Integrated circuits employed in space applications generally have very low-volume production and high performance requirements. Therefore, the adoption of Commercial-Off-The-Shelf (COTS) components and Third Party Intellectual Property cores (3PIPs) is of extreme interest to make system design, implementation and deployment cost-effective and viable w.r.t. performance. On the other hand, this design paradigm exposes the system to a number of security threats both at design-time and at runtime. In this paper, we discuss the security issues related to space applications mainly focusing on threats that come from the adoption of the well-known RISCV microprocessor. We highlight how Hardware Trojan horses (HTHs) and Microarchitectural Side-Channel Attacks (MSCAs) may compromise the overall system operation by either altering its nominal behavior or by stealing secret information. We discuss the security extensions provided by the RISC-V architecture as well as their limitations. The paper is concluded by an overview of the issues that are still open regarding the security of such microprocessor in the space domain.

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Soft errors in embedded systems' memories like single-event upsets and multiple-bit upsets lead to data and instruction corruption. Therefore, devices deployed in harsh environments, such as space, use fault-tolerant processors or redundancy methods to ensure critical application dependability. Another rising concern in secure, critical space applications is the possible introduction of hardware Trojans in an untrusted phase of the manufacturing process. Besides environmental side-effects, an adversary that has injected a malicious mechanism e.g., in the processor or memory can trigger unwanted behavior or leak sensitive information. Techniques to prevent or mitigate hardware Trojans are important to ensure hardware security. Leveraging the openness of the RISC-V ISA, this paper introduces a novel solution to improve the security and dependability of softcores with a low area and latency overhead. The instruction validator which is the first part of this solution can effectively detect hardware Trojans and multiple-bit upsets in the instruction memory by checking instruction/address pairs using a Bloom filter probabilistic data structure. The second part of the solution is the proposal of an error correction code instruction memory using Hamming single-error correction to detect and correct single-event upsets. It has also been proven that the Hamming decoder improves the detection performance of the instruction validator.

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RISC-V is an open and modular Instruction Set Architecture(ISA) which is rapidly growing in popularity in terrestrial applications. This paper presents the place in future space embedded systems ESA's roadmap for RISC-V based processors. In order to satisfy different applications with contrasting requirements in satellite data systems, four different types of processors are identified: 1) General-Purpose (GP) processors for payloads 2) main platform On-Board Computers (OBCs) controllers 3) low-area/low-power microcontrollers (uCs), 4) enhanced payload processors with support for Artificial Intelligence (AI). We also describe the state of the art of the RISC-V software ecosystem, including the currently available hardware platforms, with a focus on developments for space applications and what has already been done in the European Space Industry. Finally, planned activities are presented, with a focus on the role of the European ecosystem.@en

The use of deep neural networks (DNNs) in terrestrial applications went from niche to widespread in a few years, thanks to relatively inexpensive hardware for both training and inference, and large datasets available. The applicability of this paradigm to space systems, where both large datasets and inexpensive hardware are not readily available, is more difficult and thus still rare. This paper analyzes the impact of DNNs on the system-level capabilities of space systems in terms of on-board decision making (OBDM) and identifies the specific criticalities of deploying DNNs on satellites. The workload of DNNs for on-board image and telemetry analysis is analyzed, and the results are used to drive the preliminary design of a RISC-V vector processor to be employed as a generic platform to enable energy-efficient OBDM for both payload and platform applications. The design of the memory subsystem is carried out in detail to allow full exploitation of the computational resources in typically resource-constrained space systems.

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This paper discusses principles and techniques to evaluate processors for dependable computing in space applications. The focus is on soft errors, which dominate the failure rate of processors in space. Error, failure and propagation models from literature are selected and employed to estimate the failure rate due to soft errors in typical processor designs. A similar approach can be followed for applications with different radiation environments (e.g. automotive, servers, experimental instrumentation exposed to radiation on ground), by adapting the error models. This detailed white-box analysis is possible only for open-source Intellectual Property (IP) cores and in this work it will be applied to several open-source IP cores based on the RISC-V Instruction Set Architecture (ISA). For these case studies, several types of redundancy described in literature for space processors will be evaluated in terms of their cost-effectiveness and expected final in-orbit behavior. This work provides a comprehensive framework to assess efficacy and cost-effectiveness of redundancy, instead of listing and categorizing the techniques described in literature without assessing their relevance to state-of-the-art designs in space applications.

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The aim of this paper is to assess the feasibility and on-board hardware performance requirements for on-board telemetry forecasting by implementing a Recurrent Neural Network (RNN) on low-cost multicore RISC-V microprocessor. Gravity field and steady-state Ocean Circulation Explorer (GOCE) public telemetry data was used for training RNNs with different hyperparameters and architectures. The prediction accuracy of these models was evaluated using mean error and R-squared score on the same test dataset. The implementation of the RNN on a RISC-V embedded device, representative of future space-grade hardware, required some adaptations and modifications due to the computational requirements and the large memory footprint. The algorithm was implemented to run in parallel on the 8 cores of the microprocessor and tiling was employed for the weight matrices. Further considerations have also been made for the approximation of sigmoid and hyperbolic tangent as activation functions.@en

A new methodology for Total Ionizing Dose (TID) tests is proposed. It is based on the employment of an on-chip ⁹⁰ Sr/ ⁹⁰ Y beta source as alternative to standard methods such as ⁶⁰ Co gamma rays and electrons from LINAC. The use of a compact beta source for TID tests has several advantages. In particular, the irradiation of devices with more than one radiation source results in a better representation of the complex space radiation environment composed of several types, energies and dose-rates. In addition, the use of an easy handling beta source allows the irradiation of electronic devices without any damage to other auxiliary circuit. In this work, ⁹⁰ Sr/ ⁹⁰ Y beta source dosimetry and related radiation field characteristics are discussed in depth. In order to validate the proposed source for TID tests, a rather complex device such as the “SPC56EL70L5” microcontroller from ST-Microelectronics was exposed to ⁹⁰ Sr/ ⁹⁰ Y beta rays. The results of this test were compared to that of a previous test of another sample from the same lot with a standard gamma ⁶⁰ Co source. The electronic performances following the two irradiations have been found to be in excellent agreement, by demonstrating therefore the validity of the proposed beta source for TID tests.

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This paper proposes a roadmap to address present and future needs in space systemswithRISC-Vprocessors. RISCVis an open and modular instruction set architecture, which is rapidly growing in popularity in terrestrial applications. To satisfy different applications with contrasting requirements in satellite data systems, four different types of processors are identified: 1) low-area/low-power microcontrollers, 2) on-board computers, 3) general-purpose processors for payloads, and 4) enhanced payload processors for artificial intelligence. Several solutions based onRISCVare proposed for eachof these types of processors and comparedwith proprietary commercial-off-the-shelf andspacegrade solutions. An extensive analysis of the results available fromliterature is conducted to show that RISC-V has the potential to solve such a wide range of needs. This paper will also show the unprecedented number of open-source implementations and models that were developed in a relative short time on a single instruction set architecture. Future space systemscouldbenefit frommanyof those developments, andthisworkidentifies andhighlightswhat is stillmissing to satisfy the specific needs of processors for space, especially in terms of fault tolerance and technology readiness level. @en

This paper analyzes the contribution of caches to failures at processor level due to soft errors. In order to do this, approximated methodologies to estimate the percentage of the total Sensitive Area (SA) of a processor for each unit during early design exploration are proposed. Then, to identify the most vulnerable units, a metric called Relative Soft Error Vulnerability (RSEV) is defined. The analysis shows that caches are the most vulnerable units of state-of-the-art processors and that, even when considering higher-frequency and more complex pipelines representative of next-generation processors for space applications, the final in-orbit failure rate is dominated by failures caused by upsets in cache arrays. Even when protecting memory arrays with information redundancy, the large fraction of upsets occurring in caches is potentially the biggest threat to processor availability and reliability, especially if errors are modelled with invalid assumptions and are not properly handled when detected.

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This paper presents preliminary position on the use of the novel, free and open RISC-V Instruction Set Architecture (ISA) for on-board electronics in space. The modular nature of this ISA, the availability of a rich software ecosystem, a rapidly growing community and a pool of open-source IP cores will allow Space Industry to spin-in developments from terrestrial fields (in terms of security, artificial intelligence, support for operating systems, hardware acceleration etc.) while focusing its efforts mainly on aspects related to the specific needs of on-board electronics for space applications (e.g. fault tolerance, observability, error signaling, etc.). This will improve reuse and avoid the necessity of developments from scratch when not strategically needed, eventually increasing productivity and reducing costs. The use of an open, non proprietary ISA will allow ad-hoc design of microarchitecture-level soft error countermeasures that can greatly increase the robustness of Application Specific Standard Products (ASSP) and FPGA implementations.

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The tolerance to the cumulative effects of ionizing radiation is one of the most important parameters to keep into account when selecting an EEE component for space applications. TID sensitivity is normally investigated measuring changes induced by gamma rays from 60Co sources to nominal parameters of a component or to its expected functional behavior. In this work we propose an on-chip 90Sr/90Y electron source as an alternative methodology for TID tests.60Co and 90Sr/90Y TID test setups for a complex SoC are compared in terms of complexity and of experimental results, investigating the use of a 90Sr/90Y as well as the established 60Co. We show that 90Sr allows a simpler test setup, manages to reproduce specific modes of failure obtained with 60Co and causes failures at comparable total doses. This makes 90Sr an interesting alternative to 60Co qualification and the use of untested components, to be further investigated especially for complex COTS SoCs.@en

The use of System-on-Chip (SoC) solutions in the design of on-board data handling systems is an important step towards further miniaturization in space. However, the Total Ionizing Dose (TID) and Single Event Effects (SEE) characterization of these complex devices present new challenges that are either not fully addressed by current testing guidelines or may result in expensive, cumbersome test configurations. In this paper we report the test setups, procedures and results for TID testing of a SoC microcontroller both using standard C60o and low-energy protons beams. This paper specifically points out the differences in the test methodology and in the challenges between TID testing with proton beam and with the conventional gamma ray irradiation. New test setup and procedures are proposed which are capable of emulating typical mission conditions (clock, bias, software, reprogramming, etc.) while keeping the test setup as simple as possible at the same time.@en

The domain of space avionic systems is changing extremely rapidly, compared to other technical domains in space-faring industry, under the pressure of an intense competition, the continuous emergence of new markets and players, the need for cost reduction, as well as an increased obsolescence rate of components and processes. This rapidly changing landscape is as well opening a large amount of opportunities for the space avionic systems: the new high-performance processors architectures and silicon processes, which offer the possibility to integrate different functions until now implemented on several boards either in a single chip (SoC), or in application-specific standard products (ASSP) or in new large FPGAs are allowing multi-fold gains in performances and miniaturization for electronic systems. Another example are digital sensor buses, already heavily used in automotive and embedded applications and now also introduced in space systems to tackle mass, power reduction, increase of accuracy and increase of testability. Reliability and availability constraints remain the main driving requirements for established space hardware manufacturers. Most of the connected world infrastructure, as well as critical services in commercial and governmental domains are still highly dependent from space assets, and avionics-related failures may account for a large part of the system's downtime. In this context, the emergence of space systems based on only Commercial-Off-The-Shelf (COTS) (like Cubesats) is not necessarily helping, since in order to cut costs the rigorous test and quality assurance processes applied to bigger satellite are waived underestimating how unforgiving space environment can be for electronics.

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This paper presents an intended test setup and methodology for testing micro-controller SoCs against the effects of ionizing radiations. The method structure is based on a modular test sequence for test definition, coding, validation and setup. It will be illustrated by the relevant example of a microcontroller solution including lockstep options. Our methodology proposes using low-energy protons for irradiation, and this paper compares this approach with current techniques, showing how proton testing is becoming increasingly interesting, especially for ultra-deep submicron processes in proton dominated environments like low-shielded Low Earth Orbit missions or aircraft avionics. Beyond the convenience of a simplified test setup one of the main advantages of the proton irradiation approach is that it can be used for simultaneous Single Event Effects (SEE) and Total Ionizing Dose (TID) characterization, closer to the "test as you fly" approach.

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This paper discusses radiation tests on complex System-on-Chip (SoC) controllers using Low-Energy Protons (LEPs). The aim of this novel set of guidelines is to be also applicable to System In Package (SIP) or hybrid components that are now often used to overcome printed circuit board's real estate restrictions in Hi-Rel electronics.

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