Apollo 6 (also known as AS-502), launched on April 4, 1968, was the final unmanned Apollo test mission. Its objectives were to demonstrate trans-lunar injection capability of the Saturn V with a simulated payload equal to about 80% of a full Apollo spacecraft, and to repeat demonstration of the command module's (CM) heat shield capability to withstand a lunar re-entry. The flight plan called for following trans-lunar injection with a direct return abort using the command and service module's (CSM) main engine, with a total flight time of about 10 hours.
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| Apollo 6 official NASA cachet on cover with Kennedy Space Center machine cancel. |
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| Apollo 6 Spacecraft Swanson cachet cover with PAFB postmark, April 4, 1968. |
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| Apollo 6 USS Okinawa Beck B747, the correct cover for USS Okinawa. |
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| USS Okinawa ship's cachet applied on a plain cover (top) and at the back of an Apollo 6 "Orbit Covers" (bottom). |
