Show and Tell - New engine exhaust effects

K^2 · March 14, 2021

On 3/11/2021 at 6:56 PM, Redneck said:

those mach/shock diamonds are not easy to recreate. Been trying to get just the right look and feel in blender for starship raptors engines is a challenge

Not bad. It looks like you are using surfaces for everything. Have you tried using volumetrics to smooth it out?

Edit: Wait, is the whole point to try and get it into a mod? Because then, yeah, you might not have access to these game-side. You can fake it with a bunch of planes and a clever shader, but that's a different level kind of work.

Edited March 14, 2021 by K^2

Wubslin · March 30, 2021

Hey, I've got something I want to contribute to this (basically dead) thread.

Keeping the discussion going on realistic exhaust plumes, I want to talk a little bit about what a real project Orion drive plume may resemble. Specifically, I was watching some of the amazing animations over at Hazegrayart's youtube channel, and I noticed something interesting in the visuals which I suppose had read about but not actually ever visualized before:

For those not familiar, the working principal behind an orion drive isn't just to set off a normal nuclear weapon behind a huge pusher plate for propulsion. When the fissioning pit of a nuclear weapon or orion charge releases its energy as hard X-rays shortly after reaching a supercritical state, nearby materials which are not able to be fully ionized (and are therefore opaque to those X-rays) will rapidly absorb the radiation and heat to tremendous temperatures. This causes the heated layer to vaporize and expand, producing a tremendous recoiling force. This principle is used to compress a shell of uranium containing fusion fuel in the "secondary" stage of a thermonuclear weapon, but it's also the main working principle behind the propulsion charges in an orion drive as well as the infamous "Casaba Howitzer" space claymore.

Here a reference diagram for a pure fission or boosted fission orion charge is pictured. There's a U-238 hohlraum of a certain thickness and a channel filled with a light material designed to soften emitted and re-radiated X-rays into a more even haze (modern devices may employ highly classified doped aerogels used in real weapons such as FOGBANK or SEABREEZE) At the end of this channel, is a rather thick disk of more U-238 or in this case, Tungsten. If the small fission weapon in pink is the fuel, then that disk is the propellant. The point of all this typing I'm doing is to say that the real reactive mass which propels an orion vessel is the vaporization of the reaction mass disk and its subsequent impact on the pusher plate. When the fission device goes off and its plutonium pit emits its plateau-shaped curve of X-rays, an incredibly thin layer vaporizes and recoils back, exposing yet more surface underneath to be heated by X-rays. By the time the the expanding pit disassembles and the heat output comes to a conclusion, the first few millimeters or so of the propellant disk have essentially served as rocket fuel to accelerate and launch the bulk of the mass (now an expanding mass similar to a fluid) forward towards the pusher plate.

As shown in the above screenshots, Hazegrayart depicted the look of this expanding mass as a sharp cone protruding in one direction. A section from the Orion drive wikipedia page which references a paper published in 1963 described the distribution as "cigar shaped", but regardless of artistic interpretation it's very cool to see this feature in any form.

Here's really the only animation that I know of so far which shows off the KSP 2 orion drive in action, and so far it looks really good. The way the vaporized charge speeds away in a ring shape like a miniature supernova is accurate to a nuclear weapon going off in space. Clearly, this work has been inspired by test footage from operation Starfish. Although it does appear to be an actual ring (as if it were a mushroom cloud vortex moving through a fluid) and not a spherical shell of expanding gas.

(Image is blue here because the explosion is being looked at through an atmosphere. Note the fluid tendrils reaching out as the explosion presses out into the exceedingly thin atmosphere.)

I guess if there's one thing I want to conclude after writing all of this, I think it would be neat in that animation to see some of those interesting effects present in the final orion exhaust animation. It would be cool to see more of a stand-off distance between the bomb and the pusher plate, as well as some sort of blinding, linear protrusion that instantaneously reaches out from the epicenter of the blast to shower the plate. Some additional linear movement in the opposite direction would also be appropriate. Perhaps that "ring" shape could be turned into a spherical shell, which has a hole punched in it as it moves outward and part of the expanding gases are occluded by the pusher plate or something.

(Links to the videos I mentioned earlier, I really recommend everyone check them out.)

Edited March 30, 2021 by Wubslin