Vehicle-scale integration and test requires closed-loop simulation using full-scale avionics systems or even entire vehicles. Incorporation of simulation data into real systems is problematic because real system sensors report the real laboratory environment, not the simulation environment. Past methods have attempted to simulate the physical sensors, or have added simulation interfaces to the flight sensor electronics. Both approaches are intrusive and costly to incorporate in an actual flight system design. The first approach requires dozens to hundreds of contact points between the vehicle and the simulation hardware. The second approach adds complexity, cost, and failure modes to the flight system hardware and firmware.

Time Triggered Ethernet (TTE) is a deterministic extension of Ethernet that precisely times the transmission of each message per a pre-calculated schedule to guarantee media access for critical messages, e.g. flight control. The remainder of the network bandwidth is available for conventional use, with strict guarantees that critical messages will not suffer interference from other traffic. For guaranteed message delivery, TTE messaging is supported via a parallel redundant network infrastructure, where each network node has multiple (typically two) network ports. All node ports #1 are interconnected by a unique network. All nodes ports #2 are interconnected by another unique network. Redundant messages are transmitted and received in parallel on as many networks as are implemented. The first valid instance of each message that arrives at a receiving node is used by the system. The other redundant instances of each message that arrive at a node are discarded.

The invention uses this first-arrival principle to force the system to use simulation sensor data preferentially over flight system sensor data. On the real system, each node has more ports (3) than the number of redundant networks implemented (2). The unused third ports on each node are available for injection of simulation data. For each flight system message that needs to be replaced by a simulation message, the simulation system will send said message at a pre-determined time — a few microseconds earlier than the corresponding flight system message — to ensure that the simulation data is received first and used by the system, and that the corresponding flight system data are discarded.

This invention is unique and novel because it leverages the characteristics of a time-deterministic redundant network to integrate simulation data into the closed-loop test environment on a per-message basis, with no changes to the flight system hardware, firmware, or software. The flight system data continues to flow across the flight networks, and is available for recording and analysis, but is ignored by the flight system software, having been replaced by simulation data. The only flight system impact is the wiring necessary to connect the simulation system to the unused network node ports on the flight nodes that receive simulation data.

To make and use this invention, the simulation system is connected to the flight system under test via unused redundant network ports on each flight system node that needs to receive simulation data. The simulation system is implemented such that its TTE network topology mirrors the flight system topology to facilitate reuse of flight system configuration products. The simulation system network is configured with a version of the flight system configuration products (scheduling and routing tables), where the timing of simulation system message transmissions has been accelerated to ensure first arrival of the simulation system messages versus the flight system messages. (Simulation message acceleration of 20 microseconds seems adequate to ensure correct operation.)

Alternative realizations of this invention could use unique Port ID, unique Message ID, or unique Source Address to preferentially select simulation data over flight system data, independent of message arrival time. These alternate approaches could serve to enable incorporation of simulation data into systems that lack spare ports for the direct insertion of simulation data.

This work was done by William Smithgall, Brendan Hall, and Srivatsan Varadarajan of Honeywell for Johnson Space Center. MSC-25172-1

NASA Tech Briefs Magazine

This article first appeared in the January, 2016 issue of NASA Tech Briefs Magazine.

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