Engineering topics

San Martin, A. M.

Publications and source records attributed to San Martin, A. M..

3 records

NASA NTRS1992

New definitions of pointing stability - ac and dc effects

For most imaging sensors, a constant (dc) pointing error is unimportant (unless large), but time-dependent (ac) errors degrade performance by either distorting or smearing the image. When properly quantified, the separation of the root-mean-square effects of random line-of-sight motions into dc and ac components can be used to obtain the minimum necessary line-of-sight stability specifications. The relation between stability requirements and sensor resolution is discussed, with a view to improving communication between the data analyst and the control systems engineer.

Lucke, Robert L.↗

NASA NTRS1986

Sensitivity of synthetic aperture radar boresight orientation to orbit parameters

Attendant upon the use of synthetic aperture radar (SAR) in upcoming planetary missions, is the need to assess errors in the pointing angles of the instrument boresight due to spacecraft ephemeris errors. Developed herein are the constrained analytic partials of these boresight angles not only with respect to a motion-related, cartesian frame but also with respect to classical orbital elements. While both systems have great utility for spacecraft based instruments, the former system should prove useful for SAR instruments on aircraft.

Russell, R. K.↗

NASA NTRS1986

Design of robust failure detection filters

An essential aspect of the design of control systems for large, flexible spacecraft is fault tolerance. Because it is anticipated that a large number of sensors and actuators will be required to realize good control over these assemblies, the detection and isolation of component failures cannot be based on direct comparisons among replicated components. Instead, the notion of 'analytic redundancy' must be employed for the FDI function. Unfortunately this makes the FDI function sensitive to modeling errors which are certain to exist in the large space structure problem due to model truncation and parameter uncertainty. This paper addresses the robustness to model error of one method of FDI residual generation - the failure detection filter. Initial designs were found to be extremely sensitive to modeling error. The sources of this sensitivity are analyzed and modifications to the design are suggested. The improved filter is shown to have much better visibility of the failure signatures relative to the background due to modeling error.

San Martin, A. M.↗