**1. Introduction**

Theoretical aerodynamic study, computational fluid dynamics (CFD) analysis, and wind tunnel tests are the three pillars of every aerodynamic design process. In this paper, the emphasis is on how CFD and theoretical study can be complementary and how to prepare the wind tunnel test.

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The present project, commissioned by the S3-Swiss Space System, deals with the development and qualification of three stages to orbit a composite vehicle. The first and second stages, the Airbus and the Suborbital Aircraft Reusable (SOAR) vehicles, respectively, are reusable, whereas the third stage is an expandable booster. All details of the SOAR mission are in Ref. [1] see **Figure 1**. This project requested the design of new supports for the separation wind tunnel test in the VKI facility and the study of the respective interferences.

The S3 SOAR separation from the Airbus A300 is a critical issue during the mission. The aerodynamic coefficients are affected by the proximity of the vehicles. To correctly design the separation, the aerodynamic database must be known with sufficient accuracy. For this reason, an important campaign of wind tunnel testing is necessary.

An earlier wind tunnel campaign had already been performed with the construction of an initial aerodynamic database [2]. To carry out further wind tunnel experiments, an improve‐ ment in the knowledge of support design is required. In fact, to design supports for the SOAR, in this configuration, is particularly complicated due to the presence of the Airbus below and behind the vehicle (the A300 empennage also impedes the use of a support from the base). Effectively, the first sting designed produced considerable interferences on the model. Therefore, the purpose of this work is to design supports for the SOAR vehicle in the following two configurations: scale 1:180 for the wind tunnel test of the SOAR in the presence of the Airbus and scale 1:80 for the wind tunnel test of the SOAR alone.

**Figure 1.** Illustration of the main steps of the mission.
