NASA - National Aeronautics and Space Administration

Since 1989, the Fleet Leader Program has played a vital role in NASA’s ability to detect, predict, and prevent orbital maneuvering subsystem (OMS) and reaction control subsystem (RCS) life-dependent failures and anomalies before they affect the shuttle fleet. WSTF has performed comprehensive test article functional tests that simulate orbiter flight and maintenance downtime period activities, and special propulsion subsystem tests, using all of the Fleet Leader test articles.

One of NASA’s early challenges was to understand the effect of using a leaking thruster on orbit. The WSTF Fleet Leader Aft Reaction Control Subsystem (ARCS) and Forward Reaction Control System (FRCS) test articles were used to perform real-time anomaly testing to understand the effects of firing a leaking thruster and the impacts it would have on the subsystems in order for the shuttle program to determine whether a shuttle in orbit could successfully and safely fire a leaking thruster.

Another challenge the Shuttle Program faced was dealing with chips and chip growth in the thruster chamber coatings. The ARCS Fleet Leader test article was used to test several thrusters with natural and man-made chips in the chambers to gather data on chip generation and chip growth. The data obtained during these tests have allowed the program to better address chips in thruster chambers and make informed decisions on whether a thruster with chips is still serviceable.

With the impending retirement of the Space Shuttle Fleet in 2010, the Fleet Leader test articles at WSTF are being retired and removed from service. After decades of testing, the FRCS test article was removed from service in July 2006 and the OMS test article was lifted out of the test stand in May 2007.

Special Testing

Other special tests have been performed to support the Fleet Leader Program, such as the OMS/RCS Crossfeed Line Gas Sweep Test (Test Stand 301), the Forward Interconnect System Test using FRCS Test Article (Test Stand 328), and Chamber Chiplife.

In addition, the following are examples of Fleet Leader special tests:

• Understanding Fuel Oxidizer Reaction Products (FORP).
  WSTF discovered corrosion products in the accumulation of a FORP mixture and determined accumulation rates of FORP within the pressure chamber (Pc) tube.
• Understanding Iron Nitrate.
  WSTF conducted impact studies upon various components and systems, and developed techniques such as molecular sieves to reduce iron nitrate contamination of nitrogen tetroxide systems. Molecular sieve units to remove iron nitrates from nitrogen tetroxide were built for use at WSTF, Kennedy Space Center, and other government facilities.
• Auxiliary Power Unit (APU) hydrazine propellant tank.
  The APU Hydrazine Propellant Tank is constructed of light-weight material to lessen the weight-load on board the Space Shuttle. As part of the Fleet Leader Program life-cycling tests performed on shuttle components and systems, the APU hydrazine propellant tank is pressurized and depressurized and then examined for metal fatigue. This life-cycle testing demonstrates how well the thin, light-weight construction hydrazine tank is maintaining capability.

For additional information, contact David L. Baker at (575) 524-5605, or david.l.baker@nasa.gov.