Performance Characterization of Space A Plug-and-Play Avionics Applique Sensor Interface Module

The Air Force Research Laboratory (AFRL) Space Vehicles Directorate is currently developing Space Plug-and-Play Avionics (SPA) as a means of enabling rapid assembly, integration and test (AI&T) of spacecraft in support of Operationally Responsive Space missions. The SPA architecture is based on prefabricated panels and an embedded SpaceWire network. The networked panels are assembled into a box like structure to form the spacecraft’s bus. Spacecraft components are then added to the panels and network to form a functioning spacecraft. Since most legacy spacecraft components inherently do not have a SpaceWire network interface, an Applique Sensor Interface Module (ASIM) is used to integrate a legacy component into the network. The ASIMs manage all network traffic between legacy components and the rest of the spacecraft, and as a result, introduce propagation delays that can negatively impact time critical processes such as spacecraft attitude determination and control. This paper documents testing performed on ASIMs in order to measure and characterize the ASIM propagation latency. Tests were performed on a PNP Innovations Generation 2 ASIM using current (as of January 2011) firmware and core software. The test harness used was a Field Programmable Gate Array (FPGA) based logic analyzer developed by AFRL, housed in the responsive space test-bed (RST) in Albuquerque, NM. Testing consisted of measuring the propagation delay of individual ASIMs during data transmission and command receive functions as well as measuring propagation delay due to data interface functions that are specific to the spacecraft components connected to the ASIM under test. Results are used to develop and populate analytical models for the propagation delay for individual ASIMs. These models can be used by SPA-based spacecraft developers to understand how ASIM propagation delay will impact overall system performance. Additionally, the results of this research will demonstrate the feasibility of SPA as a data bus standard alternative to more traditional data bus standards such as MIL-STD-1553.