1. Controller Area Network in NanoSatellites
Johan Carvajal Godinez,
Erik Orsel and Jian Guo
Space Engineering Department
Faculty of Aerospace Engineering
Delft University of Technology

2. Outline Motivation Bus communication requirements
Bus communication survey in nanosatellites
Why adopting CAN protocol?
How to influence CAN adoption on nanosats
Opportunities
Challenges
Conclusions
Questions
Name
Function

3. More sophisticated missions
Motivation for adopting a new communication protocol
From To
More sophisticated missions
(image credit: CalPoly)
(image credit: Planet Labs)
Centralized Bus
Architecture
Distributed Bus
Architecture

4. Bus communication requirements for nanosatellites
Constraints
Scalability
Flexibility
Standard interface support: mechanical and electrical
Fault, detection, isolation and recovery capabilities
Environmental resilience
Implementation support from component vendors
Implementation complexity  Development time
Reliability

5. Communication protocol Number of Times (total percentage)
Communication protocols in nanosatellite missions
Communication protocol
Number of Times (total percentage)
I2C 13
SPI 9
UART 8
CAN 3
Zigbee 2
USB
RS485 1
Time period:
Number of missions: 24
Minimum satellite mass: 0.8 kg
Maximum satellite mass: 15 kg

6. Main bus communication protocols for nanosatellites
Combination of different protocols within the same mission is implemented at least in the 50% of the cases
Master-Slave topology configuration
was predominant (SPI/I2C)

7. Why SPI/I2C is used in nanosatellites?
Pros
Cons
Easier to implement: from hardware and software perspective
Supported in most of microcontrollers families
Flown many times – High TRL
Lack of FDIR capabilities – reliability concerns
Data throughput is limited for most sophisticated payloads
Mission specific implementation. No sharing of lessons learnt.
Easier to implement, but they have reliability and performance concerns

8. Opportunities New payload integration: cameras, or imaging devices
Establishing a common implementation baseline within the CAN standard.
Exploring the use of open source community (i.e. GitHub project ) to establish and maintain a robust CAN library implementation.

9. Designed for distributed architectures
Why adopting CAN protocol in nanosatellites?
Pros
Cons
Support multiple masters within the bus  designed for redundancy
Higher throughput performance (up to 1 50 m)
Sophisticated error detection mechanism within the frame.
Modularity: layered implementation approach
Implementation complexity increase with respect to I2C/SPI
Time delays due to arbitration
Power budget
Designed for distributed architectures

10. Proposed approach for CAN assessment
Systems Eng. perspective
Implementation perspective
Use cases for specific DelFFi mission as reference.
Requirements and stakeholders analysis  trade-off criteria.
Design options using:
“Pure” CAN
CANopen
CAN Aerospace
CubeSat Space Protocol
Verification and validation activities
Documentation of computer activity flow ICD (Done)
Command database definition (in progress)
Simulation cases for 2 CAN implementations (comparison purposes)
Test cases on mission scenarios

11. Proposed telemetry packet structure
Source: DelFFi software Activity Flow ICD

12. DelFFi Sequence Diagrams
Source: DelFFi software Activity Flow ICD
Simplified configuration for simulation purposes

13. Challenges
Defining the best approach for determinism: event-triggered vs time-triggered
Enabling methods and tools for CAN ICD implementation, in order to create a proper message structure
Influencing the implementation of application programming interfaces (API) for increasing abstraction (See CubeSat Space Protocol Stack)

14. Conclusions, so far…
There is a need for a more reliable, and better performance bus communication protocol in nanosatellites missions.
CAN offer the required capabilities to achieve more complex missions with nanosatellites
Efforts shall be done to influence a faster development cycle by standardizing implementation (focus on higher layers)

15. References
[1] Selva, D., & Krejci, D. A survey and assessment of the capabilities of Cubesats for Earth observation. Acta Astronautica, vol 74, pp May 2015.
[2] Taylor, C; Furano, G; Valverde-Carretero, A; Marinis, K; Magistrati, G; Bolognino, L; Jansen KLR; CAN is space, status and future after ECSS-E-ST-50-15C Release on DASIA 2015 proceedings
[3] Khurram, M.; Zaidi, S.M.Y., CAN as a spacecraft communication bus in LEO satellite mission, Proceedings of 2nd International Conference on in Recent Advances in Space Technologies, RAST 2005., vol., no., pp , 9-11 June 2005.
[4] CubeSat Space Protocol (CSP) open source repository from GOMSPACE:

16. Questions?

17. Nanosatellite Mission Database
Source: eoportal

18. CubeSat Space Protocol Stack: CSP…
Source: J. D. C. Christiansen, “CubeSat Space Protocol (CSP) Network-Layer delivery protocol for CubeSats and embedded systems,” pp. 2–11, 2011.