|McAdams leads the team that designs
the trajectory for the MESSENGER spacecraft
In the early 1980s, a young James V. McAdams was offered an opportunity to work as an engineering intern at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. His experience working on the Galileo mission to Jupiter with top-notch mission design experts and planetary scientists soon convinced him that he wanted to pursue this type of work as a career.
He recalls interesting extracurricular activities during this time, including tours of California's Goldstone Deep Space Network antenna facilities and of the Palomar Observatory (led by planetary geologist and comet/asteroid expert Eugene Shoemaker), observing the formation and early activities of the Planetary Society, attending press conferences at JPL for the Voyager 2 Saturn encounter, and close-up views of two rocket launches and two of the first four Space Shuttle landings.
"My long-time interest in science and math led me to pursue degrees in aeronautical and astronautical engineering," says McAdams. "But it was my JPL experience that ignited my interest in planetary exploration."
McAdams worked at JPL every other semester during three of his undergraduate years, assisting Galileo mission designers with trajectory design graphics and software development for the spacecraft's orbital phase at Jupiter. He joined Science Applications International Corporation (SAIC) in 1986, fresh out of graduate school and three weeks before the Space Shuttle Challenger ended in catastrophe shortly after liftoff. "Along with the shock and sadness that everybody was feeling, I remember also wondering if the tragedy would have any impact on planetary exploration."
At SAIC, he worked for eight years on missions to asteroids, comets, the Sun, solar system escape, and most planets. "Designing the paths and correction maneuvers needed to efficiently deliver spacecraft to their destinations requires a lot of math and attention to details," McAdams says. He had the fortune of working alongside such stalwarts as Alan Friedlander, Bob Farquhar and David Dunham on Mercury orbiter, Pluto flyby, and Near-Earth asteroid rendezvous mission studies that led to actual planetary exploration missions.
"I was involved in the earliest phases of the Near Earth Asteroid Rendezvous (NEAR) mission and the formation of NASA's Discovery Program for low-cost planetary exploration while at SAIC," McAdams says. The NEAR mission was the first of NASA's Discovery missions and the first mission ever to go into orbit around an asteroid. Its name was later amended to NEAR-Shoemaker in honor of Eugene Shoemaker, who died in a 1997 car accident while on an annual study of impact craters in the Australian outback. Carolyn Shoemaker, Eugene's widow and an astronomer who holds the record for the most comets discovered by an individual, named asteroid 17408 after McAdams, citing his contributions to the NEAR mission.
As funding appeared to be drying up at SAIC for the work he was doing, McAdams joined APL to continue working on the NEAR mission. "I transitioned to APL as the lab's mission design capability was being formed," he says. In fact, McAdams was one of the first three people-Farquhar and Dunham being the other two-to comprise the Space Department's mission design group. "I enjoyed being part of a team that had regular meetings to discuss the design, assembly, testing, launch, and operation of a spacecraft," McAdams says. "An interesting aspect of mission design is being a primary source of information that helps people refine the design and operation of particular components and instruments of the spacecraft." His work on the NEAR mission resulted in five awards, including two NASA Group Achievement awards.
In 1996, about two years after arriving at APL, McAdams was asked to explore trajectory options for sending a spacecraft into orbit around Mercury. (Early trajectory design work for MESSENGER benefited from contributions of JPL's Chen-wan Yen, who was the first to identify the trajectory strategy used by MESSENGER.)
|McAdams works with summer intern student Kevin Webb
to design a web-based visualization tool for
MESSENGER's first flyby of Mercury
"Due to Discovery Program limits on launch vehicle capability and the timing of MESSENGER's launch, the trajectory is more complicated than most," McAdams says. For one, travel to Mercury and entry into orbit about Mercury requires an extremely large velocity change because of the planet's very high orbital velocity. Further, Mercury does not have an atmosphere that can be used to help slow the spacecraft on arrival; the spacecraft must use rockets to slow down enough to go into orbit. To make the trip feasible, MESSENGER makes extensive use of gravity-assist maneuvers. These reduce the energy (and thus fuel) requirements but greatly prolong the trip.
McAdams leads the team that designed MESSENGER's complicated trajectory, which includes a flyby of Earth, two encounters of Venus, and three flybys of Mercury before settling into its orbit around Mercury in 2011.
"It's a privilege to be a part of this team," McAdams says. "I can't think of any other career that so closely mirrors my temperament, talents, and interests."
As complicated as designing spacecraft trajectories is, McAdams has made it his business to make the information about MESSENGER's journey to Mercury accessible to the public. With the help of high school students and college interns, he has created a variety of web-based tools and animations "to communicate some of these complex technical aspects of the mission in ways that can engage the public," he says.
McAdams is a member of APL's Principal Professional Staff. He holds an M.S. in Aeronautical and Astronautical Engineering from Purdue University and resides in Baltimore with his wife, Vicki, and four children.
by Paulette Campbell, Johns Hopkins University Applied Physics Laboratory