After first reviewing the gravitational wave (GW) spectral classification. we
discuss the sensitivities of GW detection in space aimed at low frequency band
(100 nHz-100 mHz) and middle frequency band (100 mHz-10 Hz). The science goals
are to detect GWs from (i) Supermassive Black Holes; (ii) Extreme-Mass-Ratio
Black Hole Inspirals; (iii) Intermediate-Mass Black Holes; (iv) Galactic
Compact Binaries; (v) Stellar-Size Black Hole Binaries; and (vi) Relic GW
Background. The detector proposals have arm length ranging from 100 km to
1.35x109 km (9 AU) including (a) Solar orbiting detectors and (b) Earth
orbiting detectors. We discuss especially the sensitivities in the frequency
band 0.1-10 microHz and the middle frequency band (0.1 Hz-10 Hz). We propose
and discuss AMIGO as an Astrodynamical Middle-frequency Interferometric GW
Observatory.Comment: 10 pages, 2 figures, 1 table, Plenary talk given in Joint Meeting of
13th International Conference on Gravitation, Astrophysics, and Cosmology and
15th Italian-Korean Symposium on Relativistic Astrophysics, Ewha Womans
University, Seoul, Korea, July 3-7, 201
