High performance telescope system design for the TianQin project

China is planning to construct a new space-borne gravitational-wave (GW) observatory, the TianQin project, in which spaceborne telescope an important component laser interferometry. The aimed transmit beams between spacecrafts for measurement of displacements proof-masses long arms. should have ultra-small wavefront deviation minimize noise caused by pointing error, ultra-stable structure optical path temperature jitter, ultra-high stray light suppression ability eliminate background noise. In this paper, we realize system design with as well ultra-low distortion space-based GW detection mission. requirements demand extreme control high image quality and extraordinary ability. Based on primary aberration theory, initial mentioned four-mirror explored. After optimization, maximum RMS error less than lamda/300 over full field view (FOV), meets budget design. back reflection also analyzed. at position bench 10-10 transmitted power, satisfying space detection. We believe that our can be good candidate guide any other similar science project.