Design Your Own Rocket

A lot of the software packages I've covered in recent articles havebeen focused strictly on doing computations on your machine, separatefrom the real world. So in this article, I explore how to use your computer todesign something you can build and use in the real world: yourown model rocket. Let's take a look at the OpenRocket utilityand see how it can help you design your own rockets. OpenRocket even can runsimulations on your designs to show how they should behave in flight.

Mostdistributions should include a package for OpenRocket. For example, inUbuntu, you would install it withapt-get installopenrocket. It isactually a Java program, so you always candownload the jar file directlyfrom the Web site. To run it,you need to have a reasonably up-to-date Java VM installed as well.

When you first start it up, you are presented with an empty screen, ready tobegin designing your first rocket. A project window pops up, allowing youto enter details like the design name, your name and design notes. You canbuild your rocket from a series of components. You probably will wantto start with the nose cone by clicking on it from the "Add newcomponent"window. It then will appear in the bottom section, beginning yourdesign.

You will notice that OpenRocket already begins to make calculationsbased on your design. You will see a small blue circle that denotes thecenter of gravity of your rocket. The center of gravity is the pointthrough which all of the mass acts. There also is a small red dot thatmarks the center of pressure. This is the point through which all of theatmospheric forces act. OpenRocket calculates these values as you makechanges to your design.

You can edit almost all of the parameters for each component.There are two ways to edit these component parameters. Youcan double-click on the component of interest in the design window toaccess the edit window. There also is a list of the component layers in thetop half. You can highlight the component of interest here and then clickon the Edit button.

What you can change will depend on which componentyou are trying to edit. The first component to design probably is the nosecone. You can select what kind of profile your nose cone should have,such as conical or ellipsoid. You can set the length and base diameter,as well as the wall thickness. But, OpenRocket goes even further. Youcan select the kind of material from which your nose cone should be made. Thedifferent types of materials have different densities, which changes theweight of your component.

Several different material presets are available,but you also can go ahead and define your own custom material type. Thiscustom material either can be used just for one design, or you can add itpermanently to your materials database if it is something you willbe using over and over again. You even can set the type of finishyour rocket will have. This finish can be different for each component,or you can apply a common finish to your entire rocket.

When first starting OpenRocket, you get a new project dialogwhere you can enter details of your rocket.

You can edit many details of the different components by double-clickingthe component of interest.

The rocket engine database has lots of information on many differentbrands.

The next part of your rocket is the actual body tube. If your rocketis going to have a single stage, you will need only a single bodytube. For multiple stages, you will need a separate body tube foreach stage. Opening the edit window for the body tube allows you tochange the tube length, diameter and wall thickness. You also canchange the material from which the body tube is made.

Because bodytubes usually contain a rocket motor, you can set the motor thatyou want to use as well. To do so, open the edit window andclick on the motor tab. You can click the Select Motor button andchoose from a large selection of commercially available motors. This listof motors includes technical information, such as the thrust curve andthe run times, as well as physical characteristics like the length,diameter and weight.

As with the other sections of the application, youcan define your own custom entries. This means even full-on DIYmodel-rocket enthusiasts who build their own motors can use OpenRocketto design their rockets.

The component list includes other items likeparachutes, shock cords, connectors and blocks, so you candesign your rocket as a complete model.

The final stage is to add tailfins to your rocket. As with the other components, there are well designedpresets available that will satisfy most design needs. You can edit someparameters to customize the fins to some degree. If that's not enough,there is a freehand option where you can design your fins from scratch.

OpenRocket is not only a design program. You also can take your modelrocket and run an analysis on it to see how it will behave in flight. Theanalysis section looks at individual components and shows how theyaffect the stability, drag and roll characteristics of your rocket. Youcan set parameters like wind direction, angle of attack and speed, andcalculate how it will behave in flight. This is great functionality, butOpenRocket goes even further. It can take your original design and try tooptimize it for the best flight characteristics. You can optimize basedon altitude, velocity or some other combination of characteristics.

Onceyou have a final design, you can run it through simulations. The simulatorcan apply different conditions on your rocket, like applying crosswindsor taking Coriolis effects into account, and it shows how your model rocketshould behave. OpenRocket uses JFreeChart to plot your rocket's behaviorbased on the simulation results.

You even can add your own code to thesimulation to add extra effects. One way to do this is using Python andjPype to use Python code in the simulations. Additionally, you have the abilityto write and use your own expressions in the simulator. This allowsyou to customize the simulator to a great degree without having to addexternal code. Then, you can see the limits of what your model should beable to handle and how high it will go under different conditions. Thisis really great in helping you decide when the weather is going to betoo rough for your design.

You can run an analysis on the different components of your rocket.

You can optimize your rocket to maximize certain parameters.

You can run full simulations to see how your rocket willbehave in different conditions.

I have covered only the features available in the most minimal way. If you areinto building and flying model rockets, your time definitely will be wellspent poking around all of OpenRocket's available features.The Rocketry Forum hosts a forum where you can askfor further help. And once you have gained some experience, you cangive back by helping other new rocket enthusiasts. Go ahead and designyour fleet, and get yourself out into the wild frontier of space!