Papers & Publications

Article

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.

DOI: https://doi.org/10.2514/1.A36174

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

Research article

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.

DOI: 10.21203/rs.3.rs-4977412/v1

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

Conference Paper

Parametric grid fin design study for the T3 vehicle within SALTO

Paper for 24th DGLR STAB-Symposium13 and 14 November 2024, Regensburg, Germany

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

Conference Paper

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

75th International Astronautical Congress (IAC)

14-18 October 2024, Milan, Italy

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

Article

End-to-End GNC Solution for Reusable Launch Vehicles

This paper presents an autonomous end-to-end guidance, navigation, and control (GNC) solution for a reusable launcher, addressing the challenges of precision pinpoint landing and reusability. The proposed GNC system integrates advanced onboard trajectory optimization and

H_{\infty}

control to ensure robust performance across re-entry, aerodynamics, and landing phases. This work discusses the GNC design and definition and introduces the strategies adopted both for the guidance and the control design to handle rapidly varying dynamic environments and strict landing requirements. Particular attention is given to design choices in the guidance optimization problem and the control definition for each phase, which were made to enhance the harmonization of the guidance and control (G&C) system. The proposed GNC is integrated in a high-fidelity Functional Engineering Simulator (FES) and its robustness is assessed in a real-world scenario, considering a downrange landing mission of the RETALT1 (RETro propulsion Assisted Landing Technologies Two-Stage-To-Orbit vehicle) rocket.

DOI: https://doi.org/10.3390/aerospace12040339

Jacopo Guadagnini, Deimos Engineering and Systems SLU
Pietro Ghignoni, Deimos Engineering and Systems SLU
Fabio Spada, William E. Boeing Department of Aeronautics & Astronautics, University of Washington
Gabriele De Zaiacomo, Deimos Engineering and Systems SLU
Afonso Botelho, Deimos Engineering and Systems SLU

Conference Paper & presentation

Building an aerodynamic model of a vertical landing reusable launcher based on CFD and wind tunnel experiments in SALTO and CFD4SALTO

The 3rd International Conference on Flight Vehicles, Aerothermodynamics and Re-entry (FAR)
18 – 22 May, 2025, Arcachon, France

Since the Falcon 9 first stage successfully landed the first time in 2015, the perception of reusability of launchers has drastically changed. While it was formerly considered a costly, complex and unprofitable solution, it is now seen as indispensable for the cost effective and environmentally friendly space transport.

In this context, the SALTO (reusable Strategic Space Launcher Technologies & Operations) project, funded by the European Union in the frame of the Horizon Europe programme, is supporting the ESA Themis programme in which a demonstrator for a vertically landing launcher first stage is built. A first version for this demonstrator is propelled by one Prometheus engine with about 120 t thrust and performs simple trajectories. This version is called T1H, where the H stands for the “Hop Test” to be performed. A later version, called the Themis 3 or T3, shall have 3 engines and perform more complex flight trajectories. In SALTO the Hop Test of T1H is performed and technologies for the T3 vehicle are matured. In the ESA FLPP project CFD4SALTO, CFD computations for the generation of the aerodynamic databases of the T3 vehicle are performed and the extrapolation of wind tunnel experiments to flight are investigated.

The task of the DLR in SALTO is, among others, the aerodynamic design of the T3 vehicle. This paper summarizes how the aerodynamic model of the T3 vehicle is set up. First the strategy for the aerodynamic modelling is described. Then, the various flight configurations are defined. Consequently, the strategies and mathematical formulations are elaborated which are applied to reduce the large amount of necessary data points. Afterwards, low-fidelity computations (generated in SALTO) and high-fidelity computations (generated in CFD4SALTO) are compared to show to which extent simplified modelling approaches can be used for the sizing and aerodynamic design, but to also highlight their limitations. Lastly, the paper discusses first wind tunnel experiments performed in the Trisonic Wind Tunnel Cologne (TMK) for the assessment of the aerodynamic performance of the configuration and for the verification of the modelling approaches.

DOI: https://doi.org/10.5281/zenodo.17199286

Ansgar Marwege, German Aerospace Center (DLR e.V.), Germany
Josef Klevanski, German Aerospace Center (DLR e.V.), Germany
Junnai Zhai, German Aerospace Center (DLR e.V.), Germany
Ali Gülhan, German Aerospace Center (DLR e.V.), Germany
Jan Vos, CFS Engineering

Conference Paper & presentation

Scalability of aerodynamics from demonstrator to full flight scale of a vertical landing reusable launcher

The 3rd International Conference on Flight Vehicles, Aerothermodynamics and Re-entry (FAR)
18 – 22 May, 2025, Arcachon, France

In the last decade, the vertical landing of launcher first stages has gained large interest due to the successes of SpaceX with its Falcon 9.

In this context, the SALTO (reusable Strategic Space Launcher Technologies & Operations) project, funded by the European Union in the frame of the Horizon Europe programme, is supporting the ESA Themis programme in which a demonstrator for a vertically landing launcher first stage is built. A first version for this demonstrator is propelled by one Prometheus engine with about 120 t thrust and performs simple trajectories. This version is called T1H, where the H stands for the “Hop Test” to be performed. A later version, called the Themis 3 or T3, shall have 3 engines and perform more complex flight trajectories. In SALTO the Hop Test of T1H is performed and technologies for the T3 vehicle are matured.
DLR has various tasks in the scope of the SALTO project. One of them is the investigation of the scalability of the technologies developed for the demonstrator to full-scale flight vehicles. This paper will focus on the scalability of aerodynamics between vehicle sizes, e.g. if the grid fins are designed for the trajectory of a specific demonstrator – are these grid fins then representative for a full-scale flight vehicle; are the flying qualities of the complete launcher configurations comparable; etc.

For this purpose, two preliminary full-scale launcher configurations have been designed based on the same technologies as used in the SALTO project (mainly the same Prometheus engines and the same assumptions for these). In this context, a DLR in-house toolset named AIOLOS has been used for the preliminary launcher design. The toolset had been developed partly in scope of SALTO, with the aim of considering the launcher reusability already in the first launcher design loop; this has been achieved by expanding the existing launcher design mathematical model for a general reusable or expendable launch vehicle. Based on these full-scale launcher configurations, in this paper, the aerodynamic similarity parameters, the aerodynamic design, and the aerodynamic modelling approaches are compared between the full-scale launcher configurations and the T3 demonstrator.

DOI: https://doi.org/10.5281/zenodo.17200016

Ansgar Marwege, German Aerospace Center (DLR e.V.), Germany
Pawel Goldyn, 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

Conference Paper & presentation

Flight dynamics evaluation for the T3 suborbital flight test

The 3rd International Conference on Flight Vehicles, Aerothermodynamics and Re-entry (FAR)
18 – 22 May, 2025, Arcachon, France

Almost 10 years after the first successful landing of a Falcon 9 booster, reusability of first stages is still a feature that only SpaceX has been capable to master. Nevertheless, reusability is now part of the baseline design of several launch system currently under development, in the US and China. In this context, the SALTO project, funded by the European Commission and coordinated by ArianeGroup (AGS), aims to raise the maturity level of the first European reusable rocket technology.On one side SALTO will perform, for the first time in Europe, hop-flight tests of a small-scale reusable rocket first-stage demonstrator – named the T1H – to validate the landing phase. In parallel, key technologies will be developed to be integrated in the next suborbital flight vehicle – named the T3. In particular, the T3 will be a large-scale demonstrator that will fly at very high-altitude in the atmosphere and perform all the most relevant maneuvers that are needed to return and recover the first stage of a launcher. During the test mission, it will fully control its attitude making use of grid fins and thrust vector control.Deimos’ contribution to SALTO includes support to the aerodynamic design of the T3 taking the responsibility of the flight qualities analysis and of the control laws assessment for the suborbital test mission. The trimmability, stability and controllability of the vehicle is evaluated during the full flight envelope to support several iterations of the aerodynamic design. In addition, the feasibility of the suborbital mission is studied in detail and the trajectory optimized to increase the representativity of the suborbital flight test with respect to dynamic conditions that a reusable booster will have to face during the return path. Finally, Deimos will also continue the development of state-of-the-art control laws initially developed in the RETALT project and adapted to the T3 scenario, that are being tailored to the suborbital mission and will be tested up to TRL 5.Funded by the European Union under the grant agreement ID 101082007. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Health and Digital Executive Agency. Neither the European Union nor the granting authority can be held responsible for them.

DOI: https://doi.org/10.5281/zenodo.17200107

J. Gutiérrez Briceño, Deimos Engineering and Systems S.L.U.
G. Medicil, Deimos Engineering and Systems S.L.U.
A. Princil, Deimos Engineering and Systems S.L.U.
G. De Zaiacomo, Deimos Engineering and Systems S.L.U.

Conference Paper & presentation

Analysis of unsteady pressure loads on the Themis T3 vehicle in unpropelled backward flight

The 3rd International Conference on Flight Vehicles, Aerothermodynamics and Re-entry (FAR)
18 – 22 May, 2025, Arcachon, France

The commercial success of the SpaceX Falcon 9 rocket has proven that reusable space launch systems are viable concepts for increasing the efficiency and reducing the cost to access space. Even though this system has been operational since 2015, no other company from the sector of space transportation has yet managed to successfully land the first stage of a rocket, neither in Europe, Asia or the US. In order to facilitate the development of a reusable launcher in Europe, the EU has financed several programs and initiatives to develop Vertical Take-off Vertical Landing (VTVL) capabilities. One of these is the Horizon Europe project SALTO (reusable Strategic Launcher Technologies and Operations) with support from ESA’s Themis program. The goal is to design a rocket prototype to deliver up to 2000 kg into low Earth orbit. Themis uses the Prometheus Methane-LOx engine and is designed for reusability with a landing accuracy of 20 × 20 meters. During the project SALTO, several hop tests are anticipated. This current study focuses on the aspect of unsteady pressure loads on different parts of a reference configuration for a future demonstrator, also known as the T3 vehicle. In this work we will use the DLR TAU code together with a scale-resolving detached-eddy simulation (DES) turbulence model to resolve vortex shedding and the impingement of vortices on different parts of the vehicle at two flight conditions. The results show the spatial distribution and amplitude of pressure fluctuations on the vehicle surface and help to identify the regions of highest loads. By using methods from signal analysis, the study also provides frequency spectra of the unsteady pressure loads that could serve as an input for structural analysis. This paper will also investigate the sensitivity of predicted unsteady pressure loads towards mesh refinement.

DOI: https://doi.org/10.5281/zenodo.17200246

Tim Horchler, German Aerospace Center (DLR e.V.), Germany
Mariasole Laureti, German Aerospace Center (DLR e.V.), Germany

Conference Paper & presentation

Aerothermal analysis of Themis T3: influence of nozzle cluster geometry on the base heating and heat loads on the grid fins

The 3rd International Conference on Flight Vehicles, Aerothermodynamics and Re-entry (FAR)
18 – 22 May, 2025, Arcachon, France

The Horizon Europe project SALTO (reusable Strategic Space Launcher Technologies & Operations) supports ESA’s Themis program by testing key technologies for reusable launchers. In this framework, aerothermal CFD (Computational Fluid Dynamic) analyses have been performed to assess the heat loads acting on the surface of Themis T3, a reference configuration for a future demonstrator, during its entire flight trajectory. This paper shows representative flow field solutions and heating patterns for critical phases of the ascent and re-entry flight with a focus on the base area and aerodynamic control surfaces. The impact of nozzle cluster geometry and gas generator exhaust, used to feed the turbopump and subsequently injected in dedicated nozzles, on the base heating has also been evaluated.

DOI: https://doi.org/10.5281/zenodo.17200335

M. Laureti, German Aerospace Center (DLR e.V.), Germany
S. Karl, German Aerospace Center (DLR e.V.), Germany

Conference Paper

Development and manufacturing of a landing leg system for reusable launchers T(hemis)3 in the SALTO project

The EU decided to maintain its own independent access to space. To foster the European industry competitiveness, the cost of the European launch systems needs to be reduced and flexibility needs to be improved. The reuSable strAtegic space Launcher Technologies & Operations (SALTO) European Union (EU) project aims at investigating launch system reusability technologies for a Vertical Take-off Vertical Landing (VTVL) launcher configuration. Within this context, MT Aerospace (MTA) develops a landing leg system for the T(HEMIS)3 launcher. The Themis programme is an ongoing European Space Agency (ESA) programme that is developing a prototype reusable rocket. Previous gained knowledge from the project RETALT (Retro Propulsion Assisted Landing) is transferred to a full-scale demonstrator, which is manufactured and finally tested. In this paper a development logic is presented, which considers the following topics:

Requirement screening
Assessment of landing leg concepts
Design and analysing components of the landing leg
Manufacturing of the landing leg
Deployment testing of the landing leg

Christoph Thies, MT Aerospace
Peter Ortmann, MT Aerospace
Carl S Modén
Thomas Zenker

Conference Paper

76th International Astronautical Congress 2025,
29 September – 3 October, 2025, Sidney, Australia

Development and Test Results of an additively printed 240N Class Monopropellant Thrusters

As of today, monopropellant thrusters in the thrust range between 100N and 500N are used for launcher Roll and Attitude Control Systems (RACS), exploration vehicles and for deorbit purposes of larger LEO satellites. Current developments aim at lowering the manufacturing cost by using advanced manufacturing technologies like 3D printing and the need to replace classical toxic Hydrazine by more benign, so-called green solutions. The actual paper presents the development work that was done on a 240N thruster class family that can operate either with classical hydrazine as propellant (performed under an ESA GSTP funding) or with Hydrogen Peroxide as propellant (performed Horizon Europe funding in the frame of SALTO project). Based on existing heritage designs a 240N class thruster was designed in a fully printed version, optimized for easy manufacturing and structural robustness and then hot fire tested.

Ulrich Gotzig, ArianeGroup GmbH Im Langen Grund, 74239 Lampoldshausen, Germany
Malte Wurdaka, ArianeGroup GmbH Im Langen Grund, 74239 Lampoldshausen, Germany
Nicholas Harmansaa, ArianeGroup GmbH Im Langen Grund, 74239 Lampoldshausen, Germany
Michael Funka, ArianeGroup GmbH Im Langen Grund, 74239 Lampoldshausen, Germany

Papers & Publications