Search

It is now well known that all instruments devoted to ionizing charged particle measurements flying in space are never perfect. Response analysis for each instrument is very time consuming but must be always done before any use of those data. For such purpose a software has been developed at ONERA-DESP under CNES funding to analyze saturation, contamination and other problems in any instrument and to cross calibrate measurements between spacecraft in an easy way. The software allows to compose time series plots of various spacecraft/instruments to compare them in a quick way, to plot correlation between two data sets and check for the coherence among all data. Moreover, the IPSAT software allows to plot in situ measurement along various orbits for any time from 1990 to present. The available data range from public access to private access to ONERA or partners. The available orbits with measurements on-board are LEO, MEO, GEO and some GTO and HEO with more or less continuous time coverage. The current data base is now about 400 Go. This can be very helpful for spacecraft anomaly analysis especially in case the spacecraft has no radiation measurements on-board. The IPSAT software can be accessed on the web after being registered.

The present work summarizes durability tests of white antistatic silicone paint, SCK5, in a simulated low-Earth-orbit atomic-oxygen environment. Two types of the simulation systems were used: a plasma asher and a laser-detonation source producing a 5-eV atomic-oxygen beam. The SCK5-coated samples were also exposed to argon plasma, in order to separate between chemical effects of atomic oxygen and physical effects introduced by the plasma. A comparative study of the erosion yield, the surface morphology, and the chemical composition resulting from exposure to similar equivalent atomic-oxygen fluences in both types of simulation systems was performed. The SCKS exposed to oxygen plasma showed significant cracking, whereas similar exposures to the 5-eV atomic-oxygen beam exhibited no cracking. In both cases the exposed samples showed a decrease of the carbon atomic concentration and an increase of the oxygen concentration in the upper surface layer. It is concluded that the erosion of SCK5 by the oxygen plasma is considerably more severe than by the 5-eV atomic oxygen, at least for the specific case of a porous siliconic material, tested in the present work. The observed results are most probably associated with the nature of the reactive species in the plasma asher, their omnidirectional flux, and the high porosity of SCK5 coating.

The present work describes the modification of a commercial pulsed laser detonation source, used for simulating the low Earth orbit 5-eV atomic-oxygen environment. In this facility the pulsed atomic-oxygen beam originatesfrom a plasma and is accompanied by high levels of vacuum-UV radiation. Thus, the exposure of materials to the atomic-oxygen beam is therefore an exposure to a combined atomic-oxygen and vacuum-UV environment creating synergistic erosion effects. A simple, low-cost system, based on the selective reflection of oxygen atoms, was developed in order to remove the vacuum-UV component from the atomic-oxygen beam. This system reflected about 50% of the original atomic-oxygen content. The vacuum-UV content in the reflected atomic-oxygen beam was reduced to 0.03% of its content in the original atomic-oxygen beam. Chemical changes occurring in Kapton HN and Tefzel (ethylene-tetrafluoroethylene copolymer) under vacuum-UV irradiation were used to prove that the reflected residual vacuum-UV radiation has no effect on the tested polymers.

Thermally Stimulated Creep (TSCr) mechanical spectroscopy has been used to analyze molecular movements in KMU-4lcarbon/epoxy composite material around the glass transition temperature. This technique is powerful to characterize the microstructure and micromechanical properties of the epoxy matrix and their evolution upon thermal aging. Three cooperative submodes have been distinguished by resolving the fine structure of the material complex α-retardation mode. The elementary processes constituting this mode possess activation enthalpies and preexponential factors that strongly depend on the thermal history of the sample. The activation parameters of the composite are subject to perceptible evolution due to postcuring degradation. The α-mode associated complex spectrum shifts towards higher temperatures by 27°C as a consequence of a series of quenching in the temperature range 260 to 0°C; the material shows a rise in the fragility and a deterioration in the crack-growth resistance qualities. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 342–350, 2002

The Scanner for Radiation Budget (ScaRaB) instruments are a series of Earth Radiation Budget (ERB) radiometers of which the first flight model (FM1) was launched on a Russian METEOR satellite in 1993. A second model (FM2) was launched on the Russian RESURS satellite in July 1998. The FM2 instrument worked perfectly until the failure of the platform transmitter in April 1999. Considering both missions, ERB data were obtained over sixteen months with ScaRaB. In order to obtain a good correlation between calibrations on the ground and in space in the long-wave spectral domain, the spectral response has been re-estimated using an original method. As the solar ground calibration and the integrating-sphere calibration are conducted in an enclosure purged with dry nitrogen, the detector gain differs from the gain under vacuum, and a correction factor must be applied. A new correction coefficient has been determined through analysis of the ScaRaB data sets, leading to satisfactory agreement between long-wave vacuum calibration and solar calibration.

The ScaRaB instruments are a series of Earth Radiation Budget radiometers of which the first flight model (FM1) was launched on a METEOR satellite on 25 January 1994. A second model (FM2) was launched on the Russian Resurs satellite in July 1998. Results obtained from FM1 indicated the need for more accurate ground calibration for FM2 and the spare model. Besides spectral response characterization (from 0.2 µm to 50 µm), channel gains and absolute filtered radiance of the on-board lamps and on-board black bodies have been measured, using different reference sources: laboratory black bodies, an absolutely calibrated integrating sphere, and the Sun. The black bodies ensure the validity of the calibrations in the long-wave spectral domain, while the Sun and the integrating sphere check the short-wave spectral domain. After a brief description of the ScaRaB instrument and its main characteristics, this paper describes the procedures and results, including the associated uncertainties, for the measurements of the broadband channel gains: these need to be accurately calibrated and compared. Points of interest and also weaknesses of the three methods are compared in order to lead to the most realistic uncertainty budget.

The Materials Exposure and Degradation Experiment (MEDET) was recently launched to the ISS on Space Shuttle Flight IE, as part of the EuTEF payload on the external payload facility of ESA’s Columbus module. The experiment will operate in‐orbit for at least 1.5 years, and has the overall objectives of evaluating the effects of the complex low Earth orbit space environment on material properties, investigating material degradation due to contamination, characterising the local ISS environment and measuring the local micro‐particle flux. This paper gives a brief overview of the experiment function and the material samples which are being exposed, before presenting some of the early flight data. In this phase of the mission, all of the instruments are operating successfully, and continuously acquiring data. The preliminary results mainly concern the environmental sensors, which are operating at relatively high acquisition rates (e.g. one reading every few seconds). It has been shown that the docking of the Space Shuttle to the ISS has a significant effect on the local pressure environment. The more complex degradation experiments are acquiring at much slower rates (e.g. one reading per day) and several more months of space exposure will be required before sufficient data is generated to reach conclusions about the behaviour of the materials. However, preliminary data is presented.

SCK5 is a white antistatic silicone paint developed by CNES and manufactured by MAP (France). The present work summarizes durability tests of this paint in a simulated low earth orbit (LEO) atomic oxygen (ATOX) environment. The paint was applied on various substrates including Kapton film, Duroid 5880 (a glass/Teflon PTFE composite) and TMM3 (a ceramic/thermoset polymer). Two types of ATOX simulation systems were used: an RF oxygen plasma, and a laser detonation source (manufactured by PSI) producing a 5 eV ATOX beam. Both types of simulation facilities generate VUV radiation in addition to oxygen species. Dedicated experiments were performed to distinguish between VUV and ATOX effects. The SCK5 coated samples were also exposed to RF argon plasma, in order to separate between chemical effects of atomic oxygen and physical effects introduced by the RF plasma.

Material properties are of primary interest for spacecraft designers and their evolution as a consequence of exposure to the space environment must be accurately predicted. In this context, CNES, ESA, the University of Southampton and ONERA are participating in a co- operative effort to develop a test-bed called the Material Exposure and Degradation Experiment (MEDET). The experiment will be integrated on the European Technology Exposure Facility (EuTEF), and as such will be placed on the Columbus External Payload Facility, an exterior platform on the International Space Station. The objectives of the experiment are concerned with the effect of the complex space environment on the optical and thermo-optical properties of materials and the characterisation of the ISS environment. This paper describes the MEDET system configuration, the different scientific experiments, the control electronics and the overall implementation of the payload.

The status of the SPOT 1 calibration after nearly two years of flight is discussed in terms of measurements in the preflight period, validation in the post launch assessment and monitoring during flight. The results obtained with preflight sources, with an on board solar sensor and with test site measurements with ground truth on White Sands (New Mexico) are compared. Mention is also given to measurements with an on board internal lamp for calibration monitoring, intercomparisons between the two HRV's instruments by histogram matching, and analyses of images of snowy test sites for multiband calibration. The data are discussed and interpreted in this paper and finally lead to an estimation of the most likely calibration coefficients as well as an estimation of their accuracy.

The radiometric resolution of SPOT imagery is limited by two independant phenomena : -the instrument noise generated along the image columns by the CCD arrays detectors, the electronics and the quantization process -the equalization defaults due to the fact that each CCD array detector has a different sensitivity and dark current This effect is taken care of by image radiometric preprocessing at the ground segment level ; the residual errors and imperfections may be considered as an additional noise generated along the images lines. During SPOT post launch performance assessment, the noise along columns is estimated by recording the signal delivered by an onboard calibration lamp on each detector over a several seconds period. The determination of the so-called "relative calibration coefficients" which permits the equalization preprocessing is made by analyzing the signal delivered by the calibration lamp The calibration device is designed so as to project the light of the reference lamp onto the detectors through the whole telescope optics. The characteristics of this device are measured on ground and controlled after launch by testing several technological parameters. An independant estimation of these calibration coefficients can be made by imaging areas of high and uniform reflectance such as large and flat snowy surfaces. This paper presents the results of these various investigations.