Valdivino Santiago

XIPE: the X-ray imaging polarimetry explorer

Abstract X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017. The proposal was, unfortunately, not selected. To be compliant with this schedule, we designed the payload mostly with existing items. The XIPE proposal takes advantage of the completed phase A of POLARIX for an ASI small mission program that was cancelled, but is different in many aspects: the detectors, the presence of a solar flare polarimeter and photometer and the use of a light platform derived by a mass production for a cluster of satellites. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus. Two additional GPDs filled with a 3-bar Ar-DME mixture always face the Sun to detect polarization from solar flares. The Minimum Detectable Polarization of a 1 mCrab source reaches 14 % in the 2–10 keV band in 105 s for pointed observations, and 0.6 % for an X10 class solar flare in the 15–35 keV energy band. The imaging capability is 24 arcsec Half Energy Width (HEW) in a Field of View of 14.7 arcmin × 14.7 arcmin. The spectral resolution is 20 % at 6 keV and the time resolution is 8 μs. The imaging capabilities of the JET-X optics and of the GPD have been demonstrated by a recent calibration campaign at PANTER X-ray test facility of the Max-Planck-Institut für extraterrestrische Physik (MPE, Germany). XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil). The data policy is organized with a Core Program that comprises three months of Science Verification Phase and 25 % of net observing time in the following 2 years. A competitive Guest Observer program covers the remaining 75 % of the net observing time.

A Practical Approach for Automated Test Case Generation using Statecharts

This paper presents an approach for automated test case generation using a software specification modeled in statecharts. The steps defined in such approach involve: translation of statecharts modeling into an XML-based language; and the PerformCharts tool generates FSMs based on control flow. These FSMs are the inputs for the Condado tool which generates test cases. The idea is to demonstrate that by using a higher-level technique, such as Statecharts, complex software can be represented with clarity and rich details. A case study was on an implementation of a protocol specified for communication between a scientific experiment and the on-board data handling computer of a satellite under development at National Institute for Space Research (INPE)

An Environment for Automated Test Case Generation from Statechart-based and Finite State Machine-based Behavioral Models

Automated test case generation from behavioral models like finite state machines (FSMs) and statecharts has long been studied. Environments that enable a test designer to model a real complex software and to obtain test cases to validate such a software are mandatory in an automated test approach. This paper presents an environment, GTSC, which enables test sequences to be obtained from both Statechart-based and FSM-based behavioral models. The environment supports test case generation from some test methods for FSM, such as switch cover, DS and UIO methods, and also from some test criteria for Statecharts based on the SCCF family. Two case studies involving embedded software developed for two computers of scientific experiments of a satellite under development at National Institute for Space Research (INPE) are presented in order to show the usefulness of the environment.

Designing fault injection experiments using state-based model to test a space software

Software for space applications requires significant testing. This paper presents an evaluation of the CoFI testing methodology as applied to actual space software, where deterministic fault cases derived from state-based models were executed using the software-implemented fault injection technique. Different models were used to represent the behavior of embedded software in a real satellite computer under the presence of both normal inputs and external faults in communication, processor, and memory. CoFI methodology was used for model construction, the Condado tool for test derivation, and the QSEE-TAS tool for test execution. In total, 8,620% of 471 fault cases detected errors in the software; this is a very large number, and more so considering that the software had already been tested by the company which developed it before being subject the CoFI methodology.

On Comparing and Complementing two MBT approaches

At INPE1 researchers and software engineers have been using Statechart-based testing for some time to test on-board satellite software. On the other hand, a group of researchers at CIFASIS2 and Flowgate Consulting have been applying Z-based testing for unit testing. Both groups started to compare their approaches and tools a year ago. What started as a comparison to share ideas and results, is now turning into the realization that actually both techniques complement and benefit from each other, yielding a more effective and wider Model-Based Testing (MBT) approach. In this paper we present the results obtained so far in comparing and complementing these two MBT techniques.

Shortening Test Case Execution Time for Embedded Software

Cost-effectiveness is perhaps the most driving characteristic behind a test automation approach aiming to spend less time in testing a software and finding as many faults as possible. Many research papers have been addressing the automation of test case generation activity by means of models, methods, tools and frameworks. However, in a practical software development environment it is not reasonable to automate test case generation if it is not possible to automatically execute them stimulating the software and capturing actual results. This paper presents the results obtained by using a tool, QSEE-TAS, that automates both test execution and test process documentation generation. It also presents the main features of such a tool. Three different embedded software products for computers of scientific experiments of satellites under development at National Institute for Space Research (INPE) were selected for showing the usefulness of QSEE-TAS compared with previous testing execution tools used at INPE.

A Brazilian Software Industry Experience in Using ECSS for Space Application Software Development

This paper presents the tailoring of ECSS software product assurance requirements aiming at the development of scientific satellite payload embedded software by a Brazilian software supplier. The software item, named SWPDC, developed by DBA Engenharia de Sistemas LTDA within Software Factory context, is part of an ongoing research project, named Quality of Space Application Embedded Software - QSEE, developed by National Institute for Space Research — INPE, with FINEP financial support. Among other aspects, QSEE project allowed to evaluate the adherence of a Software Factory processes to INPE’s embedded software development process requirements. Although not familiar with space domain, the high maturity level of such supplier, CMMI-3 formally evaluated, facilitates the Software Factory to comply with the requirements imposed by the custumer. Following the software verification and validation processes recommended by ECSS standards, an Independent Verification and Validation - IVV approach was used by INPE in order to delegate the software acceptance activities to a third party team. ECSS standard tailored form contributions along the execution of the project and the benefits provided to the supplier in terms of process improvements are also presented herein.

Evaluation of Test Criteria for Space Application Software Modeling in Statecharts

Several papers have addressed the problem of knowing which software test criteria are better than others with respect to parameters such as cost, efficiency and strength. This paper presents an empirical evaluation in terms of cost and efficiency for one test method for finite state machines, switch cover, and two test criteria of the statechart coverage criteria family, all-transitions and all-simple-paths, for a reactive system of a space application. Mutation analysis was used to evaluate efficiency in terms of killed mutants. The results show that the two criteria and the method presented the same efficiency but all-simple-paths presented a better cost because its test suite is smaller than the one generated by switch cover. Besides, test suite due to the all-simple-paths criterion killed the mutants faster than the other test suites meaning that it might be able to detect faults in the software more quickly than the other criteria.

Testing Environmental Models supported by Machine Learning

In this paper we present a new methodology, DaOBML, to test environmental models whose outputs are complex artifacts such as images (maps) or plots. Our approach suggests several test data generation techniques (Combinatorial Interaction Testing, Model-Based Testing, Random Testing) and digital image processing methods to drive the creation of Knowledge Bases (KBs). Considering such KBs and Machine Learning (ML) algorithms, a test oracle assigns the verdicts of new test data. Our methodology is supported by a tool and we applied it to models developed via the TerraME product. A controlled experiment was carried out and we conclude that Random Testing is the most feasible test data generation approach for developing the KBs, Artificial Neural Networks present the best performance out of six ML algorithms, and the larger the KB, in terms of size, the better.In this paper we present a new methodology, DaOBML, to test environmental models whose outputs are complex artifacts such as images (maps) or plots. Our approach suggests several test data generation techniques (Combinatorial Interaction Testing, Model-Based Testing, Random Testing) and digital image processing methods to drive the creation of Knowledge Bases (KBs). Considering such KBs and Machine Learning (ML) algorithms, a test oracle assigns the verdicts of new test data. Our methodology is supported by a tool and we applied it to models developed via the TerraME product. A controlled experiment was carried out and we conclude that Random Testing is the most feasible test data generation approach for developing the KBs, Artificial Neural Networks present the best performance out of six ML algorithms, and the larger the KB, in terms of size, the better.

On Proposing a Test Oracle Generator Based on Static and Dynamic Source Code Analysis

Test oracles have become a welcoming approach as a very efficient support for testing any type of application. Since oracles generation can be a very laborious work, several techniques have been studied in order to perform an automatic or semi-automatic generation. However, the construction of an automated test oracle is not a trivial task, especially in terms of the inference of verdicts and detecting defects. Therefore, this research proposes a strategy to construct an automated test oracle based only on a model generated from reverse engineering, and to detect defects by a combination of static and dynamic source code analysis with a minimum manual labor from testers. We have applied our methodology to some interesting case studies and compared with other tools in order to show usefulness of our approach.