Making a simple rocket

This tutorial aims at explaining how to create a simple rocket for Orbiter by using Anim8or and configuration files or Multistage.dll. We will start with a some basics to know about what a rocket is, create a simple single staged rocket and later add a second stage as final step. It is not about designing the rocket for a special mission, just experimentation.

Basics about rockets

See also Rocket and Rocket engine for more details

First some explanation what a rocket actually is.

A rocket is a machine which ejects mass for generating velocity. Nothing else. Keep that in mind when looking at a rocket or designing one.

Why explain so much for a simple rocket, which could like anything in Orbiter? Because it gives the rockets character, and this makes them look more realistic, than a simple bald cylinder with a conical rocket engine at the end.

A rocket gains velocity by ejecting mass through a rocket engine. The concept is plain conservation of impulse (or Newtons third law). Every second, the rocket ejects propellant mass through the nozzle of the rocket engine. The impulse of this mass is compensated with the remaining rocket accelerating. The more mass getting ejected (This property is called mass flow) or the faster this mass gets ejected (called average exhaust velocity or specific impulse), the more velocity the rocket gains.

For ejecting mass every second, this propellant mass also has to be delivered from the tanks inside the rocket to the engines every second. This job is done by the propellant utilization system. It's operation can best be described as a really large spray dose. The propellants get pressurized to press them into the pipes to the rocket engines. The higher the pressure or the higher the diameter of the pipes, the more fuel can get pressed every second through them. That is not unimportant, regarding the fact that large rockets burn many tons of fuel every second. The pumps of the SSME could drain the volume of a typical swimming pool in seconds!

The primary way to accelerate the exhaust is to use chemical energy: The propellants get combusted at high pressures inside the engine to generate heat. A rocket is thus also often called a "controlled explosion".

The rocket engines create very large thrust forces, so they also need to be installed to the rocket with very strong structures. These structures are called thrust structures. As most of the rocket structure will be made of tank walls for lightweight construction, the thrust structure will usually transfer the forces from the engines to the sides of the rocket.

When flying in the atmosphere at supersonic speeds, an aerodynamic shape will be required. This is usually done by stacking the tanks over each other for keeping a small frontal cross section and put a conical or ogive nose over them.

The rocket also needs some way to control the direction of flight. Who ever attempted to balance a long stick on your hand, knows the problem: It wants to flip over and is pretty instable. Common ways to control this are:

• Smaller rocket engines around the rocket, called reaction control system.
• Make the main rocket engines tiltable. This is called thrust vector control (TVC).
• When flying mostly inside the atmosphere, fins can get used. That is the simplest way for our purpose.
• Spin the rocket quickly. This keeps it pointing on one direction.

So, the parts our tiny rockets will have, from top to bottom, are:

• Aerodynamic nose
• Tanks
• Propellant utilization systems
• Thrust structure
• Fins

Rockets also have many more components needed for operation, but let's stop with the boring theory.

A small first step

The most simple rocket is a one staged rocket, like for example the infamous V-2. It consists only of a section of tanks, a single rocket engine, some fins and a nose cone.

In Anim8or, we create first the tank section as simple cylinder. Give it about 10m length and 2m diameter. We don't mind how realistic it really is, as long as it looks at least like it.

Next, draw one half of the the profile of a simple rocket engine at the origin of anim8or coordinate system. Make it roughly suitable in size for the rest of the rocket. Lathe it with 12 sides. It is enough for us.

Make a nose cone.

Aiming higher

We need more velocity. Instead of making the rocket just larger, we use a very smart and known strategy. We add a new stage.

Open the anim8or file of the simple rocket we already made and cut out the nose cone. Create a new object and paste the nose cone into it. (clone the object of your first rocket if you want to keep it). We will use this as rough guide for fitting the new stage on the remaining rocket. Copy the rocket engine from your old rocket. We use it again for the new stage. also take the thrust structure with it.