The National Space Society was established in the United States in 1987/88, with the merger of two already very active space organisations; the National Space Institute (NSI) and the L5 Society. Both groups had been operating since the mid 1970's at a time in the U.S., when the space program was being dramatically scaled back. With the end of the Apollo/Moon program in 1972 and the one-off Apollo-Soyuz mission in 1975, the space program was seen as having no new goals to achieve, public opinion critical of continued space ventures. With a lack of clear political direction and with the space shuttle program still many years away from its first flights, numerous space 'activist' groups sprang up, to promote a new and more vigorous space effort and to highlight the benefits of space exploration, education and development to the public.

From among the many groups formed, the National Space Institute and the L5 Society emerged as two of the leading pro-space organisations. Both groups were well supported by members of the general public and had the backing of many well recognised professionals from the media, scientific, academic and astronautical communities.

The L5 Society was established as a result of the 1975 Summer Study'at Princeton University and M. I.T., where students and teachers participated in programs to develop concepts for the creation of space colonies. 'L5 emerged from the idea of placing large orbiting colonies at two of the Lagrange- points (L4 & L5), which are stable regions of gravitation within a planet's orbit (approximately 60 degrees preceding and following the body's path), where a colony could be placed with the correct initial location and velocity and literally stay forever. "L5" eventually became the nickname for any stable orbit above the Earth's radiation belts, and no farther away than the Moon, where a station could be placed. Becoming a citizens' group independent of any institution, the L5 Society formed to supply information on the new possibilities of space development (especially colonisation) and to publish commentary in newsletter form- Both the L5 Society and the NSI developed their own programs of space activism, promoting space research, development and exploration to the general public.

Internationally (prior to the merger), the L5 Society had been developing chapters around the world, and in Australia, three chapters had been established. The 'Southern Cross L5 Society' was formed in 1979, with groups in Sydney, Adelaide (in 1984) and Brisbane (in 1986). The Australian L5 chapters pursued some public information activities to promote 'space', but for the most part were little more than 'space clubs' with a relatively small membership holding meetings and going on the occasional field trip, The three chapters operated independently of each other while sharing a national newsletter called 'L5 Space News' (produced in Sydney). This remained the status of the Society for many years, with little progress being made on the pro-active, pro-space front.