The microchannel plate (MCP) has been used for decades as a photon, electron and atoms detector in most of the space instruments dedicated for X-rays, energetic neutral atoms, and charged particle imaging. The deep-space missions, as nearfuture ESA Jupiter Icy moon Explorer (JUICE) mission, expect very low temperature conditions on the destination orbit. Since instruments are usually calibrated on the ground under the “room” temperature, it is very important to know the variation of the detectors properties with temperature. The resistance and the gain of the MCP detectors, dedicated for the JENI (PEP package) instrument onboard of JUICE, were measured as a function of temperature at INTRASPEC TECHNOLOGIES, Toulouse, France for the temperature range -50 to +50°C and at the CALIPSO-3 facility of the Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France for the temperature range -25 to +25°C using samples from PHOTONIS France and PHOTONIS USA. It is also important to know how the resistance of the MCP detector behaves with temperature either to properly size the high-voltage source or, conversely, to choose a technology according to the size of the MCP detector and the maximum current that the high-voltage source can supply. Since the environment of Jupiter is very severe, the instruments will operate in the presence of high-energy particles that will induce background noise on the MCP detectors due to the shielding of the instruments against radiation. Therefore, the background noise in the Jovian environment represents a crucial issue for the MCP detectors whose gain can be degraded prematurely if too much charge is extracted from them due to the induced particles. Ours measurements show that the resistance of the MCP detector increases when the temperature decreases and is influenced by its self-heating, whereas the gain behavior depends on the technology of the MCPs. This is an important result which can be used to optimize the gain performance and the lifetime of the MCP detector. These experimental tests were funded by the French Space Agency CNES.
The increase of performance of new optical instruments for science and Earth observation always leads to higher requirements in terms of contamination due to particle sedimentation in cleanrooms and deposition of chemical species in vacuum environment. Specific cleanliness control procedures are implemented in order to mitigate the risks of contamination on optical sensors and sensitive diopters, especially when used for UV applications. Such procedures are commonly carried out in cleanrooms and are described in both European ECSS-Q-ST-70-50C and NASA SN-C-0005D standards. UV light at 365 nm is often used for the inspection of optical sensitive surfaces to localize and to evaluate the amount of fluorescent particles, essentially coming from textile fibers. But other groups of compounds can be observed with a different spectral response and distribution, like adhesives and resins or even organic residues. Therefore, we could take advantage of this spectral information closely linked to specific molecules for partial identification of these materials before further investigation involving wipe on flight model and measurement in a laboratory.
Optical instruments for space applications with improved performances (smaller pixels and spectral range extension) are becoming more and more sensitive to chemical contamination and particle sedimentation. Outgassing under vacuum conditions causes dramatic flux losses, especially in the UV bandwidth. Furthermore, it is difficult to perform physicochemical analyses of contaminated surfaces on flight models, in a clean room. Conventional analytical techniques such as FTIR (Fourier Transform Infrared interferometer) need the tool to be in contact with the studied area, which is forbidden when working on satellites. In addition, it does not give any information about the distribution of the contaminants in the field of view. The probed area is large, mono-pixel, and the sensitivity of the instrument is too low for hundred nanometer thin film deposits. A first study has shown that we could benefit from using the UV/visible fluorescence spectra to partially identify contaminants and polymer materials. The shape of the fluorescence spectra of adhesives, paints and varnishes have specific signatures that could be recorded into a designated reference database. The location of the presence of these contaminants on such sensitive optics is also relevant. To acquire both these parameters, we designed a specific compact hyperspectral instrument to remotely acquire cube images (500x500 pixels) in a 5 degree field of view, and on a wide range of continuous wavelengths from UV at 320 nm up to the near infrared at 1000 nm. This paper will present the chosen trade-off between different critical optics for a new portable version of this instrument. It is dedicated to space and cultural heritage applications and the first results on an engineering prototype will be shown.
The reliability of bipolar silicon-based phototransistors was investigated through evaluation tests for space
applications. First of all a preliminary evaluation program including thermal cycling, vibrations and shocks test, radiation
test and high-temperature operating life test was carried out to assess the overall quality of these phototransistors. During
life test abnormal fluctuations of phototransistors collector current measured under constant illumination have been
observed. In order to solve this problem, a failure analysis was conducted. Mobile charges located in the photobase
passivation layer were found to be at the origin of these fluctuations. Based on these results a new methodology for
device selection was proposed to achieve, despite to that issue, high reliability in operating conditions.