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