by S. Prasad Ganti
The “Lucy” spacecraft was launched recently on a twelve year mission to visit asteroids. Asteroids are left over remnants from the sculpting of the solar system about four and half billion years ago. Spacecraft in the past have visited asteroids. Both as flybys and landings. What is different about this mission is the number and types of asteroids to be visited over a longer span of time when the spacecraft crisscrosses the orbit between Earth and Jupiter a few times. After launch the spacecraft was found to have a minor handicap in terms of a lack of confirmation of the latching of one of the two solar panels. Regardless, the spacecraft has been pushed out of the Earth’s bounds on its way to the asteroids. Will Lucy be lucky and complete its mission ?
Asteroids are pretty interesting as they are the left over building materials from the formation of our solarr system. It is like some pieces of bricks, stone, wood, pipes and electrical cables lying around even after a building is complete. They offer some clues about how the building was constructed. Majority of asteroids are located in the asteroid belt between Mars and Jupiter. Thousands of pieces orbiting the Sun in a narrow band. In addition, there are some asteroids in the vicinity of Jupiter. Jupiter being such a massive planet – a big ball of gas, has its own entourage of remnant debris as it orbits the Sun. These asteroids are called Trojans. They move in the same orbit as Jupiter moves around the Sun. Not around Jupiter. They are concentrated in two areas in Jupiter’s orbit around the Sun. These areas are called Lagrange points – named for a French mathematician called Joseph Lagrange. At these points in space, the gravity of Jupiter is negated by the gravity of Sun and the asteroids can park themselves peacefully without the pulls of the massive bodies. There can be 5 possible Lagrange points named L1 through L5 for any two massive objects in space. In case of Trojans, the asteroids are parked in L4 and L5 points. The picture below shows the asteroids and the path Lucy will take. It is a great picture courtesy Southwest Research Institute. Lucy would be visiting one main asteroid (named Donald Johanson) and 7 Trojan asteroids as per the picture below.
Now let us come to the naming of the spacecraft. Lucy is named for a 3.2 million year old hominid skeleton (a human like ancestor) discovered in 1974 by a paleoanthropologist named Donald Johanson. And where did Johanson get the name from ? From a Beatles song “Lucy in the sky with diamonds” which was playing at the campsite in Africa when the discovery was made. In 2025, Lucy will reach the main asteroid between Mars and Jupiter, not surprisingly named Donald Johanson. Other Trojan asteroids will follow later as per schedule given in the picture. These encounters are all flybys with no orbiting or landing on any of the asteroids. Extensive imaging will be done as Lucy flies by each of the asteroids. The images will be captured in multiple wavelengths in order to determine the detailed geophysical features.
The mission is planned for twelve years but could be extended on how things go. A lot depends on the power source for Lucy. Typically spacecraft going that far out from Sun do not depend on solar energy as Sun’s light dims with the distance. Lucy is being powered by two massive solar arrays each generating about five hundred watts of energy at such distances. Closer to Earth they generate a lot more power. All the electronics on the Lucy are expected to operate within this power budget. The power generated is about half of a typical household iron used for pressing clothes. It is a great design indeed !
Because of the size of the solar arrays, they have been folded at the time of launching from Earth. They are expected to unfurl once in space and latch so that they retain the shape on the journey to the asteroids. One of the arrays did not confirm the latching process. It seems to be functioning fine regardless. The lack of confirmation may just have been a miss. Keeping the power generation in mind, Lucy has been steered beyond the confines of the Earth. Mission control will keep an eye on the journey and whatever they can do to fix or get a confirmation that everything is OK. They have a few years to work out the kinks during this long journey. It is like watching a car move while checking remotely on what is wrong with it and hopefully fix. Good luck to Lucy mission to achieve its goals and much more!