ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 199 of 422
failures of the on-board electronics has been reduced as a consequence mainly of the two shuttle
accidents (even if they were not caused by the DHS).
Currently, it is impossible to design a truly 99.999 % reliable on-board data handling system.
The biggest issue is the high degrees of customization present in any space electronics.
Commercial electronic manufacturers have succeeded in having yields of some hundred of
defective parts over millions about deeply embedding standardization in any electronic product.
3.3.6.1.4 Standardization in avionics
Standardization in commercial electronics started from leader computer manufacturers mainly
for peripheral interconnect. Now standardization, through ISO and IEEE is involving practically
any part of the design and commercial life of electronic and software products. The most recent
successes in standardization were USB, that in its latest version is becoming the de-facto
standard for external peripheral interconnection, POSIX, that as software standard allows the
concurrent development of LINUX kernel by thousands of sparse users, IEEE 1451 standards
family, including multidrop transducer bus, mixed mode transducer and wireless transducer
network now used even in newest commercial airliners. The unrivalled father is the TCP/IP, so
well known as the ‘standard among the standards’ taken as model for future standards
development.
The current avionics are based on well-established standards as regarding ground-spacecraft
communication (CCSDS, ESA PSS) and hardware level discrete interfaces (ESA TTC-01B). The
future standards that will cover all the interfaces and protocols layers required to ensure the
independence between the hardware level and the applications are still in development.
In the framework of the CCSDS organisation, several SOIS workgroups and “BoFs” (Bird-of-a-
Feather”) are currently active:
The on-board bus and LAN workgroup defines services for the transfer of data over on-board
buses and individual on-board LANs (local area networks) that constitute a single subnetwork.
The avionics architecture shall be an open architecture based on well known industrial standard.
It will act at all layers, from hardware to embedded software to human interfaces, especially
regarding the internal communications and interconnections for the different level of the design
to facilitate the subcontracting of avionics subelements in accordance with any geographical
return or other political constraint whilst minimising the risks at integration level.
Among other standardization efforts, the CCSDS 'SOIF' [RD31] providing isolation between the
software applications and the communication’s logical and physical layers can be seen as the
base common language towards a distributed intelligence spacecraft, capable of having
functional redundancies to increase the system reliability.
3.3.6.1.5 Distributed control
From the Mars Sample Return mission on, in the framework of the Aurora project, the
application of the newest standards is mandatory.
Nevertheless, the current avionics architecture and the ones foreseen for the ExoMars and Mars
Sample Return missions are rather centralized (like the current HICDS demonstrator
architecture). The standards required to implement centralized architecture are the ones that will
be available at first. The subsequent missions (like the Human spacecrafts) will require more