ESA GNC Conference Papers Repository
Effectiveness and limitation of IMU-GPS integrated navigation and gps attitude determination for launch vehicle guidance
Navigation error is one of major factors deteriorating rocket's ascent guidance accuracy and inertial navigation with high performance Inertial Measurement Unit (IMU) has been used to meet such high requirement of navigation for rocket's ascent guidance. Although high performance IMU is very accurate, the IMU is very expensive and its high price is bottleneck for price competitiveness of rocket avionics. Thus, we has been studying a low cost and accurate navigation system using low cost MEMS gyros, MEMS accelerometers and GPS navigation modules for rocket guidance. IMU-GPS integrated navigation and GPS attitude determination are applied for the navigation system. The technical issues of the low cost and accurate navigation system for launch vehicle are as follows . 1) Navigation error mitigation on Geo-Transfer Orbit (GTO) 2) Accurate attitude estimation using GPS module measurements 3) Radiation tolerance and vibration tolerance of low cost MEMS gyros, MEMS accelerometers, and GPS navigation modules First, this paper evaluates guidance errors of H-IIA launch vehicle ascent guidance including long coast GTO mission and shows that more than 60 percent of guidance error is caused by navigation errors at the end of long coast GTO mission which is at the apogee of GTO and its elapse time from lift-off is about 24000 seconds. Next, this paper shows the effectiveness of IMU-GPS integrated navigation for rocket guidance during ascent phase and the limitation of IMU-GPS integrated navigation for guidance during long coast GTO phase. Since we cannot use GPS navigation for long coast GTO phase,we applied precision state propagation method for position and velocity estimation. Using H-IIA rocket flight data, we evaluates the IMU-GPS integrated navigation during ascent phase and the precision state propagation method for long coast GTO phase. Then, this paper shows the rocket guidance errors caused by navigation error on rocket's attitude. Conventional rocket ascent guidance uses IMU inertial navigation and the navigation error on attitude, which is reference frame error of IMU inertial navigation, is increasing according to elapse time from flight mode on just before the lift-off. Especially, if we use MEMS gyros and accelerometers for rocket guidance, the navigation errors on attitude increase rapidly. To mitigate this navigation error on attitude, we can apply GPS attitude determination for rocket ascent guidance. GPS attitude determination has advantages on implementation and cost compering other attitude sensors such as star tracker and earth sensor. This paper shows the effectiveness and limitation of GPS attitude determination for rocket including evaluation results of GPS attitude determination accuracy using ground experiment data and using H-IIB rocket flight data. Finally, we summarized technical issues and future works on low cost and accurate navigation system using low cost MEMS gyros, MEMS accelerometers and GPS navigation modules for rocket guidance.