ECSS-E-ST-50-15C
Adoption Notice
Maurizio Caramia
1
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The EXOMARS Mission
The ExoMars mission is split into two steps:
• The 2016 mission launched on 14th March 2016 consisting of a Trace Gas Orbiter (TGO) and an EDL
Demonstrator Module (EDM)
• The RSP mission (planned in 2020) consists of a Rover accommodated inside a Descent Module (DM)
carried to Mars by a Carrier Module (CM)
EXM 2016 Mission
2
EXM RSP Mission
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CAN + CANOPEN
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EXOMARS Physical Layer
The Selected physical layer is the RS485
(DS16F95 transceiver) with daisy chain
topology according one of the two options
proposed by the CAN ECSS
The fail safe network is implemented within
the master node
The daisy chain connection is realized at
harness connector level
3
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EXOMARS CAN Transfer Layer
• Taking into account that OBC SW cycle has a period of 100 ms during which TMs have to be
acquired/elaborated and CMDs have to be generated, TM/CMD exchange will be regulated
according to periodic timing windows delimited by two SYNC messages and divided into two phases:
one dedicated to TMs reception (70ms) and one dedicated to CMDs generation (30). The period of
each window will be 100 ms.
• After a node power-on, reset node, reset application or bus switch slaves nodes shall consider the first
SYNC message received after an NMT command “Go to OPERATIONAL” as the start of the first
TM/CMD window.
t
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TPDO TM k
TPDO TM 2
TPDO TM 1
SYNC
t=100ms
OBC SW cycle, i
4
CMD 2
CMD 1
TPDO TM m
t=30ms (TBC)
SDO
TM
TPDO TM n
TPDO TM 2
TPDO TM 1
NMT “Go to
Operational”
SYNC
TM sub-window
CMD sub-window
t=70ms (TBC)
CMD n
TM sub-window
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OBC SW cycle, i+1
CABCOM From Scientific to Telecom applications
Starting from the EXOMARS experience, TAS executed the ESA CABCOM study with the following main
goals:
To implement a fully ECSS-E-ST-50-15C compliant CAN bus solution for SATCOM
To validate the implemented CAN solution in a dedicated test bench with HW in the loop
To upgrade the CCIPC to include:
A-cyclic Synchronous PDO capability
Reception of Broadcast PDO for time distribution
Upgrade the CCIPC reconfiguration algorithm to support the infinite bus toggling.
5
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CABCOM Physical Layer
Four subnetworks composed of 31 node
each operated in time multiplexing by a
single master
Subnetwork 4
M
Node 92
Master Node
Two different physical layers have been
considered according the CABCOM study
requirements:
RS-485 network
Node 96
Node n
Node 121
R
Subnetwork 3
M
Node 62
Node 65
Node n
Node 91
R
Subnetwork 2
M
Node 32
Node 34
Node n
Node 61
R
M
Subnetwork 1
Node 2
Node 3
Node n
Node 31
ISO-11898 network
A single network with 120 nodes operated
in time multiplexing by a single master
6
Master Node
R
M
Node 2
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Node 3
Node n
Node 121
R
CABCOM CAN Transfer Layer
Each TS is organized in different windows in which different message transaction will be applied:
Synchronous Window (SW):
in this window only Synchronous PDO transactions are allowed
The window starts with the SYNC message generated by the Master and last 1 second
After the SYNC message, all the S-TPDO generated by the NODEs belonging to the specific TS
will be received by the Master
The synchronous windows Length parameter of each Slave node will be set to avoid S-TPO
transmission outside the SW
Asynchronous Window (AW):
In this window only the Asynchronous On-request transactions are allowed.
The Master will send the TM_RQST command to all slaves belonging to this window
The Slave will reply with the requested parameter
A complete transaction (Master Request and Slave Reply) will be completed before the start
of a new transaction.
Only requests to the nodes belonging to the specific TS will issued by the Master
The AW will last 6 seconds
Configuration Window (AW):
In this window only the Configuration (non-acknowledged) commands will be issued by the
Master
After the Configuration Commands the Master Shall issue its HearthBeat Message
The AW will last 1 seconds
7
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ECSS-E-ST-50-15C requirement analysis
226 requirements
8
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ECSS-E-ST-50-15C requirement analysis
21 deleted
226 requirements
12 modified
19 to be tailored
173 accepted
1 new
9
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ECSS-E-ST-50-15C requirement analysis
21 deleted
226 requirements
12 modified
19 to be tailored
173 accepted
1 new
Deleted requirements are all related to the RS485 physical layer
Modified requirements: typo corrected, all references to RS485 have been removed, references to
external standards have been removed as much as possible
To be tailored are mission dependent: need for isolated transceiver; bus topology requirements;
need for SDO service; need for SCET; bus redundancy architecture
New: one requirement dedicated to the Sampling point settings have been added
10
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ECSS-E-ST-50-15C requirement analysis
21 deleted
226 requirements
12 modified
19 to be tailored
173 accepted
51 SS and EQT
205 requirements
44 SS
110 EQT
1 new
Deleted requirements are all related to the RS485 physical layer
Modified requirements: typo corrected, all references to RS485 have been removed, references to
external standards have been removed as much as possible
To be tailored are mission dependent: need for isolated transceiver; bus topology requirements;
need for SDO service; need for SCET; bus redundancy architecture
New: one requirement dedicated to the Sampling point settings have been added
11
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ECSS-E-ST-50-15C requirement analysis
21 deleted
226 requirements
12 modified
19 to be tailored
173 accepted
51 SS and EQT
205 requirements
44 SS
110 EQT
1 new
Mandatory: Requirements applicable to both Full and Minimal
Protocol implementation covering:
49 Full Protocol
205 requirements
112 Mandatory
34 Minimal Protocol
• Physical layer requirements
• CAN data link layer requirements
• CANOpen mandatory services (OD, NMT, PDO)
Full Protocol: contain the full set of CANOpen services (EXOMARS
heritage)
Minimal Protocol: contains a subset of CANOpen services (no
SDO) to support SATCOM payload busses (NEOSAT heritage)
12
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ECSS-E-ST-50-15C requirement analysis
21 deleted
226 requirements
12 modified
19 to be tailored
173 accepted
51 SS and EQT
205 requirements
44 SS
110 EQT
1 new
44 SS only
171 Full Protocol
49 Full Protocol
205 requirements
78 Mandatory
15 Master
34 Slave
112 Mandatory
34 Minimal
41 SS only
156 Minimal
13
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66 Mandatory
11 Master
38 Slave
Conclusions
RS485 physical layer has several drawbacks:
•
Limited number of nodes
•
It requires a failsafe network
•
•
The fail safe network is usually implemented within the On-Board computer electronics :
•
It shall be powered in hot redundancy
•
Special care shall be taken to its distribution to main and redundant OBC boards. Usually the main board accommodate only the main CAN bus fail safe network while the
redundant board accommodate the redundant one.
Only 5volts transceiver are available
Sampling point configuration shall be reprogrammable
•
The sampling point is function of the bus length. The worst case bus length could be reached during the On-ground testing
activities if a bus repeater is not introduced between the test equipment and the Spacecraft.
Special care shall be taken to the Endianness management.
•
Dedicated guidelines should be added in the ECSS
As matter of fact, the protocol above the CANOpen layer is mission dependent. It shall be covered by a dedicated specification
explaining how the CANOpen services are used (NOTE: the ECSS only specified which CANOpen services can be used and How they shall
be implemented)
14
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Thank you!
Questions
15
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