ARTEMIS operations - Experiences and lessons learned

Abstract

THEMIS, a constellation of five spacecraft, referred to as probes, was launched in 2007 to study the physical processes leading to the aurora. In 2009, THEMIS successfully completed its primary mission phase. As an ambitious mission extension, the constellation was then split into two new missions -THEMIS-Low and ARTEMIS. THEMIS-Low refers to three of the five probes that continued magnetospheric observations in Earth orbits while the remaining two probes started a new lunar mission called ARTEMIS. The two ARTEMIS probes were transferred from Earth to lunar orbits via low-energy trajectories with Earth and lunar gravity assists. The complex mission design and navigation operations took the two probes on trajectories along weak stability boundary manifolds, venturing out as far as 1,500,000 km and 1,200,000 km from Earth, respectively. Upon arrival in the lunar environment, both probes were first inserted into libration point orbits where they spent up to ten months collecting science data. Periodic stationkeeping maneuvers were executed to ensure the two probes would not be ejected from these unstable orbits. In 2011, both probes were successfully inserted into stable, retrograde and prograde lunar orbits, respectively. We report on the challenges with executing the complex navigation plans, discuss experiences and lessons learned from operating two spacecraft in lunar libration point orbits for the first time ever, and finally cover mission planning and science operations in the lunar environment.

Attitude dynamics in the circular restricted three-body problem

“…The ARTEMIS spacecraft waives attitude control requirements to conserve propellant and avoid any residual ∆V from attitude maneuvers. An undesired net thrusting force would, in fact, negatively impact a trajectory that is very sensitive to disturbances [13]. In a multi-body regime, firing thrusters for attitude correction and reaction wheel desaturation may perturb a sensitive orbit, resulting in additional propellant cost for orbital stationkeeping.…”

“…Essentially, in the proper circumstances, the natural dynamical flow may assist, or even replace, the attitude control action. maneuvers were a serious concern for some past applications [11,13,14]. In the Genesis mission, the thruster configuration is unbalanced for constraints on the science payload and attitude corrections produce an important deterioration of the orbit [11].…”

“…Linear stability for out-of-plane small rotations may be deduced, again, analyzing a characteristic equation as in Eq. (13). For an axisymmetric spinning satellite, the coefficients for the characteristic equation are a function of a spacecraft location, mass parameter, nondimensional spin rate as observed in CR3BP rotating frame, σ, and the ratio between axial and transversal inertia, k = I a /I t .…”