  In future geocentric space-based gravitational-wave observatory missions,
eclipses due to passing through the Moon's and Earth's shadows can negatively
impact the sciencecraft's thermal stability and steady power supply. The
occurrence should be reduced as much as possible in orbit design. In regard to
TianQin's circular high orbits, we tackle the combined challenges of avoiding
eclipses and stabilizing the nearly equilateral-triangle constellation. Two
strategies are proposed, including initial phase selection and orbit resizing
to 1:8 synodic resonance with the Moon, where the latter involves slightly
raising TianQin's preliminary orbital radius of $1\times 10^5$ km to $\sim
100900$ km. As the result, we have identified pure-gravity target orbits with a
permitted initial phase range of $\sim 15^\circ$, which can maintain
eclipse-free during the 3+3 month observation windows throughout a 5-year
mission started in 2034, and meanwhile fulfil the constellation stability
requirements. Thereby the eclipse issue for TianQin can be largely resolved.
