(This is if you have the MyM launcher, idk about getting to this on other launchers) Open the MyM launcher, right click Galactic Science, and try a force update. Anything missing should be replaced. Otherwise you may have to just fully reinstall Galactic Science.
Hello! To be of further assistance, we need your crash-report (instructions at mym.li/crash) to help determine the exact nature of the error. Your Paste ID is invalid; please make sure you set the duration long enough for us to view. Without a crash-report, the staff and the community are unable to do much about your issue. Thanks in advance for your cooperation. Sincerely, yurikha27