Lucy (spacecraft)


Lucy is a NASA space probe on a twelve-year journey to eight different asteroids. It is slated to visit two main belt asteroids as well as six Jupiter trojans – asteroids that share Jupiter's orbit around the Sun, orbiting either ahead of or behind the planet. All target encounters will be flyby encounters.
The Lucy spacecraft is the centerpiece of a US$981 million mission. On 4 January 2017, Lucy was chosen, along with the Psyche mission, as NASA's Discovery Program missions 13 and 14 respectively. It was launched on 16 October 2021. In November 2023 and in April 2025 it flew by and photographed asteroids Dinkinesh and Donaldjohanson, respectively. Lucy will reach its first main target, the Jupiter Trojan asteroid Eurybates, in August 2027.
The mission is named after the Lucy hominin fossils, because study of the trojans could reveal the "fossils of planet formation": materials that clumped together in the early history of the Solar System to form planets and other bodies. The hominid itself was named after the 1967 Beatles song "Lucy in the Sky with Diamonds". The spacecraft carries a disc made of lab-grown diamonds for its L'TES instrument.

Overview

Lucy was launched from Cape Canaveral SLC-41 on 16 October 2021, at 09:34 UTC on the 401 variant of a United Launch Alliance Atlas V launch vehicle. It gained one gravity assist from Earth a year later on 16 October 2022, and after making a flyby of the asteroid 152830 Dinkinesh in 2023, gained another gravity assist from Earth in 2024. In 2025, it flew by the inner main-belt asteroid 52246 Donaldjohanson, which was named after the discoverer of the Lucy hominin fossil. In 2027, it will arrive at the Trojan cloud, where it will fly by four Trojans, 3548 Eurybates, 15094 Polymele, 11351 Leucus, and 21900 Orus. After these flybys, Lucy will return to Earth in 2031 for another gravity assist toward the Trojan cloud, where it will visit the binary Trojan 617 Patroclus with its satellite Menoetius in 2033. The mission may end with the Patroclus–Menoetius flyby, but at that point Lucy will be in a stable, 6-year orbit between the L4 and L5 clouds, and a mission extension will be possible.
Three instruments comprise the payload: a high-resolution visible imager, an optical and near-infrared imaging spectrometer, and a thermal infrared spectrometer. Harold F. Levison of the Southwest Research Institute in Boulder, Colorado is the principal investigator, with Simone Marchi of Southwest Research Institute as the mission's deputy principal investigator. NASA's Goddard Space Flight Center executes the mission under the direction of the Planetary Missions Program Office at Marshall Space Flight Center for the Planetary Science Division-Science Mission Directorate at NASA HQ.
Exploration of Jupiter Trojans is one of the high-priority goals outlined in the Planetary Science Decadal Survey. Jupiter Trojans have been observed by ground-based telescopes and the Wide-field Infrared Survey Explorer to be "dark with... surfaces that reflect little sunlight". Jupiter is from the Sun, or about five times the Earth-Sun distance. The Jupiter Trojans are at a similar distance but can be somewhat farther or closer to the Sun depending on where they are in their orbits. There may be as many Trojans as there are Main-belt asteroids.

Development

NASA selected Lucy through the Discovery Program Announcement of Opportunity released on 5 November 2014. Lucy was submitted as part of a call for proposals for the next mission for Discovery Program that closed in February 2015. Proposals had to be ready to launch by the end of 2021. Twenty-eight proposals were received in all.
On 30 September 2015, Lucy was selected as one of five finalist missions, each of which received US$3 million to produce more in-depth concept design studies and analyses. Its fellow finalists were DAVINCI, NEOCam, Psyche and VERITAS. On 4 January 2017, Lucy and Psyche were selected for development and launch.
On 31 January 2019, NASA announced that Lucy would launch in October 2021 on an Atlas V 401 launch vehicle from Cape Canaveral, Florida. The total cost for the launch was estimated to be US$148.3 million. On 11 February 2019, SpaceX protested the contract award, claiming that it could launch Lucy into the same orbit at a "significantly cheaper cost". On 4 April 2019, SpaceX withdrew the protest.
On 28 August 2020, NASA announced that Lucy had passed its Key Decision Point-D with a "green light" to assemble and test the spacecraft and its instruments. The spacecraft instruments arrived beginning with L'LORRI on 26 October 2020. On 30 July 2021, the spacecraft was transported on a C-17 transport aircraft to Florida for launch preparations, and Lucy was encapsulated into the rocket fairing on 30 September 2021.
Lucy was launched on 16 October 2021 at 09:34 UTC at the opening of its 23-day launch window.

Scientific instruments

The science payload includes:
  • L'Ralph – panchromatic and color visible imager and infrared spectroscopic mapper. L'Ralph is based on the Ralph instrument on New Horizons and was built at Goddard Space Flight Center. It will be used to measure silicates, ices, and organics at the surface. The L'Ralph instrument has a three-mirror anastigmat design f/6 with a 75mm aperture. The telescope structure is composed from one aluminum block to provide an athermal imaging system. A beamsplitter transmits the longer wavelength light to LEISA and reflects light short of ~960nm to MVIC. The instrument is passively cooled with a diameter radiator that cools the LEISA detector to ~100K. A new component of the L'Ralph instrument compared with its predecessors is a scan mirror assembly. The scan mirror is used to sweep the target across the Ralph focal planes to build up either visible images or infrared spectra.
  • L'LORRI – high-resolution visible imager. L'LORRI is derived from the LORRI instrument on New Horizons and was built at the Johns Hopkins University Applied Physics Laboratory. It will provide the most detailed images of the surface of the Trojans. L'LORRI uses the same detector and has the same optical design as New Horizons LORRI. The primary mirror has a diameter of 20.8cm, the system has a focal length of 262cm, and the detector is a 1024 × 1024 thinned back-illuminated frame transfer CCD from Teledyne e2v. Each pixel subtends 5μrad and will have a point-spread function with a FWHM of less than 15μrad. Differences from the heritage instrument worth noting are the addition of redundant electronics, memory to store LORRI data, and the difference in the instrument accommodation. On New Horizons, the LORRI instrument is inside of the spacecraft, but on Lucy L'LORRI is mounted on an Instrument Pointing Platform.
  • L'TES – thermal infrared spectrometer. L'TES is similar to OTES on the OSIRIS-REx mission and was built at Arizona State University. It will reveal the thermal characteristics of the observed Trojans, which will also inform the composition and structure of the material on the surface of the asteroids. OTES was used to derive the surface composition and thermal inertia of the asteroid Bennu. However, because the Trojan asteroids at 5AU are much colder than Bennu, the Lucy mission does not plan to use L'TES to derive surface composition. Instead, L'TES will be used primarily to infer regolith properties. L'TES has the same optical–mechanical design as OTES, including a 15.2cm diameter Cassegrain telescope, a Michelson interferometer with chemical vapor deposited diamond beamsplitter, and an uncooled, deuterated L-alanine doped triglycine sulfate pyroelectric detector. L'TES has only small differences from the heritage instrument including removing a potential stray light path by modifying the telescope baffle and primary mirror inner diameter and improvements to the metrology laser system. An internal calibration cone blackbody target provides radiometric calibration. The L'TES instrument collects data from 6–75μm and has a noise equivalent spectral radiance of 2.310–8Wcm−2sr−1cm−1 between 300cm−1 and 1350cm−1. For surfaces with temperatures greater than 75K, L'TES will determine the temperature with an accuracy of 2K. The 50% encircled energy of the instrument subtends 6.5 mrad. L'TES has one mode of taking data. It continuously collects interferograms and transfers them to the spacecraft for storage before downlink. The instrument will start collecting data one day before closest approach, which is before the target fills the instrument's FOV. The data collection will continue until one day after closest approach. The L'TES instrument will measure the radiance of each Trojan asteroid at four locations at different local times of day with the additional requirement that one observation measures a location within 30° of the subsolar point and another measures the unilluminated surface.
  • The radio science investigation will determine the mass of the Trojans by using the spacecraft radio telecommunications hardware and high-gain antenna to measure Doppler shifts.
  • T2CAM – terminal tracking camera would be used to take wide-field images of the asteroids to better constrain the asteroids shapes.

    Golden plaque

On board the spacecraft is a golden plaque that contains its launch date, the positions of the planets at the launch date, the continents of Earth at the time of launch, its nominal trajectory, and twenty speeches, poems, and song lyrics from people such as Martin Luther King Jr., Carl Sagan, The Beatles, and more. Because the spacecraft will not leave the Solar System or be intentionally crashed into a planetary body, there is a chance that future generations of humanity will be able to recover it.