Breakthrough Starship wants to use a 100 Gigawatt laser array to push an ultralight 4 meter X 4 meter nanocrystal solar sail.
StarChip is the name used by Breakthrough Initiatives for a very small, centimeter-sized, gram-scale, interstellar spacecraft envisioned for the Breakthrough Starshot program. The light sail is envisioned to be no larger than 4 by 4 meters (13 by 13 feet). The material would have to be very thin and be able to reflect the laser beam while absorbing only a small fraction of the incident energy, or it will vaporize the sail. The light sail may also double as power source during cruise, because collisions with atoms of interstellar medium would deliver 60 watt/m2 of power. They want to keep the light sail and the Starschip under 1 gram of mass. A penny weighs 2.5 grams.
A 2018 paper described the material challenges of the Starchip and its Solar sail.
Lubin’s preliminary calculations indicate that a 100-GW phased laser array 10 km on a side could accelerate each Starchip spacecraft to 0.2c (20 percent of the speed of light) by firing for roughly three minutes.
A group that already made nanocrystal films 16000 times larger is adding origami construction into the films to add more components and structure without making the system heavier. They are making the photonic chips 50 nanometers thick.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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So a laser facility of 36 square miles minimum (6 miles on a side)? Trying to figure out where they would put it. Have to be out in orbit or close to one of the earth's poles, right? To keep the laser locked on the target while the Earth rotates? If in orbit or close to the poles, where would the power come from? 100 Gw is a lot of power.
Maybe they could build 2 or 3 facilities spaced across different longitudes on the surface of the earth, one taking over when the other loses line of site. Flat, stable surfaces of 36 square miles linked to 100 Gw power supplies.
I guess if we ever figure out commercial nuclear fusion, this would be something of use…
Thanx! Makes sense. So, the spacing makes things worse as it gets larger. But at a distance, the waves blend back together as the resolution of the spacing itself is lost.
Sure…
The practical 'imagination view' of this is that as waves travel further from a point-source, the curvature of the wavefronts flattens. Kind of obviously, right?
When the curvature has flattened to where the beam-to-beam overlap approaches the wavelength of the source, then the difference between a tightly packed and a point-source-loosely-packed array attenuates to 'no difference'.
However, there is no magic wand in Physics!!!
Should one have a large array (say 1,000,0000) of 'naked laser diodes' (which EACH have an exit dispersion measured in tens of degrees!) be set up without collimating per-diode lenses, while technically at far field there will be the synthetic aperture effect, the overall pattern of lobes will cover the tens of degrees. Power lost.
If, however, the same million lasers are arranged in an array having say 10 cm spacing (100 m by 100 m), with each laser sporting a little square of Fresnel sheet lens to collimate to ¹⁄₁₀₀° collimation, then at far field, the lobe span will remain at ¹⁄₁₀₀°, and the in-phase synthetic aperture enhancement will follow geometric wave field physics, just as in the naked case.
Anyway, that's as good as I can summon, without more coffee.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
Is there a *common sense* description of how this comes together at the distance? And also, does this apply if the array is extremely sparce, not tightly packed? Not trying to get extra detailed work from you, as I could not follow it in all likelihood anyway. Thanx!
Not really … one can (and I did when I was much younger and less put off by convoluted math) do the calculations and show that sparse arrays 'synthetic aperture' lobes at close field are indeed limited by the seamless packing of the emitters, but at far field, are fine with having only modestly 'good quality' Fresnel lenses collimating the beams.
Physics is a harsh mistress. Sometimes she gives, sometimes she takes, and only rarely does arguing with her change her mind.
The meaning of a word is its use -Ludwig Wittgenstein
They have to be so tightly packed that there is not diffraction edge between the lasers. Sparce array fallacy otherwise. I think!
Thanx Thanx Thanx!! I was beginning to doubt.
Here's one for you …
The force of Sol's gravitational pull at any distance from it is G₁/r² where 'G₁' is Sol's intrinsic gravitational pull at '1 meter', and 'r' is the distance from the center of Sol.
Sunlight intensity per m² is also P₁/r². Well … it isn't hard to see that both gravity and sunlight scale in proportion to each other.
This means that a 'sail' at 1 unit distance from Sol will be attracted to Sol gravitationally the same proportion as it is repelled by the power of sunlight hitting the face of the sail sheet.
At 1 AU (earth's orbit) from Sol, Sol's gravitational pull is 0.005926 N/kg (= m/s²); At 1 AU, reflecting only 50% of Sol's 1363 W/m² of sunlight delivers (0.50 × 1363 ÷ 299,792,458 c) = 4.55 µN (micro newtons) of outward illumination pressure.
Therefore, 1 gram of mass per m² (i.e. a very light sail) would be 75% balanced by solar illumination pressure. Pretty good! Either the reflectivity of the sail needs to increase 33%, or, the mass per m² needs to drop 25%.
That's how close it is.
BUT… the real take away is that at ANY distance from Sol, whatever sail-thing you got, including a payload, must not exceed 0.75 g/m² or so, to be balanced in a 'sol stat' non-orbiting configuration. The nice part is that any Sol orbital motion increases the maximum mass per m², substantially. Obviously, at 1 AU, if an orbiter has a velocity equal to Earth's… then no solar sail is needed at all.
Heehee…
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
That 10 km means an array of many smaller lasers, say spaced every meter or so (for 100 million of them) in a 10 km by 10 km square or circular matrix.
Very carefully changing the phase of the lasers would result in a synthetic beam having far, far tighter dispersion 'at the target' than any individual laser could muster. And the phase-matching has a convenient freebie … due to lasers' ability to phase lock to a weak 'incoming beam' reflected from a distant target.
Kind of magical.
A hundred million one kilowatt lasers is, while grandiose, certainly in the realm of 'conceivable'. It is a (# × power) issue…
⋅-=≡ GoatGuy ✓ ≡=-⋅
They're spinning it for stability, and to keep it from folding up like that sheet I tried using for a parachute when I was seven. Increased tensile load, in return for reduced rigidity demands. But I still have doubts about high acceleration light sails with concentrated loads.
Like I said, there's a reason Forward's Starwisp concept used distributed circuitry. Several, actually.
The mass-distribution-versus-acceleration 'problem' is heightened as a function of what? (I'm asking rhetorically…)
Seems to me that the thinner the film reflecting the powerful laser beam, not withstanding invoking magic of extraordinary materials with tensile strengths seriously exceeding carbon nanofibers … that the lighter the film, the less 'point mass' tensile strength it has. As in a 'pea' centered in a 4 meter diameter sail. A 'pea' is about right in mass; maybe a gram.
At an acceleration of, oh, 213,000 m/s² (21,500 G), which a 100×10⁹ watt beam would impart, for 300 seconds, delivering 20% of 'c', the effective newton-share of the pea would be 1.5 gram ÷ 1000 × 213,000 = 320 N of force. Dead weight of over 32 kg or 70 pounds.
Recalling that our nanofilm is on the order of what, nanometers thick … that is an AWEFUL lot of newton-weight to keep from ripping right through and being left behind. Oh, sure … like an old-fashioned (17th century!) hot-air balloon, one supposed clever fractal step-ups from naked film to nanofibers, to nanostring, to nano-rope, to macro-strings … to support the 30 kilogram effective mass pea. Pea chip.
Seems though that every effort to make the whole thing lighter serves to make the whole thing accelerate faster, thus at least linearly (if not cubic) increasing stress on the film's substrate netting. Gah… I have to do a computational calculus optimization, to see how this works…
GoatGuy
⊕1 to my mentor…
To be fair… or rather generous… to Elon
Really, in the end, the RECURRING issue ( have with this article, and so many others like it is 'anchor-less grandiosity'.
The peeps promoting the reaction-massless Mach Effect thruster immediately scaled their grandiosity from micronewtons to meganewtons, and thereby projecting interstellar star travel on the order of decades, and interplanetary on the order of hours-to-days. But alas, the METs seem to be vanishing; the results are being challenged, and the scaling looks to be a myth.
This design calls for a wisp of a film, illuminated by billions-of-times-brighter light than Sol affords Terra, for minutes-to-hours; it further blithely proposes accelerations of 25,000+ times that of Earth's sea level gravity. The power levels — 100 billion watts optical, continuous power, are tens of thousands of times larger than anything achieved here on planet Dirt. Grandiosity, magnified.
The Z-pinch (not really), but pinch fusion peeps insist their experiments can be scaled to hundreds of millions of watts, and result in interplanetary transit times of hours-to-days. Ignoring that there is a LOT OF MASS needed to support that kind of power, that kind of exhausted reaction mass, that kind of parasitic waste heat dissipation. Ah… grandiosity. SciFi story lines.
It goes on and on.
We truly are in an era where Musk can call his great big can of gasoline a starship. And no one significantly challenges it.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
well. i don't think we're talking caravel sails of the 1500s. Ribbing, nodes, redundant size, self-balancing/ re-directing, and a internally-robust material (doesn't fray) likely means that 75% of the sail thrust-area intact or more means the payload arrives within timeline window.
In terms of the plot of Footfall, we'd been invaded by an alien species with orbital superiority, and the only way we had to take the fight to them was covertly building Orion battleships. The higher acceleration and lesser delta V ended up dictating a kamikaze style attack.
Yah. Isp and N/W (newtons per watt) are definitely inversely related. F/P = 2 / (G⋅Isp)
But for a given number of newton seconds (integrated thrust), higher Isp also linearly uses less reaction mass. Which, if one is trying to span the stars, is a good thing.
Even so, doing the calculations with that mean old Tsiolkovsky's Rocket Equation … ΔV = G Isp ln( M₀ / M₁ ), it becomes apparent that we'd need the Isp to get to near lightspeed, but the acceleration times would become ridiculously long. Because force goes lower and lower for a particular power input.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
sentient does not equal intelligent. many robots can be trained to show reasonably convincing sentience – sense and react to that sense (harm, etc) and internalize the location/ effect/ circumstances. It does not include – in academic definitions – the identification of the self.
agreed. several robust craft have been damaged/ re-directed by clouds of space dust and micrometeroid showers. Micrometeroid detectors on extra-orbital missions have indicated millions of impacts of less than a mil thoughout the solar system – some impacts up to a fraction of an inch. Too hazardous for larger tensile structures. Unclear whether such 'clouds' can be tracked or predicted.
Not convinced that multi-metre sails can survive the likely projectile impacts.
Yes, I should of said simple solar system lightsails.
Thanx! I'm much less aggressive than the laser interstellar plan, more interested in say a sail that would provide thrust equal to solar gravity, so one could either remain stationary or have a way to drift stuff slowly in the Sun's orbit, to bring it in for raw material. I clearly remember that 10% of the mass of a settlement or whatever devoted to Drexler simple lightsail was *supposed* to do this. Is that very incorrect? Seems like a good deal if the sails are, as everything should be, reusable. Perhaps use saftey margin energy to move these along when avail. Nit pick!! G is a constant from which g can be derived.
If you give up on the basic idea of getting the object beyond this solar system in a life time you can do it with such a diffuse power source.
The biggest issue remains: solar energy varies inversely by distance to Sol, and at Earth's distance, it is pretty dilute, at only about 1,300 W/m². Putting that in perspective, for a PERFECT sail (i.e. 100% reflective at all wavelengths), one gets exactly 2/c or 6.67 nanonewtons per watt, or 8.7 micronewtons at 1 AU. Per square meter of sail.
Putting THAT into perspective, the if the 2 grams, 4×4 m thing is accurate, that'd be 4 m × 4 m × 8.7×10⁻⁶ N ÷ 0.002 kg = 0.0694 m/s² or about 0.00707 G's of acceleration for the entire spacecraft.
Now, the acceleration would last so long as the spacecraft were loitering near 1 AU. And, putting 0.0694 m/s² to something longer term, it becomes 5994 m/s per day or 518,000 km/day². Not exactly records shattering, but not bad.
By comparison, focussing gigawatts on this little sail would result in an acceleration of well over 25,000 Gs'. Hence why it theoretically 'could' get to 20% of lightspeed in only 3 (in my calcs, 5) minutes.
Millions of times more focussed energy.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
I'm not up to snuff on lasers. I remember reading somewhere that the NIF (National Ignition Facility) in California had the world's largest laser, around 1000 meters in length. So how should I read this in the article above:
Lubin’s preliminary calculations indicate that a 100-GW phased laser array 10 km on a side would be used to accelerate the spacecraft.
What does 10 km on a side mean? Is that the total length of all the different lasers before they are combined?
Interesting. Should start small and build some prototypes. It is the kind of thing were you don't need a big break thru. All of the technology exist now. You just of to integrate them. You could use the laser to put the probe in orbit. Then open the sail and let the laser accelerate the probe. Sending probes to the planets would be easily achievable milestones.
Except that the fithp didn't have FTL, they just had a fairly efficient fusion drive. Our Orion drive technology had less ISP, but considerably better acceleration.
Sounds like the fithp from Footfall. Hyperadvanced alien race from Alpha Centauri invaded a alternate history Cold War-era Earth but they got their tech from their "master" species that died out and left all their tech behind. So they didn't earn any of their knowledge or technology. It would be like dogs eventually becoming sentient and inheriting all that we leave behind if we went extinct.
In the story, they plan to incorporate humans into their "herd" for that very reason- they actually NEED us to help colonize the rest of the solar system because they are too dumb to do it themselves. Great read; highly recommended. Larry Niven was one of the authors.
I once read a science fiction story in which we sent an interstellar probe to some other star, and aliens from that star came to visit via their FTL drive. Turned out they were super impressed by our technology. We said what are you talking about, you have FTL. They said yeah but we just got lucky and stumbled across that. But your probe! So much complicated stuff, so elegant and tiny!
I think a nanotech light sail would impress those guys.
A fundamental issue for high acceleration solar sails is uniformity of mass distribution: Assuming the light is uniform, so must be the mass distribution, or else different parts of the sail try to accelerate at different rates, and either the sail tangles, or it tears. Because such ultra-light sails can't have substantial tensile strength, or really any rigidity at all. They don't accelerate like a rigid disk, but rather like a bunch of loosely coupled small sails flying in formation.
That's why Forward's "Starwisp" concept had distributed circuitry, not a chip.
So, I don't see how this ultra-light sail actually hauls along a concentrated payload.
In fact, I think that, realistically, you'd need to incorporate some kind of meta-material variable reflection so that the parts of the sail could locally negate internal stresses and modulate their acceleration to stay together.
Richard Norte is a good friend of mine. His technology is amazing.
What about non laser simple solar lightsails?
The origami photonic crystal materials science research is interesting in and of itself. Wish there was some more accessible documents about that.