End Of Expected Life Research Articles

Improving tail accuracy of the predicted cumulative distribution function of time of failure

Prognostic information is used to make decisions such as when to perform maintenance or - in time sensitive and safety critical applications - when to change operational settings. Where distributions about expected end of life (EOL) are available, these decisions are often based on risk-informed thresholds, for example a 2σ or 3σ criterion which considers the probability of making a bad decision at 5% or 0.3%, respectively, as tolerable. Sampling-based techniques such as Monte Carlo Sampling (MCS) and Latin Hypercube Sampling (LHS) can provide effective approaches to the propagation and analysis of uncertainty. Due to its efficient manner of stratifying across the range of each sampled variable, LHS requires less computational effort than MCS and is therefore more often used. However, since the focus is placed on accurately predicting the tails of the Cumulative Distribution Function (CDF) of Time of Failure (ToF) sampling-base techniques may not properly represent these areas. Although one might be tempted to use a brute force approach and simply increase the number of samples, some safety-critical applications may be computationally constrained. Such applications include electric UAV where the decision making process has to be fast in order to take action as soon as possible. This paper explores the ability of MCS and LHS to perform tail prediction with small sample sizes. The results show that LHS does not provide a significant advantage over MCS in terms of characterizing the tails of the CDF of the battery End of Discharge (EOD) prediction. Then, a methodology that combines MCS and Kernel Density Estimation (KDE) is investigated. The advantages of KDE in terms of reducing sample size while improving tail accuracy are demonstrated on battery end-of-discharge data.

Investigation of radiation damage due to particle irradiation on Silicon Drift Detector for Chandrayaan-2 mission

This paper presents the work carrie dout in support of Silicon Drift Detector (SDD) characterization for the Chandrayaan-2 instruments namely Solar X-ray Monitor (XSM) and Alpha Particle X-ray Spectrometer (APXS). The XSM and APXS instruments use SDD to detect X-rays from the Sun and fluorescent X-rays from the lunar surface respectively. The aim of this study is to understand and quantify any spectroscopic performance degradation of these X-ray spectrometers due to space radiation in the SDD during its operational period. Any radiation damage to the SDD leads to increase in the detector leakage current and thus degrades the spectroscopic performance, mainly the energy resolution. The expected end-of-life (EOL) 10 MeV equivalent proton fluence was modeled using SPENVIS simulation software. The Silicon Drift Detector was irradiated with 10 MeV protons for the doses up to 24 krad in logarithmic steps and measured the energy resolution and the leakage current at each dose. The spectrometer energy resolution degraded from ∼ 142 eV at 5.9 keV to ∼ 250 eV for the cumulative proton dose of ∼ 11 krad for the mission life of one year. This satisfies the performance requirement of the SDD based X-ray spectrometers onboard Chandrayaan-2 mission.

Thermal annealing response following irradiation of a CMOS imager for the JUICE JANUS instrument

ESA's JUICE (JUpiter ICy moon Explorer) spacecraft is an L-class mission destined for the Jovian system in 2030. Its primary goals are to investigate the conditions for planetary formation and the emergence of life, and how does the solar system work. The JANUS camera, an instrument on JUICE, uses a 4T back illuminated CMOS image sensor, the CIS115 designed by Teledyne e2v. JANUS imager test campaigns are studying the CIS115 following exposure to gammas, protons, electrons and heavy ions, simulating the harsh radiation environment present in the Jovian system. The degradation of 4T CMOS device performance following proton fluences is being studied, as well as the effectiveness of thermal annealing to reverse radiation damage. One key parameter for the JANUS mission is the Dark current of the CIS115, which has been shown to degrade in previous radiation campaigns. A thermal anneal of the CIS115 has been used to accelerate any annealing following the irradiation as well as to study the evolution of any performance characteristics. CIS115s have been irradiated to double the expected End of Life (EOL) levels for displacement damage radiation (2×1010 protons, 10 MeV equivalent). Following this, devices have undergone a thermal anneal cycle at 100̂C for 168 hours to reveal the extent to which CIS115 recovers pre-irradiation performance. Dark current activation energy analysis following proton fluence gives information on trap species present in the device and how effective anneal is at removing these trap species. Thermal anneal shows no quantifiable change in the activation energy of the dark current following irradiation.

Proton irradiation of swept-charge devices for the Chandrayaan-1 X-ray Spectrometer (C1XS)

This paper presents work carried out in support of swept-charge device (SCD) characterisation for the Chandrayaan-1 X-ray Spectrometer (C1XS) instrument. A brief overview of the C1XS instrument is presented, followed by a description of SCD structure and operation. The SCD test facility and method of device characterisation using two different drive sequencers to assess leakage current and spectroscopy performance (FWHM and noise at Mn Kα) are then described. The expected end-of-life (EOL) 10 MeV equivalent proton fluence for the SCDs of C1XS was modelled using Monte Carlo simulation software and used in a subsequent proton irradiation study involving eight SCDs. The irradiation study was carried out at the Kernfysisch Versneller Instituut (KVI) in the Netherlands and characterised the impact of 50% and 100% of the expected Chandrayaan-1 EOL proton fluence on the SCD operational characteristics. The radiation environment modelling, irradiation methodology and post-irradiation characterisation of the devices are presented in this paper and recommendations about the planned C1XS operational temperature and shielding are given.