Papers & Publications

Preliminary Design of Expendable and Reusable Mixed-Staged Launch Vehicles

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.

Pawel Goldyn, German Aerospace Center (DLR e.V.), Germany
Ansgar Marwege, German Aerospace Center (DLR e.V.), Germany
Johannes Riehmer, German Aerospace Center (DLR e.V.), Germany
Josef Klevanski, German Aerospace Center (DLR e.V.), Germany
Ali Gülhan, German Aerospace Center (DLR e.V.), Germany

Experimental Investigations of Fluid-to-Vehicle Interactions during a Reusable Launcher’s Touchdown Impact

Several programmes are dedicated worldwide to the development of reusable vertical take-off vertical landing (VTVL) launch vehicles. Thereby, the touchdown event with its associated impact forces and shocks poses load cases to the vehicle being new in the launcher domain. Furthermore, the application of related knowledge from planetary, exploration-type landers has to be taken cautiously due to the differences between those types of vehicle, particularly with regard to their tank configuration and structural sizing. Depending on flight test conditions and operational concept, non-neglectable amounts of liquid propellant can still be inside the tanks at landing and interact with the vehicle. These interactions cause dynamic and structural effects that affect the landing stability and structural integrity of the vehicle. This study aims to experimentally investigate the fluid-vehicle interactions of a fully functional touchdown demonstrator during touchdown. For this, a vehicle landing engineering model is equipped with a circular cylindrical tank and a series of touchdown test with varying horizontal landing velocities and fill levels is conducted. Thereby, the main objectives are to prove repeatable landing behaviour under sloshing impact for constant landing conditions, characterise the fluid impact on landing stability and investigate the fluid-structure interactions on the tank. Therefor test data of different test cases is compared and analysed with regards to dynamic behaviour and structural responses.

Caroline Krämer, German Aerospace Center (DLR e.V.), Germany
Lars Witte, German Aerospace Center (DLR e.V.), Germany

Paper for 24th DGLR STAB-Symposium

Parametric grid fin design study for the T3 vehicle within SALTO

Numerical simulations were conducted to investigate the aerodynamic performance of grid fins for a reusable first stage, within the SALTO project. The influence of the descent trajectory was taken into account. This study provides a systematic overview of the geometric parameters of grid fins and their effects on mass and steering forces generated. The results are compared to a baseline geometry. Parameter combinations were analysed that lead to a slightly lighter and aerodynamically improved geometry.

Jens Neumann, German Aerospace Center (DLR e.V.), Germany

Paper for 75th International Astronautical Congress (IAC), Milan, Italy

Autonomous Flight Safety System - Embedded Software and Hardware equipment for New Space Ground and On-Board safety

The current access to space context imposes objectives of cost, launch rate, and campaign agility to enable the business model of both spaceport and launcher operators. In this scenario, the reduction of ground infrastructure and operations becomes a necessity in the roadmaps of New Space players. Flight safety system is responsible for the launcher neutralization, i.e., mission termination, based on the launcher and mission diagnostics. That system requires as input the launcher telemetry with independent tracking data (typically from radars) to properly and safely assess the launcher status, with emphasis on its dynamics, relying on the decision-making process of the mission termination to the ground safety operators.

An on-board Autonomous Flight Safety System (AFSS) is a strategy that enables the launcher to assess its own status and that of the mission in real time. This strategy has a major impact on ground infrastructures (radars, ground TM processing IT systems, safety operators, operators training simulators) and operations (preparation of the campaign, delay in the safety chain from the launcher to the human on the ground and back to the launcher with the neutralization telecommand). The result is both safer missions and a significant reduction in ground infrastructure and operational costs. In a reusable launcher context, the autonomous onboard safety strategy allows multi-object simultaneous tracking, enabling the facto the reusable strategy itself. Collaterally, the AFSS described in this paper extends the launcher diagnostics beyond the strict flight safety needs towards a whole launcher status awareness through Integrated Vehicle Health Monitoring (IVHM), enabling a safer re-entry phase based not only on dynamics but also on vehicle status after the ascent phase. Following that axe, diagnosis of all subsystems during the flight provides valuable data for prognosis and predictive maintenance after landing, contributing to optimal refurbishment operations.

This paper presents the design, architecture, and development for the safety software responsible for real-time diagnostics and decision-making. The policy and regulations applied at Spaceports constrain the use of fully on-board autonomous solutions. Therefore, the software is conceived to be operational in two scenarios: ground and launcher on-board. The ground AFSS allows a human operator in the safety chain as supervisor and less solicited hardware. This ground AFSS approach makes it possible to qualify the safety software in a relevant operational ground environment to either increase the TRL towards the on-board version or to provide a solution for those actors in the market who prefer a ground version. The validation of the ground version is described here, as well as the preparations for the on-board Software/Hardware adaptations.

Alejandro Sabán-Fosch, GTD SSI, Spain, Department of Physics, Universitat Politècnica de Catalunya, Spain
Eduard Diez-Lledo, GTD SSI, Spain
Manel Soria, Department of Physics, Universitat Politècnica de Catalunya, Spain
Miquel Sureda, Department of Physics, Universitat Politècnica de Catalunya, Spain

Papers & Publications