1. ECSS-E-ST-50-15C Adoption Notice
Maurizio Caramia
ESA CAN WorkSohp 2017

2. CAN + CANOPEN The EXOMARS Mission EXM 2016 Mission EXM RSP 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
EXM RSP Mission
CAN + CANOPEN
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3. 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
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4. 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.
SYNC
t=100ms
TPDO TM 1
TPDO TM 2
TPDO TM n
TPDO TM k
CMD 1
CMD 2
CMD n
OBC SW cycle, i
CMD sub-window
TM sub-window
NMT “Go to Operational” TM
SDO
t=70ms (TBC)
t=30ms (TBC)
TPDO TM m
OBC SW cycle, i+1 t
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5. 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.
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6. CABCOM Physical Layer Master Node
Subnetwork 1 M R
Node 3
Node n
Node 32
Subnetwork 2
Node 34
Node 61
Node 62
Subnetwork 3
Node 65
Node 91
Node 92
Subnetwork 4
Node 96
Node 121
Node 31
Two different physical layers have been considered according the CABCOM study requirements:
RS-485 network
Four subnetworks composed of 31 node each operated in time multiplexing by a single master
ISO network
A single network with 120 nodes operated in time multiplexing by a single master
Master Node M
Node 2
Node 3
Node n
Node 121 R
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7. 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
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8. ECSS-E-ST-50-15C requirement analysis
226 requirements
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9. ECSS-E-ST-50-15C requirement analysis
21 deleted
12 modified
19 to be tailored
173 accepted
1 new
226 requirements
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10. ECSS-E-ST-50-15C requirement analysis
21 deleted
12 modified
19 to be tailored
173 accepted
1 new
226 requirements
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
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11. ECSS-E-ST-50-15C requirement analysis
21 deleted
12 modified
19 to be tailored
173 accepted
1 new
226 requirements
51 SS and EQT
44 SS
110 EQT
205 requirements
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
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12. ECSS-E-ST-50-15C requirement analysis
21 deleted
12 modified
19 to be tailored
173 accepted
1 new
226 requirements
51 SS and EQT
44 SS
110 EQT
205 requirements
Mandatory: Requirements applicable to both Full and Minimal Protocol implementation covering:
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)
49 Full Protocol
112 Mandatory
34 Minimal Protocol
205 requirements
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13. ECSS-E-ST-50-15C requirement analysis
21 deleted
12 modified
19 to be tailored
173 accepted
1 new
226 requirements
51 SS and EQT
44 SS
110 EQT
205 requirements
44 SS only
78 Mandatory
15 Master
34 Slave
171 Full Protocol
49 Full Protocol
112 Mandatory
34 Minimal
205 requirements
41 SS only
66 Mandatory
11 Master
38 Slave
156 Minimal
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14. Conclusions Only 5volts transceiver are available
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)
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15. Thank you!
Questions
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