Cesic a new technology for lightweight and cost effective space instrument structures and mirrors

Paper number

IAC-05-B1.3.03

Author

Mr. Christophe Devilliers, Thales Alenia Space, France

Coauthor

Mr. Matthias Kroedel, Germany

Year

2005

Abstract

A general problem that arises during the design phase of an aerospace system and when verifying the control performance and stability robustness is to assess vehicle compliance with a set of mission requirements, in face of uncertain parameters ranging in given subsets. In particular, during the Flight Control Laws (FCL) design and verification phases, robustness analyses are frequently required in order to drive the FCL refinement process. In these cases, it is useful to estimate the uncertainty ranges that guarantee compliance to a requirement, in order, for instance, to establish the limiting operating conditions for an FCL candidate. The present paper deals with the problem of analyzing the robustness with respect to parametric uncertainties of FCL for vehicles performing an atmospheric re-entry. This is a challenging application for robustness analyses, because, among others, of stringent requirements on the trajectories that can be safely flown, and of significant uncertainties on the design parameters, most notably on aerodynamic coefficients.

State-of-the-art robustness analysis techniques mainly exploit the possibility of describing the nonlinear system dynamics applying the small perturbation theory around pre-defined stationary equilibrium points. However, given the unsteady nature of the re-entry trajectory, the extended range of flight regimes, the large uncertainty and disturbances ranges, the vehicle trajectory can be poorly represented assuming trimmed stationary flight or quasi-steady maneuvers, which calls for different approaches. Presently, when analyzing a re-entry mission, only Monte Carlo based simulations are used with the drawback to not get useful information for vehicle or control system design refinement and or modification, but giving only a global assessment of the system compliance to a requirement, assuming pre-defined statistic characterization of the uncertain parameters (which are not always available).

A novel approach to robustness analysis in the uncertain parameters space is presented, aimed at improving the efficiency of the design upgrade process with respect to conventional techniques, especially when applied to re-entry applications. To this end, the robustness analysis problem is formulated as determining the subset of the uncertain parameters domain in which a criterion translating mission requirements is matched. The practical stability concept [1] is proposed as a robustness criterion, which allows handling rigorously re-entry applications peculiarities. A hybrid probabilistic – deterministic approach is envisioned, combining practical stability analysis methods for Linear Time Varying (LTV) systems with an approximate description of the original nonlinear system by a certain number of its time-varying linearizations. In particular, suitability of the LTV approximating systems is evaluated making use of the Unscented Transformation technique [2]. Then, the practical stability analysis is performed by means of a deterministic approach exploiting the convexity–preserving nature of LTV systems [3]. Finally, the method effectiveness and potentials are ascertained by application to various test cases within the framework of the Italian Aerospace Research Center (CIRA) experimental vehicle USV [4].

REFERENCES

1. Dorato, P., “An Overview of Finite-Time Stability,” Current Trends in Nonlinear Systems and Control: In Honor of Petar Kokotovic and Turi Nicosia, edited by L. Menini, L. Zaccarian, and C. T. Abdallah, SystemsControl: FoundationsApplications, Birkhäuser Boston, 2006, pp 185-195. enumerate
2. S. Julier, J. Uhlmann, and H.F. Durrant-Whyte, “A new method for the nonlinear transformation of means and covariances in filters and estimators," IEEE Transactions on Automatic Control, vol. 45, no. 3, pp. 477-482, March 2000. enumerate
3. Tancredi, U., Grassi, M., Corraro, F., Filippone, E., Palumbo, R., Russo, M., “A Novel Method for Flight Control Laws Robustness Analysis over Unsteady Trajectories”, Proc. of the 17th IFAC Symposium on Automatic Control in Aerospace, June 2007, Toulouse, France enumerate
4. Pastena, M., Di Donato, M., Palma, et al. PRORA USV1: The First Italian Experimental Vehicle to the Aerospace Plane. AIAA/CIRA 13th International Space Planes and Hypersonics Systems and Technologies Conference, AIAA-2005-3348 , Capua, Italy, 2005.

Abstract document

IAC-05-B1.3.03.pdf

Manuscript document

IAC-05-B1.3.03.pdf (🔒 authorized access only).

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