I read a paper ‘Contact Among Galactic Civilizations by Relativistic Interstellar Spaceflight’, presented by Carl Sagan. This paper was dealing with alien civilizations. An estimate of advanced technical civilization on planets of other stars depends on our knowledge of the rate of star formation, the frequency of favorably situated planets, the probabilities of the origin of life, intelligence of technical civilization , and lifetimes of civilization. Actually, these parameters are poorly known. Yet, the estimate of present paper lead to ~106extant advanced civilization in our galaxy. The most probable distance to the nearest such community is the several hundred light years. Interstellar spaceflight at relativistic velocities has several obvious advantages over electromagnetic communication among those. One striking feature is that with uniform acceleration of 1g to the midpoint of journey , and uniform deceleration there after, all points in galaxy are accessible within lifetime of human crew, due to time dilation. In this paper some of the technical problem in the construction of starship capable of relativistic velocities are discussed including ramjet , fusion propulsion and other. It is assumed that there exists in the galaxy a loosely integrated community of diverse, cooperating in the exploration and sampling of astronomical object and their inhabitants. If each such civilization launches one vehicle per year, the mean time interval between sampling of average star would be 105, that between sampling of a planetary system with Intelligent life would be 105yrs, that between another would be 103yrs. It follows that Earth was visited by advanced ET at least once during history, and perhaps history and legends proves it too.