"ECHO I and II satellites" . . "Echo 2" . "1968-05-25" . "Project Echo" . . "ECHO 1" . "Project_Echo#Echo_2" . "ECHO II" . . "Echo Satellites 1 and 2" . "Echo II" . "Echo" . "1960-08-12" . "Echo balloon satellites" . "Echo II balloon satellite" . . . . . "Echo 1" . . "Echo 1 and 2" . "2.445714E8" . . "the ECHO satellite" . . . . "NASA A-11" . . "00049" . "1960-009A" . "ECHO I" . "Project Echo" .