  Gravitational wave (GW) detection in space is aimed at low frequency band
(100 nHz - 100 mHz) and middle frequency band (100 mHz - 10 Hz). The science
goals are the detection of GWs from (i) Supermassive Black Holes; (ii)
Extreme-Mass-Ratio Black Hole Inspirals; (iii) Intermediate-Mass Black Holes;
(iv) Galactic Compact Binaries and (v) Relic GW Background. In this paper, we
present an overview on the sensitivity, orbit design, basic orbit
configuration, angular resolution, orbit optimization, deployment, time-delay
interferometry and payload concept of the current proposed GW detectors in
space under study. The detector proposals under study have arm length ranging
from 1000 km to 1.3 x 109 km (8.6 AU) including (a) Solar orbiting detectors --
ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical
Devices] optimized for GW detection), BBO (Big Bang Observer), DECIGO
(DECi-hertz Interferometer GW Observatory), e-LISA (evolved LISA [Laser
Interferometer Space Antenna]), LISA, other LISA-type detectors such as ALIA,
TAIJI etc. (in Earth-like solar orbits), and Super-ASTROD (in Jupiter-like
solar orbits); and (b) Earth orbiting detectors -- ASTROD-EM/LAGRANGE,
GADFLI/GEOGRAWI/g-LISA, OMEGA and TIANQIN.
