Research On Uncertainty Evaluation Method Of Liquid Rocket Engine Thrust Vector Measurement

In recent years,the aerospace industry is advancing by leaps and bounds,more and more spacecraft are successfully launched.For the control of these spacecraft’s orbit change,rendezvous and docking and so on,the attitude and orbit control engine needs to generate thrust to complete,so the attitude and orbit control rocket engine plays a very important role in modern space vehicles.The thrust generated by the rocket engine during the ignition is a space force vector,and the direction of the force generally deviates from the geometric centerline of the engine nozzle.The thrust vector can be described by parameters such as thrust deflection δ,thrust deflection angle α and so on,it is necessary to measure the thrust vector parameters,and at the same time,the specific requirements for the uncertainty of measurement are put forward.At present,the GUM method(Guide to the Expression of Uncertainty in Measurement,GUM)in JJF 1059.1-2012 has been used to evaluate the uncertainty of thrust vector measurement.However,there exist some problems,such as the probability distribution assumption of input and output,the nonlinear model approximation and the inaccuracy of inclusion interval,which has certain limitations.This paper proposes a new small sample uncertainty evaluation method in the field of liquid rocket engine test—the Monte Carlo uncertainty evaluation method based on the principle of maximum entropy,which is applied to the thrust vector measurement.The main tasks of this paper are as follows:Research on the modeling of uncertainty evaluation by establishing uncertainty measurement model,uncertainty analysis model,uncertainty high-order propagation model and uncertainty evaluation model for thrust vector measurement;Use the GUM method to evaluate the uncertainty of thrust vector measurement system,since the GUM method does not consider the higher-order terms and related terms,through quantifying errors,it is found that the uncertainty is reduced by 24%,indicating that the higher-order terms and related terms cannot be ignored.Analyze the limitation of GUM method for thrust vector measurement;By researching the applicability of the Monte Carlo method,combining it with the principle of maximum entropy and the rejection sampling method,a small sample uncertainty evaluation method applied to thrust vector measurement is studied.This method can not only be applied to thrust vector measurement,but also can be used to evaluate the uncertainty of other physical quantities such as pressure,temperature,flow and so on,so it has universal applicability;Research the algorithm and write a small sample uncertainty evaluation software based on MATLAB to simplify the process;Evaluate the uncertainty of the existing thrust vector measurement system by the Monte Carlo method.Compared with the GUM method,the results show that for the thrust parameters,the GUM method only meets the requirements of the standard uncertainty,and the extended uncertainty does not meet the requirements.The advancement and practicability of the measurement system are controversial,but through the Monte Carlo method uncertainty assessment,since the Monte Carlo method adopts a real simulation strategy,the results obtained are more in line with reality,the standard uncertainty and the extended uncertainty both meet the index requirements,which further verifies the advancement of the measurement system;Verify the validity of the GUM method based on the adaptive Monte Carlo method.The results show that for thrust vector measurement the GUM method has not passed the verification,so Monte Carlo method is used as the main method for evaluating the uncertainty of thrust vector measurement.