Aerospace Team Scores In Trajectory Design Challenge

Dr. Chris Ranieri indicates a point of interest on a trajectory graph. Other members of the competition team, left to right, are: Greg Fruth, Rosemary Huang, Jacob Breeden, and Jason Anderson. (Photo: Elisa Haber)

Ten Aerospace engineers embarked on a problem-solving mission last spring that was touted as a “nearly impossible” interplanetary trajectory design challenge. The team had just one month to compete with the best engineers and mathematicians in the world with one interesting caveat — they had to work on their solution on their free time.

Billed as the America’s Cup of rocket science, the Eighth Global Trajectory Optimization Challenge (GTOC) catapulted the Aerospace team to produce outstanding results – placing eighth overall out of 35 teams. Only 17 of the teams were able to come up with viable solutions to the challenge.

The Aerospace team comprised Dr. Chris Ranieri, Greg Fruth, Dr. Wayne Hallman, Rosemary Huang, Jacob Breeden, Shaun Brown, all of the Flight Mechanics Department; Jason Anderson, Launch Enterprise Engineering; Dr. Michael Norman, Performance Modeling and Analysis Department; Marc DiPrinzio, Mission Analysis and Operations Department; and Ben Wright, Embedded Control Systems Department.

Ranieri, the project lead, will attend the American Astronautical Society/American Institute of Aeronautics and Astronautics Space Flight Mechanics Meeting in Napa, Calif. next month to see how other winning competition participants solved the challenge.

“The competition is an exciting time to tackle interesting optimization problems that The Aerospace Corporation typically does not often explore,” Ranieri said. “However, the techniques and methods are easily translatable to our typical Earth-centered trajectories, and many of our team members have an inner passion for exploration missions to the moon, Mars, Jupiter, asteroids, and beyond.

“This gives us a chance to develop new tools and methods that eventually work their way back into our day-to-day jobs. It is also a great chance to work with various team members from across The Aerospace Corporation’s organizational chart — and that collaboration opportunity is also exciting,” he said.

The theme for the GTOC8 challenge was created by the last winner, Jet Propulsion Laboratory Outer Planets Mission Analysis Group, which was also free to define the competition rules.

Members of the GTOC team frequently met during their lunch periods. (Photo: Elisa Haber)

Members of the GTOC team frequently met during their lunch periods. (Photo: Elisa Haber)

The GTOC8 problem was to create a Very Long Baseline Interferometer (VLBI) using three dispersed spacecraft. In layman’s terms, a VLBI uses observers at dispersed locations to all look at a distant radio source (a star, quasar, galaxy, etc.) at the same time, according to Ranieri. By using software to fuse the data from the dispersed observers, the VLBI in essence artificially creates a significantly larger receiver than could ever actually be built (let alone fly in space).

“If you recall the movie ‘Contact’ with many radio dishes in the desert — that is a land-based example of a VLBI. To maximize a VLBI’s effectiveness, the observers have to be as far apart as possible,” Ranieri said.  “For the GTOC8, the three spacecraft can use three methods to create this separation: large initial chemical impulsive maneuvers, long duration electric propulsion maneuvers, and gravity assists from the moon.”

The competition challenge was to design a mission that optimized the number and quality of VLBI observations using a combination of those methods. Each observation was weighed based on the VLBI size, the location of the observed radio source on the intergalactic sphere around Earth, and how many times the same source was observed during the three-year mission.

Ranieri explained that most of the team does its work onsite, doing a little work before the workday begins, working some during their lunch breaks, and staying longer at the end of the workday.  For some team members, the work then continues on from home at night and it does spill into the weekends occasionally.

“We were very satisfied with our solution,” Ranieri said. “Although we did not win the competition, even submitting a valid solution is a victory in and of itself. Our normal customers do not typically ask The Aerospace Corporation to solve problems of this nature (especially the gravity assist part). That, combined with our real work commitments during the competition make us happy with any valid solution that we can submit,” he said.

So, what did the Aerospace team’s solution look like?

“We used the initial impulses of each vehicle to start the process of reaching the moon,” Ranieri said. “These impulses are not big enough to get all the way to the moon to start lunar gravity assists; these gravity assists are critical to achieving high scores as they can very quickly change the size, shape, and orientation of the spacecraft’s orbit. To get the rest of the way to the moon, we used the electric propulsion engines to perform a six-month elliptical spiral transfer out to the moon,” he said.

During this initial transfer to the moon, the team was able to obtain a few low-scoring observations. They set up the initial transfers such that two vehicles intercepted the moon at the same location while the third vehicle encountered the moon about three days later than the first two encounters. This delay, along with the trajectory shaping of the lunar gravity assists, helped create the VLBI diversity.

“Our biggest challenges are the lack of nine to five work on the GTOC, combined with our lack of interplanetary trajectory design tools and experience,” Ranieri said. “We have world-class optimization methods at our disposal for both local and global optimization problems, however for each GTOC, we have to quickly pivot to solve new problems with new dynamics that our standard tools cannot easily handle. Other competing organizations and universities typically have more time to devote to the four weeks of the competition and many of their interplanetary tools are more refined than ours.”

Aerospace has competed in the GTOC’s 3 through 8. It tied for first place in the GTOC4, losing on the tiebreaker. It placed fifth in the GTOC3, and otherwise has placed eighth or ninth on all other editions.

“We welcome new ideas and perspectives as the problems are challenging and out-of-the-box,” said Ranieri.  “Even if people do not have experience using the Flight Mechanics Department’s tools, there are always new tools that need to be developed for each new competition and there is also the opportunity for team members to learn prior to or during the competition,” he said.

—Gail Kellner