How best to arrange a network of light-focusing satellites closely orbiting the sun

Question

It is the not-too-distant future in an alternate timeline, and humanity has tripled-down on solar power.

We built a network of solar focusing satellites that orbit Sol at close range (so they can capture more sunlight). "Close range" means somewhere between the orbit of Mercury and the solar corona. So, not as close as the Parker probe, but still pretty close. The details of how they focus the light without being incinerated are outside the scope of this question; assume handwavium.

These satellites focus light at a variety of targets distributed throughout the solar system to provide power, all of which have super-advanced solar-conversion tech aboard. The targets that get the most love are, in priority order:

1. Electric-powered "solar trains" on their way to and from Earth's space facilities. Each must be powered continuously for the bulk of its climb and descent. We have five or six of these at present.
2. Large permanent space stations near Jupiter, Ceres, and Saturn, whose batteries need to be recharged every month or so. (The colonies are primarily robotic, hence their outsized consumption.)
3. A giant solar-collection station in orbit around Earth, which charges massive batteries that we then carefully land on Earth. It demands power continuously, and can handle the light from 2 satellites simultaneously. It does not provide all the power Earth needs, but we want it to do more; the limiting factor is the number of batteries we have, and we're building more (subject to material scarcity).

These satellites must be very hardy to survive so close to Sol, so building them is expensive and consumes scarce resources. Thus, we haven't built a bajillion of them; more in the neighborhood of two or three dozen. (Though that number is up for grabs.)

We obviously want each satellite to have line-of-sight on as much of the solar system as possible for as much time as possible. Each satellite has a "firing arc" of 50° from its Solar radius (apologies if I've expressed that weirdly).

So: what kinds of orbits are best-suited for these satellites?

Here are a couple of obvious ideas, which (for starters) I'd appreciate help evaluating:

• one evenly-spaced ring around the sun, in the plane of Earth's orbit
• evenly spaced around the entire surface area of the sun, with orbits calculated to avoid collisions

The biggest objection I can think of to the ring is that many targets will frequently be obscured by planets, leading to blackouts.

The biggest objection to the second pattern is that the limited firing arc means that many satellites would have line-of-sight on nothing for a long time, which means we'd need to build a gazillion satellites (which we haven't), which once again leads to power blackouts.

You might think that Earth can take a blackout because we have other sources of power, but the environment is near the breaking point, and the Terrarium Laws are absolute and totally merciless: anyone who tried to turn on a coal plant for even a few minutes would be summarily executed. If that means a hospital full of babies dies, that is what happens.

The stations and the space trains really can't take a blackout either: the few people on them will die without heat and recycled atmosphere, and if station-keeping goes untended for too long, the station itself could be lost.

If the solution requires a minimum number of satellites higher than what I've proposed, feel free to add them, but then I want some kind of demonstration showing that nothing lower than your number will suffice. Assume my number is 36.

If the firing arc is unworkable, you can change that, too, subject to similar requirements about proof.

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Edit to add: there are no mirrors or lenses anywhere in this system. At least, nothing anybody would recognize as such. I said "handwavium," and that's all you're going to get (in this question). I think this would not evade the problem of etendue, but it should short-circuit a host of other concerns that answerers might get tripped-up by.

Answer 1

The approach is fundamentally flawed. Focusing optics, whether mirrors or lenses (realistically mirrors in applications like this), obey conservation of etendue. The incoming light comes spread across an angular area, and that spread still exists after passing through a focusing element.

It works out such that for a mirror to just equal the sun's intensity, it must appear as large as the sun from the viewpoint of the target it's focused on. Your arrangement with the focusing satellites as close to the sun as possible is the worst possible case, maximizing the required mirror sizes. Equaling the intensity of the sun with this setup would require a mirror the size of the sun. A mirror at the distance of the moon would "only" need to be as large as the moon (which coincidentally has about the same angular size as the sun as seen from Earth). One in geostationary orbit would be about 3500 times smaller than one near the sun, with about 12 million times less surface area.

Placing satellites near the sun only makes sense if the conversion is done at the satellite, and something else used to transport the power to its point of use. Microwave beams would likely be more efficient to generate and collect than lasers, but it's easier to get narrower beams with lasers. And even with these, longer distances mean more transmission losses and larger transmitters/reflectors, and it's unlikely that putting them as close to the sun as possible is the most effective use of resources. There's plenty of room in Earth orbit for big solar collector arrays, and you could easily arrange things so only a small fraction of the arrays could ever be in Earth's or the moon's shadow at any given time.

Answer 2

The biggest obstacle your mirrors will have to go around is the Sun itself, meaning that you would prefer a polar orbit for them, rather than an orbit laying in the ecliptic.

When you are above the poles, you can sweep basically the entire ecliptic plane with your mirror as you please. If you are on the ecliptic, there will always be some portion of the sky blocked by the Sun itself.

Answer 3

Choice of orbit is an interesting topic, but..

How to target high energy interplanetary light beams ?

Precision of the beam will be the main challenge and I even think it's a show stopper.

Sending high energy concentrated light beams has been discussed in the past, when solar satellites in Earth's orbit were considered. Even from 100-400 miles altitude, a tiny direction fault of the beam would impose huge safety risks on the planet surface. Here you propose to send beams across the solar system.. such problems multiply. Even when the alignment error is extremely small, e.g. a beam gets 10e-11 degree misaligned, or your solar sat gets displaced 2 microns, because a dust particle impact. The beam will not hit the intended receiver, it can be miles off at the target.

Also at this scale, take into account any gravitational fields in the path of the light beam (planets, moons) will bend the light beam and result in angle deviations.

Solution

As mentioned above, the easiest orbit (equatorial) has also the disadvantage of not being effective for >50% of the time. imho there is no reflected beam solution at all.

Consider instead: storing the solar energy on the spot, by synthesizing some type of fuel in the process.. and then move that fuel out and distribute it, using robot spacecraft.

Answer 4

Shooting a moving train full of people with concentrated light from a far-off satellite seems like asking for trouble. I am sorry. I am shy at parties, too. Maybe I am too risk averse?

Other ideas

1: Satellites can bounce light to each other. If you really like satellites beaming light, you can have one without a straight shot pass the light to one that does.

2. Venus has lots of sunny real estate. Huge solar collectors orbiting Venus could collect a lot of energy and if that cools down Venus so much the better. Or Mercury - you could have your plant on giant circumplanetary train tracks to crawl along in pace with the long Mercury day.

3. Turn solar energy into fungible, portable energy ASAP. You are charging batteries with it and that is good. Maybe charge those batteries on the satellite or on Venus? Or if you are really digging the cross-space energy beam, shoot it someplace no-one will get hurt when the beam gets frisky. Maybe Luna? The old beam scars of molten moonstuff will be interesting to see for new arrivals.

4. Batteries shmatteries. Batteries are fine but kind of 1970s. I am sure you can come up with more energy-dense near future methods to save solar energy. Different species of antimatter? Something even cooler (hint: make it "quantum"! That means it is cool.) Or retro - the moon has lots of aluminum. Aluminum metal is a great way to store energy and it is very stable.