ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I

With dramatic technology developments and improvements, deep space laser ranging will become ideal for gravitational-wave detection, and testing relativistic gravity and measuring solar-system parameter to an unprecedented accuracy. ASTROD I is such a mission with single spacecraft; it is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) with 3 spacecraft. In this paper, we will present the progress of ASTROD and ASTROD I with emphases on the acceleration noises, mission requirement, charging simulation, drag-free control and low-frequency gravitational-wave sensitivity.