NASA selects a plan to "swarm" Proxima Centauri with tiny probes
sciencealert.com
sciencealert.com
The article's title is 'NASA Selects a Wild Plan to "Swarm" Proxima Centauri With Thousands of Tiny Probes'
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Strictly speaking at this point it's more of a blue sky proposal than a mostly sketched out plan.
1. Extremely high duty cycle 100 gigawatt laser. (edit: now apparently it's an "array" because someone with a brain mentioned that a 100 gigawatt laser is ludicrous) That's right 7 peak summer output Grand Coulee Dams and 12 Palo Verde nuclear power plants with all reactors operating simultaneously COMBINED would be needed to power this laser.
2. "Swarm" (jfc buzzwords) craft that are currently impossible to create. The swarm behavior including networking, sensors, radio, and command and control do not exist and are impossible at a simple base level when considering RF energy requirements even with far-future theoretical energy harvesting technology.
3. Perfectly-spherical-frictionless-cow-ifying the EXTREMELY REAL effects of space weather. Forget the interstellar medium, these things will be blown out of the beamwidth by the time they reach jupiter's orbit from solar winds alone.
That's not how this stuff works. You would use some sort of large capacitor/battery bank which is charged by a much smaller power draw over a long time, and then dump the energy over a short time.
The laser array currently operating at the National Ignition Facility has a peak output of 500 TW, more than three orders of magnitude higher than the number you called ludicrous. Obviously Starshot would be applying that power for a much longer time interval, and indeed would be a global undertaking dwarfing NIF. But it doesn't need 100GW of dedicated power plants.
> ground-based lasers would then focus a light beam on the crafts' sails to accelerate them one by one to the target speed within 10 minutes, with an average acceleration on the order of 100 km/s2 (10,000 ɡ)
Well damn, then. I missed that when I was reading about it before. https://en.wikipedia.org/wiki/Breakthrough_Starshot
This means that the laser is on most of the time.
If the laser has 70% efficiency, and is on 35% of the time, you need 100 / .7 * .35 = 50GW average (and 100 / .7 = 142GW when lasing). Any storage you have would have to be long term, because you need to lase when the spacecraft is overhead and not at night.
Launching 20 per day over a 10 minute span each is 200 minutes; you still need 12GW average over the day.
And you need an insane amount of storage-- if 12% of the energy comes directly from the power plant, you need to store 53 terajoules, which is about 60,000 tonnes of lithium batteries per daily shot. (It's more than that, because you're power/discharge rate limited, and it's going to wear out that minimum amount of batteries quickly).
No he didn't. I did.
> Launching 20 per day over a 10 minute span each is 200 minutes; you still need 12GW average over the day.
Where are you getting 20/day from? I didn't see it on this OP link or the Wikipedia page. I'd have guessed more like once a week, which is 100 MW. That's a reasonable size for a gas turbine power plant, which seems like an appropriate expenditure for a project like this.
As a point of reference, the entire globe launches something to space every couple days on average.
I know some of the folks involved and they are working on 50 years to launch. It's a long term (multiprong) research project.
I wouldn't call it a scam, I would call it "blue sky" (if it weren't a space project!)
Uh, don't we already have "moonshot" for this kind of endeavor, which the name "starshot" already plays on / speaks to?
I.e. far enough in the future to safely assume all current employees will happily retire. Isn't that brilliant?
But we're ready to start thinking about it. Just like we dreamt about rockets going to the moon decades before we attempted going to the moon.
Post-docs need to write papers. Let them write some about an impossible thought experiment.
If they go past that though…
I had one building inspector tell me that when he found the obvious thing that was obviously obvious, he would then look for the thing trying to be hidden.
Also it's not necessary (or technically, it's actually impossible) to have 100% duly cycle laser for propulsion.
It's definitely a megaproject, but it's not a "scam"
Is this in space or on the ground?
Any optics experts able to chime in?
The smaller the hole the laser light comes out of, the more it spreads.
This is a big, several kilometer phased array, which has an effective hole size of a few kilometers. As a result, divergence is less.
I just recently watched a great video explaining how lithography machines push the limits of what's possible: https://www.youtube.com/watch?v=rdlZ8KYVtPU&t=1151s
Note that the best ASML machines can eke out an improvement on the order of a factor of two at best, not two thousand, which is what would be likely needed to power space probes at light-year distances.
https://en.wikipedia.org/wiki/Gaussian_beam#Beam_waist
the divergence angle is inversely proportional to your aperture diameter
https://en.wikipedia.org/wiki/Airy_disk
in theory by putting a bunch of laser emitters in solar orbit and operating them as a phased array you can make an aperture the size of the solar system. 1.22λ/d at, say, 400nm and 2 astronomical units of diameter is about 1.6 attoradians of divergence; at a radius of 4.3 light years (the distance to proxima centauri) this works out to an airy disk focal point of 66 microns. optical phased array lasers have been demonstrated https://en.wikipedia.org/wiki/Phased-array_optics but nobody knows how to make one out of satellites yet
i've only glanced at the proposal https://arxiv.org/pdf/2309.07061.pdf and they're proposing 4.1-meter-diameter 3.6-gram probes, which would allow you to use a phased array about a million times smaller, about 5 million km, 13 times the distance to the moon. i don't see where they're proposing how they propose to beam 100 gigawatts onto the probes so i don't know if this is their proposal
dispersion, by contrast, which means wavelength-dependent indices of refraction, doesn't affect lasers and doesn't happen in a vacuum; probably the person who mentioned it was using the wrong term by accident and meant divergence
If you put 100 gigawatts on a 4.1 meter diameter very thin reflector, you're going to melt it. That's 10 gigawatts/square meter. Most of the light misses the targets.
> i don't see where they're proposing how they propose to beam 100 gigawatts onto the probes so i don't know if this is their proposal
A phased array on Earth, several kilometers in scale.
> but nobody knows how to make one out of satellites yet
Probably no one ever will make a huge (solar system scale) coherent power transmission system out of satellites, because of the thinned array curse-- https://en.wikipedia.org/wiki/Thinned-array_curse
It would be cool if we made a very large scale telescope, where a sparse array is less of a problem.
Although we would need heavier support structure then. And the risk of micrometeoroids collision will be higher.
The problem is, until we figure out how to stop burning fossil fuels and fix climate change, the amount of spare power we have is actually a large negative number.
“the energy source for a lightsail is photos (which have no mass and move at the speed of light).”
So, it can be powered by memes?
"A swarm whose members are in known spatial positions relative to each other, having state-of-the-art microminiaturized clocks to keep synchrony, can utilize its entire population to communicate with Earth, periodically building up a single short but extremely bright contemporaneous laser pulse from all of them."
The probes can get power from the launch laser.
At least that’s the idea I got from talking to some of these folks last year.
KNIGHT: "This is not good."
If you think this sort of thing is possible you really don’t understand how far it is.
To put it in relative perspective, if we represent the furthest distance humans have ever traveled as 1.3cm then the nearest star is 200 kilometers away.
Of course, the real problem with the analogy is that the fastest you can go 1 cm in this universe is about 8 minutes. So the absolute shortest time it takes you to travel that 2.7km is 4.2 years. That's a few hundred cm per year. But in reality the best we could possibly do is a few tens of cm per year (e.g. c/10), and even that's in the realm of science fiction.
On the bright side, humanity has the Solar system all to itself with wonderful natural barriers to invasion and conquest. So we have time to figure out how to not blow ourselves up and/or stop dismantling our life support system to make Ikea furniture.
1 cm x 60,000 = 600 meters
Which is less than 0.5% of the distance to Alpha Centauri (“200 km” in the analogy, 25 trillion miles in real units)
Edit: a neighboring comment pointed out that on this scale of distance to moon ~= 1 cm, the Alpha Centauri system is more like 1000 km away. So voyager is less than 0.1% of the way.
Without that natural assistance, humans don't have the ability to leave the solar system - we just can't build a rocket powerful enough.
The Jupiter launch window opportunity comes every 13 months so we can do that whenever we want. And we can launch rockets directly out of the solar system if we want; New Horizons had a backup plan of launching direct to Pluto if it had been delayed and missed the Jupiter-Pluto alignment.
That all said, the planetary slingshots aren't nearly enough to cross interstellar distances in a timespan measurable in human generations. We want something like 5% of the speed of light for that, where Voyager is going 0.005%.
It seems like the alignment you refer to inspired the launch of Voyager 1 and 2 because they could visit so many planets at one time, and indeed it did slingshot them at quite some speed. However newer launches have reached similar speeds, and will escape the solar system due to improvements in launch technology.
Moon: 238,900 miles --> 1.3 cm or 0.00 km
(This defines the scale as 0.0000054416073670992 cm / mile.)
Voyager 2: 12,000,000,000 miles --> 65,299.0 cm or 0.65 km
Proxima: 25,000,000,000,000 miles --> 136,040,184.2 cm or 1,360.40 km
The kuiper belt is outside the solar system and then there is the shell of the Oort Cloud that Voyager won't pass through for ages. So it's been decades and we haven't even truly sent anything outside the solar system.
This is all assuming I remembered the terms correctly. Maybe someone who knows this field can comment. Point being getting to another star would take a lot of time :)
Interstellar space is big.
The ISS (1998) travels at 17,400 mph.
There's abundant precedent of accelerating to high speeds in space, where there's no friction with an atmosphere that slows you down and where you can use gravitational fields as sling shots.
0.3c might seem high but if you keep accelerating you will eventually reach that speed.
But there's zero precedent for slowing down once you get somewhere (in 10,000 years)
Which means that a ground station can keep beaming light at them causing them to accelerate.
However the point remains that it’s simply impossible.
My original analogy of 1.3cm versus 200km was wrong according to another commenter in fact it’s more like 1.3cm versus 1,300km - so vastly impossibly far out of the range of anything that could be conceivably be done under any plausible scenario.
Everything is impossible until it's done.
It’s not simply a country we haven’t found yet with a six month sailing journey.
The six month sailing journey sounds waaaaay more ominous.
Imagine this was Proxima Centauri doing the same mission on our solar system. Assuming that some of the swarm was on target enough to go thru the inner solar system:
Mars is ~13 light minutes from the sun. So double that for the whole diameter of the orbit, 26 light minutes. At .2c that's 130 minutes total transit time (less really unless it passes really close to the sun). So probably less than 2 hours total in the inner solar system. And that's assuming you can hit that small of a target from 4.25 light years away.
Light distance Sun-Saturn is 1.3 hours. 2.6 diameter. 13 hour transit time for most of the solar system.
You don't know where the planets actually are going to be, or were to point a camera or any other instrument, except the sun. And you have probes that weigh grams.
That's a tough problem, without considering the laser.
But I like thinking about it.
SpinLaunch - Developing a system that spins a payload at ultra-high speeds inside a vacuum chamber, then launches it into the sky using stored rotational energy. They claim it could launch small satellites for a fraction of the cost of traditional rockets.
Launchloop - Proposed concept of using a powerful electromagnetic accelerator called a Launchloop to fling payloads into space. It would use low-cost electricity rather than expensive rocket fuel. Still in early feasibility stage.
TAES - Developing a space trebuchet mechanism that uses centrifugal force similar to how a trebuchet launches projectiles. They're aiming to launch 6U CubeSats (10x10x30cm) to Low Earth Orbit for a relatively low cost per launch.
Rocket Lab - Makes small Electron rockets for launching 150kg payloads to LEO. Over 20 successful launches to date and helping enable more frequent smallsat launches.
Virgin Orbit - Uses a modified Boeing 747 to carry a 2-stage LauncherOne rocket to altitude, then releases and ignites to place payloads in orbit. Aims for frequent, affordable smallsat launches.
It is because it’s about speed, not altitude. Witch Spinlaunch, they plan to laumch around 5000kmph, and you need a speed of around 25000kmph to reach orbit.
In other words, they would need to use their setup to launch a rocket of a size of 1/2-3/4 of size of a falcon1 to get into orbit, and even then, unless they land the second stage, they will come out far more expensive than what SpaceX is doing.
The tech may work on moon, but even on Moon a different solution - similar to maglev - may be better, bacause there would be no issues with crazy centrifugal forces.
Anything launching from earth will require some sort of a rocket fuel (or some new laws of physics), because even if you managed to launch at the speed of 25000km/h from the ground, the payload would slow down before it left the atmosphere.
Project HARP was shooting 16 inch artillery shells at 2100m/s, and they reached 180km altitude, i.e. the atmosphere was slowing it down only for 15%. While higher speeds cause higher losses, the larger payloads would benefit from decreasing surface-to-volume ratio, plus if one launches from say a plateau in Andes where atmosphere is aleady thinner, I think the losses will be similar for large payloads at speeds close to orbital.
And if you're building a fully reusable rocket system, then neither size nor fuel matter as much as the simplicity and reliability of launch and landing. And here traditional rocket systems will win on Earth.
On Mars or Moon, with less gravity and atmosphere these systems will be more feasible though since they can possibly launch into orbit without rocket boosters.
According to a quick search, the asteroid that killed the dinosaurs had about 300 zettajoules of energy. 1 zettajoule is 1,000,000,000,000 gigajoules.
So it would be on the order of a trillionth as much energy as the Chicxulub impact.
I love Breakthrough Starshot but this is an interesting risk to think about.
Should we similarly be afraid of making radio broadcasts lest our intended recipients interpret our beaming of energy as a hostile act? A somewhat similar concept is actually mentioned in the novel Blindsight. You could even go full Dark Forest and say that we're a threat simply by existing all the while brazenly advertising our presence through the oxygen in the atmosphere.
I also giggle at the idea of a highly advanced civilization arriving at earth to tell us humans exactly what they think of someone firing a relativistic shotgun at their planet. Even if it was only loaded with bird shot.
On Earth, we get about 1kW/m2 from the sun. So 100GW is what we get from a 100km2 patch of land. So, all the energy from the system is enough to turn night into day for an area the size of a medium sized city.
Of course, it is not a continuous beam, so it would be more like an explosion. It would be nuke-sized if it wasn't for losses, but obviously, there would be losses. But the thing is, we are not destroying planets with the energies we get from a 100GW laser.
Edit: Also, at these speeds, the probe is a bunch of high energy particles causing nuclear reactions along their way, things like chemical bonds don't make much sense. There is an XKCD What-If about relativistic object hitting earth. Not the same scale, but it may give some idea of the physics involved. https://what-if.xkcd.com/20/
I don't think people realize how mind-bogglingly, incomprehensibly HUGE space is. It's BIG. Like think of the biggest thing you can comprehend, and it's not even the size of an atom in comparison to even "short" distances in space.
>On the other hand I can't understand the propulsion mechanism.
Yes, i also think the laser propulsion isn't the one to go, at least with the current tech. With current tech my bet would be on ion drive https://news.ycombinator.com/item?id=38445404