Simulating a Shuttle Crash in Houdini

How It Started

I live in the building right in front of the one we see in the video. One day I just grabbed a camera and thought “Why not try to do something cool with that?”

Creating the Building

The first challenge was to model the building with the right proportions. At that time I didn’t know exactly how things would go, maybe I would destroy the entire building or maybe just a few parts of it so I had to model everything in a proper manner to eventually destroy every part later.

Every time I needed information such as the size, I could look out of my window to easily get it. In real production, you have to gather every piece of information that you can before going into modeling.

The main building was quite straight forward to model but the things which really took time were those little details such as signs, props on the balconies, props inside stores, etc. This is where Houdini came really handy! It turned out very useful when I needed to add a lot of different props such as shutters, curtains and all kind of elements that you can find on a balcony in a random way to make it look less computer-generated. I did a little setup to scatter those elements with different positions for each apartment. Those little details really help to sell the shot.

On top of a large number of props in the building itself, I also added a lot of different elements such as trees, cars, rubbish papers on the ground and so on on the street. Houdini is really good at handling a large amount of geo and the geometry is packed before scattering so the polycount of your scene doesn’t get out of control. Viewport navigation was still relatively smooth even with everything in.

Shuttle Crash Simulation

First, I had a plate shot with a camera. I tracked it, imported camera and dots information into Houdini, so I could then add the shuttle and hand-animate it according to the camera’s movement.

Once I got the trajectory of the shuttle I could boolean fracture the building according to that, activate pieces nearby the shuttle and start the main RBD simulation.

And then you stack simulations on top of each other as you do in a standard destruction work.

• Main simulation: concrete building with glue constraints
• Secondary sim: glass shattering in front of the shuttle
• Third sim: extra pieces of concrete flying
• Fourth sim: particles falling off of concrete
• Fifth sim: smoke

This time I even added other small simulations such as vellum sim for the curtains (that you don’t really notice in the end result but without it, you would just have curtains flying into the air) or trees being destroyed by concrete falling on them.

To handle the interaction between the shuttle and the building I put a convex decomposition node after the shuttle geo, assemble it and copy-paste the transform node which is animated. This way bullet solver only interprets the geo once and moves it one frame to another.

What Could be Improved

I got the feedback from the community that the shot is cool but the shuttle is too slow comparing to what it should be in real life.

On top of that, I really wanted to see that shuttle passing by and slowly destroying the building so I think I could add a parachute behind the shuttle to make it all work. Plus that would add another level of detail with the fabric interacting with concrete. It could have been a cool improvement but I must move on.

Hadrien Palanca, FX Artist & 3D Generalist

Interview conducted by Kirill Tokarev