As with most any important agency, NASA has a bevy of documents critical to its formation and evolution into the organization as we know it today. Presented below are a few of the most important.
National Aeronautics and Space Act of 1958
NASA was formally created on July 29, 1958 with the signing of the 'Space Act' by President Eisenhower. The law was crafted in the shadow created by Sputnik, the first artificial satellite launched into space by the Soviet Union nine months earlier. Follow the link below to read the act in its entirety: http://history.nasa.gov/spaceact-legishistory.pdf
President Kennedy's speech to Congress on May 25, 1961
In this historic speech, given only twenty days after Alan Shepard became the first American to penetrate the barrier of space, President Kennedy issued the challenge that "...this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth." Follow the link below to read the full text of this momentous address:
http://www.jfklibrary.org/Research/Ready-Reference/JFK-Speeches/Special-Message-to-the-Congress-on-Urgent-National-Needs-May-25-1961.aspx
Rogers Commission Report on the Challenger Disaster
Minutes after the January 28, 1986 explosion of the space shuttle Challenger, NASA and the U.S. government as a whole began investigating the cause of the explosion. The result is an enormously long document that permanently altered how humans enter space. Follow the link to learn more about Challenger: http://history.nasa.gov/rogersrep/genindex.htm