In 2045: Alpha Centauri

We’ve talked about project Breakthrough Starshot which aims to send a solar sail probe to Alpha Centauri within 20 years. A little basic math and knowing that Alpha Centauri is 4.3 light years away means you are going to need to travel over 20% of the speed of light to make the trip in that time. Some new papers have proposed ways to address a few of the engineering problems.

The basic idea is simple. A very small probe is attached to a very large sail. But calling it a solar sail is a bit of a misnomer. The motive power for the sail would be a powerful laser, which provides more reliable power to the tiny probe’s propulsion system. The problems? First, the thin sail could tear under constant pressure. The answer, according to one of the papers, is to shape the sail like a parachute so it can billow under pressure.

The other problem is not burning the sail up. Space is a hard environment to dump waste heat into since radiation is the only way to transfer it. Another paper suggests that nanoscale patterns on the sail will allow it to release waste heat into the interstellar environment.

The proposed sail is 3 meters wide and made of ultrathin sheets of aluminum oxide and molybdenum disulfide. The sail would carry a probe about the size of a common microchip. We’ve looked at their plans before, but the new papers are a sign that engineering is progressing on the design.

We imagine there will be more problems to solve, of course. But access to space is becoming easier, so it is entirely possible that real tests are in the near future. We aren’t sure, too, how a microchip-sized probe communicates back to Earth about what it finds. Reflecting the laser seems difficult and you can’t reverse course and travel back down the beam. For that matter, how much instrumentation can you pack into something that small that — presumably — gets power from the laser or the alien sun.

Then again, we applaud bold new ideas and we’d love to see something take a ride to another star in, at least, time for our kids to see it. There have been a few practical uses for sails already. Then, too, someone may have sent one here from somewhere else already.

90 thoughts on “In 2045: Alpha Centauri

  1. I think a lot more interesting options are going to open up when we finally get a handle on fusion. I think we’re closer to that than launching this interstellar flight.

    1. That would be neat, yes. A good power source would also solve the potential issue of not having enough energy left to slow down on arrival.

      – That’s what solar sails perhaps have “fixed” by design, by the way.
      Once approaching a foreign solar system, its sun’s light rays will hit the solar sail from the other side and slow down the probe.

      On the other hand, though, probes could still be nicely accelerated with today’s technology.
      The Voyager sisters weren’t meant to travel at maximum speed, for example. They rather were designed to collect data from the planets and moons in our own solar system at a reasonable speed. For an an interstellar mission, probes like this could gain a much higher velocity by doing a few proper swing-by maneuvers..

      1. I’m no science gal myself…. But considering it’s embarking on an intergalactic journey….. solar flares may be relevant for ,maybe, the 1st inch of it’s mile journey…..

    1. Fif you read the artcile? “probe about the size of a common microchip” – do you know anything the size of a microchip that can transmit 4.3 light years? If so, you’ll be collecting your noble prize pretty soon.

      And the light sail is 3m across – so again 4.3 light years, do you think we are going to see if your do morse on it with ripples?

      And for the people muttering about ftl communication – are they expecting that to a) happen anytime soon, but more importantly b) even if it does happen it’s probably going to need a decent bit of equipment and power. In the size of a microchip? Noble prize again…

      The only option for that size would be orbit then come back. Without a launching laser. I don’t think my grandchildren (I don’t have any yet) would be alive to see it…

      1. Yes, I do. We can already receive light affected by dust grains from much farther.

        The math on communicating back is straightforward, and not really super-difficult. By far the sketchier part of the entire idea is the idea that something that small can *survive* 20 years.

        The link budget was almost the only part of Starshot I found plausible.

        1. Many billions of trillions of grains of dust, not a single object the size of a postage stamp.
          As for the issue with radio communications, take a look at how much difficulty we have communicating with the Voyager probes, and those are still relatively close and have high gain antennas aimed right towards us. Receiving a signal from something like what is proposed in this article is just not possible with our current understanding of radio physics. Look up the radio inverse square law, if you’re curious.

        2. “As for the issue with radio communications, ”

          Of course you don’t do radio. You can’t focus it well enough. It’s actually not bad enough that it’d be impossible, because we can build wacko-huge radio telescopes. But optical’s just easier.

          “Look up the radio inverse square law, if you’re curious.”

          Hey, it’s right on slide 12 here, too!

          (the original stuff’s at arXiv:1801.07778 )

          The link budget math’s on slide 26, it’s not complicated. Huge freaking telescopes help. Yes, a 100 W laser on a gram-scale device is sketchy as hell (it’s intensity modulated, so this is just peak power) but of all of the engineering issues that’s probably the *most* practical.

          Keep in mind I’m not saying this is *easy* – I’m saying of all the challenges involved this is probably the one that’s *easiest*. We’re really, really good at this kind of stuff. Building a gram-scale device to last 20 years while being blasted through the ISM at 0.2 c? Not exactly in our wheelhouse.

      2. I like to think that developing nascent technologies with a proposed utility in mind is still worthy and inspiring even if they can’t be put to use right ‘now’.

        We might as well be asking… Where are they going to fit the brakes?

        And how long will something travelling at 20% the speed of light spend in a solar system? 24 hours?

        I know the odds are low but I hope our postage stamp doesn’t hit anything interesting because if it weighs 5 grams it’ll impart 80 billion joules of energy into it. Hehe.

        Can we slingshot back?

        1. It can probably do a solar brake once it reaches near enough. A slingshot back would probably be the better option. Due to it’s size, remote comms might be impossible, but it can probably return with locally saved data.

    1. I wonder if it is because it would be hard to make a perfectly reflective surface. I imagine even with a 99% reflective surface it would still be abosrbing quite alot in that 1%, and if it’s as thin as they say I can’t imagine the mass would be very high.

    2. It is reflective. Not 100% though, sails like these are more like 90%. It’s a compromise with the materials and their lightness. That the sail is curved instead of perfectly flat. You can probably do better if you don’t have to handle a wide range of frequencies of light (like from the Sun), so the laser could be promising.

    3. Of course the sail’s reflective. It’s right in the paper, the reflectance is near 100%.

      Thermal management’s a big issue because absorptivity (thus reflectance)/emissivity are equal (Kirchhoff’s law). If you reflect all light in a band, that means you can’t emit light in that band, either. This is the whole “stupidly hot aluminum bleachers” issue – aluminum reflects sunlight really well… but the few percent that it *doesn’t* reflect, it can’t get rid of. So it heats up to crazy temperatures.

      Which is why satellites use selective surface coatings: they reflect well in the solar band (where they look white) and emit well in infrared (where they would look black). So that’s the challenge here: you need to be highly reflective (low absorptivity/emissivity) where the laser is, and highly emissive (low reflectance) in the infrared.

      And that’s really, really hard. Hence the nanopatterning being necessary, and the fact that they are looking at sail temperatures on the order of 1000 K limited by the fact that it literally vaporizes above that temperature.

  2. If that sail could only act as a solar cell and a reflector, as well. Then it would be perhaps somehow possible to have an antenna and a power source for a transmitter. Unfortunately, a a probe of the size of a stamp is not good enough. If it was the size of a shoe box, at least, then, maybe..

  3. I do hope we get FTL communication soon (kind of looks promising). This would make sending probes to other star systems a lot more valuable, such as being able to explore the star system, try to fly by planets. A multi-year communication delay of multiple years would make that hard.

      1. I’d have thought the problem wasn’t in transmitting data but in having a receiver back here sensitive enough to pick it up.

        It already has a powered transmitter – the sail itself, by how the sail inherently works (reflecting light from the laser). It’d only need to change how much it reflects (or the wavelength, or the angle, etc) by a tiny amount. That’d also be how it could receive data too.

        Keep the proble small & simple, and the big complex thing that’s hard to move stays here (the second big complex thing that’s hard to move, after the laser itself).

        1. I’ve actually looked into that concept of using a laser to paint something reflective and then just putting a shutter in front of it for example and modulate the return. Even from the distance to the Earth to the Moon it takes an enormous amount of data collection to find the corner reflectors left there by Apollo. So at 4 plus light years your data rate might be like one bit every nine months or a year or something. Granted, the sail is bigger but it isn’t designed to reflect like the corner reflector and it will have 20 years of wear on it at the end. So I suspect that might even be an optimistic number.

          1. ” it takes an enormous amount of data collection to find the corner reflectors left there by Apollo.”

            Huh? They do it continuously with a 30 inch telescope. That’s how we know the distance to the Moon, after all. Plus the corner reflectors are *tiny*, so you barely get any power back.

            The Starshot link budget stuff isn’t crazy (it’s probably the only part that *isn’t* crazy). Huge freaking telescopes (30+ *meters*) do wonders for link budgets. And they aren’t even going nuts like putting them on the Moon or something.

    1. “I do hope we get FTL communication soon (kind of looks promising).”

      I’m sorry to tell you that there are absolutely zero even remotely plausible FTL communication schemes out there. They all require non-standard physics (or very likely will). Sadly, science reporting is super-awful and continues to confuse people on this. Even the reporting that’s *not* confusing (as in, anything not involving ‘quantum teleportation’ which has nothing to do with FTL communication) tends to only report the initial paper that’s written, and not the follow-ons that say “yeah… no.”

        1. Hey, it’s not actually the physicist’s fault! It’s an engineering issue. You want to get to Alpha Centauri in a month, sure! I can get an electron there in a month, no problem!

          1. Rog77, the Nobel for that should have been given to one A. Einstein, unfortunately quite a lot of anti-Semitism got in the way. It’s pretty well known that a traveler can get anywhere in the universe in any timeframe if it can choose its speed. Unfortunately only the traveler gets to experience that timeframe.

          2. @Shannon

            I will hand it to you that you are technically correct, but I would say that most people would take the amount of time a probe takes to get somewhere to be measured from the start point, as opposed to the “clock” of the object – especially so in a discussion on FTL comms/travel.

          3. Yup. The whole “FTL” thing is just to avoid the annoyance of time dilation. But a 25 MeV electron zips from here to Alpha Centauri in about a month.

            You want to get to Alpha Centauri in a month? No problem! Let’s say your spacecraft (no fuel) plus you, is around 1000 kg. Just need to load up with a few tens of thousands of kg of positrons/electrons.

            Like I said, it’s an engineering problem.

          4. @pat, well in that case I can get you a photon there in an instant, using only the bits in my cupboard. But I think we both know this isn’t what irox was talking about.

          5. “@pat, well in that case I can get you a photon there in an instant, using only the bits in my cupboard.”

            Yeah, but I’m not made of photons. I can easily get a human to Alpha Centauri in a month. Bit by bit.

            “But I think we both know this isn’t what irox was talking about.”

            Well, yeah, but you’re the one blaming physicists for being the problem! You wanna go explore strange new worlds? No big deal! Just find a way to rebuild a human on the other side and I’ll get you there in a *snap*.

          6. @Pat although I was clearly taking the P originally; though you do raise an interesting point re moving things bit by bit – now if I can liberally steal (and misunderstand) Prof Penrose – just using light, we can change the universe that comes after this one, so if we can simulate it well enough we can put someone somewhere before they arrive…
            But that all sounds a bit quantum to me.

          7. @Shanon of course the traveller can chose their own speed and timeframe. It’s their intrinsic rights. What we need is legislation to ensure that everyone else recognises the timeframe they’ve chosen, and that anyone who doesn’t isn’t allowed to post about it. If people are saying the law of causality prevents it, we should use the new legislation to punish them, because the travellers might be damaged by their insinuations.

      1. s/FTL/wireless/ and you ramble is valid 130 years ago….

        “They all require non-standard physics” that gets a chuckle.

        Sorry to break it to you, but science isn’t finish/done, and the physics we accept as “standard” is wrong, we just don’t know it yet…

          1. Yup, I’d hazard a guess that the first human communications were radio-based. Specifically in the visible light spectrum.

            More seriously – fire beacons and stuff are great examples of low-latency but high-speed communication, and smoke signals would be higher latency but higher bandwidth? And of course limited to daytime.

          2. My absolute favorite example of people not realizing what wireless communication is was an Adam Ruins Everything video where he said that autonomous vehicles would be able to start instantly at stoplights because “they communicate at the speed of light.”

            My brain just short-circuited with “what… exactly… do you think the stoplights are doing?”

          3. Not really. Basically “wireless” communication never existed until after the telegraph. Sure, there were primitive communication methods that didn’t require wires (voice, semaphores, smoke signals, etc.) but those were never called wireless. The term ‘wireless’ didn’t come into existence until the 19th century.

            Anyway, the FUD you’re spreading about FTL comms has no substance, you only attack how people are reporting on it, and do nothing to backup your claims that’s it’s implausible. This is of course similar to many other attempts to hold humanity back from technological advancements…

          4. “The term ‘wireless’ didn’t come into existence until the 19th century.”

            Because… that’s when ‘wires’ started being used for communication…? “Wireless” came into existence *because of* wires.

            Humans have been communicating without wires *forever*. Communicating with radio wasn’t some grand scientific breakthrough. Literally the same guy who discovered long-wavelength EM waves (radio) realized it was just light.

            “and do nothing to backup your claims that’s it’s implausible.”

            What, exactly, do you want backed up? The fact that we’ve observed a grand total of zero examples of effective faster than light motion outside of the inflationary period?

            “This is of course similar to many other attempts to hold humanity back from technological advancements…”

            FTL communication or travel is *not* a technological advancement. You know what would be? Human suspended animation, massive life extension, or brain virtualization. All of those would allow for exploring the galaxy and are completely within the current known laws of physics.

            This is why dreaming about FTL is silly. Because it’s a waste of effort. It’s like people trying to produce a perpetual motion machine. Scientists knew that idea was crap a long time ago, but people kept clinging to it.

          5. Can’t tell if you’re acting dumb to troll people, or, erm, you’re not trolling….

            Glad you’re coming around to see that wireless comms came after wired comms. Feel free to keep splitting hairs and play word games on that one if you like… Although, disappointed you see Radio communication and smoke signals as the same thing…. You’re kind of flat earthing things here.

            Also, interactions between entangled quantum particles have been shown to happen faster than the speed of light. While this alone does not get us FTL communication, it certainly knocks down your “total of zero examples of ” FTL claim.

            Our future is not built on “current known laws of physics”. If it was, we would never have put anything in orbit because the Earth is flat….

          6. “Also, interactions between entangled quantum particles have been shown to happen faster than the speed of light.”

            No, they haven’t. This is the “I’m sorry to tell you” part. Sadly, science journalism is terrible and trying to describe the intricacies of “our math and language for this sucks” is completely lost. What you’re talking about is not FTL communication. It’s just an example of where our analogies for things totally breaks down. Entanglement *is* weird. It’s just not weird in the way you think it is. (*)

            An “interaction” in physics involves an exchange of some sort, a Feynman diagram. Something that I can write down as a Lagrangian element. That’s the only way information flows in physics. This is what the word strictly means. Physicists would (should) use it properly. Journalists don’t.

            What you’re talking about is when a measurement is performed on an entangled state, the state breaks down instantly. So if the state is separated by huge distances, people talk about the state collapsing instantly.

            But that’s not an interaction. It’s casting a shadow on the Moon with your fingers. The shadow appears and disappears *instantly* between the two points. The shadow cannot carry information between the two points faster than light, because it’s *not an interaction* between those two points.

            It’s exactly the same in quantum entanglement. The interaction happened when the entanglement was formed (forming the shadow). The measurement later (measuring the shadow on the Moon) just reveals that interaction. The revelation happens instantly, but that’s all it is – a revelation, not an interaction.



            Those are good introductions, but still not perfect. Some of the language is couched in “well, *if* we could do this, but we can’t” – and that implies that the issue it’s technological. It’s not technological. The “if we could do this but we can’t” part is *fundamental* – it’s saying “if we could communicate faster than the speed of light, we could communicate faster than the speed of light.”

            It’s a similar issue with wormholes and warp drives. You can write down geometry of space to be whatever you want. Einstein’s equations link that to the stress-energy tensor of matter. So people write down these weird-ass geometries and journalists (and sadly, some theorists who don’t know how to communicate with the public) say “oh, wormholes are possible in general relativity” – when in fact, the exact *opposite* is true. Wormholes are just geometry. General relativity *tells* you that in order to have that geometry, you need physics that doesn’t exist. That’s literally what it’s saying.

            Yes, people keep messing around with things to produce new and different models that use different physics that doesn’t exist, but in the end it’s still “physics that doesn’t exist.”

            Again, the best reason for why this is true is simple: we don’t see any evidence of FTL communication after the inflationary epoch. Anywhere. There was evidence of radio communication before we used it. There was evidence of flight before we built planes. There was evidence of nuclear reactions before we used them. There was evidence of space travel before we did it.

            There is no evidence of FTL anything after the inflationary epoch. None.

          7. Err… I said it wasn’t FTL comms. But it is an example of something that appears to be happening faster than light speed.

            Again, as I said, this is NOT FTL communications, but it’s *something* that appears to happen faster than is should with our current “standard physics” model should allow. (Hope you caught that bit this time.)

            Sorry, your moon shadow example is not instantaneous and is limited by the speed of light. There will be a delay between you moving your hand and any observed changes to the shadow on the moon. This is not an analogy for quantum entanglement/spooky-action-at-a-distance. I am familiar with the moon shadow, or laser dot, example, trying to demonstrate “FTL”, but it’s not related to spooky-action-at-a-distance.

            Also, I don’t like the term “FTL communication”, I think “near instantaneous communication” or something like that is a better description (FTL is hard for many people to wrap their heads around, also I don’t believe anything will be actually be truely FTL for this type of communication anyway – it would work via some other mechanism most likely).

            Anyway, you’re still coming across as somebody telling people to stop trying to building rockets/satellites because the Earth is always going to be flat.

            The current state of physics/science is not the end, lots of things in our current “standard physics” model will turn out to be wrong.

            You are right to be skeptical, you are wrong to be dismissive.

      2. They haven’t even been able to reconcile Relativity and Quantum theory, so until we have a hell of a lot better understanding of physics I’d say everything is up for grabs.

        1. “They haven’t even been able to reconcile Relativity and Quantum theory,”

          The Universe has.

          *glances around*

          Don’t see any wormholes or faster than light asteroids.

          There’s exactly *one* example of FTL travel in the ‘standard view’ of the Universe that you can point to: cosmic inflation (and *maybe* dark energy eventually). That’s pretty much the best hope we’ve got, and it’d take particle accelerators the size of the freaking Solar System to hit those energies even for an instant.

          Every example of “advanced technology” we currently have existed in the Universe before we did it. Radio transmitters, nuclear reactors, quantum systems. I’ve never understood this hope people cling to that there’s some weird magic FTL cheat code.

          You don’t need FTL travel to explore the Universe. You just need a longer-lived species, and *that* is also something that exists in the Universe already.

          1. Well, the most distant galaxies (pretty much anything ~18 billion light years away or more) are receding from us at an apparent velocity of faster than light. But that’s space expanding, not motion per se.

  4. From the project’s website: Images of the target planet could be transmitted by a 1Watt laser onboard the nanocraft, in a ‘burst mode’ which uses the energy storage unit to rapidly draw power for the power-intensive laser communications mode. Upon approach to the target, the sail would be used to focus the laser communication signal.

    For a 4m sail, for example, the diffraction limit spot size on Earth would be on order of 1000m. A kilometer-scale receiving array would intercept 10-14 of the transmitted signal. The main challenge is to use the sail as diffraction limited optics for the laser communication system. This would be achieved by shaping the sail into a ‘Fresnel lens’ upon approach to the target. The sail structure could be different at the launch and communication phases. In order to maintain a high transmission through the Earth’s atmosphere, the communication would need to operate at a wavelength shorter than that used by the launch laser system, due to the Doppler shift of the nanocraft relative to the Eart

  5. Saying it’s impossible to ride back up the beam isn’t entirely true. Dr. Robert Forward devised a conceptual system involving a sail which breaks into two pieces, with the larger part uncoupling from the payload and acting as a reflector to decelerate the payload sail. He used it as background for his novel Flight of the Dragonfly. A cheesy and lovable sci fi novel, by the way. I do recommend it.

    Granted I put absolutely no stock whatsoever in the feasibility of Starshot (wanna explore nearby systems? Let’s build a huge telescope in cislunar space) but in principle it could work.

  6. 20% of light speed is 196,714,216 Feet per second
    .50cal bullet travels at 2800 Feet per second
    A speck of dust hitting the probe or sail would utterly disintegrate them.

      1. How the heck would charging the sail work? The dust grains are neutral. Even if they weren’t, at 0.2c they’re not going to get deflected freaking 4+ meters away.

        Also, that’s not even how polarized hull plating works in Star Trek (at least it’s not how it’s supposed to work). It’s not pushing stuff away with electromagnetism. It’s holding *itself together* with electromagnetism.

    1. “A speck of dust hitting the probe or sail would utterly disintegrate them.”

      Not really. At those speeds it’s actually hard to do damage because you spend so little time in the vicinity of the object. It’d just rip a tiny hole in the sail, and that’s it.

      Bullets do more damage if they *don’t* go straight through you.

  7. I notice a lot of comments with this kind of theme: “But what about sending information back, HUH?” “But what about hitting dust, this project will never work” etc, etc. Along the lines of this webcomic:

    …as if the whole point of this effort isn’t to address these very issues, that there hasn’t ever been real research on these questions, and that the folks involved with this effort have never thought about such things.
    There’s a page full of references addressing these and other concerns. You can find more by looking in and The British Interplanetary Society in particular has a bunch of resources looking at how to address these problems.

  8. Well they won’t just send one, will they?

    Maybe there will be a steady stream/swarm of the things that will pass data between themselves in much shorter hops all of the way back to earth?

    1. Exactly what I was thinking! A stream of them relaying messages back via an error correcting protocol. Tiny super-capacitor to store energy. Angling their solar sails to miss or deliberately fly into the star. Practice with outer solar system planets first. Chance of hitting something accidentally out their is infinitesimally infinitesimal.

  9. Greetings from Moscow!

    A 10-gram object crashing into atmosphere at near-relativistic 0.2C would obliterate a huge area of that newly discovered planet, since it’d explode with a force of 18,000,000,000,000 joules. Or 4,302 kilotonnes of TNT. Or 4.3 megatonnes – a rather large nuclear weapon.

    Please correct me if I’m wrong.

    1. It’s not quite that simple. The Sun, for instance, is bathing the planet in around 4E17 joules *every second* – or around 100 *gigatons* of TNT. But the planet clearly isn’t obliterated.

      It just depends on how the object would dissipate the energy. And in fact, that helps it survive the trip: a hydrogen atom at 0.2c actually dumps *less energy* in a thin material than one at 0.1c (about half) even though you’d expect it to dissipate 4 times more, because you’re on the declining part of the Bethe-Bloch curve.

      This is how proton therapy works: most of the energy is dissipated when the particles finally stop, so you can tune the energy to target a tumor, because the proton beam barely dumps any energy into the rest of the body. So similarly you can figure if the object’s thin, it doesn’t absorb anything.

      1. At 0.2C, a micro craft (still a macro object unlike protons in a beam) entering dense atmosphere of a habitable planet would be no different from it hitting a brick wall. Most of the energy would release within a rather localised area. It’d be an atmospheric explosion of the Chebarkul meteorite type, only more powerful and much nastier because of gamma radiation.

  10. They could try some sort of interference with the host star light in a coded way. A sensible telescope could capture small dips in the star bright containing the encoded message. It should reach us in 4.3 light year.

  11. Your remark is silly, especially in light of the fact Philip Lubin of NASA, astrophysicist Avi Loeb of Harvard and >Stephen Hawking< himself have participated in the project and they say you're wrong. The communication is expected to be by laser from the destination with the signal capable of being picked up by a 30m telescope, 3 of which, the GMT, 30 Meter and ELT, will be in full operation by then.

  12. Actually come to think of it. Deliberately hitting a celestial object with something with the kinetic energy of nuclear weapon but the size of a postage stamp might produce some interesting spectroscopic results. I wonder if we could see them.

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