Volume 10, Number 5 • September/October 2002 • Aerospace Technology Development

Virtual Propulsion System Meets Real-Time Diagnostic System

NASA researchers recently demonstrated successful real-time fault detection and isolation of a virtual main propulsion system. Using a detailed simulation of a vehicle propulsion system to produce synthesized sensor readings, the NASA team demonstrated that advanced diagnostic algorithms, running on actual flight-class computers, could successfully diagnose the presence and cause of faults in real time. This demonstration was conducted as part of the NASA Propulsion IVHM Technology Experiment (PITEX), an effort led by Glenn Research Center at Lewis Field in Cleveland, OH, with Ames Research Center at Moffett Field, CA and Kennedy Space Center in Florida as the other participating Centers. Ames Research Center manages the Integrated Vehicle Health Management (IVHM) project for NASA’s 2nd-Generation Reusable Launch Vehicle Program.

The goal of this research is to mature and demonstrate key Integrated Vehicle Health Management (IVHM) technologies—one of several technologies that are involved in NASA’s Space Launch Initiative (SLI), an Agency-wide effort to significantly increase crew safety while reducing payload launch costs. PITEX operates as a key element of a Risk-Reduction Task being performed for NASA by the Northrop Grumman Corporation in El Segundo, CA. “NASA is committed to changing the way we operate and maintain launch systems. Information technology can lead the way, and demonstrations like this are part of making sure we are on the right path,” said William Kahle, IVHM project manager at NASA Ames.

Glenn researchers developed a detailed simulation of a main propulsion feed system, which they ran under both nominal and fault conditions to generate time histories of propulsion system parameters. Noise was superimposed on the simulation output to provide realistic sensor signals. Typical propulsion system failures, such as valves sticking open or closed, regulator problems and sensor and microswitch failures, were injected at various points in a simulated mission.

The simulated data were fed, in real time, to IVHM software running on a computer, designed and assembled by Kennedy Space Center, that is a commercial-grade version of actual flight hardware. “In all cases, the PITEX diagnostic software detected and isolated the injected fault correctly,” said Claudia Meyer of GRC, PITEX team lead. In addition, resource utilization tests were
performed to measure the real-time performance of the diagnostic software on the flight-like hardware. Data revealed that resources were largely underutilized, indicating that the diagnostic system could be expanded to cover additional components.

The PITEX diagnostic solution features monitor software that processes the raw sensor data and Ames-developed model-based diagnostic software—Livingstone—that detects and isolates anomalies. Livingstone uses a qualitative model of the system to predict the expected state; system-level reasoning is performed to resolve differences between the observed and expected states.

In continuing work, the PITEX diagnostic solution is being migrated to Northrop Grumman’s IVHM Virtual Test Bed (IVTB). In the IVTB, a broad range of vehicle subsystem health managers, in addition to propulsion, will be considered, and the benefits of coordinating the subsystem health managers through area and system-level health managers will be demonstrated. “The PITEX team is really blazing a trail that IVTB, and eventually the whole SLI program, will follow to create and validate future health-management systems,” said Dr. Stephen Brown, Northrop Grumman Corporation chief scientist for the IVHM task. “Real-time health management, such as demonstrated by PITEX, will lead to revolutionary improvements in the safety and cost of future reusable launch vehicles.”

The Space Launch Initiative is NASA’s technology research and development program aimed at dramatically increasing safety and reliability, and reducing the cost of a 2nd-generation reusable launch vehicle. All NASA’s Field Centers and the Air Force Research Laboratory are actively participating in the Space Launch Initiative and are vital to its success. NASA’s Marshall Space Flight Center in Huntsville, AL leads the Space Launch Initiative for NASA’s Office of Aerospace Technology. Q

Further information on the Space Launch Initiative can be found at the following Web sites: http://www.slinews.com and http://www.spacetransportation.com

NASA Official: Jonathan Root • Web Design: Printing & Design Office, NASA Headquarters • Credits