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The need for three degrees of freedom (3DOF) trajectory calculation arises due to two key requirements: First, a precise 3DOF trajectory prediction is an important subroutine of a comprehensive conceptual design tool for launch vehicles, as the main purpose of such a tool is to design a vehicle that is capable of transporting a payload to the desired orbit as realistic as possible. Secondly, it is extremely important to determine the drop zones of separated stages or fairing of the launch vehicle with high accuracy regarding safety and reuse issues. Besides, it may be crucial to determine the landing position of payload in a suborbital launch. For early phases of the conceptual design process, 3DOF trajectory prediction is recommended practice for a satisfactory design analysis. This paper aims to present two different 3DOF trajectory prediction tools, developed simultaneously for both multistage suborbital and orbital launchers, called Sonda-M and Sonda-S. Trajectory predictions are carried out for REXUS-5 sounding rocket of Eurolaunch and predicted results are compared with campaign report accessed from open literature for further evaluation of developed tools.

There are several reference and standard atmosphere models which are claimed to be valid and accurate for different regions all over the world. Launchers, during their atmospheric flight, exposed to aerodynamic drag forces. Magnitude of these forces and trajectories of the launchers directly depend on the atmospheric conditions. It is a must to model the atmosphere accurately before the trajectory analysis in order to determine the trajectory of the vehicle precisely. Since there are no detailed atmospheric studies related to Turkey, which include atmospheric properties at high altitudes above 30 km, it is required to investigate the effect of regional and seasonal changes on a possible trajectory of launch from territory of Turkey. In this study, effect of different atmospheric conditions on the altitude and range of a vehicle is investigated. Study was performed using the real atmospheric values obtained from sounding balloon measurements and different models for higher altitudes that are not covered by the measurements. Two different locations are inspected regarding the change in atmospheric properties and one of these locations is more deeply investigated to clarify the effect of seasonal changes on a hypothetical launch of a suborbital launch vehicle. Main variable for the investigation is the atmospheric temperature over the investigated region at a certain time of year with respect to elevation. Keywords-trajectory analysis; suborbital launch vehicle;sounding balloon; atmosphere models; seasonal effects I. INTRODUCTION Atmospheric properties such as temperature, pressure and density plays an important role on the design of suborbital and orbital launch vehicles. These properties are also used in structural and thermal analysis in addition to the prediction of the trajectories. It is important to model the atmosphere as accurate as possible in order to obtain correct results. Many atmosphere models are prepared with help of different kinds of measurements and statistical approaches. Atmosphere models include information about many features like chemical composition, kinetic and dynamic viscosity, solar flux and molecular oxygen density in addition to the basic properties such as temperature, pressure and density distribution.