Meet: Dan Johnston
Trajectory and Aerobraking Design Analyst
Global Surveyor Operations Project, Navigation Team
Jet Propulsion Laboratory, Pasadena, California
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
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.
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.
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
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.
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.