NASA (National Aeronautics and Space Administration) regularly releases data (media files) free for public use. This does not include the NASA logo, insignia, or company identifiers.
As per NASA's guidelines: "NASA content – images, audio, video, and media files used in the rendition of 3-dimensional models, such as texture maps and polygon data in any format – generally are not subject to copyright in the United States. You may use this material for educational or informational purposes, including photo collections, textbooks, public exhibits, computer graphical simulations and Internet Web pages. This general permission extends to personal Web pages.
News outlets, schools, and text-book authors may use NASA content without needing explicit permission, subject to compliance with these guidelines. NASA content used in a factual manner that does not imply endorsement may be used without needing explicit permission. NASA should be acknowledged as the source of the material. NASA occasionally uses copyright-protected material of third parties with permission on its website. Those images will be marked identified as copyright protected with the name of the copyright holder. NASA’s use does not convey any rights to others to use the same material. Those wishing to use copyright protected material of third parties must contact the copyright holder directly."
However, when NASA releases an image with an identifiable person in it, that person must give permission for their likeness to be used.
Nasa has also released free eBooks for downloading and enjoying. Note that this does not give you rights to print the eBook, only to download and view.
In short, using media NASA releases is not against copyright law, as long as you credit NASA for the creation of the media and there are no people in the media. You cannot claim it as your own. You may also download and read their free eBooks, but you cannot print them yourself.
NASA free eBooks and media:
Copyright
https://www.nasa.gov/multimedia/guidelines/index.html