1、Lessons Learned Entry: 1395Lesson Info:a71 Lesson Number: 1395a71 Lesson Date: 2004-04-02a71 Submitting Organization: WSTFa71 Submitted by: Ronald LerdalSubject: Simplified Simulation for Control Validation Abstract: A potentially complex test was innovatively implemented to take advantage of existi
2、ng capabilities using sound engineering, insight into key test equipment and program capabilities, and successful integration of a sophisticated test article with less than up-to-date equipment and facilities.Description of Driving Event: The WSTF Propulsion Computer Engineering section was given a
3、task (via Space Act agreement) to develop, validate and implement a very challenging rocket engine control software module for use in initial developmental ground testing operations. This custom control and monitoring software was to be used for safely establishing the closed loop startup and shutdo
4、wn profiles of a liquid propellant rocket engine with a gas generator powered turbo-pump propellant feed system. There were several critical pressures and turbo-pump vibration parameters that had to be monitored while valves were being cycled to allow safe buildup of gas generator pressure, turbo-pu
5、mp speed, manifold pressures, and combustion pressure. At any time during the startup or main stage process, if any of these critical parameters deviated from predetermined nominal limits, then a sequence of commands had to be issued for safely shutting down the engine. The design and code generatio
6、n for the control and limit shutdown algorithms was relatively straight forward, but the challenge was to ensure it would all work correctly prior to firing up a developmental rocket engine for the first time. A process was needed to ensure that the software and hardware involved would correctly res
7、pond to all critical control parameters. This process had to simulate failures during all stages of operation while providing simulated feedback for the closed loop startup, main stage, and shutdown modes. A rocket engine simulator was required to validate the control system for this one-of-a-kind d
8、evelopmental engine. This simulator would then have to be implemented in a system that could provide not just mathematical values, but electrical signals for communicating pressure values and vibration monitoring events back to the control system. High Provided by IHSNot for ResaleNo reproduction or
9、 networking permitted without license from IHS-,-,-fidelity modeling of rocket engine processes is very complex and to develop a math model that runs in real-time is even more complex. In previous projects of this type, actual hardware components electronically similar to the rocket engine valves, a
10、ctuators, and pumps had to be assembled into a crude engine breadboard. All these components then had to be individually connected to the data acquisition and control system for validating the monitor and control algorithms. In addition, time delay relays and signal generators would have to be integ
11、rated with the breadboard components to provide enough precision for validating the fast, time critical, transient response requirements. The facility where this rocket engine was to be tested already had a programmable logic controller (PLC) in place for controlling some test facility support funct
12、ions. Although not fast enough to control or provide high fidelity real-time engine simulation it was ideally suited for issuing signals back to the engine control system in response to the control system program output commands. It could also be used to sequence various failure simulation signals f
13、or validating correct responses to possible engine problems during all stages of operation. The complexity of designing a complete real-time breadboard or math model simulation of the rocket engine was replaced using simpler PLC ladder logic. It was used to provide feedback defined by the engine des
14、igners for the critical control points in the power up and power down staging process. This in essence allowed using a very simple empirical model of the engine for our validation simulator. It was then also possible to easily inject simulated failures at various critical times to ensure safe operat
15、ion of all control and emergency shutdown algorithms. This technique could be applied to many dynamic process algorithms on systems that have a few fairly well defined critical control points.Lesson(s) Learned: A combination of technical insight and innovation plus understanding of test article requ
16、irements together with extensive experience with the test facility and support system can lead to test success at reduced costs.Recommendation(s): When a dynamic process must be simulated, analyze the critical parameters to find discrete points at which control actions must be performed. Then build
17、a simple empirical model, which may be developed and run on a slower and easier to program and integrate platform such as an industrial PLC. This simplified approach to the validation using hardware and software tools already in the system reduced validation time and costs. Evidence of Recurrence Co
18、ntrol Effectiveness: N/ADocuments Related to Lesson: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NPR 7120.5, NASA Program and Project Management Processes and RequirementsMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Space Operati
19、onsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Administration/Organizationa71 Configuration Managementa71 External Relationsa71 Facilitiesa71 Human Resources & Educationa71 Policy & Planninga71 Procurement Small Business & Industrial Relationsa71 Program and Project Managementa71 Research
20、 Developmenta71 Risk Management/Assessmenta71 Safety & Mission Assurancea71 Softwarea71 Test & Verificationa71 Test Articlea71 Test FacilityAdditional Info: Approval Info: a71 Approval Date: 2004-04-26a71 Approval Name: Jan Jungewaeltera71 Approval Organization: WSTFa71 Approval Phone Number: 505-524-5161Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
