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EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) is a 6U cubesat designed to reach an Earth-Moon libration orbit. It is a JAXA (Japan) and University of Tokyo technology demonstration mission with the primary objective of demonstrating trajectory control techniques exploiting Sun-Earth_Moon dynamics, with the possibility of reaching an Earth-Moon libration orbit. It will also perform scientific observations with a suite of instruments. EQUULEUS will be launched as a secondary ride-on satellite on the Artemis 1 Space Launch System.

EQUULEUS is a 6U cubesat with dimensions 10 x 20 x 30 cm and a mass of approximately 11.5 kg. Power (50 W at 1 AU) is provided by two deployable solar arrays and batteries. Propulsion and attitude control are achieved using the AQUARIUS system, a warm gas propulsion system with water as the propellant. The system comprises 8 water thrusters, with a planned thrust of 3.3 mN and an Isp of 70 seconds. Total mass of water propelled is 1.22 kg, providing a total delta-v of 77 m/s. Communications are through an X-band transponder and one medium-gain and one large-gain antenna. EQUULEUS carries three scientific instruments: PHOENIX, an extreme ultraviolet imager; CLOTH, a dust detector; and DELPHINUS, a camera designed to detect impact flashes.

After launch in late 2021 or early 2022 as a ride-on payload on the SLS with Artemis 1, EQUULEUS will be released to perform a lunar flyby, followed by maneuvers exploiting Earth-Sun-Moon dynamics to bring it to a libration orbit around the Earth-Moon L2 LaGrange point using a minimal amount of propellant.

Alternate Names

    Facts in Brief

    Launch Date: 
    Launch Vehicle: SLS Block 1 Crew
    Launch Site: Cape Canaveral, United States
    Mass: 11.5 kg
    Nominal Power: 50 W

    Funding Agency

    • Japan Aerospace Exploration Agency (Japan)


    • Planetary Science
    • Engineering

    Additional Information

    Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



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