A Project ECHO balloon. Constructed of mylar of less than a hair’s width, and launched by rocket, the balloons would inflate after ejection; they could be seen from the ground as they passed overhead.
Image: NASA.

In 1960 on this date, NASA launched the third ECHO test balloon to an altitude of 225 miles. Radio transmissions were reflected via the 100-foot-diameter inflatable sphere from Holmdel, New Jersey, to Round Hill, Massachusetts.