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Space

Inside 'Starshot', the Audacious Plan To Shoot Tiny Ships To Alpha Centauri (technologyreview.com) 229

Posted by EditorDavid from the good-morning-Starshot dept.
"Starshot wants to build the world's most powerful laser and aim it at the closest star. What could go wrong?"

An anonymous reader quotes MIT's Technology Review: In 2015, Philip Lubin, a cosmologist from the University of California, Santa Barbara, took the stage at the 100-Year Starship Symposium in Santa Clara. He outlined his plan to build a laser so powerful that it could accelerate tiny spacecraft to 20% of the speed of light, getting them to Alpha Centauri in just 20 years. We could become interstellar explorers within a single generation. It was quite the hook.

Because Lubin is an excellent public speaker, and because the underlying technologies already existed, and because the science was sound, he was mobbed after the talk. He also met Pete Worden, a former research director of NASA's Ames Research Center, for the first time. Worden had recently taken over as head of the Breakthrough Initiatives, a nonprofit program funded by Russian technology billionaire Yuri Milner. Six months later, Lubin's project had $100 million in funding from Breakthrough and the endorsement of Stephen Hawking, who called it the "next great leap into the cosmos."

Starshot is straightforward, at least in theory. First, build an enormous array of moderately powerful lasers. Yoke them together—what's called "phase lock"—to create a single beam with up to 100 gigawatts of power. Direct the beam onto highly reflective light sails attached to spacecraft weighing less than a gram and already in orbit. Turn the beam on for a few minutes, and the photon pressure blasts the spacecraft to relativistic speeds.

Not only could such a technology be used to send sensors to another star system; it could dispatch larger craft to Earth's neighboring planets and moons. Imagine a package to Mars in a few days, or a crewed mission to Mars in a month. Starshot effectively shrinks the solar system, and ultimately the galaxy.

It's fantastic. And also a dream. Or a sales pitch. Or a long-term, far-out project that can't be sustained long enough for the nonexistent technologies it requires to be built.
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Inside 'Starshot', the Audacious Plan To Shoot Tiny Ships To Alpha Centauri More

Inside 'Starshot', the Audacious Plan To Shoot Tiny Ships To Alpha Centauri

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  • In-fact you can send an entire convoy which would chain relay the transmissions back to earth

    • Re:Great idea (Score:5, Interesting)

      by lgw ( 121541 ) on Saturday July 13, 2019 @03:53PM (#58920830) Journal

      There are several real problems with the approach. Not a problem is "it's just a flyby" - with a solar sail you can decelerate into the target system well enough, it just takes several times longer.

      The three biggest problems are:

      * You can't focus a laser forever. You need a chain of lasers or repeaters, which is a much larger problem to arrange. However, if you really didn't care about efficiency, you can make it work.

      * Drag. Interstellar space is reasonably empty, but drag becomes a real problem when your talking percents of c. It's why the Brussard ramjet doesn't work. And it means you can't just use a huge sail to get around the laser focusing problem.

      * Debris. While it's not frequent, a tube the diameter of your ship's cross section and several light years long is rater a lot of cubic kilometers of volume. Satellite armor should work fine against the smallest dust particles at any velocity, but it's effectively ablative. And all it takes is a single grain large enough to not vaporize itself when hitting a sheet of tinfoil and you're done.
       

      • The craft has a mass of less than a gram. Space dust isn't going to be abrasive to the craft, it is going to be an interstellar car wreck.

        • Re: (Score:2)

          by lgw ( 121541 )

          The craft has a mass of less than a gram. Space dust isn't going to be abrasive to the craft, it is going to be an interstellar car wreck.

          Space dust comes in all sizes, from atoms to planets. You can armor even a small probe against the smallest (and by far the most common) dust. Satellite armor is basically a sheet of foil spaced away from the hull, and a hull that's thick (by spacecraft standards - think soup can vs coke can). But that foil vaporizes as dust and debris hit it.

      • The larger immediate problem is that any such array is a very convenient weapon against targets in LEO. I'm afraid I see no way to prevent the use of such laser arrays against Terran or orbital projects, except perhaps by setting up the lasers on the far side of the moon.

        Larry Niven and Jerry Pournelle explored the problem in their Kzinti stories. To quote them about the "Kzinti lesson": "a reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive."

        I think this lesson wou

        • That's a selling point not a problem. Having effective ballistic missile defence justifies the cost of construction.

          • An effective ballistic missile defense would be wonderful, if and only if it were not profoundly more effective and easily used as an offensive system. Such a laser array would be far more effective against targets in stable orbits, even if it lacked the power to punch through the Earth's atmosphere to strike ground targets. Striking and disabling a missile, especially the larger ICBM's designed to leave the atmosphere and hardened to survive re-entry, is a vastly harder problem. Focusing on a larger, harde

      • with a solar sail you can decelerate into the target system well enough

        Can you also aim it to go near an interesting planet? Otherwise it's just going to crash into the star.

        Satellite armor should work fine

        Budget is 1 gram. You don't get much armor for that.

        • Re: (Score:2)

          by lgw ( 121541 )

          Can you also aim it to go near an interesting planet? Otherwise it's just going to crash into the star.

          With a sail it would end up in some orbit, but I seriously doubt you could aim it. I don't understand how a probe that small would see anything at any distance, though.

          Budget is 1 gram. You don't get much armor for that.

          You need some, though. For armor for a probe with a 1 cm^2 cross section, you basically need a sheet of foil 1 cm^2 spaced a bit ahead, and the front of the hull of the craft needs to be relatively thick. I think you could make that part work, as you only need to armor the front, but it would be expensive in mass as there's a minimum thick

      • * Drag. Interstellar space is reasonably empty, but drag becomes a real problem when your talking percents of c. It's why the Brussard ramjet doesn't work. And it means you can't just use a huge sail to get around the laser focusing problem.

        Nope. As best I understand it, this is completely backward. The Bussard ramjet takes that would-be drag and turns it into propulsion instead.

        However, that won't work without a massive on-board energy source. If you're relying on the interstellar gas or particles for your energy too, you likely won't make it. That's where drag comes in.

        • Re: (Score:2)

          by rtb61 ( 674572 )

          Which is why you, hmm, exclude quantum space. Create a sufficiently strong field to displace quantum space so it no longer travels through you ;). Then create an imbalance in the field to promote directional quantum displacement and away you go. Creating the very strong, very tight, high density fields not that easy and you certainly need the energy and nano structures to do so. Not how strong the fields, it's how dense they are and tightly bound to the mass and energy source you are attempting to accelerat

          • travelling faster than gravity

            What the heck is travelling faster than gravity? The 1G counterforce created by accelerating ship? That's still way slower than the speed of light. Otherwise, gravity is an instantaneous force; there's nothing faster than instantaneous.

            • Exactly! WTF does "faster than gravity" mean? The GP post reads like pseudo-scientific nonsense.

              Small correction though....gravity us not instantaneous. Gravitational waves propagate at the speed of light.

              If gravity was instantaneous, FTL communication could be "easily" achieved by moving significantly large masses around. (insert yo mamma joke here)

        • Re: (Score:2)

          by lgw ( 121541 )

          Nope. As best I understand it, this is completely backward. The Bussard ramjet takes that would-be drag and turns it into propulsion instead.

          That was his idea, but it doesn't work. The drag of the matter the large scoop accumulates exceeds the thrust provided by the fusion of the hydrogen, beyond some speed.

          Think about it this way: the thrust provided by burning one atom of hydrogen is constant, but the drag increases with speed, so eventually the drag must win.

      • Debris can be overcome by sending lots of ships: each is so tiny you can afford to lose some. The bigger problems as I see it are two-fold: how does a ship under 1 gram in mass send a signal powerful enough to reach 4+ light years back about what it sees and how do you steer it accurately enough to get to a nearby star?

        The distance involved is so immense that even if you could convert the entire mass of the ship to energy I doubt you would see it from Earth and the tiniest of deflections near the start o

        • Re: (Score:2)

          by lgw ( 121541 )

          Depends on the density of debris. If the probe had a cross section of 1 cm^2, it would encounter the debris in ~1000 km^3 of space per light year traveled. If a grain of dust large enough to kill it exists, say, every 100 km^3, "just send lots" won't work.

          • Wouldn't work, and would create a funny jet of impacting "particles" that would get more dense over time.
            ET Observer: "That system is sending out a strange jet of particles that becomes briefly visible when it collides with the interstellar medium."
        • Aiming means sending millions of ships along a spread. One of them will be on course. Signal return is done via relay, you send them out in a stream and they only have to transmit to the nearest one to get through.

      • I thought the bussard ramjet doesn't work because there isn't enough hydrogen between stars, so you can't reasonably create a large enough field to grab enough for propulsion without magical energy sources and materials.

        • Re: (Score:2)

          by lgw ( 121541 )

          That's just a question of speed (thus the ramjet analogy). Once you start talking about speed in %c, you don't need a huge scoop. If you could get going fast enough, you'd encounter enough hydrogen to fuel the engines. What kills it is that, per hydrogen atom, drag increases with speed but energy does not.

          It's still a viable idea for decelerating as you approach your target, which could help a lot. For a ship that carries all it's reaction mass, it's cruise speed is effectively limited to roughly the en

      • >tube the diameter of your ship's cross section and several light years long is rater a lot of cubic kilometers of volume

        It exists for a fraction of a microsecond. I am not sure whta were you trying to achieve with your dumbass illustration.

        • Re: (Score:2)

          by lgw ( 121541 )

          How do you figure the statistics around hitting dust and debris? Once you're going fast enough, you only care about stuff hitting the front, so you can just look at the volume of space swept by the craft in its journey. Whatever the average amount of dust and debris is in such a volume is what you're going to hit, on average.

          Oh, and since we're doing personal attacks, you're ugly and your mother dresses you funny.

      • There are several real problems with the approach. Not a problem is "it's just a flyby"

        True. But your own objections are really just "second order objections" -- things that may or may not be a problem if the technologies to do this really existed, or had some reasonable hope of existing. But they don't. They really, really don't. Without the essential enabling technologies debating problems with the mission profile is complaining about things that will never be faced in reality.

        The best thing that can be said about this project is that the physics is not imaginary (unlike any warp drive or a

      • >You can't focus a laser forever.
        You don't have to.
        Momentum of light = E/c. If we're delivering 100e9W of laser power, that's (100e9Nm/s) / (300,000,000m/s) = 333kgm/s^2.
        Double that (because you're reflecting it rather than absorbing it) and you're imparting momentum of 666kgm/s every second.
        Deliver that to a 10g spacecraft (Assuming the light sail is 90% of the mass), and you accelerate it at 66.6km/s^2.
        Keep that up for 450 seconds and you'd reach light-speed (ignoring relativistic nonlinearities, whic

        • Re: (Score:2)

          by lgw ( 121541 )

          Your top speed is where the drag from the sail matches the thrust from the laser. 0.2c is ... a bit ambitious. But once you drop the sail you're in the same boat - the thrust from the laser hitting the probe will roughly match the drag of the probe. If you lose the laser, the drag will be significant. The cross-sectional density of a 10 g probe will be very small, after all - the cube-square law means drag matters more on smaller craft.

          Sure, but your cross-section is only maybe the size of a postage stamp, and it doesn't matter how much dust is in the entire volume it passes through, only whether there's dust in the tiny volume it's occupying at the current instant.

          Doesn't work that way. With a 1 cm^2 cross section, you'll encounte

          • You're not going to drop the sail until it's providing negligible thrust anyway - which will likely happen after no more than a few minutes of acceleration unless you've got an entire string of laser stations deployed along the flight path.

            Okay, you're right, you're going to have to displace the average amount of material in the volume you sweep out. How much will that actually be though? Sounds like most interstellar space has an average density of well under 1 molecule per cubic centimeter, almost all o

  • Some problems (Score:5, Interesting)

    by religionofpeas ( 4511805 ) on Saturday July 13, 2019 @01:47PM (#58920246)

    Once they reach another star at 20% lightspeed, they'll do a quick flybly, and most of them aren't going to be lucky enough to end up near any planet.

    You can pack very little instruments on a tiny ship that weighs less than a gram, never mind a transmitter capable of sending data back to Earth.

    • Exactly.
      Without a means of retrieving that info before we ourselves can get there, it's completely useless as a probe.
      Limited use to prove that laser accelerated light sails work and can be aimed or steered is useful, but at those costs it had better be part of a system that can send viable probes and not just a throwaway facility.

    • Ah, no worries, they just orbit about the center of the universe and come back to us.
      With some luck they orbit about the center of our galaxy ... that would save them a few billion years of travel time :P

      • Re: (Score:3)

        by GoTeam ( 5042081 )
        Those flat-universers drive me crazy too. To send the stupid probes back to earth, all we have to do is shoot the laser from earth in the opposit direction.

    • Re: (Score:2)

      by k6mfw ( 1182893 )

      Overall an interesting challenge. Take some sci-fi idea and put it into reality. It may or may not work but hey why not.

      But gotta throw this one out, these things won't get lost in space like the Jupiter Two?

    • Re: (Score:2)

      by AmiMoJo ( 196126 )

      It doesn't matter because if they are accelerated to 20% the speed of light in a few minutes they will be compressed into small inert pancakes. Heat dissipation is probably an issue too.

  • Lasers shouldn't be ground based (Score:4, Funny)

    by 93 Escort Wagon ( 326346 ) on Saturday July 13, 2019 @01:52PM (#58920270)

    To avoid atmospheric interference, put the lasers in space. There's a company in Las Vegas - Willard Whyte Industries - that's been working on designing and building space-based diamond super-lasers. A few of those would do the trick.

    • There's a good reason why they're ground based; equal and opposite reactions. What do you think would happen to any space rig that the laser is mounted to when the laser fires?

      • That's true according to Newton's third law. Either the lasers could be on the moon, or the direction they fire could take into account the reaction-force. If the lasers were massive, the reacion-force would have less effect, but I'd imagine accelerating something to 0.2c would have a significant effect even for a laser that's much larger.
    • I'm going to kill you, Mister Bond.

  • Sol (Score:5, Funny)

    by markdavis ( 642305 ) on Saturday July 13, 2019 @01:54PM (#58920272)

    >"Starshot wants to build the world's most powerful laser and aim it at the closest star." "the Audacious Plan To Shoot Tiny Ships To Alpha Centauri"

    The closest star is Sol (the sun). Just sayin'....

    • Actually, there are a few celebrity "stars" that are even closer. Shooting some of them with the world's most powerful laser is a plan that would probably also generate a lot of excitement and would arguably also advance humanity.

  • 100GW? (Score:3)

    by lorinc ( 2470890 ) on Saturday July 13, 2019 @02:44PM (#58920530) Homepage Journal

    to create a single beam with up to 100 gigawatts of power

    Oh yeah, let's just build 60 nuclear reactors to power a big laser. That's realistic, for sure.

    • That's not necessarily how power works. It's 100 Gigawatts not 100 Gigawatt-hours. Power is different than energy. Power you can pulse. You can build a big charge over a few days (or weeks or months), fire the laser and discharge the 100 Gigawatts. It's a lot of power, but one nuclear power plant can do it just fine.

    • Oh yeah, let's just build 60 nuclear reactors to power a big laser. That's realistic, for sure.

      First, it's not a big laser, it's many lasers that have been aimed at the same spot in orbit. A spot that consists of a large light sail that is capable of holding up to the forces.

      Second, we should build 83 nuclear power reactors. That way to get to the 100 GW required each one would have to produce...

      1.21 JIGAWATTS!!

  • >>> "Starshot wants to build the world's most powerful laser and aim it at the closest star. What could go wrong?"

    When I first read that, I thought it said "Slashdot wants to build..." and I was all WhooHoo! News for Nerds, Stuff that Matters!

    Finally!

  • So how do they plan to stop? A parachute? Won't the laser burn thru it?

    And what if the laser actually manages to HIT the target? Won't they be pissed, and build a bigger one to fire back at US? This is only the first step in an intergalactic neighborhood war! Stop The Madness!

  • We could become interstellar explorers within a single generation.

    Not with this we can't. Go and look up the meanings of the word "explorer". a good answer came to the top of the list for me.

    1. someone who travels to places where no one has ever been in order to find out what is there.

    This is why there is not much exploration on earth nowadays. There are not many places people haven't been to now - at least on the surface of the earth. Notice the first word in that definition - "someone". It does not say "someone who sends out cool equipment to find out stuff. Tha

  • Yeah reaching relativistic speed in a minute ? (Score:5, Interesting)

    by aepervius ( 535155 ) on Saturday July 13, 2019 @04:09PM (#58920906)
    Pull the other one. You may have a particle jet reach relativistic speed in seconds or minute, but nothing manufactured would wistand that many g. Let us take a few minutes to be 16.6 minutes (1000 seconds), and relativistic speed 1% sped of light, that's 3.000 km.s-1, so 3.000.000 m.s-1 that means an acceleration of 3000 g over 16.6 minutes - at 20% light speed multiply g force by 20. Even solid state would have a problem for anything but a perfect sphere, not to speak of the "sail" surface needed to receive that much energy (a gram at 20% light speed, need about 7.6 10^12 J). Part of it would be transformed into kinetic energy, part of it into heat. Needless to say that much into a few grams materials, I see a problem - nothing is 100% reflectant after all.

    Basically I may have done an error, but I would really like to see their math for the engineering of the material required.

    TL;DR: baring a few order of magnitude error on my side, there is no material which can sustain such acceleration, heat energy imparted I can imagine of.

  • Mote in God's Eye? (Score:3)

    by mpercy ( 1085347 ) on Saturday July 13, 2019 @06:44PM (#58921468)

    Larry Niven wrote this story years ago, sort of.

    "The veteran hard SF writer, Larry Niven, also used the idea of laser-driven solar sails in his classic The Mote in God’s Eye. This is about the encounter between an expanding human galactic empire, and an alien race, the Moties. These are so called because their homeworld is a planet in a nebula dubbed Murchison’s Eye by humanity. The Moties are highly intelligent, but lack the Anderson Drive that has made it possible for humans to move out into the Galaxy. Instead, they have sent a vessel out on the centuries long voyage across interstellar in a ship using such a solar sail, powered by laser beam from their own system. It is the light from the laser beam which has given the Moties’ nebula its characteristic red colour.

    • Re: (Score:2)

      by hawk ( 1151 )

      That was actually Pournelle & Niven, not just Niven.

      They are one of the very rare pairs that working together exceeded the work of either on their own.

      The book is placed in Pournelle's future history. At some points, you can pick out who wrote a given paragraph by the style, tone, or theme . . .

      Pournelle commented at one point to the effect that co-writing a novel with Niven took about 60% of the time it took to write one on his own, while with anyone else it was more like 80% or 90% . . ,.

      hawk

      • EXTRA points for this - Pournelle & Niven are incredible visionaries.

        Add to this the fact that it was NIVEN who predicted an impact of transplant successes - as in harvesting organs from the 'state' executions - prisoners executed, but whose bodies then became state property, and were then carved up into organ transplant-able parts.
        Search your SciFi collection for the Niven works concerning the ARM and "Long Arm of Gil Hamilton"
        Niven, as a standalone author, deserves to be elevated to the level of Heinl

    • Good Point . . . BUT
      the color went from RED (the nearby red giant) to GREEN - the LASERs!
      Wartime on the observing planet caused problems with the observation of the MOTE, but it WAS seen as going from RED to GREEN (lasers ON) and back to RED (lasers OFF)

  • I get it, you can shotgun cheapass little probes, and maybe even juice them up fast enough that they'll get there before they fail, and send enough that random destruction otw still leaves some surviving but even assuming we've solved the problem of gathering ANY data at 0.2c....how are they sending that data back?
    The energy to send some data back is going to be rather near that of sending these little probelets there in the first place, as well as requiring likely a significant amount of the probelets comp

  • Ions (Score:2)

    by tsa ( 15680 )

    A powerful laser beam like that will ionize the air, creating a beam of ionized air all the way to the top of the atmosphere. That should give some interesting effects.

  • Wow. I guess none of these people ever read the Three Body Problem trilogy. They don't know about Trisolaris and the dark forest.

  • A Great Idea Except That... (Score:3)

    by careysub ( 976506 ) on Saturday July 13, 2019 @11:15PM (#58922198)

    None of the technologies it calls for exist, and many of them may never be feasible, but they all have to be feasible (and exist) for the scheme to work.

    Sure lasers exist, but nothing with the characteristics they demand, and lasers are at this point are a fairly mature technology.

    So far this project consists of speculative physics models that require many, many, many technology breakthroughs before the scheme can be realized. To the extent that this "Breakthrough Initiative" is doing any actual development, it is along the lines of working on the easy parts (building "bike sheds") and assuming that the hard ones will come along one of these days (but soon! since they are claiming this will be ready to launch their probe in just 30 years).

    If you look at the papers produced by this project thus far, they are doing trade-off assessments for technologies that don't exist, with no proposals for how they will be made real (if this is even possible).

    Currently this project appears to be one to generate lots of breathless hype (like the Technology Review piece in the summary, which is basically a personality hype-profile) and divert a hefty chunk of tech billionaire enthusiast spare change into the pockets of a dozen or two well known retired scientists.

    This is much like the space mining imaginary project also funded by tech billionaires, but with no actual plausible approach for doing any profitable mining.

    It is helpful perhaps to consider a comparison with the history of space travel to date. Robert Goddard visualized space travel 50 years before humans were first launched into space, wrote visionary papers about it -- but based it on actual technologies that were known to exist and could be further developed - and then he actually developed those technologies (liquid fuel rockets using inertial guidance). His work was picked by enthusiasts in Germany in the 1930s which then were expanded into industrial scale development during the war, then picked up and expanded again after the war by the U.S. and USSR.

    But the thing is they were elaborating on the same technical system -- inertial guided liquid fuel rocketry, refining and scaling it across 40 years. It took decades of work, but it was (in comparison to Starshot) a straight developmental path, elaborating the same technical solution with better materials and engineering.

    Starshot is nothing like this. It assumes many things not in evidence, and has no real road-map for getting there. The Economist has a good take on this pointing out that several technologies must be each improved by several orders of magnitude to make this possible. Getting one technology to do this is problematic and must be given fairly low odds. When something requires several such huge advances the probability of success becomes a very small number.

  • Any estimates on precision after acceleration phase?

  • "... blasts it to 20% ..." the speed of light? Yeah how long would that take. How does laser pressure change with distance? How hard is it to keep the laser precisely trained on the very very tiny package? What kind of payload is feasible; without some kind of decent communication package and sensors how do you know where the thing is? What are deceleration rates like? BUT give me 100 million and I will happily try and answer these and other questions.

  • The article completely fails to mention how they are solving the problem of how these microsatellites communicate their findings back to Earth. I've heard that one potential issue is that at that distance, the Stars' (Sol + AC) radiation is going to completely drown out the communication signals. One idea I had is that if we send a beacon-satelite to a point in a line from AC that is perpendicular to the Sol-AC vector, but is - let's say 0.4ly from AC when the main satelites arrive, that could then relay si

  • OK - been a while since posting, and this is gonna' be 'Off the Wall'

    BUT . . . what if
    There are interstellar visitors on the way to us, following the 'radio burst' signal from earth's region !
    With these little gizmos speeding down their throats at relativistic velocities (greater than 0.1% C), they are going to see this as - essentially - a shotgun blast of seriously destructive capacity AIMED straight at them.
    Also, these tiny (1 gram'ish) relativistic pellets will also be impac

  • Starshot? It's called Starwisp [wikipedia.org], and it was proposed by the science fiction writer Robert L. Forward in 1985. Revisions to the idea were published by another science fiction writer (and NASA engineer) Geoffrey A. Landis in 2000 [aiaa.org].

    The idea is pretty old at this point, and just as impractical today as when it was first proposed.

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