When I met Stanley Kubrick for the first time, in Trader Vic's on April 22, 1964, he had already absorbed an immense amount of science fact and science fiction, and was in some danger of believing in flying saucers; I felt I had arrived just in time to save him from this gruesome fate. Even from the beginning, he had a very clear idea of his ultimate goal, and was searching for the best way to approach it. He wanted to make a movie about Man's relation to the universe, something which had never been attempted, still less achieved, in the history of motion pictures.
Of course, there had been innumerable "space" movies, most of them trash. Even the few that had been made with some skill and accuracy had been rather simpleminded, concerned more with the schoolboy excitement of space flight than its profound implications to society, philosophy, and religion.
From Son Of Dr.Strangelove, an essay wrote by Clarke for Report on Planet Three (1972, read it on Google books) and reprinted with small corrections in Greetings, carbon-based bipeds (1998, p.261):
My first meeting with Stanley Kubrick took place at Trader Vic's in the Plaza Hotel. The date - April 22, 1964 - coincided with the opening of the ill-starred New York World'sFair, which, might or might not be regarded as an unfavorable omen. Stanley arrived on time, and turned out to be a rather quite, average-height New Yorker (to be specific, Bronxite) with none of the idiosyncrasies one associates with major Hollywood movie directors.
He had a night-person pallor, and one of our minor problems was that he functions best in the small hours of the morning, whereas I believe that no sane person is awake after 10 p.m. and no law-abiding one after midnight. He never tried with me his usual tactic of phoning at 4 a.m. to discuss an important idea. But his curtesy did non stop him from being absolutely inflexible once he had decided on some course of action. Tears, hysterics, flattery, sulks, threats of lawsuits, will not defect him one millimeter.
"We talked for eight solid hours about science fiction, Dr. Strangelove, flying saucers, politics, the space program, Senator Goldwater - and, of course, the projected next movie."