Effects Of The Rotational Vehicle Dynamics On The Ascent Flight Trajectory Of The Spaceliner Concept

During the preliminary design of space transportation systems the vehicle dynamics are commonly reduced to a point-mass model for definition of the flight trajectory. While this approach effectively reduces the number of model parameters in the design process, it neglects the rotational dynamics of the vessel completely. Since the rotational degrees of freedom (DOF) have a significant influence on the vehicle's controllability, a sole analysis of the translational dynamics is insufficient to assess the general feasibility of the concept. This study investigates the ascent flight trajectory of the SpaceLiner vehicle, a concept for a hypersonic suborbital space plane, based on a newly developed 6-DOF flight dynamics simulation to determine the influence of the rotational dynamics on the vehicle's controllability and performance. The first part of this paper will focus on the developed vehicle model which features a transient inertia model as well as an algorithmic-designed flight control system. The second part will present several simulations of nominal and off-nominal ascent trajectories. Based on the results it will be shown that SpaceLiner's thrust vector control system is sufficiently dimensioned for the investigated mission scenarios, while the vehicle performance is only slightly influenced by the rotational dynamics

Ultra-Fast Passenger Transport Options Enabled by Reusable Launch Vehicles

The latest architecture of the SpaceLiner 7 configuration is described including major geometrical and mass data. Some elements of the next iteration step, the SpaceLiner 8, are highlighted, having its focus on most recent analyses, partially not previously published. A passenger rescue capsule is intended to be used in case of extreme emergencies. The design of the cabin and the ejection system is refined in a systems engineering approach to obtain a feasible and viable solution. Multibody simulations of the emergency capsule separation are performed in a wide range of flight conditions and technical challenges are identified. The adaptation of the large unmanned booster stage, currently under way might include a new wing lay-out capable of swiveling-out in the lower speed regime. Advantages and technical challenges of this approach are addressed in the paper. Simulated 6DOF ascent trajectories analyze behavior of the Thrust Vector Control system in case of wind and gusts interacting with the winged configuration in nominal and off-nominal conditions

Aerothermal characterization of the CALLISTO vehicle during descent

Aerothermal loads are a design driving factor during launcher development as the thermal loads directly in- fluence TPS design and trajectory. Recent developments in reusable launch vehicles (RLV) (e.g. SpaceX, Blue Origin) have added the dimension of refurbishment to the challenges the thermal design must con- sider. For disposable launchers the heat flux due to base heating during ascent needs to be considered for aft thermal protections system (TPS) and structural design. With the current European long term strategy[1] moving towards a reusable first stage - aerothermal loads may significantly change. The CAL- LISTO vehicle is a flight demonstrator for future reusable launcher stages and their technologies. The program involves three countries and their space organizations: CNES for France, DLR for Germany and JAXA for Japan. The first tests will be conducted in 2024 from CSG, Europe’s Spaceport. The challenge is to develop, all along the project, the skills of the partners. This know-how includes products and vehicle design, ground segment set up, and post-flight operations for vehicle recovery then reuse [2–5]. For the CALLISTO vehicle the highest heat fluxes are mainly due to heating from hot exhaust gases and heated air in proximity of the aft bay and on the exposed structures like legs and fins. The development of the plume extension is different for the considered re-entry, when compared to Falcon 9, or the studies presented in [6–8]. As shown by Dumont et al.[9] the plume remains relatively concentrated at the aft end of the vehi- cle due to high atmospheric pressure and only very low fractions of actual exhaust gas species enclosing the vehicle. In the current study we conducted computational fluid dynamics (CFD) studies in order to determine the aerothermal loads on the vehicle during descent through the landing approach corridor for both phase B and phase C aeroshapes. The database development for vehicle phase B and phase C are described in detail and analyzed for some of the most prominent interfaces. The final phase C database presented allows interpolation of interface heatfluxes for the entire flight domain (M, ρ) at varying angle of attack (between 180 deg and 160 deg). Further the sensitivity of the plume-vehicle interaction to angle of attack, chemistry, thrust vector deflection and engine throttling are investigated for a critical Mach number indicating further area of improvement for future databases

Aerothermal analysis of plume interaction with deployed landing legs of the CALLISTO vehicle

The current European long term strategy aims at moving towards reusable launch vehicles (RLV) for the first stages of launchers. In accordance with this strategy the German Aerospace Center (DLR) has entered into a collaboration with the Japan Aerospace Exploration Agency (JAXA) and the French Space Agency (CNES) for the development of RLV relevant technologies. A part of this collaboration is a vertical take off and vertical landing (VTVL) reusable subscale launcher first stage demonstrator - the Cooperative Action Leading to Launcher Innovation in Stage Toss back Operations (CALLISTO). The mission of the CALLISTO vehicle is to return to the launch pad using retro propulsion and an Approach and Landing System (ALS) with extendable landing legs. This development leads to additional aerothermal design questions compared to traditional launchers. In the case of CALLISTO the highest heat fluxes are caused by heating from hot exhaust gases of the aft bay section. This especially affects the unfolded ALS during the final phase of the landing approach. The arising heat fluxes, therefore, influence the structural design and the thermal protection system (TPS) of the ALS. In this study we conduct computational fluid dynamics (CFD) investigations using Reynolds averaged Navier Stokes (RANS) methods of the aerothermal loads on the ALS during the landing phase. We use the Spalart-Allmaras turbulence model and frozen chemistry for the simulations. We analyse the flow field as well as the surface distributions. We investigate the necessity of simulations including the plume for these analyses. We use analyses of the flow fields as well as the surface distributions to investigate the influence of angle of attack, angle of roll, atmospheric conditions, flight speed and thrust level

Wind Tunnel Experiments of the CALLISTO VTVL Launcher in the TMK and HST Wind Tunnels

CALLISTO is a demonstrator for a first stage of a reusable vertical take-off, vertical landing rocket and is developed and build within a collaboration of DLR, CNES and JAXA [1]. DLR is leading the aero science team [2] and is in charge of the aerodynamic and aerothermodynamic characterization of the vehicle. Within this task, experimental work has been carried out at two different wind tunnels on two different models in order to determine the aerodynamic coefficients and uncertainties for the AErodynamic Data Base (AEDB) of the vehicle with focus on the descent flight configuration. First data was obtained in the Trisonic Wind Tunnel (TMK) at the DLR Department of Supersonic- and Hypersonic Flow Technologies in Cologne for a 1:35 model in a Mach number range from 0.5 up to 2.0. The second dataset was generated in the transonic wind tunnel (HST) of the DNW in Amsterdam for a 1:10 model in a Mach number range of 0.2 up to 1.3. Within this paper, the data from the two aforementioned facilities is compared with wind tunnel data of a simplified CALLISTO model [3,4,5] and the data [2] generated by numerical simulations. The results showed good agreement between the different facilities and datasets and was used to verify and improve the AEDB, especially in terms of uncertainties

Applying Bayesian Inference to Estimate Uncertainties in the Aerodynamic Database of CALLISTO

The three national space centers DLR, CNES & JAXA have joined their efforts in the project CALLISTO to develop and mature key technologies for future operational Reusable Launch Vehicles (RLVs). The goal of this project is to develop, manufacture and test a reusable Vertical-Takeoff Vertical-Landing (VTVL) first stage demonstrator, which will be operated at the European Spaceport in French Guiana from late 2024. One important aspect in the development of RLVs, but also of aerospace vehicles in general, is the generation of an Aerodynamic Database (AEDB) which characterizes the aerodynamic flying qualities of the vehicle. These databases are commonly aggregated from Computational Fluid Dynamics (CFD) simulations and Wind Tunnel Tests (WTTs) via simple heuristic models. Whereas this classical approach is suitable for the estimation of nominal aerodynamic coefficients, the quantification of uncertainties in this pre-flight data with respect to the final flight behavior is still a difficult task that involves a lot of human expert knowledge and "gut feeling". Particularly for launch vehicles, these uncertainties are however essential to ensure robust guidance and control algorithms, as well as sufficient vehicle performance for a selected mission profile. For CALLISTO, in parallel to a classical approach, a new methodology has now been tested to estimate these uncertainties within the AEDB: To apply Bayesian Inference to predict a probability distribution over the aerodynamic coefficients, conditional on the available test and simulation results and on prior knowledge. This methodology has already been well-established in other data science domains, but for aerospace engineering only very few use-cases are known so far. With this new approach an objectively traceable modelling of the aerodynamic uncertainties should be possible. This paper presents the current development state of the Bayesian aerodynamic uncertainties model of CALLISTO. After problem definition and a short introduction to the underlying dataset, the paper mainly focuses on the used modelling techniques and the applicability of Bayesian methods to the aerodynamic characterization problem. Selected results are shown for Bayesian models and compared against the classical modelling approach, while advantages and disadvantages of the Bayesian methodology are discussed. It is shown that the implemented Bayesian Gaussian process model can infer the typical characteristics of the AEDB from the available datasets, while having comparable prediction qualities as the reference model. Observed differences in the variance and bias characteristics are discussed for both models

CALLISTO: towards reusability of a rocket stage: current status

JAXA, CNES and DLR have decided to cooperate 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 is paving the way for future reusable launch vehicles in Europe and in Japan. During phase B important progress in term of methods and operation philosophy specific to RLV have been made. Amongst other progresses, that will ease the development of future operational VTVL, in the domain of aerodynamic modelling, GNC landing leg deployment but also flight domain definitions are presented. These are concrete results which can at least partly be useful for other RLV projects

Towards a Reusable First Stage Demonstrator: CALLISTO - Technical Progresses & Challenges

In order to investigate the capabilities of a reusable launch system, JAXA, CNES and DLR have jointly initiated the project CALLISTO ("Cooperative Action Leading to Launcher Innovation for Stage Toss-back Operations"). The goal of this cooperation is to launch, recover and reuse a first stage demonstrator to increase the maturity of technologies necessary for future operational reusable launch vehicles (RLV) and to build up know-how on such vehicles under operational and developmental aspects. As the project has now turned into the detailed design phase, significant technical progresses have been made in definition, analysis and testing of systems and subsystems. The CALLISTO vehicle itself constitutes a subscale vertical take-off vertical landing (VTVL) stage with an overall length of 13.5 m and a take-off mass of less than 4 tons, which is propelled by a throttleable LOX/LH2 engine. It is capable to perform up to 10 consecutive flights during the planned flight campaign in French Guiana. Globally, the development effort on this system is equally shared between the three project partners. This paper presents the recent achievements in development of the key technologies for the reusable launch vehicle. While the design of critical subsystems has reached PDR level, detailed analyses and first breadboard tests have been performed successfully. These results are presented and discussed within the perimeter of the CALLISTO development roadmap. Possible technical challenges are indicated and their resolution methods are examined. Finally, the upcoming development steps are described which are foreseen to move forward to the qualification and maiden flight campaign

INVESTIGATION OF THE ASCENT FLIGHT DYNAMICS OF THE SPACELINER CONCEPT AS A NON-SYMMETRIC LAUNCHER CONFIGURATION

Determining the flight dynamic characteristics of a space transportation vehicle in its preliminary design phase is a complex task since a large variety of vehicle parameters need to be estimated. For the SpaceLiner vehicle, a concept of a hypersonic suborbital space plane, such an analysis has now been established. In this study a 6 DOF trajectory simulation has been developed to assess the general feasibility of fulfilling the mission requirements during nominal and off-nominal flight conditions

Investigation of flight dynamics and effects of rotational degrees of freedom on the flight performance of asymmetric space transportation systems based on the SpaceLiner 7 concept

The SpaceLiner 7-3 is a concept for a suborbital spacecraft, which is capable of transporting 50 passengers over ultra-long-haul distances. Since 2005, this concept is has been researched by the German Aerospace Centre (DLR). This study analyzes the flight dynamics of the vehicle during its ascent flight of the reference mission from Australia to Europe. Key point of this study is the development of a flight dynamics simulation of the SpaceLiner, which can determine the evolution of all rotational and translational states of the vehicle. For the flight dynamics simulation of the SpaceLiner, the model definition of the vehicle has been extended from previous studies. Estimations of the vehicle’s moment of inertia are conducted, as well as a draining model of the propellant tanks is determined. Also the aerodynamic database of the SpaceLiner is extended by lateral and dynamic derivatives. In order to determine the control deflections of the thrust vector control during simulation, a flight control model for the SpaceLiner Vehicle is developed. The control design process for this system is automated by the relay auto-tuning method. The flight dynamics model of the SpaceLiner, as well as the corresponding flight control model, is included into a newly developed 6 DOF trajectory simulation, implemented in Simulink. This simulation features numerically robust calculations of the vehicle’s state vector in arbitrary flight conditions. The validity of the implemented simulation is proven in a cross-validation test against the commercial tool ASTOS. Based on the developed flight dynamics simulation, analyses of the flight dynamic characteristics of the SpaceLiner are performed. The aerodynamic stability and trimmability of the vehicle is determined for a nominal ascent flight. The nominal ascent trajectory is also simulated and deviations in respect to a 3 DOF reference trajectory are identified. Furthermore, first analyses of ascent trajectories under wind loads are conducted. Based on the simulation results, the feasibility of the implemented thrust vector control is reviewed