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.
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.