Please read the procedure listed below. How to do a Batch Conversion from Rocksimm RKT to OpenRocket ORK Format. Why? Two reason, don't have Rocksimm's program, have OpenRocket's program, secondly one can find a lot of rkt files and rather than opening one at a time into OpenRocket and then do a Saving As, I simply use this batch process to do the work and it works great. This video shows using the F Drive on my computer, you use whatever drive is available to you: Start off by making a folder named OpenRocket Then in that folder make two(2) sub-folders named as: ORK RKT Download and place the OpenRocket application file into the folder named OpenRocket Download all of the Rocksimm (*.RKT) files your little heart wants into the sub-folder named RKT. Go to the the Windows Command Prompt and type: cd f: (then press the Enter key) Then will need to change directory or folder where the OpenRocket application file is located. As is in this example, it would be: cd f:\openrocket (then press the Enter key) Then type at the prompt the following line text: java -cp OpenRocket-12.03.jar net.sf.openrocket.utils.RocksimConverter F:\OpenRocket\RKT\*.rkt (then press the Enter key) This will then convert all of your *.rkt files into *.ork files. Now simply select all of the *.ork files and move them to the ORK sub-folder. Or you can leave them there, but you will need to delete the *.rkt files for if you download any more rkt files and run the batch conversion process again, one will have the old rkt files converted again. This is why I move my files and then delete the rkt files. Note if your Open Rocket application and sub-folders are different, then you will need to make changes in the above commands. OpenRocket application: https://sourceforge.net/projects/openrocket/files/openrocket/12.03/OpenRocket-12.03.jar/download then search for rocksimm or .rkt files