Abstract—The paper presents aspects regarding six degree of freedom model used for attitude control of the three stages micro-launcher with a payload up to 50 kg. This work uses two separate attitude control models dedicated for different flight phases. In the ascending phases, we will control the attitude angles related to the start frame, and in injection phases we will control the attitude angles related to the geographical frame. The results analyzed will be the flight parameters in longitudinal, in lateral and in roll movement. Using this model, the attitude control of the launcher can be evaluated. The novelty of the paper consists in alternative attitude angles used for control and in description of guidance signal. Index Terms—Mathematical model, micro-launcher, attitude control, guidance signal I. INTRODUCTION The present work is a continuation of the paper [1] where using 3DOF model, based on translational equation, the ascending phase of the micro-launcher (ML) was optimized and performance for Low Earth Orbit (LEO) was evaluated. Present work proposes to develop the ML model adding the equations of the movement around center of mass (dynamic and kinematic) and the equations of the aerodynamic angles to obtain a six Degree of Freedom (6DOF) model. From the beginning, we must emphasize that the issue of launcher control is particularly important because unlike rocket with fins, the launcher is naturally unstable, which leads to the impossibility of motion assessment without the loop control of the vehicle's attitude. The attitude control of ML can be separate in two problems. First consist in choosing the right frames to express the attitude angles and define desires angles in these frames. The second problems consist in obtain a robust controller which ensure pursuit of the desire angles by the accomplished angles. In the dedicated works this problem has been addressed in different ways. In classical work [2] the translational equations are write in quasi-velocity frame and in start frame, the kinematic rotational equations are write related to the start frame, but attitude control problem does not be approached. In recent work [3] the translational equations are write in Earth frame know as Earth-Centered Inertial frame – ECI frame. The kinematic rotational equations are write also related ECI frame, which leads to complications in the description of the guidance commands. Work [4] is dedicated to solve the second problem of the launcher control, to obtain a robust controller using  synthesis technique. Related nonlinear Manuscript received May 31, 2019; revised July 1, 2019. This work was funded by STAR program, implemented with the support of ROSA, contract no. 144/2017. Teodor-Viorel Chelaru. is with University Politehnica of Bucharest, Romania (e-mail: teodor.chelaru@upb.ro). motion equations, the problem in this work is formulated in annex A, in the body frame. The work is focused on linear form of motion equation in particular in longitudinal plane. A practical approach is propose in work [5], where the main phases of ascension are defined, which helped us to approach of the 3DOF model from paper [1]. Work [6], dedicated to re-entry vehicle, propose the use of no inertial geographical frame for express attitude of the vehicle, idea that we will develop in this paper for the orbital injection phases. The present work intends to seek an answer for first formulated control problem, to choose the right frames with desire angles and to obtain a preliminary solution for ML control. Summarizing, in present work, using 6DOF calculus model, the attitude of the launcher will be evaluated using two reference frames. In ascending fazes we will use the attitude angles in order (3-2-1) related to the start frame, which allow us to consider null the yaw angle, and the link matrix without singularity for vertical position of the ML. Different from this case, for injection phases we will use attitude angle in order (2-3-1) related to the geographical frame, which allow to transpose easily the desire attitude angle from the orbital frame to the body frame. As for the translational equations, although as we have shown in works [7], [8], it is possible to work in the linked start frame, in the present work the equations in quasi-velocity frame will be used to obtain a 6DOF model compatible with the developed 3DOF model and to use the previously obtained results, especially regarding the optimization of the ascending phases. Because one of the basic ideas for a micro launcher is simplicity and low cost, and because the avionics and related software are the most expensive, the main purpose of the paper is to get a simple attitude control system based on tracking the desired attitude angles. Although the problem of the evolution of the launchers is not a very new one, with the exception of the Earth frame (ECI), which is the same, the rest of the reference systems used are different for each author or group of authors, which is why we recommend work [9] where the frames used are defined. II. LAUNCHER MOTION EQUATIONS Because the translational equations were presented in paper [1], in 3DOF model, we will remind briefly the translational equations and we will focus on rotational equations. A. Translational Dynamic Equations in Quasi-Velocity Frame Summarizing the papers [1] , [9] to obtain the translational equation in quasi-velocity frame, we start from vector equation: Nonlinear Model for Micro-Launcher Attitude Control Teodor-Viorel Chelaru International Journal of Modeling and Optimization, Vol. 9, No. 6, December 2019 310 DOI: 10.7763/IJMO.2019.V9.728