# Cis-L2 Libration Point Halo Orbit

Queqiao became the first satellite to orbit the Cis-L2 libration point (far side of the moon). Link: https://en.wikipedia.org/wiki/Chang%27e_4

Does anyone have any insight on how to model this orbit in STK?

• Cool question! As I mention in this long-winded answer a halo orbit around an Earth-Moon Lagrange point is really a Earth orbit that happens to be in a 1:1: resonance with the Moon. (Watch the Kepler Telescope video there for an analogy) If STK allows for Earth orbits that far out and it includes a real, accurate ephemeris of the Moon, then maybe it's possible. A simple, approximate orbit propagator like SGP4 couldn't because it only approximates the effect of lunar gravity. – uhoh Jan 4 at 0:51
• However, the hard part of the problem is finding the orbit first! Without a known starting state vector, you will have to search a seven dimensional space ($\mathbf{x},$\mathbf{v}, \$\mathbf{x}, t) to find the specific orbit in question, seven rather than six because the Moon's orbit is so elliptical that CR3BP may not be good enough. – uhoh Jan 4 at 1:02