Microprocessing and Microprograrnming 37 (1993) 41-44 North-Holland 41

CDPU for SOHO-CEPAC collaboration

D. Meziatl, J. Sequeiros 2, J. Medina 2 y S. S,-Snchez 1

1 Departamento de Autom6tica. Universidad de Alcal6 de Henares (Madrid). Espaha

2 Departamento de Fisica. Universidad de Alcal6 de tlenares (Madrid). Espaha

Abstract

The object of this paper, is to summarizes the basics requirements and the design proposal for the Common Data Processing Unit (CDPU) of the CEPAC instrument of SOHO space-craft. The CDPU design needs to consider the special working conditions and the environment conditions. It has been selected the usc of the CMOS-SOS technology, the MAS281 as microprocessor and total cold redundancy as architecture.

Keywords

Data processing. Space technology. Solar Energetic Particles.

1. Introduction

The CEPAC (COSTEP 1-ERNE 2 Particle Analyzer Collaboration) experiment is a solar energetic particles detector system approved by the European Space Agency as a part of the SOHO 3 (Solar and Heliospherical Observatory) payload. The SOHO space-craft launching is foreseen for June 1995 and it will be located in a ring-shaped orbit around the Lagrange point L1, nearly to 1.5 millions km of the Earth to Sun-Earth line. The nominal live of the experiment should be at least 2 years with a possible extension up 4 year.

The CEPAC instrument block diagram is showed in the figure 1. The institutions involved in the development of the instrumentation arc, besides Alcahi University, Turku University (Finland), Kiel University (Germany), St. Patrick's College (Ireland) and the Technical Research Centre (VTT, Finland).

2. Requirements

The special working conditions of this kind of missions force to consider, besides the general aspects of system processing or system reliability requirements, another specific ones as:

• Restrictions which are imposed in the design characteristics: mass, volume and power consumption limitations; the need of resisting extreme vibration conditions; chemical and electromagnetic cleanness exigency; etc 4.

• Environment conditions which the system should be submitted, including atomic oxygen, several plasma ions types, special thermal environments and, basically, cosmic radiation.

• No-repairing working during the mission life.

The CDPU should be able to control the detectors working (ON/OFF, checking, state control, etc.) and it also should be able to act as

* This work is sponsored by the CICYT, Ref. ESP 88-0306-C02

42 D. Meziat et al.

a data acquisition system which collects scientific information as well as housekeeping information, performing the necessary treatment and preparation for the transmission to the

Earth. The communication with the earth station is performed using the space-craft OBDH (On Board Data Handling) subsystem, to which the CDPU should be connected.

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CEPAC (SOHO) Figure 1. Functional diagram for CEPAC.

3. Design It is mandatory to include methods of reliability improvement, that should combined fault prevention techniques (conservative design, components quality, special level of cleanness in the assembling room, use of analysis techniques and structural design for the software, etc.) with the fault tolerance techniques (redundancy at level of the treated information and the hardware and software used in the design). The fault prevention techniques

acquire great prominence for the indicated restrictions.

It is necessary the use of high reliability components, that complied the standard ESA/SCC-C in a general manner and the ESA/SCC-B for the components which are used in the interface module with the OBDH.

At the technology level it has been selected the use of the CMOS-SOS (Silicon on Sapphire). In this technology all the transistors are silicon isles over sapphire substrate insulator. The SOS process offers significant

CDPU for SOHO-CEPAC collaboration 43

advantages over others CMOS technologies. The absence of bulk silicon substrate reduce the parasitic capacitances, improving speed and reducing power consumption. The sapphire substrate is inherently radiation resistant, and hardens the device against transient and cosmic rays upsets, eliminating the whole risk of hard error or latch-up, that might cause serious disruption to systems.

It has been chosen the Marconi Electronics Devices (UK) MAS281 as microprocessor. This microprocessor, beside being the CMOS-SOS technology, comply the MIL-STD-1750A standard, which provides a good software development environment. From the point of view of the radiation resistance this microprocessor has the next performances.

• Single cvcn upset 2.10 -10 errors/bit day.

• Latch-up free.

• Total dose > 10 6 Krads.

For power consumption problems the stored program in ROM must be translate to RAM memory when the system is power up.

At the architecture level, it has been designed using total cold redundancy, with a redundant unit powered off, identical to the active unit (Figure 2). Both units (CDPU nominal and CDPU redundant) have its own OBDH interface circuits, to avoid a singular point of failure.

The CDPU is allocate inside a aluminium (AL2618A) box with a wall thickness of 0.8mm.

For the software implementation it has been used the ADA language, developing some critical time routines in assembly language. The compiler used (TLD cross compiler) provides valid code for the MIL-STD-1750A standard and it has the possibility of acting as the interface with the assembly language.

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Figure 2. Functional Architecture for C D P U .

44 D. Meziat et al.

4. Results

The CDPU engineering model (EM) has been manufactured (by Alcatel Espacio which is the contracted industry) and at the moment we are in the integration phase with this model.

Some physical dates for the EM are the following:

• Mass 2374 g.

• External dimensions.

- High: 88.15 mm.

- Large: 245.51mm.

- Wide: 204.17 mm.

The power consumption are show in the next table.

FUNCTIONAL PEAK POWER REMARKS MODES

POWER UP 2200 mW T < 3s

ERROR RECOVERY 2200 mW T < 3s

WATCH-DOG FAULT 2200 mW T < 3s

NORMAL MODE 1100 mW During mission

CDPU IDLE STATE 850 mW Memory not accessed

C D P U p o w e r c o n s u m p t i o n .

We have made the functional verification in the two first environments and are in progress the Thermal Vacuum Test.

References

1 Kunow, Horst et al. COSTEP Comprehensive SupraThermal and Energetic Particle Analyzer for SOHO. ESA SP-1104, February, 1989. 75-80.

2 Torsti, Jarmo et al. ERNE Energetic and Relativistic Nuclei and Electron Experiment. ESA SP-1104; February, 1989. 81-84.

3 Domingo, Vicente and Poland, A.I. SOHO an Observatory to Study the Solar Interior and the Solar Atmosphere. ESA SP-1104, February, 1989. 7-12.

SOHO Experiment Interface Document. Part A. PLP /410S/EID.

4

The integration with the other CEPAC instruments is being performed in the Espoo VTT Technical Research Centre of Finland. The validation test will allow to guarantee the required design conditions. The integration and verification is being done in three separate environments:

• Clean room.

• EMC test room.

• Thermal vacuum chamber.