Using L1 Lagrange point to block energy from the sun?

Question

Working on a near future fantasy world and am trying to work on a mechanism for magic being discovered/unlocked. My current thought, which is what I'm trying to get a feasibility check on, is that all magical energy in the solar system comes from Sol. In the far past a magic using civilization placed an object/device at the L1 lagrange point that somehow absorbs or reflects all of the magical energy that would have flowed to/through the Earth. Their reasons for doing this an unknown since almost all traces of the time before magic was sealed has been lost. The only things that survive are the occasional artifact or obscure piece of text that only now makes sense in the context of magic actually existing.

So my question is around what would be involved with placing an object at L1 and how/when would humans have discovered and/or accidentally destroyed it?

The issues that I'm aware of is that L1 is a naturally unstable point, any drift will cause the object to accelerate away from the point, either toward the Earth or Sol.

Another issue I see that will need to be addressed is that the massive amount of energy that this object is reflecting or absorbing would be exerting a force propelling it away from Sol so the object would need to be somehow using the incoming energy to keep itself in position.

So my question is about how these issues may be addressed and if there are any other issues that I'm not seeing that need to be addressed.

Answer 1

Such station-keeping will be easy if you

Put the Structure Farther Than L1

If a strong wind is knocking you off of a hilltop, you move downhill into the wind a little bit and gravity will help counter the force. Simply move it a bit closer to the sun, just enough that the sun's inward gravity and outward radiation pressure reach equilibrium. Adjustments will require only minimal thrust, easily powered by absorbing some radiation instead of reflecting it all.

Now, for some other fun problems!

It Must Be Flexible and Super-Light

A rigid structure would require incredible amounts of handwavium. It's gonna have to be wider than the earth to fully block it; across that distance, any conceivable material would be shredded in moments. A sheet-like material would have to be so thin and stretchy that it might stretch credibility, so I'd recommend something more like a huge swarm of small reflector devices. Either way, that much mass is going to have non-trivial self-gravity to adjust against, but it still seems feasible.

It Can't Be Flat

A flat disc would be closer to the sun in the center, and the continual stress would require even more handwavium. It probably wouldn't be a spherical segment either; keep in mind that L1 is a Saddle Point. Objects are pulled inward in lateral directions but outward in forward and reverse, so I'm wildly guessing that it would be more conical at some radii. Regardless, the outer reaches will have less stability and require more station-keeping.

Small-Body Collisions

It's gonna get pummeled by dust and micro-asteroids, and maybe even the occasional larger asteroid or comet. That requires self-repair, and redundancy to avoid temporary breaches.

Remember the Penumbra

Because the sun is not a point light source, leaving earth would initially only get you into the penumbra, so the effects would increase gradually with distance.

Solar Dynamism

The sun is super active, and it has no solid surface. It has several layers, each with interesting properties, and its atmosphere is quite large. Also it's output varies quite a lot, and from time to time it sends out massive prominences and solar flares. The builders would've chosen a reasonably safe diameter to keep things quiet most of the time, but I'd imagine that occasional major solar events might temporarily increase magical activity on earth. Similarly, they had to pick a margin of acceptable failure from damage, so perhaps a catastrophic damage event could make things get interesting as well!

Alternatively, photons aren't the sun's only output...

The Magic Stuff (Magicons?) Could Be More Like Electrons

The sun's powerful donut-shaped magnetic field pumps out a ton of charged particles, which would be roasting us if not for the earth's magnetism deflecting them. An object with a strong magnetic field can deflect particles in an area much larger than itself. Just a thought!

Answer 2

I think there's already a lot of knowledge in the comments, but for the sake of an answer here goes:

There Are Some Issues With Stability

As you mention L1 is unstable, so station keeping is required. You also assume your object experiences a force from solar radiation pressure (SRP), so it will require additional thrust/complexity in station keeping. If we assume your object is not magical (can only humans use magic?), then it will need some sort of propellant to do station keeping. Technology such as solar sails would be available to a civilization as complex as the one you suggest, but would not work to provide force to counter SRP.

So the object will require actual reaction mass, leaving a number of possibilities. We can subdivide this into to broad categories of chemical propulsion and electromagnetic propulsion. The former describes rocket engines that use combustible fuel to expel reaction mass, and the latter describes engines that use electrical fields to expel reaction mass. Avoiding the math, I am going to say your object will do better with electromagnetic propulsion. The specific impulse (equates to efficiency) of these types of systems is much higher and thus would require less propellant for the same duration of station keeping. Plus the object is absorbing enough energy from the sun to power this indefinitely. Of course you could use nuclear reactors or some such method if this is more desirable. Also note ion thrusters are currently used for station keeping, among other things.

So When Will the Object be Discovered?

1. The station keeping will require propellant if my assumptions hold. Eventually your device will run out of propellant and magic will be unleashed upon the Earth. It is also possible that someone will spot it once it moves from L1, but observing objects inside Earth's orbit is notoriously difficult due to the fact that there is a giant fusion ball in the background.
2. Someone will venture outside the shadow of the shade. Is the moon within the shadow? If not, one of the 24 Apollo astronauts who travelled beyond low Earth orbit may have realized they suddenly had special abilities which promptly vanished upon returning to Earth. Of course they might assume it had something to do with the moon itself, but if it were noticed there's a good chance the United States (remember this is the cold war) would work hard to track down the effect.
3. There are quite a few science missions that have operated at or near L1. There are four operating in that region at present. The first was in 1983. So even if someone had not pointed any instruments at L1 prior (unlikely but hard to say what they would have seen/not seen), the device would have likely been discovered by science missions. This could have happened due to sensors, gravitational perturbations, or a direct collision.

Latest Possible Discovery

Even if the device has enough propellant, has a shadow that covers the entire Earth-moon system, and is not spotted by any science missions, humans will eventually venture into deep space. NASA says this will be in the 2030s but there is a fair chance it could be later. Serious domestic conflict on Earth could certainly prolong the wait. However, this is your hard cutoff. Once humans travel outside the shadow, the cat will be out of the bag.

Using the propulsion issue (could run out at any time) and the deep space missions (could potentially be delayed indefinitely) as minimum and maximum cutoffs, you really don't have to bracket the discovery date. It is up to the narrative. However, to be believable, the device would likely be discovered sometime in the 20th century.

Answer 3

The magic civilization was not trying to put the Absorber there. They were trying to throw it into the Sun.

The thing at the Lagrange point is sentient, and magical. When it was on Earth it caused all kinds of trouble absorbing magic. The ancient civilization decided to get rid of it through the time honored technique of throwing it into the sun.

The plan backfired. Rather than continue to the sun, the Absorber wound up at L1. The flow of magic traps it there, like flowing air will trap a ball within its stream. The magic flow stabilizes the Absorber against orbital decay.

It is a good place for absorbing magic which it does, more than it ever could on Earth. Rather than a focal disruption it disrupted the entirety of magic on Earth, causing the fall of that ancient civilization.

The Absorber has been there a long time, trapped. It has been alone for a long time, staring at the stars, soaking up magic, to the point where it has become a sort of deranged demigod.

Answer 4

I feel like you're overthinking this.

No real issues with stability

Since this object was made by an advanced civilization sufficiently advanced for its technology to be indistinguishable from magic even without the fact of it being magic, fuel to keep its position is not at all a concern. Its bigger concern is dealing with all of the fuel it's getting.

This object is in the path of all of the magical energy coming from the sun. It's in the path of all of the light, solar wind, and solar flares coming from the sun. It therefore has all of the energy it needs to do whatever it does, including keeping itself between the sun and the earth in a fairly stable fashion, and warping cosmic winds and solar flares around it. It needs to know where the earth is to manage this, so it would know what directions would be safe to vent its excess energy - I'm thinking basically four directions, in a square arrangement, maybe around a 45 degree offset from Earth.

Of course, it can't take a noticeable portion of the solar energy heading to Earth or we could recognize it was there based on the differences in the apparent energies received by Earth and by the other planets - unless there's one of these things hiding in their L1 spots as well. But even taking an even 0.00001% of the energy from the sun would be pretty huge. And, of course, the amount of magic energy that it's blocking that we know nothing of is entirely up to you - but realistically speaking, you're probably underestimating what it would be by a large margin.

Think about how much energy you would imagine a human would have access to, unfettered by this device, from standing under the sun at noon, a single shaft of power hitting them and the square meter around them. In two dimensions, Earth has 194 million square meters of surface area pointed at the sun. I chose noon to be able to discount the incident angle. But there's also energy lost due to passing through the atmosphere, if that matters, or passing through space between L1 and Earth, if that matters. So we're talking something in excess of 194 million times what a mage could do with one square meter of power.

Except it's more than that, because it didn't show up during our manned space exploration so far, so it's covering the moon, too. Expanding that out to a disc large enough to cover both is probably not appropriate, because there's really no need to cover out of the plane of the moon's orbit. Using a rectangle area, I think it's something over 4 quadrillion times that reference mage.

Discovery

Such an object would definitely be discovered if/when earth deployed a space craft that intersected one of the beams of diverted power. If those beams were angled above and below the plane of Earth's orbit, it would seem that would be an unlikely circumstance. This is probably a good thing, because those beams would probably be highly destructive streams of overwhelming power.

It would probably also be discovered if we witnessed anything else encountering those beams. We're talking about at least 48 million times the power of the reference mage mentioned above would have, minus a quarter of whatever the device needed to use itself. This would probably destroy anything that it hit from too short of a range, unless it was specifically made to hit it.

But it wouldn't take that. As Ben mentioned, exploring outside of the shadow produced by the device, any astronauts would be exposed to the magic that it normally shields them from. After they noticed that there was magic in space - that there were long-term effects from what they did out there, so it clearly wasn't them just going insane - it would just be a matter of time until they investigated enough to find the answer.

It wouldn't necessarily be identified just because of an unmanned mission to L1 or beyond. Assuming space wizard technology, it could be slightly out of phase with the rest of matter, such that any such devices could pass harmlessly through it. But any life sophisticated enough to harness the magic leaving the shadow of its effects would probably have a noticeable consequence.

Answer 5

You could use the "magic pressure" from deflecting the magic as a station-keeping mechanism. Basically your device will be placed some amount Sol-ward of L1, such that the outward pressure from the deflection of magic particles will counterbalance the increased gravitational pull of Sol. Then you have control loop that adjusts the angle of deflection in response to any changes in orbit - if you move too far out, then you deflect the magic out to the sides more (doing so to opposite sides will result in the momentum imparted from the deflected magicles to cancel out,) reducing the pressure and allowing the device to fall inwards. Conversely if you move too far in, you deflect the magic more directly back at the sun, increasing the magic pressure and pushing you back out.