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The Janus mission has been postponed indefinitely. The spacecraft is being prepared for long-term storage.

Janus is a mission designed to send two small spacecraft to near-Earth asteroids. Each spacecraft will fly by a binary asteroid and image it with visible and infrared cameras. The two binary asteroid systems initially chosen were (175706) 1996 FG3 and (35107) 1991 VH. The primary scientific objectives are to identify and understand the processes that lead to binary asteroid formation, and test and evaluate theories for binary asteroid evolution by studying the unique dynamical states of binary asteroid systems. Janus is part of the NASA Small Innovative Missions for Planetary Exploration (SIMPLEx) program.

Each spacecraft (Janus A and Janus B) has a mass of approximately 36 kg and is described as being about the size of a piece of carry-on luggage. Each spacecraft carries a visible and infrared imaging camera. Power is provided by deployable solar panels and rechargeable batteries. Propulsion is supplied by a monopropellant MiPS (Micro-Propulsion System) using LMP-103S green propellant.

Janus was slated for launch as a secondary satellite on the Psyche mission, but is now postponed due to a delay in the Psyche launch. Launch was scheduled for no earlier than 20 September 2022 on a Falcon 9 Heavy booster from Cape Canaveral Air Force Base into a heliocentric orbit. The following is the original mission plan, now subject to change when a new launch date is determined. The spacecraft were to be released from the main spacecraft and after an Earth gravity assist flyby in August 2025 would be targeted to their respective binary asteroid systems. One spacecraft was to fly by system 1991 VH on 3 March 2026 and the other to fly by 1996 FG3 on 20 April 2026. End of flight operations was planned for 31 May 2026.

Both binary asteroid systems, (175706) 1996 FG3 and (35107) 1991 VH, have been closely observed with photometry, spectrometry and radar. In the 1996 FG3 system, the primary asteroid is about 1640 meters in diameter, and the secondary is 515 meters. The primary for 1991 VH is 1120 meters across, and the secondary 450 meters.

Alternate Names

    Facts in Brief

    Launch Date: 
    Launch Vehicle: 
    Launch Site: Cape Canaveral, United States
    Mass: 36 kg

    Funding Agency

    • National Aeronautics and Space Administration (United States)


    • Planetary Science

    Additional Information

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



    NameRoleOriginal AffiliationE-mail
    Dr. Beau BierhausProject
    Dr. Dan ScheeresMission Principal InvestigatorUniversity of
    Dr. Jay McMahonDeputy Mission Principal InvestigatorUniversity of
    Dr. Christine M HartzellMission ScientistUniversity of
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