ESA GNC Conference Papers Repository

PEET v1.0: the state-of-the-art pointing and performance error engineering tool for space missions
M. Hirth, H. Su, T. Ott, M. Casasco, G. Ortega
Presented at:
Salzburg 2017
Full paper:

Future space missions - especially with scientific and laser-communication background - tend to rely on more and more demanding pointing performance. As a consequence even small performance changes may not only lead to additional iterations of the design, but also potentially result in prominent mission-critical changes in subsystems and equipment selection. Similar issues are also present for missions with less demanding requirements, but where the main driver in the design process is cost-efficiency. Other missions face the challenge to accurately deal with non-scalar requirements such as constraints on the power spectral density or on the probability density function of the pointing error. Thus, having at hand a clear pointing error engineering methodology to systematically assess achievable performances for various requirement categories already in early project phases becomes essential. ESA accounted for this need by publishing the ECSS Control Performance Standard E-ST-60-10C which contains solid and exact mathematical elements to build up a performance budget. In addition, the ESA Pointing Error Engineering Handbook ESSB-HB-E-003 presents guidelines for a step-by-step engineering process from pointing error requirement specification to systematic pointing error analysis, and the compilation of pointing error budgets. To complement and to support the dissemination of this pointing error engineering methodology, a software prototype called Pointing Error Engineering Tool (PEET) was developed and released under the ESA Software Community License in 2012. The tool is intended to support engineers by automating the performance management process such that the focus can be put on the identification and modelling of error source and transfer properties, rather than on discussions how performance contributors need to be interpreted and summed in a performance budget. Until the end of 2016, the PEET prototype was further developed and extended to a consolidated, fully verified and validated release version. This paper focuses on the new and extended features as a result of the recent development. The key update supersedes the restriction to the 'simplified statistical method' described in ESSB-HB-E-003. This method is based on the assumption that the central limit theorem is applicable and the total error follows a (nearly) Gaussian distribution. While such assumption is comparably easy to treat in terms of algorithms, it may lead to significant deviations from the true result, in case dominant non-Gaussian error contributions exist. The release version of PEET additionally implements the so-called 'advanced statistical method'. In particular, this implies that probability density functions of (arbitrarily correlated) error contributions - rather than only mean and standard deviation - are used for an accurate level of confidence evaluation of requirements. The benefits of this approach will be highlighted by comparing the results obtained with both methods using descriptive examples. In addition, a compliant generalization of the 'statistical interpretation' concept in the ECSS Control Performance Standard is introduced which provides more flexibility in the definition of requirements and which can help to avoid the specification of over-conservative budgets. Finally, the paper highlights the benefits of PEET and the developed concepts from an ESA and industrial user point of view. As the latter go beyond the level of detail described in the ECSS standard and the ESA Pointing Error Engineering Handbook, the results will flow back into an update of the handbook in 2017. The tool itself provides traceability and a common platform for exchange of information between various entities (space agencies, industrial prime contractors, industrial sub-contractors, satellite operators, etc.). It allows an efficient handling of budgets especially when a variety of requirements on different instruments exists. Providing budgets (applicable to general performance problems, not only pointing) in line with the ECSS standard and the ESA Pointing Error Engineering Handbook, PEET is expected to become a standard tool that will be used for any future ESA mission.