As of right now, HeartOS only recognizes Binary STL files. ASCII files are not yet supported and will cause an error to pop up when trying to open the file. It is recommended to export the file from SolidWorks (or other CAD software being used) as a Binary STL file.
In case you need help converting the file from ASCII to Binary you can use the following converter: https://www.meshconvert.com/
On this webpage, you are able to upload your file and convert it into Binary Stereolithography (.stl) file
If you are still experiencing problems after using the converter or exporting the file as a Binary STL you can get in contact with us at firstname.lastname@example.org