lucy

Navigating NASA’s first mission to the Trojan asteroids

Posted by

0


Navigating NASA’s first mission to the Trojan asteroids
This diagram illustrates Lucy’s orbital path. The spacecraft’s path (green) is shown in a frame of reference where Jupiter remains stationary, giving the trajectory its pretzel-like shape.

In science fiction, explorers can hop in futuristic spaceships and traverse half the galaxy in the blink of a plot hole. However, this sidelines the navigational acrobatics required in order to guarantee real-life mission success.

In 2021, the feat of navigation that is the Lucy mission will launch. To steer Lucy towards its targets doesn’t simply involve programming a map into a spacecraft and giving it gas money – it will fly by six asteroid targets, each in different orbits, over the course of 12 years.

Lucy’s destination is among Jupiter’s Trojan asteroids, clusters of rocky bodies almost as old as the Sun itself, and visiting these asteroids may help unlock the secrets of the early solar system. Lucy will encounter a Main Belt asteroid in 2025, where it will conduct a practice run of its instruments before encountering the first four Trojan targets from 2027-2028. In 2033, Lucy will end its mission with a study of a binary system of two Trojans orbiting each other.

Getting the spacecraft where it needs to go is a massive challenge. The solar system is in constant motion, and gravitational forces will pull on Lucy at all times, especially from the targets it aims to visit. Previous missions have flown by and even orbited multiple targets, but none so many as will Lucy.

Scientists and engineers involved with trajectory design have the responsibility of figuring out that route, under Flight Dynamics Team Leader Kevin Berry of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. One such engineer is Jacob Englander, the optimization technical lead for the Lucy mission. “There are two ways to navigate a mission like Lucy,” he said. “You can either burn an enormous amount of propellant and zig-zag your way around trying to find more targets, or you can look for an opportunity where they just all happen to line up perfectly.” To visit these aligned targets, the majority of Lucy’s high-speed lane changes will come from gravity assists, with minimal use of fueled tweaks.

Though Lucy is programmed to throw itself out into a celestial alignment that will not occur for decades, it cannot be left to its own devices. Once the spacecraft begins to approach its asteroid targets, optical navigation is the next required step.

“OpNav,” as optical navigation technical lead Coralie Adam refers to it, is the usage of imagery from the on-board cameras to determine Lucy’s position relative to the . This is a useful measurement used by the navigation team to tweak Lucy’s route and ensure it stays on the nominal flyby path. Adam works in Simi Valley, California, with KinetX, the company NASA selected to conduct Lucy’s deep space navigation.

By using the communications link from the spacecraft to Earth, Adam said, the Lucy team gets information about the spacecraft’s location, direction and velocity. The spacecraft takes pictures and sends them down to Earth, where Adam and other optical navigators use software to determine where the picture was taken based on the location of stars and the target. The orbit determination team uses this data along with data from the communications link to solve for where the spacecraft is and where it is expected to be, relative to the Trojans. The team then designs a to get Lucy on track. “The first maneuver is tiny,” said navigation technical lead Dale Stanbridge, who is also of KinetX. “But the second one is at 898 meters per second. That’s a characteristic of Lucy: very large delta V maneuvers.” Delta V refers to the change in speed during the maneuver.

Communicating all of these navigation commands with Lucy is a process all on its own. “Lockheed Martin sends the commands to the spacecraft via the Deep Space Network,” Adam said. “What we do is we work with Lockheed and the Southwest Research Institute, where teams are sequencing the instruments and designing how the spacecraft is pointed, to make sure Lucy takes the pictures we want when we want them.”

“The maneuvers to correct Lucy’s trajectory are all going to be really critical because the spacecraft must encounter the Trojan at the intersection of the spacecraft and Trojan orbital planes,” Stanbridge said. “Changing the spacecraft orbital plane requires a lot of energy, so the maneuvers need to be executed at the optimal time to reach to next body while minimizing the fuel cost.”

While Lucy is conducting deep space maneuvers to correct its trajectory toward its targets, communications with the spacecraft are sometimes lost for brief periods. “Blackout periods can be up to 30 minutes for some of our bigger maneuvers,” Stanbridge said. “Other times you could lose communications would be when, for example, the Sun, comes between the Earth tracking station and the spacecraft, where the signal would be degraded by passing through the solar plasma.”

Losing contact isn’t disastrous, though. “We have high-fidelity predictions of the spacecraft trajectory which are easily good enough to resume tracking the spacecraft when the event causing a communication loss is over,” Stanbridge said.

What route will Lucy take once its mission is complete, nearly 15 years from now? “We’re just going to leave it out there,” Englander said. “We did an analysis to see if it passively hits anything, and looking far into the future, it doesn’t.” The Lucy team has given the a clear path for thousands of years, long after Lucy has rewritten the textbooks on our solar system’s history.

Read more at: https://phys.org/news/2018-12-nasa-mission-trojan-asteroids.html#jCp

3D Printing May Have Helped Solve A 3-Million-Year-Old Death.

Posted by

0


By studying 3D-prints and X-Rays of human ancestor Lucy’s bones, scientists determined her likely cause off death.

Animal sculptor Emmanuel Janssens Casteels works on a Lucy replica

It’s one of the oldest, coldest cases in forensic science. Lucy, an early hominid who lived 3.2 million years ago, mysteriously died in her prime and remained buried in a shallow Ethiopian stream until researchers discovered her well-preserved remains in the year 1974. Was she attacked by wild beasts? Did she succumb to an ancient disease? Was she murdered by a fellow Australopithecus?

Now, a new study in the journal Nature suggests that Lucy took a 50-foot plunge to her death, likely after slipping off a tree branch while climbing or sleeping. The findings are based on a forensic and medical analysis of detailed X-Ray scans and 3D-printed replicas of Lucy’s broken bones, now available online for researchers around the world to study from the comfort of their labs.

“It’s rarely the case that the skeleton actually preserves evidence of how an individual died,” coauthor John W. Kappelman of the University of Texas at Austin told CNN. “What we’re proposing here is the first hypothesis that’s out there, and we’ve had her for 42 years now, about how she died.”

“I am not aware that anyone else has ever [done that].”

Maybe that’s how she fell to her death. For this new study, researchers scanned Lucy’s skeleton in a High-Resolution X-ray Computed Tomography Facility and printed the results using a 3D printer, so that they could study the fossils without having to travel to Lucy’s permanent home in Ethiopia. “We scanned nonstop, 24/7, for 10 days,” Kappelman told The Washington Post. “We were exhausted. I was happy to see her come, but I was happy to see her go.”

Scanning and 3D-printing is gaining traction worldwide as a tool for paleontologists and archaeologists who can use the tech to study, manipulate, and even damage faux samples without worrying about destroying priceless artifacts. “Sometimes the originals are in another museum [and] display of the specimens can make further scientific study difficult,” Kenneth Lacovara of Drexel University told The Verge in 2012, when the practice was first gaining traction. “Science has always been open source…[3D-printing is a] “platform for global collaboration among paleontologists.”

After analyzing the X-Rays and faux fossils, Kappelman noticed that Lucy’s clean fractures and slivers of damaged bone fragments looked a lot like the sort of injuries orthopedic surgeons see after patients have fallen from great heights. Of particular interest are Lucy’s arm fractures, which look very much like what happens when falling humans instinctively put out their arms to break a nasty fall. To check his work, Kappelman consulted with nine orthopedic surgeons who agreed with his analysis. Kappelman suspects that Lucy’s upright posture may have worked against her.

“The point we argue is that it may well be the evolution of these traits for bipedalism [walking upright] that compromised her ability to climb as safely and efficiently in the trees,” Kappelman told CNN. “That may have meant that her species was more subject to a higher frequency of falls.”

Kappelman’s ancient coroner’s report tells a sobering story about Lucy’s final moments. She was likely conscious when she fell 50 feet — as evidenced by the fact that she tried to break her fall — and upon impact with what may have been the rocky bed of a shallow stream, her neck twisted to the side as her ankles, knees, hip, and shoulder shattered. Fortunately, Kappelman suspects that Lucy died relatively quickly. “Lucy probably bled out pretty fast after falling,” he told Science News.

News of Lucy’s tragic demise, however, has been met with some skepticism from the anthropology community. Paleoanthropologist Tim White of the University of California, Berkeley told Science News that the Kappelman’s study is, “a classic example of paleoanthropological storytelling being used as clickbait for a commercial journal eager for media coverage” — a fairly strong indictment. In his rebuttal, White refers to reams of prior research that suggest Lucy’s bone fractures occurred after her death. In fact, White points out, broken bones much like Lucy’s can be found in ancient samples of gazelles, hippos, and rhinos — none of which typically climb (or fall from) trees.

The good news is that the Ethiopian government has released the 3D files of Lucy’s bone scans so that scientists around the world can print their own Lucy replicas to help solve the mystery behind her untimely death once and for all. As for Kappelman, the results speak for themselves. “It’s like putting yourself there at someone’s death and being able to picture that, almost as if understanding that drops us into a time machine and we fly back through 3 million years so we’re there observing how this little individual died,” he told CNN.

“It was in understanding her death that she became alive for me.”

Lucy Had a Spring in Her Step

Posted by

0


The petite 3.2-million-year-old skeleton called Lucy is one of the most famous and most complete of human ancestors. But she was found without her foot bones, so researchers have debated whether she walked as we do or retained some apelike adaptations for climbing in trees that altered her gait. Now, a 3.2-million-year-old foot bone from a member of Lucy’s species, Australopithecus afarensis, reveals that this hominin was no flat foot: It had already evolved arches and a stiff midfoot similar to living humans. That means if Lucy were alive today, she could fit in high heels or march for miles without breaking her feet. “This discovery puts the spring back into afarensis‘s step,” says co-author Donald Johanson of the Institute of Human Origins at Arizona State University (ASU), Tempe.

When Johanson and his colleagues discovered Lucy’s partial skeleton in 1974, it showed that she walked upright, confirming that our ancestors did so before their brains started getting larger. But did she walk upright most of the time like a modern human or still spend plenty of time in the trees evading predators? Mysterious footprints left at Laetoli in Tanzania show that a hominin of this time, 3.7 million years ago, did indeed have arches in its feet. But researchers couldn’t be sure who left those prints, because it wasn’t clear whether A. afarensis had an arch, says co-author William Kimbel, a paleoanthropologist at ASU.

Now, researchers think they’ve solved the mystery of Lucy’s footwork, thanks to an analysis of about 35 new individuals of A. afarensis uncovered at Hadar, Ethiopia, in the past 15 years. The key is the fourth metatarsal, a long bone that connects the toe to the rest of the foot. The way the two ends of the bone were twisted in relation to each other in the fossils suggests that when one end was on the ground, the other end was raised about 8˚ to attach to the rest of the foot, says lead author Carol Ward, a paleoanthropologist at the University of Missouri, Columbia, in a study reported online today in Science. This torsion is found in feet with well-formed arches, which are stiff enough to use the foot like a lever to push off the ground but flexible enough to also work like shock absorbers.

The bone also shows that A. afarensis had abandoned the flexible midfoot that apes use to grasp tree branches, in favor of an arch that makes upright walking more efficient. “This tells you that climbing in the trees was not nearly as important as walking on the ground,” says Ward.

Paleoanthropologist Will Harcourt-Smith of the American Museum of Natural History in New York City isn’t willing to go that far. Although he agrees that A. afarensis had some arching, it may have lacked the most important arching on the inside of the foot. Lucy’s fingers and toes also were more curved than those of living humans and her shoulder was more apelike—traits useful for tree-climbing. “It’s hard to envisage an animal that had entirely made the leap to full, obligate bipedalism,” he says.

But paleoanthropologist Jeremy DeSilva of Boston University says that the new foot bone, along with a “laundry list of other features of the lower limb” make it more likely that A. afarensis was a “terrestrial biped with little time spent in the trees.” It also suggests that it was indeed A. afarensis that walked in the mud at Laetoli. “Finally,” says paleoanthropologist Bruce Latimer of Case Western Reserve University in Cleveland, Ohio, “we can put the mystery hominid at Laetoli to rest.”

lccysource: science now