US SPACE COVER : 20TH ANNIVERSARY OF THE START OF PROJECT VANGUARD &I NFORMATION  INSERT ABOUT 55 YEARS OF SCIENCE BY THE NAVAL RESEARCH LABORATORY,  THE POSTMARK IS A FANCY CANCEL SEPT 9, 1975 , SMITHSONIAN STATION, WASHINGTON DC ON MARINER  SPACE STAMP... FREE USA SHIPPING/ $2.50 INTERNATIONAL