- Author
-
Stone, W. C.
- Title
- Development of a Fast-Response Variable-Amplitude Programmable Reaction Control System.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
-
NISTIR 5118
January 1993
238 p.
- Distribution
- Available from National Technical Information Service
- Keywords
-
active control
|
amplitude control
|
cold gas thruster
|
predictive models
|
microprocessor control
|
piezoelectric stack
|
pulse width resolution
|
reaction control system
|
system identification
- Abstract
- This report describes a high speed loading system comprised of: a piezoelectric stack and an associated microprocessor-based programmable DC power source; a low-loss mechanical displacement amplifier; a high pressure spring-loaded axial valve; an integral high pressure valve seat; an expansion nozzle; and a high pressure gas supply. A half square wave voltage signal of varying duration and amplitude was used to drive the piezoelectric stack in such a manner as to produce changing displacements which were subsequently amplified by a monolithically milled hinged anvil. The anvil is connected to a valve core which seats upon, and is normally forced closed upon a specially hardened throat of an expansion nozzle by means of a compression spring. The interior side of the thruster nozzle communicates with a high pressure gas supply. The flow of gas through the nozzle is normally prohibited by the spring loaded valve core. As the piezoelectric stack expands under computer control the valve core is lifted off the nozzle throat permitting gas to expand through the nozzle and create thrust that is directly proportional to the control signal from the microprocessor. The device is designed to operate as a stand-alone unit with a dedicated onboard microcontroller system and onboard energy storage system. Minimum pulse width resolution (base-to-base) was shown to be 0.98 ms with a lag time of 0.37 ms relative to the initiation of the drive pulse. Linear amplitude response was achieved beyond a threshold drive voltage of 80 vdc and was maintained through the limit of testing at 240 vdc. Thrust change rates of 12000 N/s were achieved. The demonstration unit developed for this study produced a peak thrust level of 15 N at operating pressures of 41 MPa.