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The Lucy mission is designed to make flyby observations of seven asteroids - one main belt asteroid and six asteroids orbiting ahead of or behind Jupiter, known as Trojan asteroids. (The Trojan asteroids are asteroids trapped in the orbit of Jupiter in two swarms. The swarms librate about two Jupiter-Sun LaGrange points, one (L4) 60 degrees ahead of Jupiter in its orbit, and one (L5) 60 degrees behind.) It's primary science objectives are to study the surface composition, surface geology, interior, and bulk properties of the asteroids, an conduct a search for satellites and rings about the objects. These objectives are meant to help shed light on four fundamental questions: 1) what were the initial stages, conditions and processes of Solar System formation? 2) How did the giant planets accrete, and is there evidence that they migrated to new orbital positions? 3) What governed the accretion, and what roles did bombardment by large projectiles play? and 4) What were the sources of primordial organic matter?

Lucy is scheduled to launch on 16 October 2021. Any launch delays will involve high delta-V penalties due to the requirement of the mission to fly by many bodies at a variety of inclinations. A small deep space maneuver (DSM) with a delta-V of 14 m/s occurs on 15 November 2021 to position Lucy for its first Earth flyby exactly one year after launch, on 16 October 2022. This is followed by a DSM with a delta-V of 898 m/s on 2 February 2024 and a second Earth flyby on 13 December 2024. This puts Lucy on a trajectory to fly by main belt asteroid 52246 Donaldjohanson on 20 April 2025. Three years later, on 3 April 2027, DSM-3, with a delta-V of 311 m/s, is planned. This brings the spacecraft inclination to 4.98 degrees for its Trojan asteroid encounters. It flies by 3548 Eurybates on 12 August 2027, and then 15994 Polymele on 15 September 2027. The goal for the Polymele encounter is to fly within 399 km at closest approach in order to enable determination of the mass to within 25%. DSM-4, with a delta-V of 122 m/s, occurs on 29 September 2027. A flyby of 11351 Leucus occurs on 18 April 2028, leading to a flyby of 21900 Orus on 11 November 2028. The orbit then leads Lucy back to an Earth flyby on 26 December 2030, which changes the inclination by almost 9 degrees in preparation for the Patroclus-Menoetius binary pair flyby on 2 March 2033. This ends the nominal mission, but the final 6-year orbit the spacecraft is in after this flyby is resonant with Jupiter's 12-year period, allowing for the possibility of an extended mission.

The first asteroid to be encountered is 52246 Donaldjohanson, in the main asteroid belt. Donaldjohanson is a C-type asteroid with a diameter of 4 km. (All diameters listed here are estimates.) The other asteroids to be encountered represent a diverse sample of the types found in the two Trojan swarms. The first four orbit ahead of Jupiter. 3548 Eurybates is a 64 km diameter C-type asteroid. 15994 Polymele is a P-type asteroid with a diameter of 21 km. 11351 Leucus is a D-type asteroid with a diameter of 34 km and an extremely long (447 day) rotational period. 21900 Orus is also a D-type asteroid, with a diameter of 51 km. The last two bodies encountered are in the Jupiter trailing swarm and are a binary pair, designated 617 Patroclus-Menoetius. The primary, Patroclus, has a mean diameter of 113 Km and Menoetius has a mean diameter of 104 km. Both are irregularly shaped and, although they can be classified as P-type asteroids, it is possible they may actually be trapped Kuiper Belt objects, effectively comets rather than asteroids. This may be found to be true for other Trojans as well.

Alternate Names

    Facts in Brief

    Launch Date: 2021-10-16
    Launch Vehicle: Unknown
    Launch Site: Unknown, United States

    Funding Agency

    • National Aeronautics and Space Administration (United States)


    • Planetary Science

    Additional Information

    Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office



    NameRoleOriginal AffiliationE-mail
    Mr. Harold LevisonMission Principal InvestigatorSouthwest Research
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