The update adds new tools, simulation options and camera types, extends the tutorials, improves the GPU solver, and introduces a brand new type of simulation - stellar evolution.
Stellar evolution simulation
A basic evolution of stars has been added in the previous update, implemented as a simple parametric relation that changes the stellar radius and surface temperature based on its initial mass and age.
This update adds a new detailed solver of stellar evolution. The solver can be enabled by turning on ‘Solve stellar structure’ in the simulation settings. When using this solver, SpaceSim solves the equations of stellar structure and calculates radial profiles of pressure, density, temperature, nuclear fusion rate, etc. The state of the star changes over time, driven by changes in composition - fusion of hydrogen into helium due to the proton-proton and CNO cycles. You can use the detailed solver to (semi-)accurately calculate the core pressure and density of stars, luminosity and surface temperature, and locations of convective zones.
Demonstration of stellar evolution for stars of various masses.
Note that the stellar evolution solver is by no means finished. The evolution currently ends at the end of the main sequence, for a number of reasons outlined in the previous blog post. The initial state of the star needs to match the expected solution, otherwise, the solver will fail to converge. Many aspects of the physical model that can affect evolution are either approximated or missing entirely (individual reaction networks, Kelvin-Helmholtz contraction, accurate model of stellar atmosphere, overshooting, rotation, …).
Supernovae & Kilonovae
When a rigid (non-deformable) star reaches the end of its life, it now explodes as a supernova. The explosion spawns a large number of massless particles, provided the star is massive enough (the mass limit can be set in the simulation settings and defaults to the Chandrasekhar limit). As a result of the supernova explosion, the star turns into a white dwarf, a neutron star, or a black hole, depending on its initial mass. Note that stars only explode when using the simple parametric solver of stellar evolution - the detailed solver currently never reaches the end-of-life stage, as explained above.
Furthermore, a new type of explosion has been added. Whenever two neutron stars collide, they merge and create a spectacular kilonova explosion. The explosion has two distinct components - the isotropic part, expanding in all directions, and the planar part, given by the orbital plane of neutron stars.
You can check out Kilonova in the eponymous simulation preset.
A kilonova explosion from the collision of two neutron stars.
New object type - Tools
The update adds a new type of object that modifies the dynamics of rigid (non-deformable) bodies. Tools can be attached to any body, but they only affect the simulation if the body is rigid.
Thruster object
A thruster can be attached to any point on the surface of another rigid object. It exerts a constant force on the attached object in the direction of the thruster, and can accelerate the object and change its rotational state. It also generates exhaust particles to give visual indication of the thruster’s activity. The speed and duration of these particles can be modified in the parameter panel of the thruster object.
Thrusters can be either always active, they can be active for a specific duration, or they can be interactively controlled by a hotkey.
You can try the thruster object by running a new simulation preset, Rocket launch.
Thruster accelerating a rigid block.
Spring object
Springs can connect two rigid objects and create a compressive force when stretched. It is made of particles just like any other object, and can therefore collide with other particles or collapse under its own gravity. Optionally, a spring can break when it’s stretched too much and exceeds its tensile strength.
There are still a few known issues with springs. The spring can become unstable at high time steps, especially when its stiffness (Young modulus) is high. Also, the simulation performance scales poorly with the number of springs in the simulation. This will improve in the future.
Planets connected by an unbreakable spring.
The same setup as above but using a breakable spring.
Graph panel
Making use of the multi-viewport functionality added in previous updates, a new panel type has been added for simulation analysis. The graph panel allows you to track the state of simulation objects (both deformable and rigid) using two arbitrary variables as the X and Y axes of the plot. It was mainly added to view the evolution in stars in the HR diagram that uses effective temperature and luminosity as the X and Y variable, but it is by no means limited to this use case.
You can plot the change of velocities over time, semimajor axis vs. eccentricity, or any other combination you choose.
Tracking eccentricities and periapsis arguments of a planetary system.
Lua text panel
The update also adds another panel, a text editor that can be used in the Setup page. It can store the simulation description or auxiliary notes, but it is mainly useful for editing and executing the Lua simulation setup, added in the previous update. The editor supports Lua syntax highlighting and can easily regenerate the simulation setup using a button or a hotkey. No need to keep the script opened in an external editor and switch between the applications anymore. Now, you can simply edit the code and hit F5 to apply changes.
Whether it’s Lua code or a simple description, the text is always saved with the simulation.
Example of generating and updating a simulation setup using the Lua text editor.
Saving a simulated body to custom objects
If you come upon an interesting planet formed from a circumstellar disk, SpaceSim now allows you to save it as a custom object and use it in another simulation. Simply select the object and click ‘Save as custom object’ from the burger menu in the right panel. The app creates a mesh given by the current shape of the object and generates textures (diffuse, specular and emission) by sampling the surface of the selected particle group. The object is then available in the ‘Add object’ panel, together with the built-in objects, workshop items and other custom bodies.
A custom planet created by merging together Earth and Venus.
Improved tutorials
This change is intended primarily for new users who are not yet familiar with the application. The update adds three new tutorials, explaining functionality that users frequently asked about: Orbits, Appearance, and History. Existing tutorials have also been updated and extended with more information. Additionally, navigating tutorials is now easier with the highlighting of UI controls that need to be interacted with.
If you are having trouble understanding some of the app's features and would like a tutorial to explain them, please reach out.
New dialog with available tutorials.
Panini projection
The raymarcher now supports another type of projection, called Panini projection. It’s a projection similar to perspective, but it handles large fields of view better and avoids the distracting distortion typical for perspective projection.
The perspective projection keeps all lines straight, and therefore projects triangles as triangles, while the Panini projection only preserves vertical lines. Projected horizontal lines are usually not straight, which results in a more natural image and reduces edge distortion. For small fields of view, both projections are almost identical.
Compared to the perspective projection, the Panini projection avoids strong edge distortions.
Locked-on camera
If you like setting up custom camera paths, you can now use another camera type, called a locked-on camera. It’s somewhat similar to the targeted camera, but the camera maintains the same relative orientation with respect to the target object. The camera thus allows you to view the same point on the surface of a planet, even if the planet rotates or deforms.
Locked-on camera supports both deformable and rigid targets.
A locked-on camera keeps the same relative position while the Earth deforms.
More GPU solver features
The update adds support for other simulation options that were previously missing from the GPU solver, mainly:
Stellar wind (radiation pressure),
Radiative cooling,
Shear strength,
Viscosity,
Black hole jets,
Supernovae,
Phase parameters (melting/boiling expansion and temperatures),
Calculating surface area of bodies,
Histograms in the statistics panel.
Besides these additions, existing features have been improved, namely:
Fixed particle absorption not conserving total mass and momentum.
Fixed collisions with small rigid objects. The simulation preset ‘Thorne-Żytkow object’ now works correctly with the GPU solver.
Made heating and appearance more consistent with the CPU solver.
Fixed stability issues of the GPU solver when particles have significantly different radii. Note that this should still be avoided if possible, as it makes the solver perform poorly.
Elastic (blue) beam colliding with a viscous (red) beam, simulated using the GPU solver.
Rendering improvements
Optimized raymarching of solid and gas particles.
Optimized rebuilding of BVHs used by the raymarcher during render iterations.
Fixed normal maps not appearing on shaped objects when using the raymarcher.
Roughness now affects refractive objects. Setting the roughness to 1 gives the appearance of frosted glass.
Earth seen through a glass when rendering using the raymarcher.
Simulation improvements
Adaptive origin can now be used by the N-body solver.
Added a new mode for the adaptive origin, ‘specific body’. It keeps the simulation origin centered at the given object and maximizes the precision of floating-point calculations in its neighborhood.
Inertial forces and supernovae now participate in adaptive time stepping.
Particles emitted by black hole jets now have a finite lifetime.
Improved stability of the IISPH solver with adaptive time stepping.
Quality-of-life improvements
Added lock groups for triplets of linked properties. By locking a property, you can choose which property changes and which remains constant when modifying another linked property. Lock groups are currently used for two triplets: radius, mass, density, and radius, luminosity, effective temperature.
You can now save the simulation/render settings as persistent defaults. Next time you create a new simulation, it will use the settings you saved.
Added more useful hotkeys (pause the simulation, next/previous frame, follow the camera path). See File > Preferences > Hotkeys for the full list.
Hotkeys are now customizable. Custom hotkeys are persistent and remain after restarting the application.
When rendering a video from the history, you can select a specific time interval instead of rendering the entire simulation every time.
The shape of asteroids can be easily changed, using a preset shape or custom mesh.
The layers of differential planets can be customized by reordering or adding new layers.
Improved handling of textures, releasing them when they’re no longer needed and thus reducing the required VRAM.
Added parameter ‘render scale’ to preferences, allowing you to reduce the render resolution and speed up the rendering. This can come in handy when using slower computers, for example laptops with integrated GPUs. The render scale can be also increased above 100% for improved anti-aliasing (essentially SSAA).
Added a Vsync toggle to preferences.
Bugfixes
Besides the fixes already listed above, the following issues have been patched:
Fixed absorption of massless particles by shaped rigid objects. Previously, the rigid objects were always assumed to be spherical regardless of their actual shape.
Removed the viscosity contribution to the shear strength. It caused stability and momentum conservation issues. Instead, it should be combined with the viscosity simulation option to achieve the same effect.
Fixed bad texture wrapping, which caused some textures to be periodic instead of being mirrored/clamped (and vice versa).
Fixed shadowmap bounding boxes being too tight in some cases and causing semi-transparent shadows.
New content
As usual, the update adds a few simulation presets, mainly to demonstrate the newly added features:
Kilonova shows a close pair of neutron stars orbiting each other, slowly getting closer due to emission of gravitational waves, and finally colliding and creating a kilonova explosion.
Moonmoon is a simple preset showing a stable orbit of a satellite around a moon, also called a submoon. It was inspired by this Youtube video.
Rocket launch demonstrates how to use the newly added Thruster object. A makeshift rocket (a cylinder with an attached thruster) accelerates, reaches escape velocity, and flies towards the moon.
Solar evolution uses the stellar structure solver to show the history and the future of the Sun, from the zero-age main sequence to the Red giant phase.
There are additions to the list of objects too:
New procedurally generated object - random main-sequence star.
The random planetary system can be customized by choosing the number of terrestrial planets, gas giants, and whether to include an asteroid belt.
What's next?
I regularly update the development progress on SpaceSim Roadmap. Check it out if you want to see what changed, or come chat on Discord if you have a suggestion for what to add.