Performance evaluation of TTEthernet-based architectures for the VEGA launcher

The objective of the paper is to propose and evaluate the performance of a TTEthernet network architecture applied in small launchers in order to interconnect the terminals (on-board computer, telemetry apparatus, Inertial Reference System, ...) performing the Guide, Navigation and Control (GNC) operations and producing/receiving telemetry traffic. The work described in the paper was been funded by Italian Space Agency (ASI) within the research agreement titled “Advanced Avionic Architecture (AAA)”. Time-Triggered Ethernet (TTEthernet) improved the performance of Avionic Full Duplex Ethernet in terms of delay determinism by introducing time-triggered mechanism and by introducing a static allocation of the network capacity for the messages needing hard delay constraints. The strongest points of the TTEthernet solution applied to small launcher with respect to the classical one based on 1553B technology can be summarized as follows: i) the connections between flight stages can be limited to switch to switch connections and this reduces greatly the connectors and harness in the launcher with the consequence to reduce single points of failure, weight and complexity of assembly and integration activities during production; ii) the compatibility with Ethernet technology allows for the use of standard mass devices (PC) to perform checks and tests in standard ground operations during launch campaign; iii) the possibility to interconnect critical and non-critical equipment on the same network without the need for a physical segregation allows for cost reduction; iv) the increase in available bandwidth allows for the support of additional functional and telemetry data We propose a TTEthernet-based architecture ad hoc for small launchers and compare it to a benchmark TTEthernet architecture in which all of the traffic (GNC and telemetry) is classified as Time-Triggered. Conversely the proposed architecture operates a traffic classification in which only GNC messages with hard delay requirements are classified as Time Triggered. The remaining telemetry messages are classified as rate constrained so as to guarantee a maximum delay only. We show how the proposed traffic classification allows for advantages in terms of bandwidth efficiency and routing computational complexity. The comparison is performed when the compared communication networks handle messages extrapolated by the message set of VEGA, a small launcher jointly designed by Italian Space Agency and European Space Agency. The type and characteristic of the messages considered allows for achieving realistic results and for evaluating the effectiveness of the TTEthernet solution applied to small launchers. The results are provided in the case of star network topology with two redundant channels. We show how the adoption of a TTEthernet as launcher network allows to satisfy all of the delay requirements of GNC messages. The achieved results show how the proposed architecture allows for a 75% bandwidth saving in the most critical network link and a 50% routing table complexity reduction with respect to the benchmark architecture.