The former chief of NASA Communications Systems, Maurice Chatelain, in 1979 confirmed many theories about NASA and alien contact. All the Apollo and Gemini flgihts were followed by UFOs. The astronauts would inform Mission Control and then be ordered into absolute silence.
Santa Claus is the term used by NASA to indicate a sighting of a UFO by a space flight. Walter Schirra was the first to make use of the term Santa Claus during his Mercury 8 flight. His report was ignored by the public. James Lovell aboard the Apollo 8 command module announced, once he had returned from the dark side of the moon, "Please be informed that there is a Santa Claus." Many sensed a hidden meaning in the words despite it being Christmas Day 1968.
NASA is a civilian agency but many of its programs are funded from the defense budget and most of the astronauts are subject to military security regulations. The National Security Agency screens all films and radio communications. The astronauts are under strict orders not to discuss their sightings.