DECIGO and DECIGO Pathfinder

A space gravitational-waveantenna, DECIGO ( DECI- hertzinterferometer Gravitational wave Observatory), will provide fruitful insights into the universe, particularly on the formation mechanism of supermassive black holes, dark energyand the inflation of the universe. In the current pre- conceptual design, DECIGO will be comprising four interferometer units; each interferometer unit will be formed by three drag-free spacecraft with 1000 km separation. Since DECIGO will be an extremely challenging mission with high-precision formation flight with long baseline, it is important to increase the technical feasibilitybefore its planned launch in 2027. Thus, we are planning to launch two milestonemissions. DECIGO pathfinder(DPF) is the first milestonemission, and key components for DPF are being tested on ground and in orbit. In this paper, we review the conceptual designand current status of DECIGO and DPF.