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A 100GW phased laser array for interstellar lightsail propulsion (2021)
- osamagirl69 3y agoKind of odd that they did not reference any of the existing work done by the breakthrough foundation/UCSB https://www.deepspace.ucsb.edu/projects/starshot https://www.deepspace.ucsb.edu/projects/starshot In particular they have a few paper about lab demos of phased arrays specifically for breakthrough starshot https://opg.optica.org/abstract.cfm?uri=ASSL-2021-JM3A.43 https://opg.optica.org/abstract.cfm?uri=ASSL-2021-JM3A.43 https://arxiv.org/pdf/2107.00568.pdf https://arxiv.org/pdf/2107.00568.pdf etc
- xibbie 3y agoIsn't it literally the first thing they reference in the introduction? > The Breakthrough Starshot Initiative [1] aims to send a probe to image a planet orbiting Proxima Centauri and return data
- whimsicalism 3y agoThey literally mention it in the first paragraph.
- PaulHoule 3y agoHow do they deal with https://en.wikipedia.org/wiki/Thinned-array_curse https://en.wikipedia.org/wiki/Thinned-array_curse ?
- tonmoy 3y agoAccording to my understanding this should not apply to lasers
- nippoo 3y agoThe thinned array curse only applies when all the sources are coherent - with the modulation system they describe, this is not the case.
- osamagirl69 3y agoThis paper assumes a dense array (containing approximately 10^8 elements)
- blincoln 3y agoIs an array of 100,000,000 lasers realistic/practical, or is this more of an "assuming a spherical cow" theoretical exercise?
- osamagirl69 3y agoNot really, with current technology such a system would be astronomically expensive (~trillions of usd to build the laser). This paper is from 2021 which is right about when the breakthrough starshot program ended.
- jacquesm 3y agoNo, this is all theory. There is no way this kind of effort will be funded, but the theoretical exercise is interesting.
- bagels 3y agoBy not building a thinned array, presumably. They have 10^8 elements.
- benfarahmand 3y agoCould these ground based lasers be used for deflecting asteroids?
- scrumper 3y agoI think far less efficiently than propelling a light sail - asteroids being not very reflective. There would be some momentum imparted by the photons impacting and more by ablation of the surface though (if the laser is powerful enough). Enough to deflect? A kiss from a kitten is enough to deflect if you do it far enough in advance…
- SoftTalker 3y agoI like the idea of diverting an asteroid by firing kittens at it.
- jacquesm 3y agoYour idea of kissing is a bit violent.
- rokobobo 3y agoTo divert an asteroid, you’d attempt to ablate a part of it, rather than just rely on its reflectivity: https://en.m.wikipedia.org/wiki/Asteroid_laser_ablation https://en.m.wikipedia.org/wiki/Asteroid_laser_ablation I imagine that tracking an asteroid and continuously pointing the laser array at a specific portion of it, will be harder than tracking a shiny light sail that’s continuously illuminated by the laser array—but as a whole, I think shooting a laser at an asteroid is one of our best bets, so having that array would be a good tool of planetary defense
- r00fus 3y agoMaybe if said asteroid were fitted with a lightsail?
- kurthr 3y ago
- ricardo81 3y agoPerhaps on the 'todo' list is pulsing over another 100GW laser to slow future objects back down from the other direction.
- gattr 3y agoThat's (hopefully) not necessary. The main idea for braking is detaching the sail from the payload, then the sail focuses the light on a smaller sail/surface on payload's forward end to brake it. Besides, let's not get ahead of ourselves with interstellar missions. Scaling this all down for intrasystem propulsion would be great as well. Anyone liked what New Horizons has shown? How about sending one small probe to Pluto per month (with travel time measured in months/weeks instead of years)?
- ceejayoz 3y agoThere've also been proposed flyby-only missions that don't have to worry about slowing down. (Unmanned, obviously.)
- shireboy 3y agoThis is something my kids and I have wondered about too and were hoping some more physics-minded soul here could rule in/out: * Base laser "pushers" on moon, Lagrange points, etc. * Use moon/earth pushers to push 1st wave lightsail craft(s) towards destination. 1st wave craft are also themselves equipped with laser pushers aimed back towards earth. * Use moon/earth pushers to push 2nd wave lightsail craft towards destination * 1/2 way to arrival, 1st wave starts pushing _back_ 2nd wave and moon/earth pushers stop pushing. * 2nd wave "stops" at destination or slows enough to be captured in destination orbit.
- cannedbeets 3y agoFor that to work, the 1st wave ships would need to carry a power source capable of driving a pushing laser. This presents a number of significant challenges: - the current plans for Breakthrough Starshot[0] are to send a centimeter-sized, ~1 gram mass spacecraft. - even such a tiny spacecraft would require a 4x4-meter solar sail and 100 GW of laser power, because photons carry such small amounts of momentum - a ground based nuclear power plant produces a couple GW of power. 100 GW of continuous laser power would require the entire output of 50+ nuclear power plants - that amount of power is difficult enough on the ground, trying to put 50+ nuclear power plants worth of energy generation on a space craft would alone be a tremendous challenge - assuming we could do that, it would weigh unfathomably more than a gram. Just the fuel alone in a ground based station is several tons; the infrastructure to turn that fuel into power is many thousands of tons more… times 50+. It would not be impossible for that amount of power generation to weigh a megaton. - assuming it could be launched from earth or built in space, and pushed by solar sail, the solar sail needed for a ship weighing a megaton would be another level of challenge. If 16 square meters of sail are needed for every gram, then a megaton would require 16x10^12 square meters. That would be a manufactured object 4,000km on a side, or roughly the size of Russia. - We haven’t accounted for the increased power needed to power this craft by sail from the ground. Momentum (let’s ignore relativity even though we are talking about reaching speeds where that starts to be important) is mass*velocity, so in order for our megaton-class spacecraft to be pushed with the same performance as a 1 gram spacecraft, we’d need to scale the momentum delivered by photons with the mass of the craft. That would require 10^12 (one trillion) times more laser photons, which would require one trillion times more energy to produce and 50+ trillion ground-based nuclear power plants. - I think it’s safe to say that pushing a megaton-class starship with lasers and a solar sail is unfeasible. But wait, if we’ve managed to assemble and launch the craft, we don’t need the ground based lasers or the sail, we can just power the ship using all those power plants on board. [1] - with a ship that large, we could take a city worth of people along for the ride, so is there still a use for the giant laser we’ve brought with us? Maybe interstellar package delivery? [0] https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot [1] https://en.wikipedia.org/wiki/Project_Daedalus https://en.wikipedia.org/wiki/Project_Daedalus
- ByThyGrace 3y agoNow I wonder how powerful one of these arrays should be before it shoves Earth with noticeable momentum. You know, as a reaction.
- adhesive_wombat 3y agoIncident solar radiation of 1kW/m² is something like 100 million gigawatts and the force from that is about half a billion Newtons, or the weight of an Iowa-class battleship.
- ilyt 3y agoAssuming this guy on quora didn't fuck up math [1], "multiple suns worth of photons" - [1] https://www.quora.com/What-is-the-total-radiation-pressure-of-all-light-emitted-by-the-sun https://www.quora.com/What-is-the-total-radiation-pressure-o...
- osamagirl69 3y agoThis paper is from 2021
- dsr_ 3y agoRemember to keep control of the death-ray in the hands of people who will not point it at their enemies. Or their friends. Or threaten to do so.
- bagels 3y agoThankfully if it's aimed at space, it's limited to shooting down planes and frying satellites.
- yetihehe 3y ago100GW? More like vaporising planes and satellites. 100GW will heat about 50T of aluminum to boiling temperature in about 1s. Of course you won't have perfect heat transfer, but if you can send that power for more than 5s, most satellites will start actually boiling and vaporising.
- ericbarrett 3y agoCould you even operate this laser terrestrially? The article says optical frequencies (visible light). I think the backscatter from atmospheric dust alone would blind anybody who glanced at it, and it would be visible for miles around.
- deleted 3y ago[deleted]
- jandrese 3y agoIt's not one laser, it's 100,000,000 single kW lasers spread across the surface of the Earth. A single kW laser is already very dangerous and stuff like reflecting off of a passing airplane will be a problem, but they'll be everywhere so you can't hide. That's probably unfair. I assume they'll be spread across deserts and other places with low population density.
- ericbarrett 3y ago
- louwrentius 3y agoI can’t be enthusiastic about anything related to space knowing that many people - especially in the USA - are homeless or are living poverty and have nothing to look forward to, and no death doesn’t count. I’m done with all those rich people vanity projects, we have enough issues here on the ground.
- andromeduck 3y agoDon't let the perfect be the enemy of the good.
- louwrentius 3y agoThere's nothing good about space stuff.
- andromeduck 3y agoThat "space stuff" is why crop failures are no longer a routine occurrence.
- louwrentius 3y agoI’m not talking about weather satellites or GPS. I’m obviously talking about the space stuff that doesn’t matter.
- ben_w 3y agoSo all the things we've actually made in space are good and all of the things that we haven't made but which inspired the people who made the real things are bad?
- kraftman 3y agoWe can do both, they aren't mutually exclusive.
- 3y ago
- danbruc 3y agoFor reference, 100 GW are 3.3 % of the average world electricity production in 2020 of 3062 GW, but this is supposedly only required for a few minutes.
- civilitty 3y agoSo it only requires 40% of all power produced by California, Oregon, Washington, and British Columbia combined [1]? For a few minutes? No problem then! Jokes aside, I don't think there are any interconnectors on the planet that can handle that amount of power for even a split second, let alone the infrastructure to supply it for minutes at a time to a single location. The biggest grid interconnectors in the world cap out at a few gigawatts. [1] https://en.wikipedia.org/wiki/Western_Interconnection https://en.wikipedia.org/wiki/Western_Interconnection
- cma 3y agoWouldn't it likely need to charge up capacitors over time anyway?
- sp332 3y agoYou would probably charge some on-site capacitors using a slower interconnect. That way you would only need a small distance to handle the discharge from the capacitors to the lasers.
- teruakohatu 3y agoThe papers call for 10^8 individual lasers. So power connectors only need to handle a small fraction of the total power.
- petrocrat 3y agoIf it's meant to transfer momentum to a lightsail, then there is no requirement that the power must be delivered to a single point on the electrical grid. Several of these lasers in a smaller form factor dispersed over a rather large geographic region can all focus on a point in orbit and transfer nearly the same momentum as a single laser focused on that point would.
- 3y ago
- jmyeet 3y agoPeople often don't realize just how much energy is required to reach even the nearest star in reasonable time. Of course it depends on how long you're willing to take to get there. I forget the exact numbers but if you start making assumptions like 1G of acceleration up to somewhere between 0.01c and 0.1c you have a travel time between 40 and 400 years to reach Alpha Centauri and an energy cost per kg of payload in the exajoule range. That's as much as 1% of the mass as energy assuming you have a perfect conversion of mass to energy. This is getting into the realm of all the energy we produce and use for the entire planet in a year. Of course we have nothing like that. We don't even have a theoretical framework for that other than possible matter-antimatter annihilation but even then you have containment issues and have to perfectly convert that to motion in the desired direction. That is nontrivial. Our best hope for doing this and carrying our own fuel is nuclear fusion (or possibly by detonating nuclear bombs behind you; yes, seriously). Even here the tyranny of the rocket equation [1] just kills you from the weight of the fuel you have to carry. Also, exhaust velocity limits how fast you can get no matter how efficient your energy production. The only viable way may in fact be to capture energy from the sun and focus it at your ship to accelerate it. Photos have no rest mass but they do have (and can impart) momentum, which is what this article is talking about. I don't know why they'd be using ground-based arrays. You'll end up cooking the atmosphere this way and losing energy if you don't. A laser array like this really has to be space-based, practically speaking. Of course you have the issue of how you decelerate at the other end. This is a not-insignificant problem that probably rquires sending automated probes ahead to construct the necessary infrastructure to decelerate you. So this article uses gigawatt level power to accelerate a "spaceship" of a few grams. I'm not sure what you do with that exactly but this goes to just how high the energy budget requirements are. Even all the hopium over various FTL methods (eg Alcubierre drive, wormholes, space-folding) have no theoretical basis (eg requiring negative mass and/or energy) but even if they did the energy requirements are completely ignored. If you look into it and arrive at any numbers at all it's things like "convert 1 Solar mass into energy". [1]: https://www.kallmorris.com/columns/tyranny-of-the-rocket-equation https://www.kallmorris.com/columns/tyranny-of-the-rocket-equ...
- semiquaver 3y ago> Of course you have the issue of how you decelerate at the other end. This is a not-insignificant problem that probably rquires sending automated probes ahead to construct the necessary infrastructure to decelerate you. But how do you get the probes where you’re going in a reasonable time frame? You can’t use the light sail method because of the same deceleration problem. So you’re stuck with the whole operation taking tens of thousands of years, which means you might as well have sent the original payload with whatever sublightspeed mechanism you would use to send the probes.
- toss1 3y agoThe biggest question is what is the point? A gram-scale probe is nice, but how is it going to return ANY useful data at all from even the nearest star system 4ly distant? Skimming the paper seems to make no mention of it Also, they're saying that it is 100GW of total power and the "ground-based laser array will be need to be kilometers in scale". Say we're talking 10 square kilometers, that's 10GW/Sqkm. With 1,000,000 m^2 per km^2, that's pumping 10 kilowatts per square meter up through the atmosphere. That means a crow-sized bird, with a wingspan of ~18"/50cm x 7"/20cm is 0.1 m^2 and will absorb a kilowatt of radiant energy. Like spreading it out on top of ten 100-watt incandescent bulbs, or directing a 1000-watt hairdryer at it. It won't fry instantly, but will rapidly overheat in the few minutes they claim it will take to accelerate the craft to 0.2c. Since they're detecting atmospheric disturbances, perhaps they could route around birds by momentarily turning off beams that would be wasted anyway? Even assuming this is a cover for an array to fry satellites or incoming ICBMs, it seems kind of frivolous... I'd love to be wrong because it'd be cool to generate those kinds of speeds, but...?
- aftbit 3y ago>Accompanied by military escort vehicles and helicopters, an ambulance departed with the Fourth Wallfacer. Against the lights of New York City, Wade’s figure appeared as a black ghost, his eyes glinting with a cold light. >“We’ll send only a brain,” he said. Still too heavy by a factor of 1000 or so. Perhaps we'd be better off building this laser array in space, using self-replicating robots to assemble cables around a moon of Jupiter to siphon power from its orbit in the magnetic field. >Electricity surges through the cable loops as they slice through Jupiter's magnetosphere, slowly converting the rock's momentum into power. Small robots grovel in the orange dirt, scooping up raw material to feed to the fractionating oven. Amber's garden of machinery flourishes slowly, unpacking itself according to a schema designed by preteens at an industrial school in Poland, with barely any need for human guidance. From one of the Dark Forest books and Accelerando respectively.
- mpsprd 3y ago>accelerating it via radiation pressure to 0.2𝑐 within a few minutes [7]. That probe must be made in unobtainium to handle that acceleration. For 0.2c in 5 minutes it's 20394G!
- MichaelZuo 3y agoProbably a typo, otherwise the writers are very confused?
- thechao 3y agoWell below the G forces experienced by smart artillery. Solid state is pretty solid.
- MichaelZuo 3y agoNot for sustained minutes, a few miliseconds.
- zardo 3y agoThat's probably worse as the jerk must also be very high
- K0balt 3y agoAbsolutely. 20kg pushing evenly on a flat piece of glass an inch in diameter is no big deal. People are forgetting that small things are really, really tough. People have a bias against high forces because they’re made of meat.
- FredPret 3y agoI'm not going to do the calculation right now, but I wonder what G-force would be needed to deform a steel shell, for example. How much worse would it be if sustained over a long period?
- K0balt 3y ago
- tekla 3y agoBullshit. We all know that the only reason for this is, is to justify Angel killing weapons. I'm all on board for that actually.
- deleted 3y ago[deleted]