Space Cover 542: Orbit Covers with a TwistOrbit covers started with John Glenn's mission (and future Project Mercury missions) with plain text cachets with the wording "Orbit Covers" after the words. The Orbit Cover Project Mercury stamp FDCs were the first to receive actual images as cachets. The most common Orbit covers for the manned flights are the Project Gemini covers – for which an album and associated printed pages for mounting the covers were produced.
These Project Gemini covers can be found relatively easily in dealer boxes of space covers. Unmanned satellite launch covers and manned events through the start of the shuttle missions can be found relatively easily as well – but they are less plentiful than the Project Gemini covers. There are even some #10 size covers produced for some Apollo and Skylab missions.
But the Orbit covers with a twist turn out to be a portion of the Project Gemini covers were produced with the "normal" flag stamp with the addition of foreign stamp stamp as well. Pictured at the top of this post is a launch cover for Gemini 5 with a Paraguay Gemini stamp added.
Another example above, is for the Gemini 10 flight, a launch cover with a Panama stamp with Gemini Titan on the launch pad and an image of President Kennedy.
I have never seen any documentation on what missions these were produced for, how many of this type of cover was produced per mission, or if only a single stamp or multiple stamps were used for a single mission. If anyone has such information please post it here.
So, while searching through your favorite dealer's space cover boxes or in the on-line stores, take a closer look at the Orbit covers – you just might find some of these for your collection.