An In-Depth Assessment of Internal Contamination in the Wide Field/Planetary Camera: Republished from the Journal of the IES May-June 1990 issue, pages 29-35

Abstract

Following thermal vacuum/thermal balance testing, a gray haze was discovered on the corners of the Wide Field/Planetary Camera (WF/PC) aperture window. The phenomenon was suggested to be a result of molecular transport from a low outgassing structural adhesive. Detailed analyses, both chemical and analytical, were conducted to assess the formation of the haze. Each material was considered individually, as it was not known if the actual contamination was a result of one, many, or possibly none of the materials considered. Results of the analytical assessment and the comparison with the aforementioned chemical analyses provided incontrovertible evidence as to the cause of the window haze. The resultant cleanup and subsequent elimination of the problem are also addressed. [Editor's Note: This 1990 paper is republished as part of the Journal of the IEST 50th anniversary celebration. It is accompanied by remarks from Patti Hansen, author of "Overview of the HST Contamination Engineering Program at 15 Years: A Cleanliness Metric for Success with Optical Satellites" paper in this issue.]

Climate Data Records from Meteosat First Generation Part II: Retrieval of the In-Flight Visible Spectral Response

“…the minimisation of the cost function has been conducted by a limited-memory variant of the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm that evaluates the gradient of the cost function and iteratively approximates the Hessian matrix without evaluating second derivatives [38]. Second partial derivatives of the cost function constitute the Hessian matrices in Equations (20) and (21), and first partial derivatives of the retrieved instrument spectral response function constitute the Jacobian matrices in Equation (22). All partial derivatives have been calculated through advanced algorithmic (or automatic) differentiation (AD) techniques, which are concerned with the accurate and efficient evaluation of derivates for functions defined in computer programs [39].…”

“…The top panel of Figure 6 illustrates the retrieved absolute Meteosat-10 HRV spectral response function when target type-specific biases are included with the modelling. Figure 7 illustrates examples of the associated posterior spectral error and correlation functions designated in Equations (22) and (23). The retrieved spectral response shows no significant degradation (viz.…”

“…The phenomenon of chromatic degradation has been well known from the monitoring and in-flight calibration of numerous optical Earth Observation instruments (e.g., SeaWiFS [14], CERES [15], MERIS [16], VIIRS [17][18][19]) and space-borne astronomical telescopes. Contaminants evaporated from an instrument's interior and condensation or UV-stimulated deposition and polymerisation of contaminant films onto the surface of optical elements have been considered as the main reasons for degradation of optical instruments in Space [20][21][22][23]. For instance, after the first Hubble servicing mission the Wide Field and Planetary Camera (WPFC) was returned to ground and several optical elements were analysed in detail to find the cause and understand the mechanism behind the observed spectral degradation of instrument performance.…”