Design for robustness using the mu-synthesis applied to Launcher Attitude and Vibration Control
- Paper number
IAC-05-C1.3.05
- Author
Prof. Yasuhiro Morita, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan
- Year
2005
- Abstract
In the paper, the design of the attitude and vibration control algorithm for a launch vehicle is introduced, which is highlighted by its robust characteristics not only in stability but in tracking performance under uncertainty of the system dynamics.
The Japan Aerospace Exploration Agency (JAXA) is planning to launch M-V rocket to inject Japan’s fifth X-ray Astronomy satellite ASTRO-EII before this coming summer. The vehicle was already utilized three times successfully by the former Institute of Space and Astronautical Science (ISAS) to launch a series of Japan’s scientific spacecraft: the world’s first VLBI satellite "HALCA" in 1997; the Japan’s first Mars observer "NOZOMI" in 1998; and Japan’s first asteroid sample return vessel "HAYABUSA" in 2003. The vehicle is a three-staged solid propellant rocket, having a 2-ton class payload capacity into a low earth orbit, and is stabilized by mobile nozzle systems. The algorithm of the second stage attitude control system involves robust characteristics against variations in the plant dynamics. To provide a controller with sufficient robustness character against such uncertainty, the H ∞ control theory was applied for the first two flights. The problem was approached within the framework of the mixed sensitivity problem to achieve better tracking performance in a relatively low frequency region as well as preferable robust stability in a higher:nominal performance and robust stability.
Beyond this, the µ-synthesis was applied at the last flight to achieve the robust characteristics not only in stability but in tracking performance: robust performance and robust stability. It is for the first time ever that the theory was utilized in Japan’s launcher control. The most difficult aspect of the design is featured by the extremely high order and unstable characteristics of the plant dynamics, thus the standard µ-synthesis approach cannot be sufficiently effective. The paper gives a methodology to apply the theory to such real systems, which reduce the level of difficulty well within an acceptable limit by preliminarily stabilizing the unstable plant through a simple local measurement feedback. Then, the standard numerical code is directly applied to yield a controller significantly easily. This modification of the design approach is prompted as the standard theory is not always effective to unstable large systems. Furthermore, the knowledge, obtained in the previous H ∞ design, is employed to reduce the amount of efforts required in selecting the weighting functions: that on robustness is taken to involve a structure of phase lead and lag elements superimposed over the 2nd-order system, which reflects the frequency characteristics of the former H ∞ controller. This converts the entire design procedure into only a straightforward parameter tuning of the weighting functions.
The paper represents a methodology for applying the µ-synthesis to the M-V second stage attitude and vibration control design: a real high order complicated problem. Its effectiveness is established by the flight results obtained by the last and upcoming launches.
- Abstract document
- Manuscript document
IAC-05-C1.3.05.pdf (🔒 authorized access only).
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