1963-11-01 USA Titan II Pogo Effect Suppression Test

A Titan II POGO effect suppression test cover featuring a “Swanson” stamped cachet, postmarked at Cape Canaveral with a machine cancel on November 1, 1963. The cover commemorates the successful test of measures to suppress dangerous longitudinal vibrations in the Titan II, helping resolve a major obstacle to the rocket’s use as the launch vehicle for Project Gemini.

The Titan II was selected as the launch vehicle for Project Gemini, but its use for crewed missions was threatened by a serious vibration problem known as POGO. The term refers to a potentially dangerous longitudinal oscillation of a liquid-fueled rocket, caused by interactions between fluctuations in propellant flow, the engines, and the vehicle's structure. These vibrations could become severe enough to affect an astronaut's vision, speech, and ability to control the spacecraft.

Earlier Titan II flights had experienced POGO vibrations at levels considered unacceptable for human spaceflight. NASA therefore imposed a strict limit of 0.25 g for Gemini and, at one point, questioned whether the Titan II could safely be used to carry astronauts. The successful November 1, 1963 POGO suppression test demonstrated that the problem could be brought under control, helping clear a major obstacle to the Titan II's eventual use for the Gemini missions.