Dr. Shannon Coffey Wins Prestigious 1999 Dirk Brouwer Award

3/27/2000 - 65-00r
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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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