate that in modern day dollars the Apollo programme would come in at $300 billion , though $100 million is a far from trivial start . But it needs to keep going and maybe a few über wealthy philanthropists is what is needed in the first instance, setting an example for others ( and eventually governments ) to follow.

  • John Walker April 13, 2016, 16:23

    Please does anyone have any ideas how useful images can be obtained given the minimal photon collecting capability and ~60,000 km/s velocity of such vehicles? Since the camera will produce images little more than a couple of pixels in size at anything over 10-20 M km distance, a mission lacking precise knowledge of the local planetary dynamics would be merely a hit and hope strategy. And on closer approach, image blur will be extreme.

    • Alex Tolley April 13, 2016, 17:24

      With the new flat lenses, perhaps a telescope can be part of the package to improve flyby resolution? Would the target satr provide sufficient energy to allow minor course corrections to provide closer flybys?

    • Mike Fidler April 13, 2016, 19:30

      First off, you could make use of the sail and use it as a telescope via a photon seive, hologram lens or a metamaterial lens. This could be designed to track the planets to image as it flybys. The setup could work as a transmitter/ receiver to send data. The sail would need to be made of a smart material and the chip could have advance AI to control it. The big idea is to use everything on the spacecraft for multiple purposes, maybe even going to the quantum level to do that.

    • Matt April 13, 2016, 19:40

      John, keep in mind that this is the beginning of a research project. There are lots of things they don’t know how to do yet. Perhaps collecting the data at the target will be an insurmountable problem, but lets give them time to try.

    • Wojciech J April 14, 2016, 7:56

      “Since the camera will produce images little more than a couple of pixels in size at anything over 10-20 M km distance”.
      One of the main issues. In 20 years time we will probably have telescopes(or at least be able to build them) that will achieve the same results(pixel sized photos of exoplanets in nearby systems) that the probe could achieve. This would come with lower cost and ability to service and upgrade them AND shorter return on investment versus long trip time of the probe.

  • Philip John Edwards April 13, 2016, 17:47

    Why don’t they build a small laser and fire it longer from inside the mother ship.

  • Adam April 13, 2016, 19:43

    A suggestion is to develop self-replicating solar-power machines to cover the Atacama in energy collectors for the laser. Such systems could then power the world – a net benefit for all.

  • Bounty April 13, 2016, 20:05

    I don’t think I like the idea of alien probes randomly entering our system at 20 percent of the speed of light. Seems like, dangerous or something. What’s the math on a 50 gram “probe” hitting the earth at .20 C ? I’m guessing it’s in the 10’s of kiloton range?

  • James Stilwell April 13, 2016, 20:55

    Reading the telling comments seems to show that there will not be an easy way to the Alpha Centauri systems…We must profit from the fly by with the return of exciting new knowledge…We will succeed with our key man exploring all the options all the time…He will keep this group forging ahead…
    It it a fated path…
    Love the site…

  • David April 13, 2016, 23:05

    Apollo was about 25 billion dollars in actual dollars and since threr are multiple ways to figure inflation various references on wikipedia come up with 100 to 200 billion. But it employed up to 400,000 people and crowned perhaps the greatest era 1870 to 1970 of technological advance since stone age to Egypt. Since then stagnatation. We manufacture about the same as then adjusted fir inflation and population…….In comparison the Wall Street bailout cost 16 Trillion. This is a bargain at 10 times the 10 billion . Who knows the spinoffs. One is asteriod defense…that alone is worth it. But the possibility of an interstellar flyby ….I can only repeat Marc Millas WOW…. Lets go

    • Eniac April 15, 2016, 18:46

      Last I heard the Wall Street bailout has been cashed in by now and cost nothing, roughly.

  • Zachary April 14, 2016, 1:10

    Suppose I am an alien living in the Alpha Centauri A/Alpha Centauri B system. Would I notice these probes?

    Likewise if aliens are sending their probes here at .2c, would we notice them? I’ve often wondered if there are artifacts in the solar system already, we just had no means of 1. seeing them, and 2. identifying them as alien. Milner’s probes would seem to be the first step towards eventually having artificial comets and asteroids around every star, and artificial moonlets around every planet.

    Thanks for your great writing Paul, it’s beautiful.

  • Dmitry Novoseltsev April 14, 2016, 4:32

    ” Picture a thin disc about the size of a round picnic tabletop. It would have miniaturized electronics onboard, including a power source, cameras, photon thrusters for navigation, and a laser for communication. Some of this kit would be bundled into the disc’s center, and some would be distributed through the rest of the sail. But it would all be a single unit: If you saw it streaking by, it would look like a flat, round sheet of reflective materia”
    See the picture the stars of the Mira in the ultraviolet spectrum taken in 2007 as part of the GALEX project [http://www.galex.caltech.edu/media/glx2007-04r_img07.html]. Speed of Mira – a total of about 130 km/s, but before it is clearly visible the detached shock wave in the interstellar gas.
    With low weight in grams and much more high (460 times) design speed design of the interstellar probe the effect will be much stronger, which will lead, firstly, to intensive braking of the sail immediately after disabling overclocking of the laser beam, and secondly, to its rapid destruction under the action of gas and dust.

    As one of the most obvious ways to solve the problem, it is advisable, after the step of laser acceleration to deploy the sail perpendicular to the direction of flight (edge of course). Then the braking and the wear will be minimal.
    If the sail is stabilized by rotation around the axis perpendicular to its plane, with a large enough frequency so that the canvas sails kept rigid and is not formed under the action of the oncoming flow, it is possible to ensure minimal even wear around the perimeter. In this way fraying when cutting, the working edge of the grinding wheel angle grinders, while its central part remains intact. In this case, the optimal, apparently, the round shape of the sail.
    If the canvas sails are electrically positively charged, as suggested earlier [http://spacecolonization.info/issues/issue-8-2014/], this provides partial protection from a collision of positive ions flying at a small angle to the plane of the sails – they will be rejected.
    If the sail is not flat, but corrugated, electrically charged and it rotates, and the payload is located in the center, after the phase of acceleration of the sail is not the ballast, and a shield from the particles of the interstellar medium. The area of the midsection of the apparatus in this case is determined by the maximum height of the corrugations, and if the thickness of the corrugated sails greater than the height of elements of the payload, their protection is ensured. For a given mass characteristics of the probe radius round sails can reach 2-3 meters. The combination of the rotation and the corrugated surface also will ensure the rigidity of the structure.
    Imparting rotation to sail in the simplest case can be made for the acceleration due to the effect of “photon turbine” – for example, if you run radial corrugations optical asymmetric (with unequal reflectance of faces), whereby under the effect of dispersing the laser beam will arise torque.

    On approaching the target it is expedient again to deploy the sail perpendicular to the direction of flight is then due to the resistance of the interplanetary medium and the oncoming solar wind can somewhat reduce the speed and increase the time of observation during the flight of the planetary system.
    Task two-time reversal of a rotating sail relative to the path may introduce some complexity because of the gyroscopic effect in spin, but in general seems to be solved.

    • Alex Tolley April 14, 2016, 11:37

      Tangentially, you raise an interesting point. We normally assume interstellar sails are accelerated withing the interstellar medium where particle density is low. In this case the acceleration to 0.2c happens within the solar system, between Earth and Mars

      The solar wind particle density at Earth is a few protons per cm^3. This suggests to me that a sail is going to be colliding with a lot of protons at up to 0.2C, well before the particle density is reduced, or the sail can reconfigure itself to reduce impacts.

      Assuming 2 minutes of acceleration, for a 1 m^2 sail, at just 1 particle cm^3, the sail will impact O(10^15) particles during acceleration. at an average velocity of 0.1c. I calculate about 2 kJ of kinetic energy from impacts. Not enough to destroy the sail, but seriously damage its electronics?

      • Michael April 14, 2016, 16:12

        We could roll the sail up into a cigar shape and then point it towards the star system, then we would

        * avoid orders of magnitudes of impacts due to reduced surface area,
        * much increased relative thickness for impacts and,
        * as importantly deflection abilities

        It would give ample protection :)

        There could also be the benefit of using ions that did pass through the shape as an energy source to power on-board systems.

        • Alex Tolley April 15, 2016, 0:28

          My calculation is just for the short boost phase when the sail must be both facing the beam and its direction of flight. After that, the sail can change its configuration to reduce its frontal surface area.

          All I can think of is to positively charge the sail to deflect the protons in its path, but I don’t know if that would be enough to work. It would also need to maintain that charge as it attracted electrons that would neutralize the charge.

          • Eniac April 15, 2016, 19:20

            I agree that could be a huge problem, with potentially no practical solution. On the plus side, the protons might punch right through without depositing much of that energy. On the minus side, any defects created by such punches might cause increased absorption of laser light, enough to finish the job of vaporizing the sail.

          • Michael April 16, 2016, 2:10

            Even at 50 times the amount of protons per cm^3 in the inner solar system it still does not exceed the total protons over interstellar space. We have a free ride up to 400-600 km/s as we will be traveling with the wind. AC is also not in the plane of our solar system so there is less material around right out to the heliopause but by that time we would have curdle up for better protection.

            @Eniac

            A proton punched hole is much, much smaller than the wavelength of light so absorption will not be possible, however if the sail is too thick heat could distort the surface to form imperfections/crystal distortion resulting in increased absorption.

            By rolling the sail up into cigar shape and facing the target stars system the intercept area is reduce by billions on nanoscale thickness sails.

            • Eniac April 16, 2016, 19:52

              @Michael
              – The “free ride” is insignificant, almost all of the time we have a near-relativistic headwind.
              – The solar wind is not confined to the ecliptic at all, so that does not help
              – Single molecule impurities are very good at absorbing and emitting light, despite being much smaller than the wavelength. This is how lasers, dyes, and colored gems work. So, dislocations in the dielectric sail could very well lead to increased absorption, and even a tiny little bit would be too much.
              – Rolling up the sail during acceleration is obviously not an option.

              • Michael April 17, 2016, 2:20

                @Eniac

                – The “free ride” is insignificant, almost all of the time we have a near-relativistic headwind.

                Admittedly it is small, though I would disagree with your near relativistic statement, 0.2c is no where near it.

                – The solar wind is not confined to the ecliptic at all, so that does not help

                There is bubbles in the solar sphere of influence due to the faster winds at the poles, so less particles to hit.

                http://inspirehep.net/record/1123063/files/McComas+al2008.png

                – Single molecule impurities are very good at absorbing and emitting light, despite being much smaller than the wavelength. This is how lasers, dyes, and colored gems work. So, dislocations in the dielectric sail could very well lead to increased absorption, and even a tiny little bit would be too much.

                Heat has the ability of causing atoms to relocate in a distorted lattice structure, annealing and recovery aids the return to crystallinity. If the sail is very thin protons should go sailing through, but it is something we know little about but can be tested on Earth.

                – Rolling up the sail during acceleration is obviously not an option.

                Never said to do it, rolling it up makes sense after acceleration. Perhaps leaving holes in the sail to allow light through to intercept gas molecules ahead is a possibility.

            • Alex Tolley April 17, 2016, 0:59

              The plane of the solar system is only relevant for dust particles. The solar wind is not constrained to this plane.

              I would certainly hope that the solar wind isn’t a show stopper for this technology in the inner solar system.

              • Michael April 18, 2016, 13:09

                The solar wind is forced into an angular rotation with the sun’s magnetic field, the polar regions less so as it rotates slower and so the solar wind can move faster and should be less dense at the polar regions.

          • Dmitry Novoseltsev April 17, 2016, 0:57

            I thought on this topic.
            http://spacecolonization.info/issues/issue-8-2014/.
            For the needs of the probe during the flight of the still want to use radioisotope energy source.If you apply a beta-radioactive isotope, in the form of a film sufficiently large area, its surface electron radiation may be sufficient to maintain positive electrical charge. In addition, flat ribbed sail (the sides) is a good radiator.

            • Alex Tolley April 18, 2016, 10:44

              @Dimitry. So your paper suggests using a radioactive surface to make the sail a combined photon and electric sail. Interesting.
              However, as you sate that solar wind pressure is orders of magnitude lower than photon pressure, I’m not sure why this makes any sense. The electric sail has much lower average aereal density than a photon sail as it can use just very thin, charged wires to form the sail.
              I’ll try to read your paper more carefully to see whether you have done the calculations that might shed light (no pun intended) on deflecting solar wind protons.

            • Alex Tolley April 18, 2016, 11:08

              @Dimitry – if you need a native English speaker to edit the language of your papers, let me know as I have time available these days.

  • Michael Spencer April 14, 2016, 6:59

    I wonder how they will find the planets? At some point, we will verify that planets exist or not in the system and have some idea of the orbit. But space is big, really big, as Adams pointed out; the planet(s) could be on the other side of whatever sun.

    Whew. Lots of problems to be addressed.

    (The project has the same sensibility as Bova’s “Mars” novel).

  • Paul Gilster April 14, 2016, 7:35

    I want to thank all of you for the comments over the past few days. Centauri Dreams flourishes because of its readers, and I appreciate your insights into Breakthrough Starshot. I’m currently airborne on my way to the Breakthrough conference. We’ll have a lot to talk about next week.

    • Jason Jackson April 14, 2016, 10:13

      This may require a deflective shield to protect against projectiles be they radiation particles, dust grains or larger objects due to the space needed to be traversed for such a voyage.

      Part of the problem is that you would have to have a very detailed idea of the possible objects at time intervals in your path in order to create a flight plan that would allow you to travel at high speed with minimum collisions.

      For any future manned missions, navigating through debris fields could be fatal for human passengers at high speed due to the g forces required which would increase depending on the separation and distribution of the objects.

      Furthermore there may be non collision interactions with objects which may be dangerous due to local factors and environment conditions whose interruption would destabilize the dynamics of a system or area maybe even catastrophically.

      There are other things such as small unseen black holes and brown stars and as of yet undiscovered interstellar phenomena.

      Of course the whole point of such missions is to investigate these issues and possible solutions. After all there is no going back to the cave as history would simply repeat itself.

  • ole burde April 14, 2016, 8:40

    Many good ideas have been suggested here . Here is one of my own , which I have tried to advance before , but now it suddenly seems much more relevant: If boosting by ground based lasers should be insuficient (because they can only boost the sailcraft for a very short time before it gets out of range ) , a series of relatively small spacebased lasers could add more acceleration power . Each one of them could be small enough to launch on a single booster , each one consisting of a modest nuclear powersource and a aray of capacitors capable of storing and releasing strong pulses of energy in the right time and direction while the sailcraft passses by . They would themselves be powered by sails and ion motors for stationkeeping ,and be deployed in a series -formation , but would not have to be positioned i an exact straight line to the target , because each one would correct for the inaccuracy contributed by the ones before it . Over time the first ones might get to far away from earth to be effective , but new improved units would be launched . This scheme is way to get around the the basic problem of dispersion of the energy beam , instead we get a perhaps easyer problem of information gathering and processing , to make our lacersattelites ‘fire’ their capacitors in exactly the right moment and direction .

  • Harry R Ray April 14, 2016, 9:42

    The only way this is NOT going to happen is if it takes TOO MUCH TIME and something BETTER comes along in the meanwhile!

  • Geir Lanesskog April 14, 2016, 11:23

    Maybe someone can check my math, because I switched from physics to history my junior year, but I calculate 1 gram at .2C as 1.8X10^15J, which works out to a half hour of 1 terrawatt output.

    In my comment on the previous post I whined about the impracticality of 100GW sustained. The former might be overcome by a slower launch rate and with about 50,000 shipping container-sized 1MWe batteries discharging, but multiply by another factor of ten… am I just wrong or is nobody checking Yuri’s math?

  • DJ Kaplan April 14, 2016, 12:13

    Thank you, Paul, for providing a platform for discussion!

    One other thing to consider #1001: Remember that we are allowing 20 years for development. In recent years, we have seen breakthroughs in artificial intelligence, materials science and robotics. By 20 years time, we will no doubt have resources to solve all of the problems that have been voiced here, and enabled feats that we haven’t imagined yet.

    This is an audacious enterprise, in an era in which just such an audacious enterprise is sorely needed. Semper ad astra!

  • Michael April 14, 2016, 12:15

    Is it just me or can anyone else see a flaw in the pictured design, if the sail is reflective would the beam not be reflected back towards the Earth blinding every sighted organism for many a kilometer. And if it went wrong blind a random path across the Earth!

    • Eniac April 16, 2016, 19:55

      The sail need not be planar, never mind perfectly planar, so at a distance there would be no harmful effects.

      • Michael April 17, 2016, 2:28

        100 GW’s of laser power will not be spread over say a couple of square kilometers, more like 100 lasers of death and blindness to anything in the atmosphere. Then there are the satellites in orbit optical and thermal systems which could be damaged, and some governments won’t like this laser system as they could see it as weapon as it could be used to blind military satellites in orbit. I would also say 100 GW’s of laser light been reflected off a say 4 sqm sail could be reflected back intensely.

        • Eniac April 24, 2016, 9:15

          As I understand the laser bursts would be timed such that no satellites would be in their path. As for the sails, I believe the moon emits way more than 100GW, and it blinds nobody. Thank God for the inverse square law….

          • Michael April 25, 2016, 0:26

            The military will not tell you where their satellites are that’s for sure and the reflection however small will show them up. And the moon only reflects around 12% on a sphere so its intensity is a lot less. Lasers are incredibly concentrated, the moon-distance experiments had about a few km dispersion at the distance of the moon, in orbit a few 100 kilometres up and it will be intense, at night it could be intense enough to blind someone upon reflection.

            • Eniac April 25, 2016, 11:29

              As far as I know, it is not hard to see satellites, so their orbits cannot be secret. In any case, if there was going to be a star shot, the military would have to be involved, anyway. That the moon reflects only 12% of the oodles of petawatts of sunlight that hit it does not change the fact that it is MUCH brighter than any sail of a few meters could ever be, even when illuminated by a 100 GW laser. Laser beams can be incredibly concentrated, but not after they are reflected by an object that is not perfectly flat. There is no need for the sails to be flat, nor any way they could be given the mechanical load on them.

  • Peter Hook April 14, 2016, 12:51

    Would the amount of data accessible to a set of starchips flying by the Centauri system exceed the amount obtainable by sending a set of telescopes to libration (Trojan) points in the Earth’s orbit and using them as interferometers? Maybe more bang for the buck from VLB interferometry. The distance between scopes in following and preceding Trojan points would be about 140 million miles. That should provide high enough resolution to pick out interesting details on the surfaces of Centauran planets and it wouldn’t require a twenty year wait to see them.

    • Eniac April 15, 2016, 19:37

      resolution is useless if you do not gather enough photons. There are very obviously many more things you can see when you are close, even if only for a few seconds.

  • Gary Wilson April 14, 2016, 13:17

    Will an early phase of the work include tests at a smaller scale? For example a 1 GW phased array pushing something larger in the way of a lightsail (to increase target size) to a slower final velocity? This new funding is absolutely what the field needed.

  • Andrew Palfreyman April 14, 2016, 14:09

    The nonrelativistic dynamical equation here is F = m a = 2 P / c. Thus the cited 100 GW power and the cited 60,000 gees results in an assumed mass of about 1 gram. So that all hangs together.

    It seems to me that any interstellar mission should be preceded by taking at good look at the destination. Waiting 20 years for a known null result (e.g. Alpha Cen is found definitively to have no interesting planets) doesn’t seem a very smart thing to do, representing as it does a huge investment of money, manpower and time. Or is “Because it’s there” reason enough? I’m tempted to say “yes”.

    At 0.2 c, we could reach the grav focus of Sol (550+ AU out) in about 16 days!! Can we imagine a collection of these butterflies somehow doing gravscope imaging? That would be wonderful.

    • Geir Lanesskog April 14, 2016, 17:36

      I did the equation on energy: 1/2 m v^2 and got 1.8X10^15. Shouldn’t the results be equivalent (or not, it’s been 30 years).

      I think for a mission to use the sun a a gravitational lens, you’d want to go a lot slower, or you’d have the fly-by problem: the lens would only work for a narrow distance and you’d have to be able to aim so that your target was in the proper position relative to the sun, so it would to a fleeting glimpse of a limited set of targets.

      I do like the concept, but slower space chips to outer planets, the Kuiper Belt and Planet Nine, if it is out there, would make much more sense to me. And be more likely to happen in this century. At least the first half.

      • Vikas Gupta April 15, 2016, 9:33

        Geir — I get 1.8 x 10^12 Joules. (0.5) * (1/1000) kg * (0.2^2) * (299,792, 458 m/s)^2 Can you check your math?

        • Geir Lanesskog April 15, 2016, 12:12

          Vikas, it is my math. I don’t have my notes, but I must have kilogramed it or something. So that makes the problem a thousand times easier than I feared and feasible to run off the current power grid, at least a few times a day, with a power-plant-sized switching yard and a field or batteries and capacitors surrounding the field of lasers.

          So cool, let’s start close and slow, work out the kinks, get pictures of Eris and Planet Nine and work our way out to Alpha Centauri.

    • Dmitry Novoseltsev April 14, 2016, 22:57

      As I understand it, is based the achievement of Sergei Korolev, is not that he launched the first satellite, or even the first man in space, and that it had created an infrastructure that with some upgrades, still in use today, including the USA and European Union. Back in 1989 in my school years I was lucky to stand on the upper pad Gagarin’s start, and it still works.
      Merit Yuri Milner, if all goes well, will not that will launch a high-speed probe to Alpha Centauri, and that he will create the opportunity to run to the nearest part of the Galaxy hundreds, perhaps thousands, of probes per year (don’t know how much maintenance will be required of laser installations and for what period of time they will be removed from service. And it certainly will not be the only such facility).

      • Peter Hook April 15, 2016, 5:03

        Are you depending on Google “translate”?
        нельзя понять!

    • Dmitry Novoseltsev April 17, 2016, 1:03

      I will be very interested when approaching the probe to use gravitational focus of the stars Alpha Centauri and look further.

  • Andrew Palfreyman April 14, 2016, 22:26

    As Claudio Maccone has doubtless pointed out, there’s a two-fold advantage in getting to the grav focus and relaying data back to Earth from there. Not only do we get a good look at the target system with unprecedented resolution (exceeding anything we are likely to build for at least a century?), but also we have unprecedented data reception sensitivity. This has the direct spinoff of dramatically reducing the transmit power requirement for the StarChip while dramatically increasing its usable transmit datarate.

    Thus Breakthrough StarShot all but begs for a gravscope at 550+ AU. There is huge synergy here.

    • Giulio Prisco April 15, 2016, 2:03

      This is a good argument, like the argument for a permanent moon base to host the laser launch system, but again it more than doubles the cost of the project.

      Of course a gravitational lens observatory pointed to Alpha Centauri could become a key part of the core mission if initial research shows that it’s the only practical way to receive data.

    • Michael April 15, 2016, 2:08

      There is also the gravity wave detector opportunity, GW’s will also be focused, perhaps use them to probe the Suns core as well.

    • DJ Kaplan April 15, 2016, 12:26

      Once you get to the grav focus, you have to stop.
      Again, quoting science fiction, “Jane, stop this crazy thing!”

      • Michael April 16, 2016, 2:13

        You don’t have to stop as the image goes to infinity, but if you want a good image it is best to.

        • Paul Gilster April 16, 2016, 10:36

          Exactly so. The focal line goes to infinity.

          • DJ Kaplan April 18, 2016, 12:48

            I see. You would focus on different things as the craft continued to fly.

            • Michael April 19, 2016, 10:26

              If we stopped and moved in an arc we could view quite a bit in great detail, if we had an orbital ‘world ship’ here going around in circles changing the inclination on each orbit over centuries we could map the entire universe to high precision using this technique. I feel the first try will be a shotgun approach with mutilple scopes going out from a single bus/communicator system.

              • Eniac April 24, 2016, 9:25

                It would not be centuries. At that distance, a single orbit takes many millenia, so it will take millions of years to map the sky even at a very coarse grid. The viewing angle of a gravscope is so ridiculously small that you have to know very precisely what you want to look at, and there is no way in a trillion years, with a trillion scopes, that you could ever hope to cover the entire sky.

                • Michael April 25, 2016, 0:33

                  ok, it will take millennia to complete orbits but the information that we would get would be enormous. The viewing angle can be made wider than you think, just reduced light collection, and nothing stops the ‘worldship’ having scopes around them.

                  • Eniac April 25, 2016, 11:40

                    No, the information that we would get from an aimless scan would be completely useless, since the sky is mostly empty of objects bright enough to be observed. Remember, there is a mismatch between resolution and light gathering power here, only bright objects will produce enough photons inside the ridiculously small viewing angle. The viewing angle cannot be made wider: It is given by the size of the receiver (the extent of the spacecraft) divided by the distance from the sun (>550AU). Did I mention that that is ridiculously small?

                    • Michael April 25, 2016, 21:20

                      Moving in and out of the focus point allows you scan a large amount of sky at reduced magnification as the rays further out are also bent. Spectrums could be compiled that would be very useful, having the world ship and out rigger telescopes traveling in the galactic plane would intercept more targets.

  • Charlie April 15, 2016, 4:08

    While I didn’t have any idea as to where alpha Centauri was in the sky above the latitude line of the southern hemisphere, I knew that it had to be about two thirds of the way to the South Pole. And the figure for the declination shown below represents the latitude line in which that star system would appear directly at the zenith. Why is this important? It would seem logical that if you had a laser system to act as the accelerant for your light craft that the laser array would be directly beneath the point where the star stood in the sky in relationship to the center of the earth.
    It’s of course quite apparent that there would be gravitational effects that would be needed to be accommodated for but I would assume it would be pretty much of the straight line shot for the initial acceleration of the object.

    What I was not prepared to find and what was very surprising is that at that latitude line shown below as the declination (but it’s also the latitude line on the earth) is actually a continuous stretch of water ! No land whatsoever !!

    Why would this be of any importance ? First of all, you’re going to have to have a place to set your laser array to allow you to accelerate the craft. Secondly, and this is the more important point, if you’re at that southern latitude the mass of atmosphere above your laser array should be at a minimum. Other points north or south of that latitude line would have a greater amount of atmosphere in which the laser would have to be shined through to allow the craft to be accelerated. At least this would seem to be a logical conclusion as to what would be considered a rather difficult maneuver to begin with.

    Finally, such an extreme southerly latitude, even if you had a landmass to place the laser array at would greatly limit your ability to use the laser array for accelerating other similar craft in solar system exploration. I would think that the ecliptic plane in which most of the planets reside is pretty far removed from that southerly latitude which would prevent the use of the laser array to accelerate similar light boosted craft. At least it would seem that way to me; any dissenters on these ideas ? The particulars for the Centauri stars are shown at the bottom…

    Right ascension 14h 39m 35.06311s[1]
    Declination –60° 50′ 15.0992″[1]

    • Eniac April 16, 2016, 20:05

      Since the boost lasts only a few minutes, you can pick the time for it whenever your target is highest in the sky, night or day. A 30 degree off-vertical would surely still work quite well with regards to path-length through the atmosphere, so you could be located pretty much anywhere on the southern hemisphere and boost to AC.

      Needless to say, then, I do not follow your argument, at all. You might be going wrong where you say “that the laser array would be directly beneath the point where the star stood in the sky in relationship to the center of the earth”, and/or some other parts I just do not understand.

      • DJ Kaplan April 18, 2016, 12:51

        Charley, I think you are assuming that the beam would be vertical or perpendicular to the earth’s surface. Perhaps that would minimize atmospheric interference, but it wouldn’t be a hard-and-fast requirement at all. As long as the vector to the target star was correct, you’d be okay.

  • spaceman April 15, 2016, 10:10

    This is very exciting. To me, one of the most exciting aspects of this project is the growing awareness, among thinkers and entrepreneurs, of the need to develop better space travel capabilities. Sagan and Hawking are right: humanity will need to colonize off earth as a buffer against extinction events.

    However, we still do not know if there are planets in the alpha centauri system! Wouldn’t it make more sense to launch such an effort once a thorough survey for planets around the nearest dozen or so stars has been completed? After all, it would be a little anti-climactic if the starshot probes blazed through the alpha centauri system and all they saw was a big, dusty asteroid belt. In my opinion, let’s say planets were found in the habitable zone of another system say 5 to 10 light years away– maybe not the nearest star— but not much further than alpha centauri, then the mission should be directed to the system with known planets. The idea of launching interstellar probes to a system that has not been shown, at the very least, to even have planets seems like a misallocation of resources.

    What is the status of the search for planets around any of the three stars in this system? How soon until we have some strong constraints? Presumably, the starshot project could plan and develop the technology before we know for sure about centauri planets and, if no planets are found there, then the mission could be pointed elsewhere?

    • DJ Kaplan April 18, 2016, 12:57

      #spaceman, you are advancing on a mistaken assumption. We have only shown that there no large (Jupiter plus) planets in the habitable zones. That’s all. And it’s no piddling thing. This means that any Earth-sized planets in the HZ would NOT have been cleared out by Jupiter-sized planets. If we had to share our orbit with Jupiter or Saturn, Earth would not last very long.

      As technology improves, we will gather more data. But it’s too early to assume that there’s nothing there.

  • david lewis April 15, 2016, 11:37

    Makes me wonder if the reason we retreated from the moon was because of how easy it would be to use it as a base to launch weapons of mass destruction. Sort of like when the US put nuclear missiles in Turkey, forcing the USSR to respond by placing them in Cuba, ending with their removal from both places. Maybe the powers-that-be agreed to no moonbases just like the idea of Orion was pushed to one side.

    Going to the sun’s focal point would be a better use of such technology. With the sun as a lens any results would be as good as being in Alpha Centauri, while the difficulty is drastically reduced. Even 1/1000c would get the probe to the focal point in 9 years rather than having a 26 year wait, and the array would only need to be 1/40,000th as powerful.

    Should the technology ever reach the 100GW range then that would mean we could send probes in the 1kg range to the sun’s focal point, allowing a thousand time the mass for instruments. Albeit it would be slow, we could even communicate with the probe and give it orders.

    Here’s to hoping it does work.

    • Eniac April 16, 2016, 20:27

      Earth orbit is a much better place to put weapons of mass destruction, and nobody has retreated from that. So, while your idea has some merit, I would have to conclude: No that’s probably not it.

      The solar focus idea is great, but it hasn’t really been vetted enough to warrant a mission. We’d want it to work when we get there, and at this point it is far from clear if and how we could achieve that.

      It is technically difficult: For a single pixel you need a telescope pointed at the sun with a coronagraph that can make out a faint Einstein ring at a certain distance around it. To get an image, you either need a large array of telescopes, or move a single one around in a scanning pattern. Or a combination of both. Each telescope/coronagraph would have to have an aperture of roughly 10 cm in order to make out the Einstein ring. The whole thing would definitely be much heavier than a kilogram.

      And, worst of all: There is no way of testing this until an actual mission is flown.

      • david lewis April 22, 2016, 15:12

        About the only WMD we have that would be suitable for earth orbit is nuclear, and we do have treaties against that. Also earth orbit is convenient for so many other things that it’s profitable to keep the capacity to get there – at least for now. ie. communications and spy satelites.

        I’m not so sure such a probe would have to mass over 1kg. If we were to try to build it today, yes, but in 20 years? 30 years?

        • Eniac April 25, 2016, 11:48

          I think you are simply wrong when you say “With the sun as a lens any results would be as good as being in Alpha Centauri”. Any photographer will tell you that being up close is always better than a bigger lens. Also, the solar gravity lens has a huge problem in that it does not gather enough light to support its immense resolution.

  • ole burde April 16, 2016, 14:11

    As this article starts out talking about Prediction , I will alow myself to wear the Prophet-hat for a minute : An earth based aray of lasers wil not be capable of accelerating a sailcraft to more than a fraction of the 0.2 C we talk about . It will be a good and afordaple way to start , but no more than that . It will be the first Stage in the accelerationprocces . The next stage will be something happening when the first i running out of range , and this creates a serious stationkeeping problem : If a linear series of spacebased lacers are relatively close to earth , it will take a lot of energy and propellant to keep them lined up towards the target star , but if the whole array are further out , the communication becomes too slow and every unit must be completely autonomous and be capable of functioning for many more years …

  • Joe Morris April 18, 2016, 17:37

    I don’t agree with the need for Earth-based lasers. The space infrastructure in 10-20 years should be able to support the lasers at one of the Lagrange points. Plenty of solar energy available. No atmospheric attenuation.

    • Eniac April 24, 2016, 9:36

      That would be way to expensive. Right now, the only affordable place to build large things is on Earth. And the laser array is so big that it strains our resources even so.

      Or maybe you overestimate our space infrastructure in 10-20 years? Perhaps in 50-100 years, when we optimistically could hope to be manufacturing complex machinery in space, space based lasers would be an option. Not for this project, though: The timeline is too ambitious, we have to leave the large stuff on Earth.

    • Andrew Palfreyman April 24, 2016, 14:40

      You won’t stay there long because of the photonic back-reaction. One needs to either import a fat asteroid there, or fire off two diametrically opposite beams and lose 50% of your efficiency.

      • Michael April 25, 2016, 10:32

        There won’t be a loss of energy if we use the opposite beam to propel another craft to the SGFP or even other stars or communication systems around the solar system. There are a few star systems where there are stars in the opposite direction or nearby.

      • Eniac April 25, 2016, 11:50

        Or stay in an off-center orbit. This is an easily solvable problem.

        • Joe Morris April 26, 2016, 9:10

          @Eniac: It’s you who underestimate the churn that’s occurring in the space industry. new low cost launchers. Space tourism. Small payloads. We are where the US was in the 1840s: a frontier being modestly developed. Two events accelerated this development: discovery of gold in California which created a spike in demand, and the opening of the transcontinental railroad, which provided low-cost, safe, and quick travel west. I believe we’re at the fringe of the demand spike, which will then force the infrastructure.