Giovanni Giusi

Preliminary study of the EChO data sampling and processing

The EChO Payload is an integrated spectrometer with six different channels covering the spectral range from the visible up to the thermal infrared. A common Instrument Control Unit (ICU) implements all the instrument control and health monitoring functionalities as well as all the onboard science data processing. To implement an efficient design of the ICU on board software, separate analysis of the unit requirements are needed for the commanding and housekeeping collection as well as for the data acquisition, sampling and compression. In this work we present the results of the analysis carried out to optimize the EChO data acquisition and processing chain. The HgCdTe detectors used for EChO mission allow for non-destructive readout modes, such that the charge may be read without removing it after reading out. These modes can reduce the equivalent readout noise and the gain in signal to noise ratio can be computed using well known relations based on fundamental principles. In particular, we considered a multiaccumulation approach based on non-destructive reading of detector samples taken at equal time intervals. All detectors are periodically reset after a certain number of samples have been acquired and the length of the reset interval, as well as the number of samples and the sampling rate can be adapted to the brightness of the considered source. The estimation of the best set of parameters for the signal to noise ratio optimization and of the best sampling technique has been done by taking into account also the needs of mitigating the expected radiation effects on the acquired data. Cosmic rays can indeed be one of the major sources of data loss for a space observatory, and the studies made for the JWST mission allowed us to evaluate the actual need of the implementation of a dedicated deglitching procedure on board EChO.

The Command and Data processing Unit of the Euclid Visible Imager: impact of the data compression needs on the unit design

The Command and Data Processing Unit (CDPU) of the Euclid Visible Imager is one of the two warm electronics units of the instrument. It implements on one side the digital interface to the satellite, for telecommands acquisition and telemetry downloading, and on the other side the interface to the focal plane CCDs readout electronics, for science data acquisition and compression. The CDPU main functionalities include the instrument commanding, control and health monitoring. The baseline unit architecture is presented, reporting the results of the phase B1 study and of the trade-off activity carried out to check the performances of the SW implementation of two different lossless compression algorithms on the baseline target processor (LEON3-FT) and on a HW compressor.

The design of the instrument control unit and its role within the data processing system of the ESA PLATO Mission

PLATO1 is an M-class mission of the European Space Agency’s Cosmic Vision program, whose launch is foreseen by 2026. PLAnetary Transits and Oscillations of stars aims to characterize exoplanets and exoplanetary systems by detecting planetary transits and conducting asteroseismology of their parent stars. PLATO is the next generation planetary transit space experiment, as it will fly after CoRoT, Kepler, TESS and CHEOPS; its objective is to characterize exoplanets and their host stars in the solar neighbors. While it is built on the heritage from previous missions, the major breakthrough to be achieved by PLATO will come from its strong focus on bright targets, typically with mv≤11. The PLATO targets will also include a large number of very bright and nearby stars, with mv≤8. The prime science goals characterizing and distinguishing PLATO from the previous missions are: the detection and characterization of exoplanetary systems of all kinds, including both the planets and their host stars, reaching down to small, terrestrial planets in the habitable zone; the identification of suitable targets for future, more detailed characterization, including a spectroscopic search for biomarkers in nearby habitable exoplanets (e.g. ARIEL Mission scientific case, E-ELT observations from Ground); a full characterization of the planet host stars, via asteroseismic analysis: this will provide the Community with the masses, radii and ages of the host stars, from which masses, radii and ages of the detected planets will be determined.

The instrument control unit of the ESA-PLATO 2.0 mission

PLATO 2.0 has been selected by ESA as the third medium-class Mission (M3) of the Cosmic Vision Program. Its Payload is conceived for the discovery of new transiting exoplanets on the disk of their parent stars and for the study of planetary system formation and evolution as well as to answer fundamental questions concerning the existence of other planetary systems like our own, including the presence of potentially habitable new worlds. The PLATO Payload design is based on the adoption of four sets of short focal length telescopes having a large field of view in order to exploit a large sky coverage and to reach, at the same time, the needed photometry accuracy and signalto- noise ratio (S/N) within a few tens of seconds of exposure time. The large amount of data produced by the telescope is collected and processed by means of the Payload’s Data Processing System (DPS) composed by many processing electronics units. This paper gives an overview of the PLATO 2.0 DPS, mainly focusing on the architecture and processing capabilities of its Instrument Control Unit (ICU), the electronic subsystem acting as the main interface between the Payload (P/L) and the Spacecraft (S/C).

Performance analysis of the GR712RC dual-core LEON3FT SPARC V8 processor in an asymmetric multi-processing environment

In this paper we present the results of a series of performance tests carried out on a prototype board mounting the Cobham Gaisler GR712RC Dual Core LEON3FT processor. The aim was the characterization of the performances of the dual core processor when used for executing a highly demanding lossless compression task, acting on data segments continuously copied from the static memory to the processor RAM. The selection of the compression activity to evaluate the performances was driven by the possibility of a comparison with previously executed tests on the Cobham/Aeroflex Gaisler UT699 LEON3FT SPARC™ V8. The results of the test activity have shown a factor 1.6 of improvement with respect to the previous tests, which can easily be improved by adopting a faster onboard board clock, and provided indications on the best size of the data chunks to be used in the compression activity.

Software design for the VIS instrument onboard the Euclid mission: a multilayer approach

The Euclid mission scientific payload is composed of two instruments: a VISible Imaging Instrument (VIS) and a Near Infrared Spectrometer and Photometer instrument (NISP). Each instrument has its own control unit. The Instrument Command and Data Processing Unit (VI-CDPU) is the control unit of the VIS instrument. The VI-CDPU is connected directly to the spacecraft by means of a MIL-STD-1553B bus and to the satellite Mass Memory Unit via a SpaceWire link. All the internal interfaces are implemented via SpaceWire links and include 12 high speed lines for the data provided by the 36 focal plane CCDs readout electronics (ROEs) and one link to the Power and Mechanisms Control Unit (VI-PMCU). VI-CDPU is in charge of distributing commands to the instrument sub-systems, collecting their housekeeping parameters and monitoring their health status. Moreover, the unit has the task of acquiring, reordering, compressing and transferring the science data to the satellite Mass Memory. This last feature is probably the most challenging one for the VI-CDPU, since stringent constraints about the minimum lossless compression ratio, the maximum time for the compression execution and the maximum power consumption have to be satisfied. Therefore, an accurate performance analysis at hardware layer is necessary, which could delay too much the design and development of software. In order to mitigate this risk, in the multilayered design of software we decided to design a middleware layer that provides a set of APIs with the aim of hiding the implementation of the HW connected layer to the application one. The middleware is built on top of the Operating System layer (which includes the Real-Time OS that will be adopted) and the onboard Computer Hardware. The middleware itself has a multi-layer architecture composed of 4 layers: the Abstract RTOS Adapter Layer (AOSAL), the Speci_c RTOS Adapter Layer (SOSAL), the Common Patterns Layer (CPL), the Service Layer composed of two subgroups which are the Common Service (CSL) and the Specific Service layer (SSL). The middleware design is made using the UML 2.0 standard. The AOSAL includes the abstraction of services provided by a generic RTOS (e.g Thread/Task, Time Management, Mutex and Semaphores) as well as an abstraction of SpaceWire and 1553-B bus Interface. The SOSAL is the implementation of AOSAL for the adopted RTOS. The CPL provides a set of patterns that are a general solution for common problems related to embedded hard Real Time systems. This set includes patterns for memory management, homogenous redundancy channels, pipes and filters for data exchange, proxies for slow memories, watchdog and reactive objects. The CPL is designed using a soft-metamodeling approach, so as to be as general as possible. Finally, the SL provides a set of services that are common to space applications. The testing of this middleware can be done both during the design using appropriate tools of analysis and in the implementation phase by means of unit testing tools.

A traffic analyzer for multiple SpaceWire links

Modern space missions are becoming increasingly complex: the interconnection of the units in a satellite is now a network of terminals linked together through routers, where devices with different level of automation and intelligence share the same data-network. The traceability of the network transactions is performed mostly at terminal level through log analysis and hence it is difficult to verify in real time the reliability of the interconnections and the interchange protocols. To improve and ease the traffic analysis in a SpaceWire network we implemented a low-level link analyzer, with the specific goal to simplify the integration and test phases in the development of space instrumentation. The traffic analyzer collects signals coming from pod probes connected in-series on the interested links between two SpaceWire terminals. With respect to the standard traffic analyzers, the design of this new tool includes the possibility to internally reshape the LVDS signal. This improvement increases the robustness of the analyzer towards environmental noise effects and guarantees a deterministic delay on all analyzed signals. The analyzer core is implemented on a Xilinx FPGA, programmed to decode the bidirectional LVDS signals at Link and Network level. Successively, the core packetizes protocol characters in homogeneous sets of time ordered events. The analyzer provides time-tagging functionality for each characters set, with a precision down to the FPGA Clock, i.e. about 20nsec in the adopted HW environment. The use of a common time reference for each character stream allows synchronous performance measurements. The collected information is then routed to an external computer for quick analysis: this is done via high-speed USB2 connection. With this analyzer it is possible to verify the link performances in terms of induced delays in the transmitted signals. A case study focused on the analysis of the Time-Code synchronization in presence of a SpaceWire Router is shown in this paper as well.

Euclid: image compression activities for the VIS instrument

Euclid is a space mission dedicated to the high-precision study of dark energy and dark matter. Its visible instrument (VIS) will acquire wide field images by means of an array of 36 CCD focal plane detectors. Considering that each acquired full frame produces a huge amount of data (~1.2GByte), an overall daily production of ~120 GByte is expected, which must be compressed to fit the 520 Gbit VIS daily telemetry. Due to the highly demanding science requirements such compression must be rigorously lossless. This software requirement is very hard to meet because of the following constraints: i) the average Compression Ratio (CR) must be greater than 2.8; ii) the activities of data compression inside the Control Data Processing Unit and transmission towards the satellite shall complete in less than 369s, that fits to the acquisition time of the near-infrared instrument; and iii) the compressors parameters as well as the transmission packet size must be tuned to ensure minimal data loss in case of transmission errors. The results obtained with 1D and 2D compression algorithms based on the CCSDS 121 and CCSDS 122 recommended standards, fed with improved focal plane simulations, have been compared to each other. Moreover, a set of various reordering and pre-processing procedures has been applied to the read-out data stream, considering different sizes of the input data segments. The overall scope of these comparative works has been not only to maximize the compression ratio and to minimize the compression time, but also to provide a trade-off between the input data size and the minimum output compressed data segment in order to minimize the data loss due to transmission errors propagation. From our test we found that performing a full (at CCD level) reordering of the read-out data-stream leads to a better compression ratio with both algorithms. The CCSDS 121, however, gives the best results in terms of CR. Finally we found that, for the considered simulated images, the standard pre-processing activities like bias subtraction, bitshift and windowing do not affect the CR significantly. Analogously an additional analysis of the effect of the expected source crowding showed that it is also not important.

The instrument control unit of SPICA SAFARI: a macro-unit to host all the digital control functionalities of the spectrometer

We present the preliminary design of the Instrument Control Unit (ICU) of the SpicA FAR infrared Instrument (SAFARI), an imaging Fourier Transform Spectrometer (FTS) designed to give continuous wavelength coverage in both photometric and spectroscopic modes from around 34 to 210 µm. Due to the stringent requirements in terms of mass and volume, the overall SAFARI warm electronics will be composed by only two main units: Detector Control Unit and ICU. ICU is therefore a macro-unit incorporating the four digital sub-units dedicated to the control of the overall instrument functionalities: the Cooler Control Unit, the Mechanism Control Unit, the Digital processing Unit and the Power Supply Unit. Both the mechanical solution adopted to host the four sub-units and the internal electrical architecture are presented as well as the adopted redundancy approach.