Payload Integrated with the Avionics Subsystem
In this third case, a fully integrated system is analyzed as shown in Figure 9 and Figure 10 (default Control Plane connections are not shown for simplicity).
In most not-so-small satellites, ADCS and C&DH subsystems are implemented as two different systems, enabling development teams to work independently and integrate the system in a later stage. This level of modularity is also beneficial in reusing modules in multiple missions.
When splitting the functionality in multiple modules, the two Data Planes FPs (8 lanes) per module defined in the standard are insufficient to connect all the electronic boards in a mesh. In this case, a star topology network can be used to increase the bandwidth between the modules with high throughput needs.
A star topology connects Payloads through a centralized Switch. In a dual star configuration, a second Switch is added to the system to increase the overall fault tolerance. Every Payload slot in the system is connected to both Switches. There is cross-strapping between the primary and redundant modules so that any one module can fail, and the remaining modules can operate with any of the primary or redundant modules.
In most not-so-small satellites, ADCS and C&DH subsystems are implemented as two different systems, enabling development teams to work independently and integrate the system in a later stage. This level of modularity is also beneficial in reusing modules in multiple missions.
When splitting the functionality in multiple modules, the two Data Planes FPs (8 lanes) per module defined in the standard are insufficient to connect all the electronic boards in a mesh. In this case, a star topology network can be used to increase the bandwidth between the modules with high throughput needs.
A star topology connects Payloads through a centralized Switch. In a dual star configuration, a second Switch is added to the system to increase the overall fault tolerance. Every Payload slot in the system is connected to both Switches. There is cross-strapping between the primary and redundant modules so that any one module can fail, and the remaining modules can operate with any of the primary or redundant modules.
Figure 1: Fully Redundant Avionics Subsystem and Payload with Dual Star Topology Backplane
The two main disadvantages of the dual-star system are SWaP and cost. As described above, the SpaceVPX standard groups the 8 data lanes in the Data Plane into two FP, reducing the flexibility of the modules. A non-standard use of the serial data lanes gives the system a higher level of reliability in exchange for bandwidth. For example, a fully functional mesh can be implemented using the 8 serial data lanes in groups of 2 lanes as depicted in Figure 10.
Figure 2: Fully Redundant Avionics Subsystem and Payload with Mesh Topology Backplane.
The bold red line between C&DH and the Modulator represents two serial data lanes used to download high volumes of data stored in the MM during periods of no visibility of the ground station.