A document summarizes a proposed metrology subsystem for precisely measuring the attitude of a large and flexible structure in space.
Two cameras would be mounted at the base of the structure:
- A star camera equipped with two separate fields of view: (a) imaging stars in the background near the structure tip while excluding the tip from view to prevent saturation from sunlight reflected from the tip, and (b) imaging the tip and have simultaneous stars in the background. First, in the absence of reflected sunlight and with the self-illuminated fiducials on the structure turned off, the star camera would open both fields of view and establish the angular relationship between the two fields of view.
- The second camera (metrology camera) is too insensitive to observe stars but sensitive enough to image a number of bright self-illuminated fiducials on the structure through a narrow band pass filter (even in the presence of sunlight) at high rates. Still in the absence of sunlight, the self-illuminated fiducials at the tip of the structure are imaged simultaneously by the star and metrology cameras to establish the relationship between the two different cameras.
During operations, the star camera would be operated in the tip-excluding configuration while the metrology camera tracked the tip. The orientation of the base to tip line relative to the stars would be determined by use of information from the metrology camera, the star camera, inertial measurement unit (IMU), and calibration data. The advantage of the proposed scheme is (1) it is possible to obtain attitude knowledge at high rates (based on IMU and metrology camera); (2) it is possible to operate when the antenna is illuminated by the Sun; and (3) it is possible to perform on-orbit alignment after launch.
This work was done by Carl Christian Liebe, Randall Bartman, Alexander Abramovici, Jacob Chapsky, Edward Litty, and Keith Coste of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Physical Sciences category. NPO-41411