Orbit design for the Spectrum-Roentgen-Gamma mission

Spectrum-Roentgen-Gamma is an international X-ray astrophysical space observatory, planned to be launched in 2019. The spacecraft will operate in the vicinity of the Lagrangian point L 2 of the Sun-Earth system. The nominal lifetime of the mission is 7 years, and it includes all-sky survey and pointed observations in the 0.1–15 keV band. The paper describes technical constraints of the mission, covering launch scenario, spacecraft structure and ground data relay network, and a design of suitable operational orbits. In addition, opportunities to achieve a suitable operational orbit are discussed, including a scenario with a lunar gravity assist and a transfer with an intermediate orbit.