 According to Jerome Clark, these gatherings coalesced the scattered contactee subculture into a recognisable movement in January 1952.This led to the annual Giant Rock Spacecraft Convention organized by Van Tassel, which began in the spring of 1953 and continued for at least another 24 years.It marked Van Tassel's most important role in UFO history In 1959 up to 11,000 people attended these conventions and heard channeled messages claiming to come from space.