Direct contact among galactic civilizations by relativistic interstellar spaceflight : draft

A draft of Sagan's paper, "Direct contact among galactic civilizations by relativistic interstellar spaceflight." The paper explores models for the distribution of technical civilizations in the galaxy. Using Frank D. Drake's equation to suggest that 0.001 percent of stars in the sky have a planet on them on which an advanced civilization resides. Sagan suggests the nearest such advanced civilization is several hundred light years away from earth. From there, Sagan explores the feasibility of interstellar spaceflight as a means for traversing such distances. The paper ends in consideration of the possibility of extraterrestrial contact with Earth in the past. The paper was initially presented at a meeting of the American Rocket Society in November of 1962 and subsequently submitted to Planetary and Space Science in December of 1962 and published in 1963.