Live From Mars was active July 1996-December 1997.

## Meet: Pieter Kallemeyn

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.

The best thing by far is knowing I'm playing a small but important role in the ongoing exploration of Mars and I'm having fun doing it. Mars is our next logical choice for a manned landing, but before we can do that we need a wealth of information obtained from the unmanned missions we're sending today. The work I do not only builds on the success of previous interplanetary missions, but will help future missions navigate their way to Mars.

What do I like the least? I don't know... Maybe when the computers go down and there's no way to get work done. Or maybe it's when things get too busy? Or maybe it's the coffee? Actually, there's so much I like about the job I barely notice things I don't like.