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Virtual Environment Simulator to Test Dynamically Executing Flight Software
Point of Contact Ted Bennett
ted.bennett@triakis.com
Dates August 2004 - August 2005
Problem Sole reliance on static analysis of processes, specifications, models and software for IV&V activities neglects a substantial verification domain. V&V can hardly be considered complete until the behavior of the controlling software has been fully tested during dynamic execution in its target operational environment. Historically this domain has only been accessible to project development teams due to the high costs of acquiring and assembling a full hardware integration/test laboratory.

While the benefit of independent verification & validation is generally accepted, recent comments by IV&V customers have indicated that the value and credibility of IV&V would be greatly enhanced if the flight software itself were to be tested. Despite this assertion, project teams are unwilling to either provide IV&V teams with access to their system integration lab, or to pay for such a lab as would be required for independent software testing.

In this case study, we will simulate the STEREO spacecraft hardware and orbital environment with sufficient fidelity to run the unmodified executable flight software. Using this pure virtual environment we will develop a full suite of nominal and off-nominal tests to verify that the software has correctly implemented the system and software design requirements. Software path coverage will be monitored and all unexercised code will be documented. Further, we will "stress test" the system to evaluate its robustness by varying instruction execution speed, propagation delays, data skew and other parameters readily adjustable in a virtual environment.

We expect to reveal many software, and potentially system issues discoverable in neither the traditional developer hardware integration & test environment, nor the IV&V analysis domain. We will compare our software test results with the results of the NASA IV&V static analysis to determine the extent to which new system and software faults may be uncovered through dynamic test of the flight software, and consequently the extent to which the value of IV&V may be enhanced.
Objective We are proposing to create a high fidelity, pure virtual environment simulation (VES) of the STEREO spacecraft capable of running the unmodified flight software & RTOS object code in its virtual orbital environment. We will use the VES to test the flight software while conducting a case study aimed at discovering the following:
  • What will flight software testing in a VES reveal that IV&V static analysis missed?
  • What will flight software testing in a VES reveal that project testing missed?
  • Does testing in the VES help in the evaluation of off-nominal behavior?
  • What does it cost to create a VES that can be used to test flight software?
The GSFC STEREO spacecraft is an excellent project platform on which to conduct our study. Being well into the life cycle effort for this project, the IV&V team has developed a highly cooperative relationship with the spacecraft project team. Project documentation is readily accessible and all results of the IV&V analysis effort are available for comparative purposes.

Triakis? IcoSim application has a unique combination of capabilities ideally suited to creating a total spacecraft system environment simulation. IcoSim will be used to simulate all of the various sensors, propulsion & communication systems, and control computer with sufficient fidelity to run the unmodified flight software. The IcoSim parts library already contains many of the complex parts required for the STEREO VES including a PowerPC core, the heart of the R6000 CPU chip around which the two spacecraft control processors have been built. Availability of pre-developed complex parts substantially reduces the time it will take to develop and test the STEREO VES.
Results Facility Initiative Technical Presentation.ppt
Triakis SAS05-FI STEREO.ppt
Keywords software design, software requirements, mission critical software, software assurance, STEREO, simulation, virtual environment simulator
Categories Domain-Specific Analysis
Dynamic Analysis
Test Analysis


Curator: Josh Stonestreet
NASA Official: Lisa Montgomery
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