NASA’s next asteroid mission, Lucy, will seek the origin story of asteroids that share Jupiter’s orbit – and already it’s been a long road to the launch pad.
The last 18 months of the mission has been dominated by numerous changes due to the coronavirus pandemic, ranging from physical distancing to manufacturing changes. Mission officials paid tribute to the hundreds of core team members and numerous other suppliers in a press conference Wednesday (Oct. 13).
“This team has put in so much work to build a spacecraft that is truly a work of art,” said Donya Douglas-Bradshaw, the Lucy project manager at NASA’s Goddard Space Flight Center in Maryland. “The spacecraft work is complete, it’s been powered on, the team is monitoring it and we are ready to launch.”
A rocket switch added to the last-minute changes in mission planning, producing wrinkles to a process that typically takes years at the least to perfect. United Launch Alliance ended up converting the rocket that was supposed to bear the OFT-2 test of Boeing’s Starliner spacecraft to the International Space Station; Starliner is off the pad indefinitely to address valve issues.
The team changed the booster configuration through modifications such as removing two solid rocket motors and replacing an avionics box, along with other adjustments to put a fairing on the rocket instead of the planned Starliner spacecraft.
“We were able to make that a positive in that we were able to use the OFT[-2] booster and convert it for use for Lucy,” Omar Baez, launch director for Lucy at NASA’s Launch Services Program at the Kennedy Space Center in Florida, said during the news conference.
Getting ready to leave Earth has been a journey already, and for Lucy’s team the key work is only about to begin. The spacecraft will zoom by eight small worlds in the next 12 years or so, with most of those flybys jetting close to Jupiter’s Trojans – asteroids trapped in the same orbit as the giant planet, thanks to Jupiter’s gravitational influence.
NASA has had a variety of asteroid missions in the past two decades, such as the ongoing asteroid sample return mission OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer), which includes Canadian participation. Internationally, entities such as the European Space Agency and the Japan Aerospace Exploration Agency have studied small worlds in recent years through missions such as Rosetta (which stayed by a comet for several months) and Hayabusa2 (another asteroid sample return mission).
But what makes Lucy stand apart is the sheer number of worlds it will study, and its first-ever visit by humanity to the Trojans. “They hold vital clues to deciphering the history of our solar system,” principal investigator Harold Levison, of the Southwest Research Institute, said in a recent statement. The institute added that the numerous asteroid close-ups it will perform will assist scientists in understanding why asteroids vary so much between types.
Here is more of what to expect from the mission, which is expected to launch no earlier than Saturday (Oct. 16).
Science questions and instruments
Lucy’s mission goals are the following:
- Map surface geology: Including albedo, shape, crater distribution and sizing, crustal structure and layering, and the relative ages of surface areas.
- Map surface color and composition: Including color, composition and regolith properties, along with distribution of minerals, ice and organic materials.
- Analyze asteroid interiors: Including masses, densities and subsurface composition (the latter of which can be obtained through features such as craters and fractures.)
- Search for satellites and rings: An ongoing investigation whereby Lucy will scan the Trojans it sees to look for rings and satellites that may not be visible in Earth-bound telescopes.
The mission instruments include:
- L’Ralph: This is made up of two instruments: A color visible imager (Multi-spectral Visible Imaging Camera, or MVIC) and an infrared imaging spectrometer (Linear Etalon Imaging Spectral Array, or LEISA). MVIC will obtain color images and map Trojan activity, while LEISA will scan for absorption lines indicating asteroid composition. The name “Ralph”, by the way, is not an acronym; it’s a reference to a 1950s character from the television show “The Honeymooners” and has heritage from the NASA New Horizons mission that flew past Pluto and Kuiper Belt objects. New Horizons had another instrument with the acronym ALICE, after another “Honeymooners” character.
- L’LORRI (LOng Range Reconnaissance Imager): A panchromatic, high resolution visible imager that will provide detailed surface images.
- L’TES (Thermal Emission Spectrometer): An infrared spectrometer similar to what flew on another asteroid mission by NASA (OSIRIS-REx) along with the NASA Mars Global Surveyor. It will examine properties such as thermal inertia, or how well asteroids retain heat – an indication of mineral composition and internal structure.
- T2CAM (Terminal Tracking Camera): A wide-field camera to obtain information about the asteroid shapes, which may give hints as to their history.
- High Gain Antenna: While this is technically a communications device, it will be repurposed periodically into a method to obtain the masses of asteroids through calculating the Doppler shift of the radio signal.
Target overview
Here’s a quick list of the targets that Lucy will visit, along with the projected visit dates on the official mission website. It is possible that investigators may add more asteroids to the list, either through long-distance imaging or through extending the mission, but that will depend on spacecraft resources such as fuel and power.
(52246) Donaldjohanson (April 20, 2025): This is a main belt C-type (carbonaceous) asteroid roughly 4 km in diameter. The asteroid is one leftover from a large collision 130 million years ago that created the (163) Erigone family of asteroids. Donald Johanson was one of the discoverers of the Lucy hominid fossil, which indirectly inspired the Lucy mission name. (The Lucy hominid team played The Beatles’ “Lucy In The Sky With Diamonds” during the 1974 excavation, which inspired the skeleton’s name; the name had resonance for the Lucy spacecraft team, which is studying the origins of asteroids and saw analogies with the origins of people.)
(3548) Eurybates (August 12, 2027): This is a Trojan C-type asteroid roughly 64 km in diameter, and late in mission planning (2019) the Lucy team found out that Eurybates has a small satellite – allowing for an unintentional but valuable investigation of two asteroids in one visit. Like Donaldjohanson, Eurybates is part of a “collisional family”, and investigators hope to learn more about why these collision groups appear so rare among Trojans. Scientists are also trying to draw distinctions between C-type asteroids (which can appear in families) and D-type asteroids (which appear to resemble icy Kuiper Belt objects). For example, the team hopes to learn why there are no D-type families in the Trojan group or the main asteroid belt. There are two hypotheses: D-type asteroids may disintegrate after colliisions, or D-types might transform to C-types post collision.
(15094) Polymele (Sept. 15, 2027): This is a P-type asteroid about 21 km in diameter; its organic composition is similar to the icy D-type asteroids, but how P-types are distinct is difficult to say because we have no samples of such asteroids yet. Polymele is also a likely collisional fragment of a larger P-type asteroid, so we may be able to infer more characteristics of the larger group by studying this single world.
(11351) Leucus (April, 18, 2028): This D-type asteroid is 40 km in diameter and has a notably long “day” of 446 Earth hours (more than 18.5 Earth days). Such a slow rotation rate means that one side of the asteroid is likely much warmer than the other side, making Leucus potentially distinct from other D-type asteroids in terms of its temperature profile and allowing (potentially) an easier time in trying to seek its composition, as the spectra lines should be distinct. Large variations in its luminosity, as seen from Earth, also suggest an unusual elongated shape – which will be confirmed (or denied) after the Lucy flyby.
(21900) Orus (Nov. 11, 2028): This D-type asteroid is 51 km in diameter and will allow for a direct comparison to Leucus, given the two are of similar size and similar composition. By then, analysis on Eurybates should also be advanced, allowing scientists to draw more distinctions between D-type and P-type asteroids based on new close-up observations.
(617) Patroclus and Menoetius (March 3, 2033): This is a binary pair of asteroids with diameters of 113 km and 104 km, respectively. The duo may be primordial or ancient asteroids from the earliest days of the solar system. Unlike the other Lucy targets, the binary pair is very inclined to the ecliptic, at 22 degrees; given fuel requirements, normally Lucy would not be able to venture so far out of the plane of the solar system. Happily, by coincidence the pair will pass closer to the ecliptic just as Lucy is in position to image them.
Orbital overview:
Lucy’s orbit is complex, bringing it in and out of the outer solar system over a period of a dozen years. Simply put, this is what to expect from the mission.
- Two Earth gravity assists and an asteroid flyby: Following launch, Lucy will swing by Earth twice to pick up speed for the trip to the outer solar system. On its way out, Lucy will fly by (52246) Donaldjohanson.
- Visiting the ‘Greek camp’: Lucy will fly by the L4 Trojan swarm first, which is nicknamed the “Greek camp” because most of the names of the Trojans here are named after Greek heroes from “The Iliad”, a tale by Homer about the Trojan War. Lucy will visit (3548) Eurybates and its satellite Queta, (15094) Polymele, (11351) Leucus and (21900) Orus.
- A third Earth gravity assist: Lucy will become the first spacecraft to make a flyby of Earth from the outer solar system, again to pick up speed and correct its orbital path for the next phase of its mission.
- Visiting the ‘Trojan camp’: Lucy will fly by the L5 Trojan swarm next, which is nicknamed the “Trojan camp” because most of the names of the Trojans here are named after the “Trojan spies” portrayed in “The Iliad.” Two very famous names from the Homeric story will play into this flyby: (617) Patroclus, and its binary companion Menoetius.
End of mission: Lucy is expected to be on the end of its mission at this point, but its orbit will remain so stable that investigators were inspired to include a mission plaque in the same vein as the Pioneer 10 and 11 missions, and the Voyager 1 and 2 missions, of the 1970s. That said, the Lucy plaque is a message to future humans and not to aliens, because the spacecraft (unlike the four predecessors that carried plaques) will remain inside the solar system.