Gravitational Wave Detectors in Space and the Detectability of Primordial Inflationary Gravitational Waves

For detecting gravitational waves in space, deep-space laser ranging using drag-free spacecraft is a common method. Deep space provides a large arena and a long integration time. Laser technology provides measurement sensitivity, while drag-free technology ensures that gravitational phenomenon to be measured with least spurious noises. In this talk, we give an overview of motivations and methods of various space missions/proposals for detecting gravitational waves, and discuss various space gravitational wave projects and proposals. We review the concept and status of space gravitational-wave missions --- LISA, ASTROD, ASTROD-GW, Super-ASTROD, DECIGO and Big Bang Observer. We give a special attention to the detectability of gravitational waves generated in the inflationary era. The sensitivity of observation down to Omega_gw ~10^-20 is possible using present projected technology development if foreground could be separated. A discussion of foreground generated by black holes during co-evolution of galaxies (an important goal of space gravitational wave detectors) will be presented.