Abstract
ESA Study on Radiation Testing of COTS Components to Verify a COTS RHA Approach
Peter Beck1, Marta Bagatin2, Simone Gerardin2, Marcin Latocha1,
Alessandro Paccagnella2, Christoph Tscherne1, Michael Wind1, Marc Poizat3
1 Seibersdorf Labor GmbH, Austria
2 University of Padova, Italy
3 European Space Agency, ESA
Abstract
Small satellites, such as CubeSat, have become a popular and cost effective manner of accessing space [1]. The increased interest in flying small satellite missions and initiation of the European Space Agency, ESA projects to improve reliability of CubeSat has resulted in an increased utilization of COTS components. Besides, COTS are not only used for small satellite applications, but there is an increase in the use of COTS also on mainstream missions. Therefore, ESA initiated a study on radiation screening of COTS components and verification of COTS Radiation Hardness Assurance (RHA) approach (CORHA). The CORHA project is coordinated by the Seibersdorf Laboratories (SL) and is performed in collaboration with the University of Padova (UPD). ESA is making use of COTS components and popular examples are, amongst others, FPGAs and memory devices (FLASH, SDRAMs, DDR2, etc.) [1]. This increase in the use of COTS components is owed to the fact that COTS often have superior performance compared to space qualified components and might work with lower resource requirements (e.g. power consumption). Although COTS components performance capabilities often outperform traditional space qualified components, there are limitations strongly complicating their use for space applications. Limitations inlcude lack of traceability, packaging constraints, radiation sensitivity and questions regarding board level and component level testing, rapid obsolescence, cost increase due to up-screening and others.
According to the ECSS Radiation Hardness Assurance standard ECSS-Q-ST-60-15C standard [2] Radiation Hardness Assurance consists of all activities undertaken to ensure that the electronics of a space system perform within their design specifications after exposure to the space environment. In this context, RHA deals with the environment assessment, the part selection, the part testing, the spacecraft layout, the radiation tolerant design as well as with the mission, system, and subsystem requirements. In principle the ECSS-Q-ST-60-15C [2] that is embedded in the product assurance standard for Commercial EEE Components ECSS-Q-ST-60-13C [3] as an applicable document does also apply to COTS devices. However, the application of ECSS-Q-ST-60-15C to small satellites that are flying COTS devices may not be practical for technical and/or financial reasons. The RHA process for such missions is therefore often defined on a case-by-case basis. Hereby the RHA for COTS is commonly based on risk management in terms of acceptance of a given risk and not on risk avoidance [1].
As a first baseline, knowledge of the radiation environment is of crucial importance for a tailored RHA-approach. Various software tools are existing (e.g. SPENVIS [4], OMERE [5], etc.) that provide engineers with meaningful radiation environment data. These data are used to perform model calculations to determine TID and TNID dose levels inside the satellite at the location of the EEE components. With a well-known radiation environment, relevant hazards are identified. A detailed evaluation of the hazards serves as a good baseline for part selection and also for the definition of the radiation tests that need to be performed. A number of radiation effects may be mitigated by design. However, these mitigation techniques need to be fully understood as they may create additional problems [1].
Again, to achieve and implement effective mitigation a good knowledge of the radiation environment and associated potential radiation effects is necessary. There are numerous mitigation techniques that may be applied to increase the radiation performance of an equipment or system. Mitigation techniques comprise methods such as single event latch-up protection, soft error rate mitigation, use of extra shielding or positioning of sensitive parts in more shielded areas of the spacecraft. Within the RHA process, the design is critically assessed to identify risks and to decide what devices need to be tested. A definition of dose level limits for TID and LET thresholds for SEE may be used as a criterion whether to perform testing of a specific device or not. The criteria for part selection should comprise the use of technologies that are less sensitive and the selection of components being testable. Available test data and flight heritage should be considered for part selection.
Board-level testing might be an effective tool. The major advantages of board level testing are the reduced test time and the fact that tested parts are exposed in application conditions. The advantages come at the cost of reduced observability; i.e. the test can be considered as go / no go tests. Also, the results cannot be reused for another application. Board level proton testing allows for SEE testing on entire boards as large-area beams are available. Also, high energy protons have a good penetration depth. However, proton SEE testing has major limitations that are small sample sizes, difficulties in identifying the SEE error mode, complicated test sequence and that testing is only applicable for the specific application. Also, the fluence needed to get sufficient SEE statistics may result in high TID and TNID dose levels.
Using COTS offers great benefits, however they come also with some serious disadvantages. Thus, the use of COTS components requires a solid understanding of the relevant processes and must be based on a comprehensive risk management. In this context it is of crucial importance that RHA for COTS is implemented already in the early phases of the project development and that there is an awareness for the need of a suitable risk management strategy. Within the scope of a critical system analysis, a large number of radiation effects may be avoided by effective mitigation techniques. Nevertheless, irradiation testing of COTS devices is important in particular for critical devices that need to be properly identified. Currently no universal RHA standards are available that are dedicated to COTS. For this reason, RHA for COTS is handled on a case-to-case base and thus is realized as tailored RHA solution for each specific application. The unfavorable situation of lacking dedicated RHA standards for COTS needs to be addressed promptly by providing standards that regulate testing of COTS components to facilitate the achievement of significant test results.
The objectives of the CORHA study are to (1) screen COTS components, (2) prepare and execute radiation test campaigns, (3) and propose an ad-hoc RHA approach for COTS components. The CORHA team will evaluate COTS technologies available on the market with respect to their TID response and to their susceptibility for SEE. During the presentation, we show a set of proposed candidates for further radiation hardness investigations. Further, based on the gathered data, review of existing standards and the most recent scientific and technical literature, we outline an ad-hoc RHA approach for COTS components, which will be investigated in more detail in the CORHA study.
References
[1] M. Poizat, A. Zadeh, C. Poivey, R. Walker, Radiation Hardness Assurance for Commercial-Off-The-Shelf (COTS) components for Small Satellites, RADHARD Symposium 2018, www.seibersdorf-laboratories.at/en/radhard/archive/2018-radhard-symposium, ISBN (Print) 978-3-902780-12-6, ISBN (Ebook) 978-3-902780-13-3, Editor: Peter Beck, Seibersdorf Labor GmbH, 2444 Seibersdorf, Austria, Publisher: Seibersdorf Laboratories Publishing, Austria, April 2018.
[2] ECSS-Q-ST-60-15C, Radiation Hardness Assurance – EEE Components, ECSS, Oct 2012
[3] ECSS, ECSS-Q-ST-60-13C, Space product assurance – Commercial electrical, electronic and electromechanical (EEE) components
[4] SPENVIS, The Space Environment Information System, software, accessible via swe.ssa.esa.int; www.spenvis.oma.be
[5] TRAD, Omere, software, accessible via www.trad.fr/en/space/omere-software
Acknowledgments
We acknowledge the support by the European Space Agency, ESA under the ESA contract – Contract No. 4000126049/18/NL/KML.