EQUULEUS: Initial Operation Results of an Artemis-1 CubeSat to the Earth—Moon Lagrange Point

EQUULEUS is a 6U CubeSat developed by the Japan Aerospace Exploration Agency (JAXA) and the University of Tokyo, aiming to reach the Earth-Moon second Lagrange point (EML2) and perform scientific observations there. After being inserted into a lunar transfer orbit by SLS Artemis-1 on November 16, 2022, the spacecraft completed checkout operations and successfully performed a delta-V maneuver and subsequent trajectory correction maneuver. This enabled a precise lunar flyby as planned and successful insertion into the orbit toward EML2, which will take advantage of multiple lunar gravity assists and the gravity of the Sun. EQUULEUS is equipped with a water propulsion system newly developed by the University of Tokyo, and became the first spacecraft in the world to successfully control its orbit beyond low Earth orbit using water propulsion. The successful precise orbit control in the Sun–Earth–Moon region by EQUULEUS, a 6U CubeSat weighing only 10kg, has opened the possibility of full-scale lunar and planetary exploration by CubeSats. This paper describes the early operational results of EQUULEUS during its flight to EML2, with special emphasis on its precise orbit determination, guidance, and control results