Many photos appear in more than one category.
An explanation of what is in each category is provided below. These categories do not contain every image that is someway related to the subject, just the most important. For example, Space Shuttle missions that involved practicing for Hubble Space Telescope servicing missions are in the database, but not included in the Hubble category. So if you do not find what you want in the subject categories, you should use the search function. Keep in mind that GRIN is a selective collection, not a comprehensive one, so you may be looking for photos that are not in the database.