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Goddard Space Flight Center, Greenbelt, Maryland 20771

diagram of spacecraft trajectory around an asteroid

ENGINEERING COLLOQUIUM

Monday, May 7, 2012 / 3:30 PM, Building 3 Auditorium

Brian Sequeira

"Autonomous Determination of Relative Attitude and Speed of Spacecraft About an Asteroid"

ABSTRACT -- The path of a probe around a small irregularly-shaped body is difficult to predict. The irregular distribution of mass of the body, and its rotational motion, produce a gravitational force on the probe that is non-central and time-varying. Other forces, such as solar pressure, are comparable with the weak gravitational force caused by the body. Therefore, the probe trajectory is non-planar, may not close on itself, is not periodic, and is very sensitive to initial conditions (prevalent at time of "orbit" insertion).

The definition and maintenance of spacecraft attitude is confounded by the irregular shape of the object and trajectory alike. Nadir may not be uniquely the shortest distance to the body's surface nor the local normal to the surface. And yet, the spatial context is crucial for the probe's suite of instruments.

In order to schedule spacecraft observations, mission planners ordinarily need to know spacecraft locations and attitudes several days in advance. Clearly, such planning is not feasible for probe trajectories around small irregularly shaped bodies. The planners' job will be greatly simplified if the spacecraft can, in real time, establish nadir, measure probe vector velocity relative to the body, and accurately determine probe altitude along the nadir. This talk will present one instrument that can accomplish these objectives.

SPEAKER --H. Brian Sequeira (Senior Member, IEEE) is a Principal Professional Staff member of the Johns Hopkins University Applied Physics Laboratory. His research interests include communications systems for near-Earth and deep space applications, and radar instruments for planetary exploration. Most recently, he was involved with mini-RF Synthetic Aperture Radar instruments that flew on the Chandrayaan-1 and Lunar Reconnaissance Orbiter (LRO) missions. He received the M.S. degree in physics, M.Tech. degree in Engineering Physics, and the Ph.D. degree in electrical engineering.


Engineering Colloquium home page: https://ecolloq.gsfc.nasa.gov