There is also RASAero, another freeware/open source rocket simulation package.

Warren

I just built a rocket in this and I like it - more intuitive than rocksim. The downside at this point is no motor imports. For odd shaped rockets this looks nice. For my 3FNC and 4FNC designs I'll stick to RAS Aero

Edward

I agree, it is much more intuitive than RockSim. It is missing some of the little niceties of RS (like easy motor imports), but does do 6 DoF analysis, I'm certainly going to continue using it to augment design and simulation.

In regards to adding motors, it actually does support adding additional motors, you just need to edit the .jar file. See the support forum posting on where to put it ( http://sourceforge.net/apps/phpbb/openrocket/viewtopic.php?f=3&t=4). I know 7zip supports modifying jar files, and it's free (and open source), WinZip might support doing this as well.

Unfortunately for hybrid and other long-burn motors, it does have known accuracy issues at the moment.

Another option is to rename the file to add a .zip to the end. Then add the files into the thrustcurve folder, save and rename back. On a side note I am running the 0.9.4pre version and working on updating things in it. One of the nice things of it being opensource. The code is being added in for data from some of the perfectflite altimeters.

Just FYI, v0.9.4 was released today. It now supports TTW fin mounts, attaching things (mass objects for electronics!) to coupler tubes, and probably a few other things.