Reusable Launch Vehicle Research Articles

Unsteady investigation on parallel separation for spiked two-stage reusable launch vehicle

Two stage to orbit vehicles can reduce weight and improve propulsion efficiency, reducing launch cycle costs. For the safety of two-stage parallel separation, a spiked Two-Stage-To-Orbit (TSTO) configuration for parallel separation was proposed, which is consisted of a waverider liked booster and a wing-body configuration. An aerospike was placed at the head of the second stage. The unsteady simulation of the TSTO interstage separation at Mach 6 was investigated using the self-developed code, CMA. The pressure contours, pitch angle and displacement variation of the two models were compared. Under the interference of the aerospike, the flow field of the blunt body exhibited significant asymmetry at the angle of attack. The oblique shock wave on the leeward side was weaker than that on the windward side, and the area affected by the shock wave on the windward side gradually moved toward the stagnation point as the angle of attack increased, thereby improving the safety of the separation process of the two stages that originally collided by changing the flow field structure. In addition, the aerospike reduces the aerodynamic interference between the two stages without changing the aerodynamic shape of the aircraft, thereby reducing the drag.

Identification of aerothermal heating for thermal protection systems taking into account the thermal resistance between layers

In this paper the aerothermal heating of a reusable launch vehicle is reconstructed on the basis of temperature measurements taken in the thermal protection system of this vehicle. The discussed integrated thermal protection system is composed of three layers. Mathematical model, describing the problem, takes into account the dependence on temperature of the material parameters as well as the thermal resistances occurring in the contact zones of the layers, which is a novelty in the proposed approach. For solving the direct problem, the implicit scheme of the finite difference method is applied. Next, by using the solution of the direct problem, the Tikhonov functional is created, which describes the error of the current approximate solution. Whereas for determining the solution of the inverse problem the Levenberg-Marquardt method, modified and adapted to the Tikhonov functional, is used. The paper presents the mathematical model of the problem and the method of solution together with the selected examples illustrating its exactness and stability. In order to better examination of the solution method some various values of parameters are taken in the demonstrated examples.

Direct-Homogenization-Based Plate Models of Integrated Thermal Protection System for Reusable Launch Vehicles

Integrated thermal protection systems of reusable launch vehicles (RLVs) can have a corrugated core sandwich structure and experience location-dependent thickness-wise temperature gradient. The sandwich structure can be optimized depending on the location on RLV using finite element method simulations of RLV components. However, such analysis can be computationally challenging due to the disparate length scales between the RLV components and features of the sandwich structure. Two different equivalent plate models based on first-order shear and normal deformation theory, and first-order shear and second-order normal deformation theory (FSSNDT) have been utilized in this work to address this drawback. A direct homogenization technique involving unit cell and cantilever beam analysis has been developed to calibrate the equivalent plate properties for different thickness-wise temperature variations. The accuracy of the plate models has been evaluated by comparing their responses with a full-scale model for different thickness-wise temperature gradients and a uniform pressure. The comparisons clearly indicate that the FSSNDT-based plate model calibrated via direct homogenization captures both the displacements and strains in the in-plane and transverse directions accurately, and can be used to perform RLV component analysis efficiently to obtain location-specific optimal design of corrugated core sandwich structures.

A reconstructed approach for online prediction of transient heat flux and interior temperature distribution in thermal protect system

Thermal protect system (TPS) is a crucial part of spacecraft to shield them from the aerodynamic heating during the atmospheric entry/re-entry. In this paper, the aerodynamic heating on the surface of a reusable launch vehicle is predicted to achieve rational design of the TPS. The conduction-radiation heat transfer in the TPS that was regard as a kind of index graded medium, was computed using finite volume method and discrete ordinate method. The extended Kalman filtering coupled with Rauch-Tung-Striebel smoother is introduced for calculating the inverse problem to obtain the time-variant heat flux and interior temperature fields in TPS. The impact of the structure parameters and future measurement temperature information on the lag and stability of retrieval results is investigated. The actual heat flux generated at NASA Langley Research Center for the Reusable Launch Vehicle is employed for examining the effectiveness and dependability of the proposed approach. The numerical results demonstrate the present approach can realize precise and on-line prediction of the time-variant heat flux and interior temperature fields in TPS.

Analysis of the development of reusable launch vehicle technology

Nowadays, with the development of the space technology and the maturity of traditional launch vehicle technology, there are sufficient foundations for the research of higher-level space vehicles. As space vehicles gradually enter the commercial market, the demand for better cost control and higher carry capacity has been put forward. The recovery and reuse of space vehicles, especially launch vehicle, often means higher resource utilization and effective cost control, which has unprecedented advantages in business mode. Many countries and organizations have shown concern about the reusable vehicles. In order to facilitate the further research of reusable rocket technology, this article summaries the research and developments of reusable vehicles over the years and sorts out the overall scheme and key technologies of it. In particular, in view of the successful case of Falcon 9, this article analyses the commercialization experience of SpaceX reusable rockets and its business model. This article may offer a reference for the reusable rocket technology development.

Mission Profile Analysis of Point-to-Point Rocket Cargo Transportation System Using Trajectory Optimization

This paper proposes new concepts for the point-to-point rocket cargo transportation system (RCTS). The RCTS is a transportation system that can deliver cargo anywhere on Earth in an hour using reusable launch vehicle technologies. As a fundamental study of global transportation on Earth, we especially address the mission profiles for short-range transportation within hundreds of kilometers using small rocket engines, which are intended for logistics transportation within neighboring countries or domestic transportation in a country. Two mission profiles of the RCTS are introduced, and the flight phases of each concept are explained in detail. The trajectory optimization problem of the RCTS is formulated based on the mission profiles, incorporating the flight constraints, boundary conditions, and an objective function that aims to maximize the payload ratio. The explicit-guidance is employed during the landing burn phase to enhance the convergence of the optimization problem by expanding the feasible region. The coevolutionary augmented Lagrangian method, one of the evolutionary algorithms, is utilized to obtain the solution for the trajectory optimization problem. The optimal trajectory and state variables are presented through numerical simulations. Additionally, parametric studies are performed to determine the payload mass trend of the RCTS. The trajectory optimization results are summarized to provide an analysis and comparison of the proposed mission profiles.

Adaptive output feedback attitude control for reusable launch vehicle with input constraints and actuator faults

This paper considers an adaptive output feedback fault tolerant control (FTC) for a reusable launch vehicle (RLV) during reentry phase for which four grid fins are used as actuators. Based on a prescribed tracking performance and an auxiliary system to deal with the input constraints, the proposed adaptive controller can compensate for the effect of uncertainties, external and internal disturbances, input constraints and actuator faults. It is shown that with the proposed scheme, the system tracking performance can be guaranteed even in the presence multiple actuator faults. The influence of the input constraints on the tracking performance is also investigated. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

Commissioning and optimal load dispatch for supplying base and peak loads from Satellite Solar Power Station (SSPS) Using Microwave Wireless Power Transfer (MWPT)

Solar power on Earth is characterized by its intermittent nature, limiting its practical application to peak loads only. However, this limitation can be overcome by implementing a concept known as Satellite Solar Power Station (SSPS), which involves deploying solar panels in space. Nevertheless, this approach poses various challenges that need to be addressed. One of the primary obstacles lies in determining the feasibility of this plan. This research emphasizes the importance of exploring economically viable methods for establishing SSPS in space, utilizing a Reusable Launch Vehicle and Hohmann’s Transfer technique. To support these proposals, optimization techniques involving multi-stage impulsive maneuvers are employed. Moreover, a comprehensive load dispatch algorithm is mathematically derived and developed to adapt to the changing demands on Earth, achieving a balance between load requirements and antenna size. In addition, discussions are conducted regarding the potential implementation of frequency reconfigurable Microwave systems for future applications. The overall objective of this study revolves around the future deployment and efficient load dispatch from SSPS to meet the energy demands of base loads on Earth, thereby making solar power a viable option.

Effects of Value-Belief-Norm Theory, ESG, and AI on Space Tourist Behavior for Sustainability With Three Types of Space Tourism

Since reusable launch vehicles have revolutionized access to space, space tourism has received enormous policy and research attention. However, such growth is occurring within a wider context of concerns over climate change, emissions, and space debris. Although the space industries have enormous environmental impacts, few studies have been undertaken on the sustainability of space tourism. Therefore, we aim to create and assess an extended value-beliefs-norms theory with environmental, social, and governance (ESG) factors, trust in artificial intelligence (AI), and the benefits of AI, in comparing three types of space tourism (Earth, suborbital, and orbital). To achieve the goals, multi-method analyses of 1,000 respondents were applied, including partial least squares-structural equation modeling, multi-group analysis, fuzzy-set Qualitative Comparative Analysis, and deep learning. Results revealed that the extended value-belief-norm model well explains space tourist behavior, ESG also has significant roles on the research model, and the three types have unique characteristics.

Analytical Sensitivity based Guidance Algorithm for Reusable Launch Vehicles

The present study is aimed at the development of an accurate and robust reentry guidance strategy for Reusable Launch Vehicles (RLVs), based on onboard trajectory planning and by using the concept of analytical sensitivities. The onboard planning algorithm generates a feasible trajectory from any reentry interface to specific target location, while satisfying all the path constraints, prior to the start of the reentry. For this purpose, the optimal control problem of reentry guidance is converted into an equivalent targeting problem in Nonlinear Programming and a simple solution methodology is devised to generate the three-dimensional trajectory. The profile tracking algorithm is developed based on the well known Linear Quadratic Regulator technique. In this strategy, equations of motion are described in polar coordinates and a direct analytical method for computation of sensitivity matrix elements is used, which ensures better mission planning and faster convergence. An additional feature of the proposed algorithm is the inclusion of an integral term in control law, which tracks the trajectory without a need for instantaneous bank reversals, even with a dispersed environment. The performance results establish adequacy and usefulness of the algorithm.

Aero-Thermal Analysis of the Critical Factors in a Winged Reusable Launch Vehicle for Safer Re-Entry

This paper presents a brief review of the critical factors and phenomena involved in the aero-thermal analysis of a winged reusable launch vehicle. The heat flux evaluation for the re-entry phase is assessed based on the suitability of the available simulation techniques under diverse conditions. This is followed by a short description of the physics involved in each of the factors, their corresponding effects on the main objective and the usual and possible future strategies to deal with them. Finally, the ultimate thermal management of the vehicle surface is discussed based on the literature reviews and a comparative study is depicted showing the benefits over previous ideas. This work can be of use for further research on low wing loading effect to validate the reduction in heat flux and hence the aero-thermal loads thereby ensuring a safer and an affordable atmospheric re-entry for future space explorers.

Parameter Optimization with Chebyshev Polynomials for Trajectory Design of A RLV

A trajectory optimal control problem is converted to a parameter optimization problem by approximating the states and control using piecewise Chebyshev polynomials. The Chebyshev points which control the polynomial fit is used to match the dynamics at the nodal points. Midpoint strategy significantly reduced the number of parameters to be optimized without having to sacrifice on accuracy. The resultant non- linear programming problem is solved using sequential quadratic programming method. Ascent phase trajectory optimization of a reusable launch vehicle having typical path and terminal constraints is taken as a test case.

Validation of Paras3d Rans Pressure Data with Flight Results Over a Wing-body Rlv Configuration at Supersonic High Angle of Attack Conditions

Winged Reusable Launch Vehicle - Technology Demonstrator (RLV-TD) was successfully flight tested by Indian Space Research Organisation (ISRO). One of the main objectives of this Hypersonic Experiment (HEX) mission is to validate the aerodynamic design and ground based aerodynamic data generation procedure. In this paper, comparison of flight data and CFD estimated pressure coefficient (Cp) over fuselage, wing, vertical tail and rudder are presented at supersonic Mach number and high angle of attack conditions. PARAS3D RANS solver is able to capture the trends as measured in flight. In general, PARAS3D CFD over predicted the compression on windward side and under predicted leeward expansion as compared to flight measurement. In general, CFD predicts Cp close to flight measured value, except over a port in the vertical tail.

Feasible options for point-to-point passenger transport with rocket propelled reusable launch vehicles

For the first time in spaceflight history the flight of a fully reusable launch system with rocket propulsion appears possible within the next couple of years. Apart from the implications for the orbital launch market, a fully reusable system could also enable an entirely new class of commercial point-to-point transport on Earth. Rocket propelled point-to-point systems promise the ability to transport passengers or cargo to any suitable landing site on Earth with extremely short travel times (typically less than 90 min). In this study the primary focus is on DLR-SART's SpaceLiner 7 vehicle concept with an initial comparison to Starship, currently being developed by SpaceX.The trajectories are identified using multi-objective optimization with evolutionary algorithms. These allow the identification of a solution space with regard to multiple objectives, in this case minimal overflight of populated areas and minimal peak heat flux, while still respecting other constraints (e.g. structural loads). The population disturbance is computed by using a global population density database and integrating the number of people along the flight track. Ideally, the solution space consists of a pareto-front which correlates to the most optimal solutions possible for all objectives.The mission analysis identifies various feasible trajectories around the world. Primarily, these routes are going along less populated areas such as the oceans and the polar regions. Especially the latter enable large longitudinal changes during the flight and consequently connecting distant places on Earth. The critical routes are large longitudinal crossings around the equator where land masses must be overflown. These shall be reconsidered and/or improved in the future.Comparing SpaceLiner to Starship, it is found that the mission profiles vary significantly. While SpaceLiner uses its high lift-to-drag ratio in the higher atmosphere to manoeuvre around large land masses, Starship can only follow the direct route. In contrast, Starship flies higher into space and thereby might avoid having large population disturbances on ground. Only the re-entry and landing are critical as it does not have significant cross range capability. As a design option for the next iteration of the SpaceLiner development, SpaceLiner 8, it is planned to assess the possibility of using a smaller wing to follow a similar coast through space like Starship and have a steep re-entry at the end of the flight instead of a prolonged glide.

Aerodynamic Interference Reduction Using Aerospike for Two-Stage Reusable Launch Vehicle

The effects of a spike on the aerodynamic interference reduction for a multibody configuration were investigated numerically. A two-stage-to-orbit (TSTO) vehicle was selected as a classic multibody configuration. A spike was placed on the nose of the orbiter to change the position and shape of the shock wave. The peak pressure and peak heat flux on the booster upper surface were reduced by 39.5% and 21.5%, respectively, after the spike was installed. The peak pressure and peak heat flux on the orbiter nose were reduced by 78.2% and 28.4%, respectively. The total drag coefficient of the whole model was reduced by 27.3%. The results show that a spike is able to reduce the shock–shock interference and the shock wave–boundary layer interference (SWBLI) between two stages without changing the aerodynamic configuration of the aircraft.

A Numerical Approach to Optimize the Design of a Pintle Injector for LOX/GCH4 Liquid-Propellant Rocket Engine

This study presents an optimal design approach of a pintle injector for a deep throttlable liquid-propellant rocket engine (LPRE). Even though the pintle injector is used in rocket engines, it has become more important since reusable launch vehicles (RLVs) recently became a trend due to their economic and environmental benefits. However, since many variables must be determined to design a pintle injector, optimizing the pintle injector design is complicated. For this, we design a pintle injector to optimize the performance parameters; the spray angle, vaporization distance, and Sauter mean diameter (SMD). To confirm the approach, we design a pintle injector using an optimization method based on convex quadratic programming (CQP) for a 1000 N thrust and a throttle ability of 5 to 1 LPRE with liquid oxygen and gaseous methane. Then, we verify the performance using a numerical simulation. Through this work, we check the effectiveness of the optimization method for a pintle injector design.

Structural efficiency evaluation of innovative reusable launch vehicles

This work is focused on evaluating the structural design of the innovative reusable micro launcher MESO, originated from the RRTB, a funded project by EU. The structural efficiency of MESO is evaluated in association with its mass budget, which is based on project’s early adopted requirements. In this particular design loop, the reusability concept is intergraded by implementing the fail-safe design approach, considering the exclusive use of high TRL aluminum alloys. The main objective of this work is achieved by developing a global Finite Element Model (FEM), comprising a set of sub-models, which represent the primary structure, the secondary structures, the equipment and their interfaces as well.The paper proceeds with the description of the modelling approach regarding mesh development and the connections created between the sub-models for assembling the integrated Global FEM of the launcher. The first iteration of the load analysis loop resulted in the extraction of the Design Limit Loads (DLL). The DLL investigated in both ground and flight cases, which comprise the most severe combination of quasi-static loads. The FEM is verified and subjected to various types of preliminary structural analysis, taking into consideration the required ECSS design and safety factors for static strength and stability assessment.The analyses results indicated the order of magnitude and the location of all weak areas of the launcher. Subsequently a preliminary sizing procedure is performed in order to prevent all failure modes according to the structural design requirements. The conclusions derived from the structural analysis of the first design loop influence the design modifications to be considered for the next design loop, where the same steps are going to be followed until the structural design requirements are satisfied once again.

Effect of passive strut angle on the vortical structures and mixing characteristics of scramjet combustor

Scramjet is considered as the future of high-speed transportation and reusable launch vehicle for satellite placement. However, the combustion of fuel at supersonic speeds is a challenge. Since combustion takes place at high velocities, analyzing the mixing of air and fuel in the engine is important for enhancing performance. The current study focuses on two passive struts that are placed at a short distance downstream of the fuel injection strut. Diverging angles of these passive struts are varied to assess the effect of the mixing and corresponding acoustic behavior. The computational study is conducted using an improved delayed detached-eddy simulation turbulence model. The single strut scramjet configuration is taken as a benchmark to compare it with different strut configurations. The mixing efficiency is highly affected by the divergent angle of the passive strut. Mixing performance enhances as the back-pressure increases due to the passive strut. If the back-pressure becomes too high due to the divergence of the passive strut angle, then the unstart phenomenon is observed. Pressure loss is observed to decrease with a decrease in the divergence angle of the passive strut. As the divergence angle of the passive strut configuration increases, low-frequency vortices are generated. The modal analysis shows the low-frequency modes responsible for the enhanced mixing performance. Overall sound pressure level increases with an increase in the divergence angle of the passive strut.

Full-scale simulations of ‘In-Air Capturing’ return mode for winged reusable launch vehicles

The recent success of reusable launchers has become a driving force for sustainable launch technologies. An innovative approach proposed by DLR, involves winged rocket stages captured mid air and towed back to the launch site by an aircraft. This recovery concept known as ‘In-Air Capturing (IAC)’, shows potential for substantial cost reduction, when compared to existing return modes. In the light of the Horizon 2020 project FALCon, full-scale simulations and sub-scale flight testing were carried out for further development of the technology. The paper summarizes the full-scale studies performed within FALCon. The full-scale test cases are introduced and the simulation framework for analysis of trajectories is presented. Then, the IAC maneuver is analyzed through trajectory simulations. Major external disturbances coming from the wake of the aircraft and flexibility of the rope connecting the rocket stage to the aircraft (after capture) are also addressed.

Multidisciplinary design and optimization of winged architectures for reusable launch vehicles

Partially reusable launch vehicle design has raised a great interest in order to minimize the costs of space transportation by recovering and refurbishing the first stage. Several configurations such as toss-back architectures are now operational. These concepts require additional rocket propellant in order to carry the boost-back and landing maneuvers, that induce several losses in terms of payload mass performance for the ascent mission. In order to limit these losses, this paper focuses on the design of two types of architectures to carry out the return-to-launch-site mission. The first, named glide-back, uses the main propulsion system of the first stage to perform a boost-back burn and returns to the landing site by a gliding mode using additional lifting surfaces. The second, named, fly-back, performs the return-to-launch-site mission using several air-breathing engines located in the nose of the first stage combined with lifting surfaces. In this paper, the design of a reusability kit, allowing to provide the first stage with both expendable and reusable capabilities, is investigated. This kit is composed of the lifting surfaces, the nose including the air-breathing propulsive system (for fly-back configuration), landing gears and additional avionics. This paper addresses the design of such reusability kits and presents the mission specifications, the design process relying on Multidisciplinary Design Optimization techniques, the vehicle performance and the optimal trajectories. Different analyses (aero-propulsive, optimal control, operational considerations, etc.) are detailed and trade-offs between the studied configurations are assessed.