NASA's Lucy spacecraft prepares to swing by earth
IMAGE: THIS ILLUSTRATION SHOWS THE LUCY SPACECRAFT PASSING ONE OF THE TROJAN ASTEROIDS NEAR JUPITER. view more
CREDIT: CREDITS: SOUTHWEST RESEARCH INSTITUTE
On Oct. 16, at 7:04 a.m. EDT, NASA’s Lucy spacecraft, the first mission to the Jupiter Trojan asteroids, will skim the Earth’s atmosphere, passing a mere 220 miles (350 kilometers) above the surface. By sling-shotting past Earth on the first anniversary of its launch, Lucy will gain some of the orbital energy it needs to travel to this never-before-visited population of asteroids.
The Trojan asteroids are trapped in orbits around the Sun at the same distance as Jupiter, either far ahead of or behind the giant planet. Lucy is currently one year into a twelve-year voyage. This gravity assist will place Lucy on a new trajectory for a two-year orbit, at which time it will return to Earth for a second gravity assist. This second assist will give Lucy the energy it needs to cross the main asteroid belt, where it will observe asteroid Donaldjohanson, and then travel into the leading Trojan asteroid swarm. There, Lucy will fly past six Trojan asteroids: Eurybates and its satellite Queta, Polymele and its yet unnamed satellite, Leucus, and Orus. Lucy will then return to Earth for a third gravity assist in 2030 to re-target the spacecraft for a rendezvous with the Patroclus-Menoetius binary asteroid pair in the trailing Trojan asteroid swarm.
For this first gravity assist, Lucy will appear to approach Earth from the direction of the Sun. While this means that observers on Earth will not be able to see Lucy in the days before the event, Lucy will be able to take images of the nearly full Earth and Moon. Mission scientists will use these images to calibrate the instruments.
Lucy’s trajectory will bring the spacecraft very close to Earth, lower even than the International Space Station, which means that Lucy will pass through a region full of earth-orbiting satellites and debris. To ensure the safety of the spacecraft, NASA developed procedures to anticipate any potential hazard and, if needed, to execute a small maneuver to avoid a collision.
“The Lucy team has prepared two different maneuvers,” says Coralie Adam, Lucy deputy navigation team chief from KinetX Aerospace in Simi Valley, California. “If the team detects that Lucy is at risk of colliding with a satellite or piece of debris, then--12 hours before the closest approach to Earth --the spacecraft will execute one of these, altering the time of closest approach by either two or four seconds. This is a small correction, but it is enough to avoid a potentially catastrophic collision.”
Lucy will be passing the Earth at such a low altitude that the team had to include the effect of atmospheric drag when designing this flyby. Lucy’s large solar arrays increase this effect.
“In the original plan, Lucy was actually going to pass about 30 miles closer to the Earth,” says Rich Burns, Lucy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “However, when it became clear that we might have to execute this flyby with one of the solar arrays unlatched, we chose to use a bit of our fuel reserves so that the spacecraft passes the Earth at a slightly higher altitude, reducing the disturbance from the atmospheric drag on the spacecraft’s solar arrays.”
At around 6:55 a.m. EDT, Lucy will first be visible to observers on the ground in Western Australia (6:55 p.m. for those observers). Lucy will quickly pass overhead, clearly visible to the naked eye for a few minutes before disappearing at 7:02 a.m. EDT as the spacecraft passes into the Earth’s shadow. Lucy will continue over the Pacific Ocean in darkness and emerge from the Earth’s shadow at 7:26 a.m. EDT. If the clouds cooperate, sky watchers in the western United States should be able to get a view of Lucy with the aid of binoculars.
“The last time we saw the spacecraft, it was being enclosed in the payload fairing in Florida,” said Hal Levison, Lucy principal investigator at the Southwest Research Institute (SwRI) Boulder, Colorado office. “It is exciting that we will be able to stand here in Colorado and see the spacecraft again. And this time Lucy will be in the sky.”
Lucy will then rapidly recede from the Earth’s vicinity, passing by the Moon and taking a few more calibration images before continuing out into interplanetary space.
“I’m especially excited by the final few images that Lucy will take of the Moon,” said John Spencer, acting deputy project scientist at SwRI. “Counting craters to understand the collisional history of the Trojan asteroids is key to the science that Lucy will carry out, and this will be the first opportunity to calibrate Lucy’s ability to detect craters by comparing it to previous observations of the Moon by other space missions.”
The public is invited to join the #WaveToLucy social media campaign by posting images of themselves waving towards the spacecraft and tagging the @NASASolarSystem account. Additionally, if you are in an area where Lucy will be visible, take a photograph of Lucy and post it to social media with the #SpotTheSpacecraft hashtag. Instructions for observing Lucy from your location are available here.
Hal Levison of Southwest Research Institute (SwRI), in the Boulder Colorado office is the principal investigator. SwRI, headquartered in San Antonio, also leads the science team and the mission’s science observation planning and data processing. NASA Goddard provides overall mission management, systems engineering and the safety and mission assurance for Lucy. Lockheed Martin Space in Littleton, Colorado built the spacecraft, principally designed the orbital trajectory and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the Lucy spacecraft. Lucy is the thirteenth mission in NASA’s Discovery Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.
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NASA’s Lucy to fly past thousands of objects for earth gravity assist
IMAGE: NASA'S LUCY MISSION PASSES AN ASTEROID. ARTIST RENDITION view more
CREDIT: NASA/SWRI
Mission engineers will track NASA’s Lucy spacecraft nonstop as it prepares to swoop near Earth on Oct. 16 to use this planet’s gravity to set itself on a course toward the Jupiter Trojan asteroids.
But they also will be closely tracking something else: more than 47,000 satellites, debris, and other objects circling our planet. A greater than 1-10,000 chance that Lucy will collide with one of these objects will require mission engineers to slightly adjust the spacecraft’s trajectory.
Although an adjustment is unlikely, and collisions are rare, the chances are increasing as the number of objects in Earth’s orbit grows, NASA experts say.
The International Space Station, for instance, has maneuvered out of the way of space debris 31 times since 1999, including three times since 2020.
“Low-Earth orbit is getting more crowded, so that has to be part of the consideration nowadays, especially for missions that fly low, like Lucy,” said Dr. Dolan Highsmith, chief engineer for the Conjunction Assessment Risk Analysis group at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The group determines the probabilities of collisions between NASA’s robotic spacecraft and Earth-orbiting objects. NASA’s Johnson Space Center in Houston does the same for crewed spacecraft, such as the space station.
Launched on Oct. 16, 2021, Lucy is on a 12-year-journey to study multiple Trojan asteroids up close. It’ll be the first spacecraft to visit these remnants from the early solar system, helping scientists hone their theories on how the planets formed 4.5 billion years ago and why they ended up in their current configuration.
But Lucy has a long way to go before it arrives at the Trojans in 2027. The upcoming gravity assist is one of three the spacecraft will rely on to catapult itself to its deep-space targets.
When Lucy comes nearest to Earth for its first gravity assist it will cruise 220 miles (350 km) above the surface. That’s lower than the altitude of the space station and low enough that the spacecraft will be visible with the naked eye from western Australia for a few minutes starting at 6:55 p.m. local time (10:55 UTC). On its way down, Lucy will fly through the most crowded layer of Earth’s orbit, which is monitored by the U.S. Space Force’s 18th Space Control Squadron. The squadron helps NASA identify close approaches.
Engineers began collision analysis for Lucy a week before the spacecraft’s Earth approach. Starting the process any earlier would render collision predictions futile, Highsmith said: “The further you're predicting into the future, the more uncertain you are about where an object is going to be.”
Determining the positions of spacecraft, plus orbiting satellites and debris, is challenging, particularly when trying to anticipate the future. Largely that’s because the Sun plays a major role in pulling or pushing objects around, and future solar activity is hard to predict. For example, the Sun’s activity — how much plasma and radiation it shoots out — affects atmosphere density, and thus how much friction will tug on a spacecraft and slow it down.
So the closer the collision assessment is to the Earth flyby time, the better. NASA sends Lucy’s whereabouts to the Space Force squadron daily. If the squadron determines that Lucy could intersect with something, Highsmith’s group will calculate the probability of a collision and work with the mission team to move the spacecraft, if necessary.
With such a high value mission, you really need to make sure that you have the capability, in case it's a bad day, to get out of the way,” Highsmith said.
Lucy navigation engineers have two maneuver options ready in case the spacecraft needs to avoid an object. Both maneuvers require engine burns to speed up the spacecraft, which is traveling about 8 miles (12 km) per second. Each maneuver can move Lucy’s closest approach to Earth up by 2 seconds or 4 seconds, respectively.
“That's enough to avoid any one thing that could be in the way,” said Kevin E. Berry, Lucy’s flight dynamics team lead from NASA Goddard.
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