Dr. Shannon L. Coffey, of the Naval
Center for Space Technology's Spacecraft Engineering Department,
was presented the American Astronautical Society's (AAS's) 1999
Dirk Brouwer Award in the field of astrodynamics at the 2000
Space Flight Mechanics Conference, held January 23 - 26, in Clearwater,
Florida. The award was presented by AAS Space Flight Mechanics
Technical Committee. The conference was cosponsored by the American
Institute of Aeronautics and Astronautics (AIAA).
Dr. Shannon Coffey was awarded
for his "significant contribution in solving critical astrodynamics
problems using parallel processing." The two significant
contributions which won him the Dirk Brouwer Award were one,
his "application of parallel processing to maintaining the
space object catalog using special perturbations and the determination
of near miss conjunctions of space objects, and two, his "advancing
the state-of-the-art of tether satellite dynamics by determining
the orbital and attitude dynamics of the TiPS satellite."
According to the award nomination,
USSPACECOM has the mission of maintaining the space object catalog.
AF Space Command is the primary Defense Operations Center of
USSPACECOM, and the Naval Space Command is the alternate. Currently,
there are nearly 10,000 objects in the catalog. Since numerical
integration techniques (special perturbations) are so computationally
intensive, simple general perturbations methods, based on a theory
developed by Brouwer, have been used for many years for the orbit
propagation.
For the past few years, Dr. Coffey
has been researching the use of parallel processing for improving
computationally intensive astrodynamics problems. He demonstrated
that the space object catalog can be maintained using special
perturbations. The software incorporates forces generated by
24 x 24 gravity field, the Jacchia atmospheric density model,
lunar and solar perturbations and solar radiation. This results
in a much more accurate determination of orbits making it possible
to maintain the catalog with more accuracy and efficiency.
The nomination further explains
that NASA has a major need to track smaller objects as small
as 1 - 5 cm for protection of the International Space Station
(ISS). A catalog with objects this small would probably contain
at least 100,000 objects. Maintaining a catalog of this size
is not feasible with the current serial computation approach.
However, it is now possible to do this with parallel processing-it
is based on the premise that "to process more objects, just
add more processors." This notable achievement is considered
to be one of the most significant breakthroughs in astrodynamics
in the past 15 years. The Naval Space Command is in the process
of implementing this new approach.
The nomination adds, COMBO, a
program for predicting close conjunctions of space objects, is
used for launches and all manned flights. Using the elements
obtained by USSPACECOM, the orbits of all objects are propagated
to determine the points of closest approach with satellites of
concern, e.g., Space Shuttle. This task is computationally intensive.
Dr. Coffey was responsible for the develop-ment of a parallel
version of COMBO that significantly reduces the computation time.
This program is now used operationally by Naval Space Command.
The award nomination continues
by describing Dr. Coffey's second significant contribution: advancing
the knowledge of tether satellite dynamics by determining the
orbital and attitude dynamics of the TiPS satellite. TiPS, a
tethered satellite developed by NRL, was launched in June 1996,
and is still in orbit. TiPS's primary objective is to obtain
a better understanding of the dynamics of tethered satellites,
accomplished primarily by laser tracking. Retro-reflectors are
mounted on both sub-satellites. Since the sub-satellites are
not in Keplerian orbits, to determine the attitude motion required
determining the orbit and attitude motion simultaneously. Under
Dr. Coffey's direction, new algorithms for the simultaneous orbit
and attitude determination of TiPS were developed and implemented
into an operational program, GEODYN, in less than one year. As
a result of his efforts, researchers now have a much better understanding
of the dynamics of tether satellites.
Dr. Shannon Coffey received his
B.A. (1971), M.S. (1973), and Ph.D. (1977) degrees, all in mathematics,
from the University of Cincinnati. From 1977 to 1978, Dr. Coffey
was Assistant Professor of Mathematics at the University of
Cincinnati.
Dr. Coffey joined the staff of
the Space Systems Division in 1978, as a research mathematician.
In 1987, Dr. Coffey was appointed head of the Mathematics and
Orbit Dynamics Section within the Spacecraft Engineering Department.
In this position, he has directed fundamental research in astrodynamics
and managed projects in spacecraft operations. He has been responsible
for flight operations for numerous NRL-built spacecraft. The
most recent activities in this area have been flight operations
for TiPS, and for the Interim Control Module that is being built
for the International Space Station.
Dr. Coffey is a Fellow of the
American Astronautical Society and an Associate Fellow of the
American Institute of Aeronautics and Astronautics.
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