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Meet: Dan Johnston

Trajectory and Aerobraking Design Analyst
Global Surveyor Operations Project, Navigation Team
Jet Propulsion Laboratory, Pasadena, California


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Mars Global Surveyor

The Mars Global Surveyor (MGS) Project began just over 27 months ago. This project has the responsibility to design, assemble, test and launch the MGS spacecraft. This spacecraft will perform an extended orbital study of the surface, atmosphere, and gravitational and magnetic fields of Mars.

Who I Am

Since the inception of this project, I have been a member of the MGS Mission and Navigation Design Team. As a member of this team, my primary responsibilities have centered in three major areas: 1) the launch vehicle mission design and planning, 2) the spacecraft trajectory (flight path) development, and 3) the aerobraking operations planning.

The launch vehicle mission design and planning activities involve working with the launch vehicle manufacturer, McDonnell Douglas Aerospace, in order to understand the performance capabilities of our Delta II launch vehicle and the limits that it places on our spacecraft design. It also involves the definition of our launch period (the time when Earth and Mars are in proper alignment for launch) as well as the definition of the near-Earth target conditions the launch vehicle must achieve in order to get (inject) our spacecraft onto a trajectory to Mars.

The spacecraft trajectory development involves the determination of the flight path of the spacecraft from injection (essentially separation from the third stage of the launch vehicle) through the establishment of our mapping orbit about Mars. A major element of this work involves the development of the maneuver scheme that will be used during flight and the associated determination of the propulsive capability the spacecraft must be able to deliver to successfully fly a given trajectory. Sufficient propulsive or delta-V (DV) capability must be onboard our spacecraft in order for us to establish the desired mapping orbit at Mars. To ensure that we launch with as much propellant as possible, this work activity is closely coordinated with the spacecraft developer, Lockheed-Martin Astronautics.

Unlike previous planetary missions, our spacecraft will be launched with an overall DV capability insufficient to establish our mapping orbit by normal propulsive means. To overcome this propulsive deficit, the MGS spacecraft will aerobrake after arrival at Mars. Aerobraking is accomplished by lowering the periapsis (closest approach) of the orbit into the Martian atmosphere and allowing drag forces to reduce the orbit energy. Once the orbit energy is sufficiently reduced we will use our limited propulsive capability to establish our final mapping orbit. Aerobraking can be described as a "controlled crash" of the spacecraft. One of my major responsibilities has been the task of integrating the operational plans and flight techniques the project will use during the aerobraking operations.

Now as we approach the opening of our launch period on November 6, the focus of my work will change from mission designer to navigator. Following launch, the MGS spacecraft becomes the responsibility of the Mars Surveyor Operations Project (MSOP). As a member of the MSOP Navigation Team, I will be responsible for guiding the spacecraft to its final mapping orbit. This will involve updating the target parameters for the spacecraft trajectory when necessary, participating in the spacecraft maneuver design and orbit determination processes, and implementing (both strategically and tactically) our aerobraking operations plan at Mars.

Job Likes and Dislikes

I enjoy the variety of technical challenges my work provides me; sometimes I even enjoy the challenges of the schedule pressures under which we work. I view my work as more than just an "eight-to-five" job; it is something I feel very passionate about. I think it is very important to explore new worlds and open new frontiers, that's what planetary exploration is all about. It is also very rewarding to watch the spacecraft "materialize" from a paper proposal to a concrete (real live) space vehicle. It is further very rewarding to participate in the launch and flight of that spacecraft to its final destination, the fourth planet from the Sun.

I think that the difficult part of my job is the realization that the spacecraft we construct and launch are by no means perfect, yet we demand and expect perfection. Like many things in life, the aerospace industry is a dynamic environment and there is often uncertainty in what we do.

Career Journey

I received my B.S. degree in Aerospace Engineering from the University of Texas at Austin in May 1984. My elective concentration was in orbital mechanics. Following graduation, I went to work for the McDonnell Douglas Space Systems Company in Houston, Texas. There I worked on programs involving the Space Transportation System (space huttle) and the Strategic Defense Initiative. In January 1988, I returned to the The University of Texas to pursue graduate-level work in my technical discipline and I received my M.S. degree in Engineering in May 1989. Following graduate school, I decided to pursue career opportunities with the Jet Propulsion Laboratory (JPL) in Pasadena, California. Initially at JPL I worked on several different missions involving Earth-orbiting spacecraft. Since 1991 my work has focused on missions to Mars, namely, Mars Observer and Mars Global Surveyor. My particular technical interests include advanced spacecraft mission analysis, spacecraft trajectory design (in particular, the spacecraft rendezvous problem) and spacecraft guidance systems.

Influences

My father was a career officer in the United States Air Force and retired from the military after 28 years on active duty. As the son of an air force officer I have been around high-performance aircraft all my life. I have always been intrigued with how and why these vehicles fly. Some of my fondest memories growing up I associate with the air force open houses staged at the different military bases where we lived and the precision-flying demonstrations held at these annual air shows. I have also always been very interested in the extension of flight to the realm of space and beyond. Ever since I can remember, I have been interested in the activities associated with the American space program and NASA. This probably comes from my recollections of watching the Apollo lunar landings and the splashdown/recovery operations on television in addition to viewing hours and hours of "Star Trek."

I also have a keen interest in history, in particular, military history and the exploration and colonization of the New World. I view the work that I now perform as an important first step in the opening of a new frontier for future generations.

Personal Information

As a military dependent growing up, I have had the opportunity to live all around the world in addition to the opportunity to travel extensively. While growing up, we moved on a fairly regular basis and by the time I started college I had lived in Louisiana, France, Germany, Texas, Virginia, Okinawa and Nebraska.

I have been married to my wife Suzanne for seven years. She is the regional property underwriting manager (commercial lines insurance underwriter) for a major insurance company. We have two daughters, Katie and Emily. Katie (3 years old) is a determined youngster who has become quite the conversationalist. Much to the relief of her parents, Emily (3 months old) is an extremely happy baby whose favorite pastime is napping.

For leisure time, I enjoy getting outdoors and playing softball and tennis. I also like going to amusement parks, movies, and the beach. As a family, we enjoy weekend camping expeditions as well as outings to the zoo and local parks.


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