Who I Am
The role of the navigator on a ship or airplane is to determine where you are and plot
a course to get to the destination. That is no different for me as a navigator for the
Mars Pathfinder mission, except that the ship is a 900-kg unmanned spacecraft and the
destination is more than 150 million miles away. There are three navigators for Mars
Pathfinder: David Spencer, Robin Vaughan and myself as NAV team leader. We're responsible
for determining where the spacecraft is, predicting where it will go in the near future,
and determining the means to correct the path in order for us to reach the surface of
Mars.
The flight path, or trajectory, of the spacecraft is decided on early in the mission's
development. Considerations such as mission objectives, launch vehicle capability and
arrival geometry are just a few of the things that are optimized in designing the
trajectory. After the spacecraft is launched, the navigators measure the range and
velocity from the Earth to the spacecraft at regular intervals. These measurements are
compared to predicted measurements based on computer models of the trajectory. Any errors
in the models are corrected until the ground-based computer model matches the actual
trajectory. If the actual trajectory is found to be off from the predetermined path, the
spacecraft's propulsion system is fired in a certain direction to add (or subtract) just
enough velocity to correct the error and put us back on course. These events are called
TCMs, short for trajectory correction maneuvers. Mars Pathfinder is planning to do four
of these during the cruise from Earth to Mars.
My Career Journey
My career really started while I was obtaining my B.S. degree in Aerospace Engineering
Sciences from the University of Colorado. In between my classes in mathematics, physics,
computer programming and astrodynamics (the study of spacecraft motion around planets) I
had the opportunity to work part-time at the Solar Mesosphere Explorer control center.
This satellite control station was owned by the university and staffed primarily by
undergraduate students who gained experience in spacecraft operations on a real satellite.
I learned about spacecraft orbits, communications, power systems and other systems vital
to keeping a spacecraft and its mission healthy. I enjoyed it so much, I stayed on
another year-and-a-half while I finished my M.S. degree. I eventually became responsible
for programming the attitude control system for the satellite. After I graduated I was
fortunate to get a job at the Jet Propulsion Laboratory (JPL) with the Galileo project's
Navigation Team as an orbit determination analyst. After five years on Galileo I was
asked to join Mars Pathfinder as "chief navigator."
Influences
I had two teachers in high school who encouraged me to pursue interesting
extracurricular activities. One was my math teacher who taught me calculus in my senior
year. She recommended I visit the University of Colorado during the summer before my
senior year to see what the engineering college had to offer. The other was an influential
science teacher who encouraged me to participate in a space shuttle experiment proposal
program for students. Although my experiment (which involved the study of thermodynamics
in microgravity) wasn't selected to fly, I learned a lot from the research it required
and I had fun doing it.