The PI's Space

Dec 20, 2018

As a discovery class mission, Lucy is led by a Principal Investigator (PI) – Dr. Hal Levison of the Southwest Research Institute in Boulder, Colorado. In the PI’s Space we will cover the Lucy mission from the perspective of the PI.

What is the role of the Principal Investigator?

Lucy, as a Discovery Class mission, is a PI-led mission. This means that the PI is ultimately in charge of and responsible for every aspect of the mission, from the mission concept and design to managing the cost, schedule, and scientific investigations. Of course the PI can’t actually do all of that, so except for occasionally needing to make decisions, I like to say the real role of the PI is much more like baby-sitting. After putting together this talented team of scientists and engineers, I work to keep the lines of communication open to make sure that everyone is working together to design and implement the best mission possible given the costs constraints of the Discovery budget.

What path did you take to become the PI of the Lucy Mission?

Since I was a kid I’ve always been interested in astronomy. I studied physics at Franklin & Marshall College and then went to the University of Michigan where I did my PhD in Astronomy studying the dynamics and formation of galaxies. It just goes to show that you may have your interests, but the likelihood that you will be spending your life doing what you think you will be doing is really small! As my career progressed I realized there was a lot more data about out our Solar System, so I started researching the dynamics, formation, and evolution of the Solar System. Of course, I once again reached a point where I realized that we needed more data to actually answer the questions that I had. This mission is giving me the opportunity to go out and get some of the data that we need to answer important scientific questions about how our Solar System came to be.

Why did you propose a mission to the Trojan Asteroids?

I have been interested in the asteroids, comets, and other small bodies in our Solar System for many years. I believe that they hold the key to understanding the origin and evolution of our Solar System. When we look at our system today we are forensic detectives trying to understand what happened billions of years ago. And, like a forensic detective looking at a murder scene, sometimes the pattern of blood splattered on the wall tells us more about what happened than the bodies on the ground. In our case, the asteroids and comets are like the splattered blood. The small bodies of the Solar System were scattered by the forming planets, leave telltale signatures of our Solar System’s rather violent history. Current models suggest that the Trojan Asteroids likely formed in the outer parts of our Solar System and they were scattered inwards during a dramatic early reshuffling of our Solar System (perhaps as we described in the so-called Nice Model). These outer Solar System relics then just happened to be stored in this relatively easy to access region of the Solar System around the orbit of Jupiter.

Lucy really is a Mission of Exploration. Not only has no spacecraft ever flown by a Trojan Asteroid before, unlike the main belt asteroids, we don’t think we even have any samples of these asteroids in our meteorite collection. Because of the proximity to Jupiter, any piece of a Trojan asteroid that escapes is much more likely to be captured by Jupiter than to make it to the Earth. Therefore we really are heading towards the unknown.

How did you come up with the trajectory for this mission?

We started out with a simple goal, come up with a trajectory to fly by the asteroid Eurybates, and the rest of the targets were really just lucky accidents. Eurybates is special because it is the largest member of the only known ``collisional family’’, the remnants of a broken up Trojan Asteroid, in either of the Trojan swarms. So by flying by that target we hope to learn a lot about what the Trojans are really made of. And fortunately we found a path to fly by it where we could also fly by a number of other targets in the L4 swarm along the way.

Originally we thought the mission would be over after we flew through the L4 swarm, but when a flight dynamicist integrated the orbit forward to make sure it wasn’t going to cause any planetary protection problems (since the orbit is crossing Mars and going out to the orbit of Jupiter we needed to make sure that the spacecraft won’t hit any astrobiologically important world like Mars or Europa), they saw that the spacecraft would fly near what are now the final pair of targets for the Lucy mission (and my personal favorites), Patroclus and Menoetious. Even the main belt asteroid that we happen to fly by, DonaldJohansen, which is really just a nice place to do a dress rehersal to make sure the mission will be ready for the Trojan flybies, turns out to be a member of one of the most recent asteroid break-ups in the main asteroid belt!

I’ve spent my career studying the dynamics of stars, planets, asteroids and comets. So in some ways I’ve spent the last 40 years worshipping at the feet of the celestial mechanics gods, and it really seems this trajectory is their way of paying me back.

How far along is this Lucy Mission now?

We are currently in what is known as Phase B, the preliminary design phase. We have completed our mission Preliminary Design Review (PDR) and have been confirmed and given permission by NASA to move forward. Starting in January we will officially switch to Phase C, a very exciting phase in which we actually start building our spacecraft and instruments. We are currently on schedule for our October 2021 launch date.