Millimetron space observatory will operate in the vicinity of Lagrange point 2 (L2) of the Sun-Earth system. The halo orbit in L2 point of the Sun-Earth system is the most suitable configuration for single-dish mode, where the best sensitivity is required. Such orbit reduces the load on the active cooling system of Millimetron observatory telescope and provides unprecedented angular resolution. The halo orbit is located near L2 point at a distance of 1.5 million km from Earth in the direction opposite to the Sun. Parameters of considered halo-orbit in L2 point are the following:
- The maximum spacecraft exit from the ecliptic plane is 910 thousand km
- Halo-orbit period – 180 days
However, additional option for Millimetron orbital configuration is now being considered. Namely, to transfer the space observatory to near-Earth orbit after L2 point. Near-Earth orbit will provide more opportunities for VLBI mode, in particular obtaining high-quality two-dimensional images of black hole shadow. The optimal configuration of the near-Earth orbit is high elliptical orbit (HEO). The transfer from L2 point orbit to HEO orbit with an apogee of up to 340,000 km and a large eccentricity (> 0.9) can be performed using a gravitational maneuver near the Moon (Kovalenko, et al., 2018) without significant energy costs (Δv ~ 100 m/s).
Parameters of possible near-Earth HEO are the following:
- Apogee – 320 000 km
- Perigee – 10 000 km
- Orbit period – 10 days
The spacecraft will be launched by a heavy-class launcher.