He conducted the first radio search for extraterrestrial intelligence and helped construct the Voyager interstellar record, which carried pictures and music from Earth out into the cosmos.
The centre-right Alliance government first presented proposals in early 2007 aimed at allowing the National Defence Radio Establishment (FRA), a state intelligence agency, to monitor a wider range of Internet and telecoms traffic into and out of Sweden.
They had no reason to doubt the truth of subsequent messages that flowed from Mr Chapman's radio, compiled by the creative minds of the intelligence service.