This is German rocket mail with a postmark for Straelen 22.5.61 (May 22, 1961).  This was carried aloft on May 21st at Paeshuhle/Straelen by rockets launched as indicated by the special rocket cachet in black ink to the left.  Rakete R3 was named for Alan Shepard, the first American Astronaut.  Only 116 covers were posted with the Alan Shepard cachet below.

A 50pfg rocket seal is printed in red on the envelope. The stamp providing surface postage was issued on April 22, 1961 honoring Scouting's 50th Anniversary.  The stamp depicts St. George, patron Saint of Scouting.

An unknown number of covers marked for the test flight were carried aloft.

SOSSI Journal VOL X, No. 10, October 1961
Ellington-Zwisler Rocket Mail Catalog,
American Air Mail Society, 1967
Dr. Max Kronstein, Rocket Mail Flights of the World to 1986
The American Airmail Society , Cinnaminson, NJ 1986.