Today, the theme has been creating the launch burst of the main reactor. As I see it, one of the most complicated endeavors in CG. At the end of the day I’m still not satisfied, but I shall stay with what I got. The idea was to render a realistic – or at least, credible – blast, only the effect of a reactor in vacuum is not as spectacular as in the atmosphere. In the end, it’s simply burning matter ejected from the exhaust.
The thrusters of the Space Shuttle firing
As an example, here is the effect you get from the exhaust of the Space Shuttle. Not very impressive. In our case, though, we’re dealing with something much more powerful, which should make a much more dramatic effect: Восход-Д weighs, according to my calculations, about twenty thousand metric tons at launch (i.e.: with the unexpended propellant still in its tanks), which means that, to accelerate it at a fraction of G (say, one tenth of gravity acceleration on the surface of Earth), you need to explode an atom bomb in its engine, with about the power of the Hiroshima bomb, every second. Not something for a half-assed chemical rocket. Soviet technology has made available for the mission nothing less than an open liquid core nuclear thermal rocket, whatever that means, with a thrust of 7 million Newtons.
The reactor of Voskhod-D
To give you an idea, the red speckle in the lower-right corner of the picture on the right is the size of a man. Not that it would be advisable to stand anywhere that near to the reactor – once activated, noone should ever approach it. A portion of the weight the thruster must move is its own weight: the guy alone weights about a hundred metric tons. That sort of parabolic dish on the left is what is called a shadow shield: to avoid loading too much mass by shielding the whole reactor, one only covers the side towards the spacecraft, so that charged particles will be radiated all around but in a shadow cone within which you can stand safely. At least: let’s hope. With the exception of propellant tanks, all of the structures of the spacecraft are contained within this cone, which is 30° in aperture – and that’s the main reason why the HAB is that far away from the main thruster. The reactor will operate at full power for three days in all, providing energy for making the spacecraft system work for the whole duration of the mission. This is called a dual-mode reactor.
The reactor of Voskhod-D firing
Going back to the exhaust, here’s what I managed, after a half day’s job. To whomever might be interested in the how and enjoys things like Blender, it is a cylinder with a texture applied for transparency – the latter created in GIMP by rendering a stip of solid cloud-noise, which has been then stretched, with an overlayed gradient to obtain the falloff transparency towards the end of the plume. The glow behind the exhaust is a vertex with a halo material with high hardness, while the radioactive lighted particles expelled from the combustion chamber (we don’t expect this Soviet build reactor to be much refined in the line of filtering exhaust) are from a circular particle emitter – they’re moved by a wind force field while gravity is set to zero. In short, a mess, and still not very credible. But, as I said, for the time being I’ll keep it as it is.
The source for most of the estimates above (and for a lot of other design tips) is a singular blog, which has gradually earned itself a reputation as an authority in the field: go to Atomic Rockets, if you would like a better in-depth.
