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Image Credit: NASA/Bill Ingalls.

Lucy spacecraft ready to begin 12-year long mission to the Jupiter Trojans

This Saturday, October 16, 2021 at 05:34 EDT (local time) / 06:34 UTC, NASA’s Lucy space probe is scheduled to blast off from Earth to begin its record-breaking 12-year long mission. The spacecraft will launch atop an United Launch Alliance Atlas V 401 rocket from Space Launch Complex 41 at the Cape Canaveral Space Force Station in Florida, USA.

As the first spacecraft in the history of spaceflight, Lucy will visit the Jupiter Trojans, two swarms of old asteroids from the early days of the Solar System never to be studied from up close ever before.

The 23-day long launch window opens on October 16 and runs through November 7, 2021. If for any reason the launch can’t take place within this time period, NASA would have to postpone the launch for several years.

Lucy and its Atlas V 401 rocket seen at Space Launch Complex 41 at the Cape Canaveral Space Force Station in Florida. Image Credit: NASA/Bill Ingalls.
Lucy and its Atlas V 401 rocket seen at Space Launch Complex 41 at the Cape Canaveral Space Force Station in Florida. Image Credit: NASA/Bill Ingalls.

The Lucy spacecraft

Spacecraft and mission overview

Lucy is a Lockheed Martin built space probe operated by the National Aeronautics and Space Administration (NASA). Lucy will visit over half a dozen asteroids, to learn more about the formation of the Solar System. As the first spacecraft in history, Lucy will visit the Jupiter Trojan asteroids, two swarms of remnants of the early Solar System, located at the Sun-Jupiter L4 and L5 Lagrangian points, 60 degrees in front and behind Jupiter on its orbit around the Sun. The primary mission will last 12 years and the probe will travel over six billion kilometers through deep space.

With deployed solar arrays, the spacecraft will be 15.82 m in diamter, 7.28 m in height and 2.00 m in width. Lucy has a dry mass of 771 kg and will weigh 1,500 kg at launch.

Artist render of Lucy and a Trojan asteroid. Image Credit: Southwest Research Institute.
Artist render of Lucy and a Trojan asteroid. Image Credit: Southwest Research Institute.

Instruments and science objectives

To gain a better understanding on the formation of the early Solar System, Lucy will study the Trojan asteroids using a range of multiple instruments. The main focus lays on the asteroids’ surface geology, color, interior composition, distribution of minerals, ices and organic molecules, as well as the discovery of small moons and rings around the celestial bodies.

L’LORRI

The Lucy LOng Rang Reconnaissaince Imager, or L’LORRI for short, is a panchromatic camera based on a Ritchey-Chrétien telescope and derived from the LORRI camera onboard NASA’s New Horizons probe. L’LORRI was built by the Johns Hopkins Applied Physics Laboratory and will take high-resolution images of the Trojan asteroids’ surfaces to study the objects’ surface geology.

L’Ralph

The L’Ralph instrument is based on the Ralph instrument onboard New Horizons, as well as the OVIRS instrument onboard NASA’s OSIRIS-REx probe. L’Ralph was built by NASA’s Goddard Space Flight Center and consists of an infrared spectroscopic mapper named the Linear Etalon Imaging Array (LEISA) and a panchromatic and color visible camera known as MVIC (Multispectral Visible Imaging Camera). The instrument will help determine the asteroids’ surface composition, by analyzing the organic molecules, ices and hydrated minerals the surfaces are made of.

L’TES

The Lucy Thermal Emission Spectrometer, or L’TES for short, is a thermal infrared spectrometer based on the OTES (OSIRIS-REx Thermal Emission Spectrometer) on the OSIRIS-REx space probe. L’TES was built by the Arizona State University and will detect far infrared radiation emitted from the asteroids. Because different materials cool down quicker than others, measuring the asteroids’ surface temperature at different times of a day will allow scientists to deduce the celestial bodies’ surface composition.

T2CAM

The T2CAM is a terminal tracking camera used to track the asteroids and to help navigate Lucy through deep space. Scientists will use this camera to take wide-field images of the Trojan asteroids to better determine their shapes.

Lucy’s name

The probe is named after Lucy, a 3.2 million years old skeleton of a female Australopithecus afarensis found in 1974 in Ethiopia. Just as the Lucy skeleton allowed scientist to learn more about humanity’s evolution, the Lucy spacecraft will provide researchers with the neccessary informations needed to better understand the formation of our Solar System.

The Lucy space probe seen at the Astrotech Space Operations Facility ahead of its launch. Image Credit: NASA/Kim Shiflett.
The Lucy space probe seen at the Astrotech Space Operations Facility ahead of its launch. Image Credit: NASA/Kim Shiflett.

The Atlas V launch vehicle

The Atlas V is an expendable, two-stage, medium-lift lauch vehicle build and operated by the United Launch Alliance (ULA), a joint venture between Lockheed Martin Space Systems and Boeing Defense, Space & Security formed in 2006.

The rocket’s core stage, known as the Common Core Booster (CCB), is 32.46 m in length, 3.81 m in diameter and is loaded with over 280 tonnes of liquid oxygen (LOX) and RP-1. The stage is powered by two Russian RD-180 rocket engines build by NPO Energomash, providing up to 4,152 kN of thrust at sea level and 3,827 kN in vacuum.

Depending on the configuration, the Atlas V can be equipped with up to five solid rocket boosters attached to the CCB. The rocket used to launch Lucy, the Atlas V 401, does not feature any additional boosters.

Atop the first stage, the Centaur upper stage is located. The cryogenic rocket stage is 12.68 m in height, 3.05 m in diameter and is loaded with almost 21 tonnes of LOX and liquid hydrogen (LH2). For the majority of launches, Atlas V’s upper stage is equipped with a single Pratt & Whitney RL10 rocket engine. For the launches of the Boeing CST-100 Starliner crew capsule to the International Space Station, the launch vehicle utilizes a dual-engine Centaur second stage.

On the Atlas V 401, the Centaur is connected to the Common Core Booster via an Interstage Adapter (ISA) and an Aft Stub Adapter (ASA).

Lucy is connected to the Centaur via the payload adapter and the Centaur Forward Adapter and was encapsulated in a two-half, 4.2 m diameter payload fairing.

The Atlas V 401 is capable of placing 9,800 kg into a 28.7° inclined low Earth orbit, 8,080 kg into a polar orbit, or 4,750 kg into a 27.7° inclined geostationary transfer orbit.

The Atlas V had its maiden flight in August 2002 and has since been launched 88 times. Its most recent launch on September 27 orbited NASA’s and the USGS’ Landsat 9 Earth observation satellite, as well as four secondary payloads.

An Atlas V 401 blast off from Vandenberg on Nov. 11, 2016, carrying the WorldView-4 Earth observation satellite into orbit. Image Credit: United Launch Alliance.
An Atlas V 401 blast off from Vandenberg on Nov. 11, 2016, carrying the WorldView-4 Earth observation satellite into orbit. Image Credit: United Launch Alliance.

Mission profile and timeline

At T-2.7 seconds, the two liquid-fueled RD-180 rocket engines on Atlas V’s first stage will ignite, lifting the rocket and the Lucy space probe off the pad and toward space.

About 1 min 19 s into the flight, the launch vehicle will break the sound barrier and will pass through Max-Q, the point of maximum aerodynamical stress.

At T+4 min and 2 s, propellant levels in Atlas V’s core stage will deplete, the rocket engines will shut down and the first stage will separate from the Centaur upper stage. This will be followed by the ignition of the Centaur’s RL10 engine just seconds later.

Once the rocket has passed through Earth’s atmosphere, the two payload fairing halves protecting the payload up to this point, will be jettisoned, exposing Lucy to the vacuum of space.

After 13 minutes and 9 seconds of flight, the RL10 rocket engine on the launcher’s second stage will shut down and Centaur will enter a 27 1/2 minutes long coast phase.

At T+40 min and 27 s, the RL10C-1 will reignite for a second, six minutes long burn.

After 58 minutes of flight, Lucy will be separated from the Atlas V’s upper stage to begin its record-breaking 12-year long mission.

Once in space, Lucy will conduct two fly bys at Earth to use the planet’s gravity to assist in its journey to the leading Trojan swarm. The first gravity assist is scheduled to occur in 2022, the second in 2024.

About 3 1/2 years after its launch, Lucy will fly by its first target, the main belt asteroid 52246 Donaldjohanson.

Another two years later, the probe is expected to arrive at the Trojan swarm located at the Sun-Jupiter L4 Lagrangian point. Lucy will first fly by asteroid 3548 Eurybates and its moon Queta on August 12, 2027, before visiting 15094 Polymele on September 15, 2027, 11351 Leucus on April 18, 2028 and finally 21900 Orus on November 11, 2028.

Its trajectory will then bring Lucy back into the inner Solar System for a third gravity assist at Earth in 2030.

Lucy is scheduled to arrive at the probe’s final destination, a binary system located at the trailing Trojan swarm at the Sun-Jupiter L5 Lagrangian point, in 2033. The fly by at asteroid 617 Patroclus and its companion Menoetius will occur on March 3, 2033. This rendezvous will bring an end to Lucy’s primary mission. If the spacecraft continues to be functioning properly, a mission extension might be considered.

An illustration of the probe's long path through the Solar System. Image Credit: Southwest Research Institute.
An illustration of the probe’s long path through the Solar System. Image Credit: Southwest Research Institute.

The target asteroids

52246 Donaldjohanson

52246 Donaljohanson, also known as 1981 EQ5, is a main-belt asteroid orbiting the Sun in the asteroid belt between Mars and Jupiter.

The asteroid was discovered on March 2, 1981 by S. J. Bus at the Siding Spring Observatory in Australia.

Donaldjohanson, which is named after Donald Carl Johanson, the co-discoverer of the Lucy fossil, has a diameter of about 3.895 km and orbits the Sun every 3.68 years.

The asteroid will be the first target of the Lucy spacecraft. The probe will fly by Donaldjohanson in April 2025 on its way to the leading swarm of Trojan asteroids.

3548 Eurybates & Queta

3548 Eurybates, or 1973 SO, is a 63.89 km large Jupiter Trojan located in the “Greek camp”, the leading Trojan swarm at the Sun-Jupiter L4 Lagrangian point.

The large asteroid has a rotation period of 8.71 h and it takes Eurybates 11.86 years to complete one orbit around its parent star.

3548 Eurybates was discovered on September 19, 1973 by the two Dutch astronomers Ingrid and Cornelis van Houten on photographic plates taken by the Dutch-American astronomer Anton Gehrels at the Palomar Observatory.

Lucy will visit the asteroid, as well as its small moon Queta on August 12, 2027. Eurybates will be the first Trojan asteroid to be visited by Lucy and the first one to be seen from a close distance.

15094 Polymele

15094 Polymele, also known as 1999 WB2, is another Jupiter Trojan asteroid located at the Greek camp.

The celestial body was discovered on November 17, 1999 by astronomers with the Catalina Sky Survey.

The asteroid has a diameter of 21.08 km, a rotation period of 5.86 hours and an orbital period of 11.77 years.

Polymele will be visited by the Lucy spacecraft on September 15, 2027, just about a month after the probe’s fly by of asteroid Eurybates and its moon Queta.

11351 Leucus

11351 Leucus, also known as 1997 TS25, is the third Jupiter Trojan to be visited by Lucy.

Leucus has a diameter of 34.16 km, a rotation period of 445.73 hours and an orbital period of 12.19 years.

Lucy will fly by the celestial body on April 18, 2028 on route to asteroid 21900 Orus.

21900 Orus

21900 Orus, or 1999 VQ10, will be the final and largest Jupiter Trojan to be visited by Lucy at the Greek camp.

Orus is about 50.81 km in size, has an orbital period of 11.60 years and was discovered on November 9, 1999 by the Japanese amateur astronomer Takao Kobayashi at the Ōizumi Observatory in Japan.

Lucy’s rendezvous with 21900 Orus will occur on November 11, 2028.

617 Patroclus & Menoetius

The spacecraft’s first target at the trailing Trojan camp at the Sun-Jupiter L5 Lagrangian point and the final celestial body to be visited by Lucy, is a binary system consisting of asteroid 617 Patroclus and its companion Menoetius.

The two asteroids were discovered on October 17, 1906 by the astronomer August Kopff at the Heidelberg Observatory in Germany and were identified as a binary system in 2001.

While 617 Patroclus has a diameter of about 110 to 115 km, Menoetius is about 100 to 105 km in size. It takes the two celestial bodies just over 100 hours to orbit their center of mass and 11.90 years for one orbit around the Sun.

Patroclus and Menoetius will be visited by the probe on March 3, 2033.


Sources:

https://www.nasa.gov/sites/default/files/atoms/files/lucy_press_kit_2.pdf

https://solarsystem.nasa.gov/missions/lucy/in-depth/

https://solarsystem.nasa.gov/news/810/inspiration-links-the-beatles-a-fossil-and-a-nasa-mission/

https://www.ulalaunch.com/docs/default-source/rockets/atlasvusersguide2010a.pdf?sfvrsn=f84bb59e_2

https://www.ulalaunch.com/rockets/atlas-v

http://lucy.swri.edu/mission/Tour.html

https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Eurybates

https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Polymele

https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Leucus

https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Orus

https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Patroclus&view=OSPDA

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