  TianQin is a proposed space-based gravitational-wave observatory mission to
be deployed in high circular Earth orbits. The equilateral-triangle
constellation, with a nearly fixed orientation, can be distorted primarily
under the lunisolar perturbations. To accommodate science payload requirements,
one must optimize the orbits to stabilize the configuration in terms of
arm-length, relative velocity, and breathing angle variations. In this work, we
present an efficient optimization method and investigate how changing the two
main design factors, i.e., the orbital orientation and radius, impacts the
constellation stability through single-variable studies. Thereby, one can
arrive at the ranges of the orbital parameters that are comparatively more
stable, which may assist future refined orbit design.
