The National Space Institute was a space advocacy group, the first of its kind, established by Wernher von Braun to help maintain the public's support for the United States space program. It has since merged, in 1987, with the L5 Society founded by fans of the Space Colonization and Industrialization work of Gerard K. O'Neill, to become the present-day National Space Society.
Wernher von Braun (1912-1977), founder of the National Space Institute, forerunner of the present-day National Space Society
Space advocacy is supporting or advocating for a human use of outer space. Purposes advocated can reach from space exploration, or commercial use of space to even space settlement. There are many different individuals and organizations dedicated to space advocacy. They are usually active in educating the public on space related subjects, lobbying governments for increased funding in space-related activities or supporting private space activities. They also recruit members, fund projects, and provide information for their membership and interested visitors. They are sub-divided into three categories depending on their primary work: practice, advocacy, and theory.
NASA's artistic poster about the human exploration of Mars: "Mars explorers wanted"