What exactly is a rocket mail cover?

Would it surprise you that the first collectable Space Covers began well before the Space Age?  Actually flown rocket mail started back in the 1930s. Private experimental rockets were used to transport letters over short distances.  These rocket mail covers are quite scarce today. Why? Because the quantity made of these early rocket mail covers were extremely low to begin with, limited to the number of letters or covers that a rocket could carry.  These early Rocket pioneers charged for their services, the money raised help to finance the expense of the rocket flights.  This cover is an example of a piece of rocket mail from 1935      flown in a rocket named Murcury launched by Karl Roberti in the Netherlands. There a re 5 identifying characteristics on this cover. First, there is a blue etiquette label that resembles an airmail label in the upper left corner reading AEROTORPEDO.  Just below this label in German Script is the phrase BT ROCKET MERCURY P14.  In addition, there is a large blue cachet reading NIGHT ROCKET LAUNCH KATWIJK-AAN  ZEE, the same place as the cancel Katwick on the sea Holland.  Next there is a magenta colored imperforate rocket mail stamp picturing the rocket launch.  Finally, this rocket mail stamp is tied to the cover by a red P14 Mercury Rocket cachet used as a cancel.  The cover is also signed by Karl Roberti and numbered in the lower left corner No 33. This cover was flown in a Rocket then posted at a post office closest to the landing site place into the Netherlands Mail System and delivered to the addessee.

More information on Rocket Mail  can be found in the Ellington-Zwisler or E-Z rocket Mail Catalog or in the Raketenpost Katalog by Sieger witten in German. Also there are serveral books written on the subject one by Dr Max Kronstein titled Rocket Mail and another Rocket Mail Flights of Stephen Smith.