>accelerating it via radiation pressure to 0.2𝑐 within a few minutes [7].<p>That probe must be made in unobtainium to handle that acceleration. For 0.2c in 5 minutes it's 20394G!
For 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.
The biggest question is what is the point? A gram-scale probe is nice, but how is it going to return <i>ANY</i> useful data at all from even the nearest star system 4ly distant? Skimming the paper seems to make no mention of it<p>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.<p>With 1,000,000 m^2 per km^2, that's pumping 10 kilowatts per square meter up through the atmosphere.<p>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.<p>Since they're detecting atmospheric disturbances, perhaps they could route around birds by momentarily turning off beams that would be wasted anyway?<p>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...?
How do they deal with<p><a href="https://en.wikipedia.org/wiki/Thinned-array_curse" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Thinned-array_curse</a><p>?
Kind of odd that they did not reference any of the existing work done by the breakthrough foundation/UCSB
<a href="https://www.deepspace.ucsb.edu/projects/starshot" rel="nofollow noreferrer">https://www.deepspace.ucsb.edu/projects/starshot</a><p>In particular they have a few paper about lab demos of phased arrays specifically for breakthrough starshot<p><a href="https://opg.optica.org/abstract.cfm?uri=ASSL-2021-JM3A.43" rel="nofollow noreferrer">https://opg.optica.org/abstract.cfm?uri=ASSL-2021-JM3A.43</a><p><a href="https://arxiv.org/pdf/2107.00568.pdf" rel="nofollow noreferrer">https://arxiv.org/pdf/2107.00568.pdf</a><p>etc
People 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.<p>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.<p>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.<p>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.<p>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.<p>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.<p>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.<p>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.<p>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".<p>[1]: <a href="https://www.kallmorris.com/columns/tyranny-of-the-rocket-equation" rel="nofollow noreferrer">https://www.kallmorris.com/columns/tyranny-of-the-rocket-equ...</a>
I 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.<p>I’m done with all those rich people vanity projects, we have enough issues here on the ground.