Mirrors, Sun, & Three Body Problem
Reflect Orbital, capturing sunlight from space & what is realistic about the interstellar communication
Siri, play “Mirrors” by Justin Timberlake.
Reflect Orbital, the new Californian startup, is promising to deliver sunlight by building a constellation of in-space mirrors. In the Three Body Problem sci-fi book, there were mirror used for bending reality by an alien civilization. You might ask - is any of this realistic?
Let’s unpack this.
The Three Body Problem
I recently started reading Liu Cixin’s The Three-Body Problem, a timeless sci-fi novel where humanity makes first contact with an alien civilization that is desperate, technologically superior, and willing to manipulate the laws of physics on Earth to slow humans’ progress.
One of the ways they do it in the novel is the “mirror experiment,” where the aliens (Trisolarans) use the Sun as a giant reflective surface to amplify signals. The Trisolarans are able to send radio signals to Earth, and the Sun amplifies them by a factor of one hundred million due to the giant “mirror” orbiting in space.
It’s elegant, and, well, it’s also physically impossible in the way it’s described. The Sun cannot serve as a mirror, because its photosphere and corona absorb and scatter instead of reflecting. There is no optical or radio regime where the Sun behaves like a smooth reflective dish.
What would actually be possible
The Sun can on the other hand act as a gravitational lens. The Sun’s mass bends light, predicted by General Relativity. This is a nice math that could work on paper, but practically would be extremely difficult because it requires placing a transmitter or receiver ~550 AU away - which no one has done yet.
1 AU ≈ 149,597,870 km AU is an Astronomical Unit - it’s the average distance between Earth and the Sun.
This equation is used to compute how much starlight or galaxy light bends around massive objects like stars, black holes, and galaxy clusters:
α^\hat = The deflection angle — how much the path of the light ray bends.
G = The gravitational constant. Sets the strength of gravity in the universe.
M = The mass of the object causing the bending (for the Solar Gravitational Lens, this is the Sun’s mass, M⊙M_\odotM⊙).
c = The speed of light in vacuum.
b = The impact parameter — the closest distance between the light ray and the center of the mass.
For the Sun, b is roughly the solar radius if the ray just grazes the limb.
Reflecting Sunlight From Space: From Znamya to Reflect Orbital
So, the Sun cannot easily be used as a mirror in the sci-fi sense, and noone is trying to use the Sun as a reflective surface - that would be naive.
But humans can reflect sunlight using actual man-made mirrors in orbit. The attempts to use the Sun to get energy, has been going on in history. The Znamya project in the 1990s when a group of Russian scientists and engineers devised a gadget that redirected sunlight lost to space back to Earth.
Reflect Orbital, the few years old US startup, is now trying to scale the idea of redirecting sunlight from orbit by a factor of a thousand.
It plans to use the Sun simply as a photon source - their orbital mirrors should intercept that sunlight and redirect it back to Earth using a network of space-based reflectors. . Their plan: a fleet of 4,000 mirrors, each about the size of a tennis court, designed to “sell sunlight” by bouncing it back to Earth and lighting up the night. Their first test satellite, EARENDIL-1, could launch in 2026. They claim it could support night-time farming, boost solar power output, and illuminate cities by creating controlled patches of reflected sunlight on demand.
Some scientists are sounding the alarm. Astronomers warn the mirrors could drown out stars; wildlife experts worry about ecosystems that depend on darkness; pilots and safety experts raise their own concerns.
Yet despite skepticism, Reflect Orbital raised $20m in Series A funding from Sequoia and Lux Capital, and even presented the idea to the crown prince of Dubai. Whether this is substance or hype will become clearer when the first satellites launch in 2026.
What to take from this? Well, as is my habit, I tend to say that I do not have enough information about the technology behind and the risk of Space Orbital, but I am excited to see how this is going to evolve. In the meantime, I recommend the Three Body Problem book - expect a detailed review soon!
Super great article - really got me thinking. Reflect's plan is a ludicrous meme. I wonder if they can do it. I feel like it might be smarter to get the solar energy up there and send it down by microwave? Feels less dangerous if the beam is focused.