6 DOF robust control for Entry Descent and Landing in planetary atmospheres
- Paper ID
2672
- author
- company
- country
Italy
- year
2008
- abstract
Many on going international space programs include robotic missions on planetary surfaces. Within those missions the approaching phase is quite delicate and greatly influences the mission design and success. Therefore particular attention is currently given to identify reliable technological solutions and analysis tools to carefully design the space system devoted to land on the surface. The presented study focuses on approaching phases to planets with atmosphere. The presence of atmosphere intrinsically introduces several uncertainties while modeling and analyzing both the system configuration and the vehicle dynamics. Not to take into account effects of those uncertainties unavoidably leads to erroneous and rough systems modeling, causing a critical effort waterfall into operations during which any lack of robustness in the system must be rapidly faced. A methodology to properly and quickly analyze the uncertainty effects space during any step of the design phase is obviously favorable. To this end, the paper proposed a technique to identify control profile robust to as many multidisciplinary uncertainties as possible. More specifically initial conditions, space system mass, aerodynamic coefficients, geometric approximations, atmospheric density and winds, gravity fields and possible different failures are part of the uncertainty set. The whole approaching phase is simulated with a 6 DOF dynamics for each of the elements involved in the entry, descent and landing sequence; therefore the parachute, the backshell and the capsule dynamics are considered. Sensitivity analysis accomplished by applying Taylor series methods is discussed to underline the effects of combined uncertainties on the precision and soft landing typical requirements violation. The procedure to obtain a robust optimal control law to dynamically manage on board a subset of uncertainties is explained. The proposed approach, based on the Taylor maps inversion, is fast and light enough to run on-board. Simulations, Montecarlo sensitivity analysis comparisons, and control synthesis are offered for a EDL in Martian atmosphere scenario. The atmosphere model is comprehensive of winds in both quiet and dust storms conditions. [1] M.Berz, Modern map methods in particle beam physics, Academic Press, 1999 [2] Braun, R. D. Manning, R.M., Mars exploration entry, descent and landing challenges, Aerospace Conference, 2006 IEEE,March 2006, Big Sky-Montana