Sol Fights Back

Artwork.

Completed 2019-08-28. Available releases:

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There's a lot going on here, you may like to refer to the annotated version.

This is a frame from an MPEG-encoded camera in the Oort cloud looking toward the Sun, which is surrounded by a Dyson swarm. The Dyson swarm is launching an RKKV by using their combined power output to pump a free-electron laser, which pushes the RKKV by photon pressure.

Each satellite in the swarm is 10000 km², which is far too small to see at this distance, but they fire collected energy to a central platform via UV laser, which causes the solar corona to fluoresce, producing visible beams. The central platform collects the energy and uses it to drive an enormous linear accelerator. Electrons are accelerated, then pinballed through an array of magnets, producing photons at any frequency up through hard X-rays.

This laser beam then hits a spacecraft, which is really more-like a very-long, thin, pole. Because the spacecraft is "only" a few thousand AU from the Sun, the beam diffraction is not very large and the laser must operate at a reduced power to avoid destroying the RKKV. As it gets farther away, beam power will increase to compensate for inverse-square diffraction loss, and the frequency will increase to compensate for Doppler loss and reduce diffraction. For now, though, the beam is firing in the soft X-ray regime, using only 0.1% of the swarm's satellites for power.

In the front of the RKKV, there are many layers of Whipple shielding, replaced continuously from the bottom, and below that, radiation shielding, to guard against the radiation produced when impacting the interstellar medium at relativistic velocities (you can see it is already glowing pink, due primarily to the formation of Hydrogen plasma). The entire thing is 50 times longer than it is wide for the same reason, albeit due to a combination of foreshortening and relativistic effects, it appears less than this.

In the middle, there is a large propellant tank, used only for course correction (realistic high-impulse drives would actually decrease the impact energy if used to propel the craft; expended propellant mass means less boom)—and yes, they do have to be high-impulse because in the RKKV's frame distances and times are contracted: rockets must thrust harder to produce reasonable accelerations in the unaccelerated frame. For reliability over a decades-long or centuries-long flight, this is just a cold-gas thruster or monopropellant.

At the bottom, the laser is hitting the vehicle. To withstand the laser, the pusher plate is 100 meters of bulk matter. Mass doesn't matter much (more mass is just more boom), and the RKKV concept works better at large-scale.

We can't see the propulsion beam, which is soft X-rays, directly, but its secondary effects are pronounced. As it hits the bottom of the spacecraft, it reflects and diffracts. However, since the RKKV is traveling at relativistic speed compared to us, the diffraction introduces to a frequency shift depending on angle. This explains why the green/blue/violet end of the rainbow is visible as a diffraction spike on the spacecraft: the diffraction shifts the laser partially into the visible spectrum.

The X-rays also diffract from the laser itself, producing the enormous hexagonal flare you see on the Sun. The X-rays produce bitflips (pink, green, black, white, and blue artifacts). Because this is MPEG-coded, the Y'CbCr color space is used. In darker regions, bitflips tend to add to the pixel values, producing magenta (higher code-points in the Cb and Cr channels correspond to this hue). In lighter regions, like the solar disk itself, bitflips tend to make pixels darker, explaining the green and black artifacts. We occasionally see blue artifacts corresponding to bitflips on yellow hues (the sun is white, and only looks yellow due to our atmosphere separating out the blue light into the sky, but yellow is still near the peak of the Sun's emission spectrum and due to the filter). I would have thought one would see red/green/blue bitflips instead, because MPEG is on the coding side, but this appears not to be the case: real-world cameras exhibit these sorts of errors. Due to electrical ringing and scanline effects, these artifacts comprise large chunks or lines in the image plane, rather than always just individual pixels, leading to fun, blocky artifacts.

The imaging technician also placed a physical filter (darker rectangle) over most of the Sun so we can resolve detail; however, this increases the frequency of bitflips, since the X-rays produce secondary radiation from Rayleigh scattering, Compton scattering, and the photoelectric effect in the additional material. The filter also fluoresces dimly under the X-rays, directly, producing cyan, which can be seen most-clearly at the edges of the filter.

Artistically, this is pretty straightforward: It's mostly gel pens, with a bit of colored pencil. The sun came out too yellow in the scan, and I spent a while trying to fix it, before concluding that it can plausibly be attributed to the filter. Coming up with a cleaned-up image I didn't hate took a surprisingly long time. I saved the result out with Krita (which didn't crash this time, wow), and resized it down to clean up the scan compression.

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