As a Prime Contractor for NASA/MSFC, Optical Sciences Corporation (OSC) personnel have accumulated over 60 years experience in support of MSFC's Structures and Dynamics Laboratory, providing key support in the area of propulsion testing. OSC has provided key test support for the following propulsion programs: Space Shuttle Main Engine (SSME), Linear Aerospike Engine, FASTRAC Engine, Integrated Powerhead Demonstrator, as well as several component level tests.

Among the propulsion systems mentioned, the most complex and highest power-density propulsion systems are the engines of the Space Shuttle. NASA's primary Space Shuttle Main Engine (SSME) engineering group is located at Marshall Space Flight Center (MSFC), the Center of Excellence for propulsion technologies. SSME static acceptance tests and component life-cycle tests are conducted at Stennis Space Center . Each SSME is equipped with four powerful turbopumps that deliver approximately 930 pounds of liquid oxygen and up to 150 pounds of liquid hydrogen per second into the main combustion chamber. The high-pressure liquid oxygen pump turn at speeds up to 30,000 rpm, while the high-pressure liquid hydrogen pump rotate at up to 36,000 rpm. The pumps are turbine shaft driven by hot, expanding gases produced by burning a mixture of hydrogen and oxygen in a pre-burner, a separate small combustion chamber above each pump. The turbine and rotor of the pumps are directly coupled, and the bearings are lubricated and cooled by the cryogenic fluids pumped through them.

Data Collection and Analysis

The collection and analysis of data play a key role in propulsion testing. In development and acceptance tests, the engines must be measured for certain sensitivities in each mode of engine operation: start-up, main stage and shutdown. For example, there are known critical speeds at which harmonic vibrations are most severe for particular components, and there are critical dynamic pressures in the pump systems at start-up and shutdown. Identifying low-energy, high frequency signals amid an intense background of combustion chamber acoustics, fluid-flow oscillations and test-stand structural responses is critical. At high rotational turbopump shaft speeds, very slight rotor or turbine imbalances can cause high-frequency synchronous vibrations. OSC personnel are experienced in the complete range of propulsion testing from the sensor, through the data acquisition process, to the analysis of the high frequency data.

Real-time Data Acquisition

OSC developed and integrated a Multi-channel Integrated High-Speed Dynamic Data Acquisition System (MIDDAS) that is now in place at Stennis Space Center for the real-time collection of high frequency data during SSME static test firings. MIDDAS is a VXI Technologies™ based data acquisition front-end controlled via a personal computer with custom software. The software developed by OSC not only allows for ease of use for test setup and support, but also provides the user with real-time display capabilities of time and frequency data, as well as, post-test processing of the data. Integration of MIDDAS at SSC decreased post-test data processing time from approximately four hours to fifteen minutes after test completion. This improved post-test processing performance allows engineers to analyze the data quicker, and respond to issues much faster; thereby decreasing the test turnaround time and reducing costs.

Analysis Software Development OSC personnel have played key roles in the development of the Operator Interactive Signal Processing System (OISPS) software used in post-test analysis of the high frequency data collected from propulsion tests. OSC has been involved in every upgrade of the software and provided development of several algorithms. OSC is currently tasked by MSFC to re-develop the OISPS software into a more user friendly environment with advanced features and capabilities. This software will be developed using the MatLab™ development platform and will incorporate both detailed and standard post-test analysis software packages.

Real-time Engine Health Management Support

OSC personnel were instrumental in the verification and integration of the Real-Time Vibration Monitoring Systems (RTVMS's) at Stennis Space Center for monitoring vibration levels of High Pressure Pumps during SSME and X-33 Aerospike testing. RTVMS provides an enhanced vibration cutoff red-line by providing near real-time amplitude levels of vibrations that are produced by the rotation of the shaft of High Pressure Pumps. The implementation of RTVMS was a first in Rocket Engine testing, and OSC also was a key member of the team that developed and implemented an experimental RTVMS for Shuttle flights. OSC engineers assisted in the hardware and software development, validation and integration of a 32-channel system that was used to monitor SSME High Pressure Pump vibration levels during STS-96. OSC also played a key role in the implementation of RTVMS algorithms into the SSME Controller and development of the Health Management Computer for future Shuttle flights. OSC contributed to the design, development and verification of the sensor validation software that is used to determine the validity of data received from accelerometers. With over 10 years experience in the real-time assessment of high-speed data, OSC engineers are currently developing the next generation RTVMS which will be a Power PC based platform with an AltiVec™ vector processor. The system will consist of a distributed network that will provide versatility in system size and real-time hardware-in-the-loop test support.

Analysis Support

OSC's vibration analyses play pivotal roles in assisting NASA engineers in locating the source of anomalous or problem vibrations, and in determining the acceptance of high-pressure pumps for flight. OSC personnel have provided high frequency dynamic data analysis for seven SSME failure incidents. Our analyses determined dynamic responses of each failure, and assist in locating possible failure causes or sources. The assessments were reported directly to the NASA failure investigation teams, and were often instrumental in the resolution of each failure. Along with failure investigations, OSC has provided NASA with support for numerous high pressure pump, low pressure pump and combustion chamber vibration anomaly investigations. Each investigation provided critical information to NASA engineers to assist in their decision to accept the hardware for flight and/or to investigate other options including hardware redesign and life cycle testing.