Josef Klevanski

In the Horizon Europe Project SALTO, a demonstrator of a vertically landing first stage with three Prometheus engines was investigated, the so-called T3. It shall be recovered with a downrange landing approach. In this paper the aerodynamic phase of the descent trajectory was investigated using wind tunnel experiments of the full launcher configuration in the Trisonic Wind Tunnel Cologne (TMK). The grid fins proved to be efficient to trim and control the vehicle. Increasing the size of the grid fins by 10% does not directly transfer into a larger trimmable angle of attack range. Modelling the engine nozzles as closed surfaces instead of open cavities introduces a systematic offset in the axial force coefficient which vanishes at zero incidence and grows to approximately 0.05 at the extremes of the tested angle of attack range, and it affects the roll moment of the undeflected configuration at the supersonic Mach numbers. This simplification is therefore acceptable for low-fidelity databases, but the nozzles should be modelled as open cavities for high-fidelity databases and for the validation of CFD computations. A Reynolds number variation showed a small but systematic effect on the axial force coefficient and on the roll moment, while no discernible effect was found in the coefficients governing the trim and the static stability. A superposition approach defined in earlier work was validated with the wind tunnel data. During ascent, the increase in length of the configuration influences the pitch moment coefficient considerably more than the deployment of the grid fins, while the deployed fins increase the axial force coefficient by approximately 17% at Mach 3.0.

CALLISTO is a collaborative project between JAXA, CNES, and DLR, focused on developing and operating a scaled reusable vertical-takeoff vertical-landing rocket stage demonstrator. This initiative is a crucial step for advancing reusable launch vehicle (RLV) technology in Europe and Japan. Significant strides have been made during the recently completed phase C of the project, particularly in aerodynamic modeling, guidance, navigation, and control design, landing dynamics, and flight domain definitions. These advancements facilitate the development of future operational vehicles and provide insights applicable to other RLV projects. This paper provides an update on the design and development status of the CALLISTO vehicle. It outlines the program objectives, focusing on mission design, vehicle life cycle, and their distinctions from legacy expendable launch vehicles in Europe and Japan. Details of the flight test plan, including in-flight experimentation, are elucidated, demonstrating incremental progress toward acquiring key technology and preparing for high-energy missions. Furthermore, the paper offers an overview of the CALLISTO vehicle’s development status, highlighting key architectural features such as load-carrying structures, avionics, rocket propulsion system, flight control systems, and approach and landing system. It underscores the milestones achieved over the past years and the progress toward the first flights. With a flight test campaign to be performed at Europe’s Spaceport in French Guiana, the CALLISTO project signifies a crucial step toward enhancing launch system affordability, competitiveness, versatility, and sustainability. This collaboration among three space organizations highlights the importance of shared expertise in advancing RLV technology and preparing for the next generation of launch vehicles.

Defining aerodynamic databases is an important yet very complex and labor-intensive task during the design of new aerospace vehicles. This is particularly true for reusable launch vehicles, as observed during the development of CALLISTO, a demonstrator for a vertical-takeoff–vertical-landing first stage that is jointly developed, manufactured, and tested by German Aerospace Center (DLR), Japan Aerospace Exploration Agency (JAXA), and French National Centre for Space Studies (CNES). In this paper, we present an inference-based methodology to define various types of Bayesian models exemplarily for a subset of CALLISTO’s Aerodynamic Database to assess their usability and prediction qualities. First, a short introduction to the underlying aerodynamic dataset will be given, which has been aggregated from various computational fluid dynamics simulations and wind tunnel test campaigns. Then, the different Bayesian models will be defined and their inference results compared against each other, according to common error metrics. It will be shown that, within the limits and assumptions of this study, several types of Bayesian models provide better accuracy in the prediction of uncertain aerodynamic coefficients compared to classical expert-fitted models for the given CALLISTO dataset. Generally, it can be concluded that Bayesian models provide a promising approach for the definition of aerodynamic databases and could also find many potential applications in other engineering domains.

One of the very first tasks in launch vehicle design is the preliminary sizing. It is necessary for further design choices, but it should deliver a precise estimate of the launch vehicle’s mass and geometry as possible. Orbital launch vehicles can be either expendable or partially/fully reusable and can assume various stage configurations. Finding an optimal solution under practical constraints is a challenging task, which gives a wide design space for potential future launch vehicles. Hence, a generalized mathematical model of a launch vehicle design has been developed and implemented as a versatile and easily modifiable programming tool for fast and parametric system characterization and optimization. The model uses several basic parameters useful in describing launch vehicles and introduces some new parameters to account for reusability. Analytical and semi-empirical correlations are used to determine the overall system and mission performance of a launch vehicle for a given reference mission, including mass and geometry, and calculate the optimal launcher staging. The implementation of the model also allows coupling with other tools, which forms a design chain with respect to aerodynamics and trajectory simulation. With this design chain, several launch vehicles have been modeled and validated, proving the applicability of the method.

Prior to landing of reusable space transportation systems, the vehicle’s landing legs needs to be fully deployed to enable a safe landing and further re-use of the space vehicle. During that phase the deployment system has to overcome harsh and challenging environmental conditions. In this study, a numerical simulator is developed in order to investigate these influences on the landing leg deployment dynamics. By means of an extensive aerodynamic database and a broad approach flight domain, the influence of aerodynamics, exhaust plume, and vehicle’s attitude on the deployment dynamics is analyzed. This study shows on the example of the first stage demonstrator CALLISTO (Cooperative Action Leading to Launcher Innovation in Stage Toss back Operations), that thrust level, vehicle attitude, and the deployment system parameters affect the deployment performance.

JAXA, CNES and DLR have decided to join their force to develop and fly a scaled reusable VTVL rocket stage called CALLISTO (Cooperative Action Leading to Launcher Innovation in Stage Toss - back Operations). This vehicle will pave the way for future reusable launch vehicles. One of its main goals is to demonstrate the mastering of key techniques and technologies that will be needed later by operational reusable launch vehicles. Indeed in the frame of CALLISTO numerous challenging technologies are being matured for the specific case of reusable launch vehicles. The challenges of a selection of key technologies developed for CALLISTO are discussed and the solutions retained for CALLISTO are presented.