KEYWORDS: Contamination, Absorption, Transmittance, Space operations, Sensors, Signal to noise ratio, Signal attenuation, Modeling, Confocal microscopy
ESA Sentinel-4 mission will monitor trace gas concentrations and aerosols in the Earth’s atmosphere with a 1-hour revisit frequency and unprecedented spatial resolution. Initial performance predictions, relying on literature/historical values for optical absorption coefficients, revealed considerable losses at the end of the mission lifetime caused mainly by high levels of absorption of light due to molecular contamination spread over the 39 optical surfaces of the UVIS channel. This publication describes the significant effort undertaken by Sentinel-4 team to establish more reliable and accurate performance predictions, and the importance of performing measurements under representative conditions of the instrument’s contamination environment. The refined performance prediction analysis was the final step of the activity, demonstrating that the end of life performance requirements of Sentinel-4 will be met.
Molecular contamination phenomena depend on temperature. For example, the morphology of a contaminant can change from a uniform film to droplets. The authors believe that the surface morphology of thin-film contamination affects optical transmittance and reflectance of camera lenses and other sensors, so it is important to gain a better understanding of the morphology of contamination. The authors investigated a simple measurement technique to determine molecular contamination morphology in a vacuum and at low temperatures using a CMOS camera sensor chip. The CMOS camera operates down to −60°C, which covers our range of interest (i.e., from −60°C to room temperature). Furthermore, using a combination of the camera sensor and the optical measurement setup in a vacuum chamber, the morphology and optical transmittance were measured simultaneously. The advantages of the technique are that the equipment is inexpensive and can be installed in many chambers now in use.
Prediction of the contamination deposits from the Total Mass Loss (TML) via a novel technique is presented. This predictive methodology, based on the multi-step dynamic outgassing test complemented with a thermogravimetric analysis (TGA), allows assigning outgassed species according to their sticking coefficients to a collector's surface. The proposed approach enables to identify major chemical species outgassed from the tested material and calculate sticking coefficients in a broad temperature range (-175 to+80°C). The preliminary results show that this method could be used as an improved procedure for predictions of deposition and reemission levels.
KEYWORDS: Diffusion, Molecules, Contamination, Physics, Data modeling, Mathematical modeling, Chemical species, Ultraviolet radiation, Chemical reactions, Mass spectrometry
Contamination modeling in Europe has long been based on physical mechanisms, such as desorption. However other physical mechanisms, such as diffusion, evaporation or mixing effects exist. These alternative mechanisms were experimentally evaluated and modelled. It was yet observed that, without an experimental capability to reliably separate the (re)emitted chemical species, it is very difficult to determine whether the modeling and its underlying physical mechanisms are representative of reality, or simply a mathematical fit of reality. This is the reason why in the last years emphasis was put on the experimental separation of species, mostly through TGA/MS coupling. This paper presents a review of these efforts and promising results on species separation to reach a really physical modeling of outgassing, deposition/reemission and UV synergy.
KEYWORDS: Contamination, Satellites, Space operations, Space telescopes, Sensors, Computer aided design, Chemical elements, Control systems, Combustion, Scattering
Increasingly satellites are carrying on-board bipropellant thrusters, especially for interplanetary missions. Many of these spacecraft are also equipped with surface-sensitive instruments, such as telescopes and detectors, which, due to the required configuration, might be impinged by the bipropellant thruster plumes and therefore contaminated by plume exhaust products. At present, there are no European analysis tools capable of determining the effects of such propulsion systems on surfaces sensitive to contamination in the preliminary design phase. This may result into a need to modify the spacecraft design in a later development phase in order to mitigate contamination effects. The consequences are additional costs, delay on schedule and possible reductions of scientific goals. This paper emphasizes the need for a tool to be used at the preliminary stage of a satellite design to analyse the contamination effects of bipropellant thruster plume impingement on sensitive surfaces. It also describes a possible approach/architecture to be used for this tool.
Conference Committee Involvement (2)
Space Systems Contamination: Prediction, Control, and Performance 2022
23 August 2022 | San Diego, California, United States
Systems Contamination: Prediction, Control, and Performance 2020
24 August 2020 | Online Only, California, United States
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.