Proposal: Pushing Light Around

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DataPacRat DataPacRat's picture
Proposal: Pushing Light Around

Putting together a couple of ideas plucked from a couple of other SF settings, and some RL proposals...

Gatecrashing p155 lists 1.5 square meters of solar panels, producing 1 kW of power under Earth-equivalent solar radiation, as having a cost of Trivial, roughly a cost of 50. I'm going to posit that a package of solar panels a hundred times the size, producing 100 kW, will have a cost of 5000, or High.

Around Jupiter's orbit, solar radiation is 1/25th as intense as around Earth, so the nominal 100 kW panel will only produce 4 kW. A hive with a protean swarm could produce said 4 kW in roughly 4 hours, which gives us a neat 1 kW per hour production rate. A single hive could produce enough panelling for, say, 60 MW, in about 7 years.

I'm also going to propose hives with protean swarms for three or four other gadgets: high-powered lasers capable of using all that solar power; the small glass granules required to form an "aerosol lens" ( https://www.nasa.gov/sites/default/files/files/Quadrelli_2012_PhI_OrbitingRainbows_.pdf ); some relatively low-powered lasers which can create optical interference patterns that control the position of those beads, allowing nearby lenses to be reshaped and re-aimed; and whatever cheap-and-dirty method can be harnessed to turn high-powered laser-light into propulsive force, whether that be a simple pile of ablative plastic to an out-and-out lightsail (in order to haul piles of those glass beads and a few low-power lasers around the system).

By my calculations, a cloud of glass beads massing around 40 tons will have a radius of around 200 meters, and can focus 60 megawatts of laser-power up to 0.2 AU away. Crank that up to a cloud of 600 tons, with a radius of 750 meters, and the range increases to 3 AU, and even larger clouds with larger ranges are possible... and with appropriate pre-planning and signalling, one cloud can collimate the beam from another, allowing such clouds to be used to direct laser-power across the whole solar system, if they're spread out widely enough.

Such power could be used to accelerate laser-sails, or to shove other kinds of rockets around if they've been built to take advantage of it... or, if there is a low-powered laser and a cloud nearby any given target, to direct multiple megawatts of power onto it. (Ie, http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Laser_Cannon--Combat_Mirror .)

All of this tech seems to be well within what's possible with EP's tech level. Which means that any individual who can afford about 30,000 credits worth of protean hives and swarms, and who's willing to wait about a decade (or who's willing to invest more in order to speed up production), should be able to dump multiple megawatts of laser power onto any target they can identify, in roughly anywhere in the inner system. Which has both useful civilian applications as well as military ones. Larger organizations, such as major militaries, should be able to assemble the infrastructure to route even larger amounts of laser-power around the system in much shorter times.

Which brings up the question: Why is there no sign of any of this being done in EP's Solar System? For example, the Jovian military could invest in many of its ships carrying around, say, 20 tons of the glass-beads and appropriate control-lasers, and enough qubits to request laser-power to be routed to their location with minimal light-speed lag, allowing them to dump immense amounts of destruction on their enemies without having to carry around the incredibly massy multi-megawatt lasers, capacitors, and other such gear.

I can make some fumbling guesses that provide better answers than 'the authours didn't think of it' :), like post-Fall nervousness about weaponry on that scale, but I haven't come up with a good idea why /nobody/ would have thrown together even modest-scale versions of this system. Maybe you've got better ideas than I've thought up so far? Or maybe I should try putting together some plot ideas around the construction and use such systems, and the people and politics surrounding them?

What do you think?

Thank you for your time,


Trappedinwikipedia Trappedinwikipedia's picture
Because lasers diffuse way to

Nah, never mind, post your calculations, I'm not going to do them.

DataPacRat DataPacRat's picture
Trappedinwikipedia wrote

Trappedinwikipedia wrote:
Because lasers diffuse way to quickly to deliver much power at long range, and no amount of perfect lenses can prevent light from self-interfering and spreading out. That keeps ranges pretty brutally short by solar system standards.

Except that that simply doesn't match up with the real-world physics. You can find the relevant equations at http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Laser_Cannon , and plug in the radii of the aerosol-cloud lenses and multi-megawatt laser powers to end up with the individual ranges I mentioned above. Which simple optics lets us then use a collimator to refocus and relay. (I have a memory that such lenses would have a transmission efficiency of roughly 96%, but can't find a definitive reference to that offhand.)

Quote:
Lasers are also not very efficient, and those number neglect the incredibly large radiators which would be needed, though I wouldn't expect them to be a large obstacle.

Eh, free-electron lasers can probably have efficiencies of over 40%, solar-pumped excimer lasers maybe 20%, quantum cascade lasers 30%, and so on. There's still lots of ways to arrange for multi-megawatt levels of heat to be radiated into the void at the source asteroids, such as droplet radiators or various kinds of heat exchangers and coolants pumping heat to standard solid radiator panels or more complicated Rube-Goldbergian setups. If this has to be treated separately from the heavy lasers themselves, we'd just have to use an extra hive-and-swarm to build piles of radiators, which doesn't significantly alter the overall project.

Thank you for your time,


DataPacRat DataPacRat's picture
Trappedinwikipedia wrote:Nah,

Trappedinwikipedia wrote:
Nah, never mind, post your calculations, I'm not going to do them.

(Didn't see you replace your post with an edit for a while.)

If you're not interested in the math, then I don't think my throwing more numbers in your direction would be any more interesting.

So a different approach: If it's possible to shoot off enough laser energy at a lightsail to do any measurable good - which, in EP, seems to be perfectly possible - then it's also possible to swap out the lightsail for an aerosol lens, and direct that laser-energy to other purposes, such as smelting or artillery. With what seems to be a relatively modest investment in infrastructure, then in parallel with today's electric-grid utilities, it should be possible to put together a "photonic grid", with fresh laser-energy constantly added, a certain amount of reserve photons "stored" by cycling around in transit at lightspeed, and various amounts of said photons available to be dumped on any given target at request.

The default EP setting seems to lack such a piece of infrastructure as of 10 AF. Given how easy a photonic-grid can be to create, it seems plausible that such a utility was being utilized pre-Fall, and destroyed during the Fall to prevent Titans and Exsurgents from causing too much further damage with it (possibly after it was used to cause some damage). However, it seems possible for an interested GM to introduce a series of sub-plots based around the reconstruction of some version(s) the grid, as various factions like and dislike the idea, and others want to nudge one, some, or all grids to more closely line up with their values.

I'm hoping some of the fine readers here might have some ideas on particular factions' viewpoints here. I'm a decent enough hand at technical details, but I'm far from an expert on the particulars of EP's political makeup.

Thank you for your time,


ThatWhichNeverWas ThatWhichNeverWas's picture
The engineering is fine. However...

Long story short - you can better results for less effort.

For propulsion, you're competing with Plasma and Fusion engines, and for interplanatary travel these have both the deltaV and thrust to get anywhere in the system pretty quickly at low cost, and pretty much everything you're moving via ship is something you want to move at a decent rate.

Militarilly speaking, the first problem is that lasers simply aren't that great as weapons - they're not great thermally, have issues with focussing, and of limited use against anything more than a couple of light-seconds away, and are pretty easy to defend against - even if you're only getting 40% of the power back as waste heat, you might only be putting 1% or less into the target.
They're great for point defence and against micrometeorites, but that's it.
And again, you can just plug your laser into your reactor and have a comperable beam without the fuss.

In the past we've had to compensate for weaknesses, finding quick solutions that only benefit a few.
But what if we never need to feel weak or morally conflicted again?

DataPacRat DataPacRat's picture
ThatWhichNeverWas wrote:Long

ThatWhichNeverWas wrote:
Long story short - you can better results for less effort.

For propulsion, you're competing with Plasma and Fusion engines, and for interplanatary travel these have both the deltaV and thrust to get anywhere in the system pretty quickly at low cost, and pretty much everything you're moving via ship is something you want to move at a decent rate.

Militarilly speaking, the first problem is that lasers simply aren't that great as weapons - they're not great thermally, have issues with focussing, and of limited use against anything more than a couple of light-seconds away, and are pretty easy to defend against - even if you're only getting 40% of the power back as waste heat, you might only be putting 1% or less into the target.
They're great for point defence and against micrometeorites, but that's it.

For the sake of all our sanity, I'm going to suggest that we pretend we've rehashed the longstanding missile-vs-laser debate and mostly ended up with the opinions we started with. :)

Quote:
And again, you can just plug your laser into your reactor and have a comperable beam without the fuss.

After doing some thinking and considering, my current thoughts are to tie this idea into the BearMail plotlines I posted elsethread a month-ish ago. Specifically as the climax of the BearMail subplots. Something along the lines of:

The LoadBears who work within Firewall have become reasonably impressed with the PCs' competence, even if there have been some disagreements about particulars. They now choose to consult with the PCs about a long-term project that's about to enter a new phase. If the PCs have previously managed to hack BearMail files, they may have come across some info on 'The Heliograph Project', involving solar panels and lasers; the FireWall LoadBears now offer the PCs more data on said project, and its several purposes. (Insert tech-specs on aerosol lenses, etc, here.) The official public BearMail corporate line on the project is that LoadBear interplanetary couriers can get extra delta-v from a given amount of propellant by using reverse bremsstrahlung trickery, which basically means shooting the couriers with lasers. A side-project of this project will involve offering a new service, in which customers can bid against each other for X megawatts of laser sent to Y coordinates, with BearMail itself bidding on laser-time for its couriers to maximize market efficiency. The pilot project will have relatively limited wattage, with perhaps 60 megawatts to be divvied up amongst all participants.

What's not going to be mentioned quite so publicly is that the LoadBears plan on buying a lot of their beam-time to send various courier-like craft off into the extreme distant reaches of the solar system, getting to at least 550 AU as fast as possible, in a wide variety of directions where nothing can be found. These craft are planned to use the sun's gravity to focus light from nearby stars, allowing for incredible amounts of detail to be learned about them and their planetary systems; and, if anyone ever makes it to one of those stars, to allow for communication using staggeringly minuscule amounts of power. (The phrase 'BearMail InterStellar' may be dropped, for the PC's amusement.)

What the Firewall Loadbears tell the PCs is that neither of these is the /real/ purpose of Heliograph. The real purpose - or, at least, the level of the plan claimed to be the most important one - is to use the whole project as bait to find out who is both willing and able to destroy infrastructure projects that are of potential benefit to all transhumanity. In other words, from a purely selfish perspective, to identify a set of targets who are most likely to be an impediment to the LoadBears' (and transhumanity's) long-term survival. A series of minor opponents are expected, those who will argue about the risks involved or whether the economics work or whether it infringes on some polity's sovereignty - these opponents, the LoadBears intend to deal with through standard corporate shenanigans (though preparing to deal with such issues will provide a handy cover story for sending the PCs around the system). But takeover attempts by would-be posthumans, or seed AGIs looking for a quick boost to their ramp-ups, or unexpectable coordinated action by egos infected with the exsurgent virus, or Titan malware that can somehow crack through one-time pads, or any number of less likely groups might be drawn into open view, potentially allowing for several of Firewall's servers to gain valuable intel - or even to directly act against them.

So... does that sound like the sort of story framework that a GM and players might enjoy? Any improvements come to your mind?

Thank you for your time,


ThatWhichNeverWas ThatWhichNeverWas's picture
Missiles or Lasers? Why not both?

DataPacRat wrote:
For the sake of all our sanity, I'm going to suggest that we pretend we've rehashed the longstanding missile-vs-laser debate and mostly ended up with the opinions we started with. :)

But it's so much fun! :P
Ah well. There's still the Catch-22 that if you want to propel ships by shooting them with high-intensity lasers, then the ships by definition can withstand being shot by high-intensity lasers.
Worse, maximising efficiency means the laser wants to use a wavelength that's as easy to reflect as possible, and the ships want to be able to handle as strong a laser as possible.

It's also worth noting that you're getting a maximum of about 0.007 Newtons of force per Megawatt. Acceleration via laser is slow.

DataPacRat wrote:
These craft are planned to use the sun's gravity to focus light from nearby stars, allowing for incredible amounts of detail to be learned about them and their planetary systems; and, if anyone ever makes it to one of those stars, to allow for communication using staggeringly minuscule amounts of power. (The phrase 'BearMail InterStellar' may be dropped, for the PC's amusement.)

What the Firewall Loadbears tell the PCs is that neither of these is the /real/ purpose of Heliograph. The real purpose - or, at least, the level of the plan claimed to be the most important one - is to use the whole project as bait to find out who is both willing and able to destroy infrastructure projects that are of potential benefit to all transhumanity. In other words, from a purely selfish perspective, to identify a set of targets who are most likely to be an impediment to the LoadBears' (and transhumanity's) long-term survival.

-(Snip)-

So... does that sound like the sort of story framework that a GM and players might enjoy? Any improvements come to your mind?


Looks like a pretty solid premise – the only suggestions I have are thematic tweaks.

Your proposed network might not be great for propulsion or the military, but it would be fantastic as a power and communications grid.
Beyond Saturn in particular, the availability of laser-beamed power would mean more security and a lower draw on resources where replenishment isn't a given.
This can also be used to slightly alter the reasoning behind your BearMail ships – they use beamed power to reduce on-board power generation and storage requirements, thus reducing total mass.
The potential thrust is simply a nice bonus.

Secondly, I don't think you could use Sol's gravity as a lens because it's too weak. However, it's also unnecessary in your setup; you can use the same principles for your bead-lens satellites to create telescopes with ridiculously large apertures, and if you have a few thousand working in concert in orbits going out to the Oort cloud you can create a single array with an aperture a light-year across.

Of course, they need a source of power and a high-bandwidth communications link.
I wonder where they could get that from :D

In the past we've had to compensate for weaknesses, finding quick solutions that only benefit a few.
But what if we never need to feel weak or morally conflicted again?

DataPacRat DataPacRat's picture
ThatWhichNeverWas wrote

ThatWhichNeverWas wrote:
Secondly, I don't think you could use Sol's gravity as a lens because it's too weak.

Busy today, better reply tomorrow, but I've got a relevant link on this point: https://www.centauri-dreams.org/?p=785 .

Thank you for your time,


Trappedinwikipedia Trappedinwikipedia's picture
DataPacRat wrote:

DataPacRat wrote:

If you're not interested in the math, then I don't think my throwing more numbers in your direction would be any more interesting.

I'm specifically not interested in doing my own math, getting different numbers, and then you posting your own which contradict. I don't really like trying to argue for or against calculations I can't see.

I also had time to read through the NASA paper properly, it's pretty neat. BUT, it never talks about using the lenses as a laser medium, and seeing as it's an exceptionally fragile (if hard to meaningfully damage physically) structure I'm very doubtful that a dust-cloud lens could be used to transmit a laser more powerful than the lasers pinning the cloud. I think it would push it out of alignment and essentially "shatter" the lens. It's my guess that your calculations are treating it as analogous to a solid lens, which I suspect is incorrect. (I did treat it that way and got results I thought were fairly similar, but without seeing the calculations idk). It's possible a really, really large cloud could reduce the intensity of the laser enough, I haven't tried to figure out how much bigger it would need to be, and there's probably some other issues hiding in there.

The authors even state: "However, it is a fact that the dynamics, controllable properties, and consequent benefits of engineering and manipulating granular matter such as dust grains, powders, and aerosols is poorly known to the space exploration community." so I would be really skeptical of any use they didn't spell out precisely.