This is a German rocket mail with a postmark 10.5.1961 (May 10, 1961). It was carried aloft by "SPEZIAL RAKETE 2" launched on May 10th as indicated by the special rocket cachet in green ink to the left.
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.
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, New Jersey 1986.