Launcher Performance Research Articles

A comparison between a conventional and augmented rail gun launcher's performance

A comparison between a conventional and augmented rail gun launcher's performance

Multi-disciplinary optimization of the low-thrust orbit raising for the hydroterra Earth Explorer mission

Hydroterra was selected in September 2018 as one of the three candidates for the ESA's Earth Explorer-10 mission. Hydroterra aims at observing and improving the understanding of fundamental processes of daily water cycle, enhancing prediction capability of extreme rainfall and related flooding. To achieve this goal, the mission concept envisages placing a satellite embarking a synthetic aperture radar instrument in geosynchronous orbit. The satellite is designed to be launched with VEGA-C into low Earth orbit and to be transferred to the operational orbit by means of electric propulsion. In this paper, the multidisciplinary optimization process carried out to obtain the baseline electric orbit raising transfer for Hydroterra will be presented. The computed trajectory will meet the mission requirements, including targeting to the operational orbit, the launcher performance model, and the target on-station mass. Additionally, system-level constraints related to the satellite design that have an influence on the ideally optimized trajectory will be derived and considered in the optimization. In particular, the impact of the solar cell degradation on the thrust and specific impulse levels of the thruster due to the passage through the Van-Allen belts, the need to re-charge the batteries before entering the next eclipse, and the agility requirements will be accounted for. The obtained results show that a feasible electric orbit raising trajectory can be successfully obtained for the Hydroterra mission.

Launcher flight control design using robust wind disturbance observation

The development of effective load relief strategies is key to the improvement of launcher flight performance as it enables a joint increase of wind resilience and decrease of mass. This is particularly relevant for reusable launchers, which are aimed at maximising operational availability and payload capacity. Yet, despite various load relief advances in the aeronautics and wind energy sectors, classical feedback-only techniques remain the state-of-practice for launchers. In this article, an improved load relief functionality for reusable vehicles is proposed based on the use of a disturbance observer for on-board wind anticipation and a load relief compensator driven by the estimate of the wind for its amelioration.Two space systems are used to demonstrate the capabilities of the proposed approach. First, it is applied to a 3 degrees-of-freedom nonlinear simulation model of DLR’s EAGLE vertical-flight demonstrator. Then, it is applied to a 6 degrees-of-freedom nonlinear simulation model of a generic lightweight, reusable launch vehicle. For both cases, the results highlight the benefits of using this type of wind-estimation/load-relief compensation schemes. Further, for the second case, which uses thrust vector control and planar fins for ascent and descent attitude control, it is also shown that the use of fins during ascent (which is not common practice), can further improve launcher performance.

Reynolds number influence on the backpressure-induced shock–boundary layer interaction in an asymmetric supersonic expansion flow

In the present study, asymmetric supersonic expansion flow produced by an annular conical supersonic nozzle has been studied under static conditions. To understand the details of Reynolds number influence on the backpressure-induced shock–boundary layer interaction, a computational program has been carried out. Particular attention has been paid to the shock physics and characteristics of shock–shock and shock–boundary layer interaction change in the flow field when applied to engines operating in different ambient pressure environments. The identification of this Reynolds number correlated flow behavior changes is important for low supersonic expansion flow in engines, as it is directly attributed to the limits of off-design capability on launcher performance. The obtained results show that Reynolds number has significant influence on flow pattern at low pressure ratio, PR, conditions. When PR grows from 2.00 to 2.10, the most prominent phenomenon is that the separation point on the upper wall keeps moving downstream while the one on the lower wall keeps still. This special flow pattern results in a gradual transition from a Mach reflection to the regular reflection. However, for results at higher pressure ratios than 2.57, the comparison between the predicted shock patterns at the three ambient conditions shows a close one for these higher PR regimes. This suggests that the Reynolds number effect is going to weaken at a higher Mach number flow regime when the flow Reynolds number increases with an increase of the pressure ratio as well as the expansion flow Mach number.

Uncertainty Analysis and Robust Design for a Hybrid Rocket Upper Stage

An uncertainty analysis is performed for a hybrid rocket engine, and a robust design method is proposed and applied to a liquid-oxygen/paraffin–based fuel hybrid rocket engine that powers the third stage of a Vega-like launcher. An indirect method is used to optimize a mission-specific objective function, which takes into account both the payload mass and the ability of the rocket to reach the required final orbit despite uncertainties. First, a screening of uncertain model parameters is performed using the Morris method. The screening shows that three groups can be distinguished: parameters with negligible or no effect on model outputs, parameters with small linear effect on model outputs, and parameters with large nonlinear effect on model outputs. The robust optimization design process is then carried out by a particle swarm optimization algorithm considering only the uncertainties of the latter group, which includes six parameters. A fractional factorial design of experiment techniques is considered to characterize the robust performance index. Average launcher performance is considered and the best solution is found by means of Box–Behnken’s array. Finally, the identified robust solution is checked against the second group of parameters uncertainties previously neglected in the robust optimization procedure. The scattering of the robust solution is small, and the robustness of the selected optimal solution is confirmed.

Plasma Actuator–Assisted Rocket Nozzle for Improved Launcher Performance

The need to avoid unstable separations and side loads during low-altitude operations imposes a strict limit on the nozzle expansion ratio of launchers propulsion systems. Remarkable performance losses are consequently induced. An innovative concept is here presented that overcomes this limit. Plasma actuators are proposed as a means to stabilize separation in highly overexpanded conventional bell-shaped nozzles. A larger expansion ratio can thus be adopted in boosters and first-stage engines, and their vacuum specific impulse is increased. The concept is here assessed by means of Reynolds-averaged Navier–Stokes simulations. The effects of the plasma actuators are described by average body force and heat source terms. The potentialities of this concept, adaptable to any bell-shaped nozzle, are assessed evaluating the possible payload gain for a representative case. The results show that the proposed concept allows for suitable payload growth and engine flexibility.

Conceptual design of CFETR ECRH equatorial launcher and upper launcher

The Electron Cyclotron Resonance Heating (ECRH) system of China Fusion Engineering Test Reactor (CFETR) is designed to inject 20 MW RF power into the plasma for heating and current drive (H&CD) applications. The ECRH system consists of 20 gyrotrons, the associated power supplies, the transmission lines and one launcher. In order to compare the launcher performance from equatorial and upper ports, two types of launcher are designed in this paper. In equatorial launcher (EL), twenty in-vessel transmission lines are divided into four groups. Every five gaussian beams from in-vessel transmission lines face one fixed focusing mirror and one steering mirror. All gaussian beams are injected into the plasma with optimal toroidal and poloidal angles calculated by C3PO/LUKE code. In upper launcher (UL), twenty-one transmission lines are supposed and divides into three groups. Every seven gaussian beams are injected into one fixed focusing mirrors and all twenty-one beams reflected to one common steering mirror finally. The optical transmission characteristics and the convergence information of gaussian beams are checked and optimized. The EL or UL is installed on the equatorial or upper port with a port-plug modular structure.

Launcher Performance with Reserves

The success probability of a space launch is guaranteed by propellant reserves. The upper-stage reserve represents a direct performance penalty because it reduces the maximum payload mass that can be injected on orbit by the launcher. The usual process consists of successively optimizing the trajectory for nominal conditions, and then assessing the necessary reserves to face the flight uncertainties. This process may yield large reserves when the trajectory is sensitive to the upper-stage features. A simple method is proposed to account for the upper-stage reserve directly within the trajectory optimization process. It results in a less sensitive nominal trajectory and, finally, a better guaranteed performance of the launcher. The method is illustrated on a classical launch trajectory optimization.

Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U

Recently published scenarios for fully non-inductive startup and operation on the National Spherical Torus eXperiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015) show Electron Cyclotron Resonance Heating (ECRH) as an important component in preparing a target plasma for efficient High Harmonic Fast Wave and Neutral Beam heating. The modeling of the propagation and absorption of EC waves in the evolving plasma is required to define the most effective window of operation, and to optimize the launcher geometry for maximal heating and current drive during this window. Here, we extend a previous optimization of O1-mode ECRH on NSTX-U to account for the full time-dependent performance of the ECRH using simulations performed with TRANSP. We find that the evolution of the density profile has a prominent role in the optimization by defining the time window of operation, which in certain cases may be a more important metric to compare launcher performance than the average power absorption. This feature cannot be captured by analysis on static profiles, and should be accounted for when optimizing ECRH on any device that operates near the cutoff density. Additionally, the utility of the electron Bernstein wave (EBW) in driving current and generating closed flux surfaces in the early startup phase has been demonstrated on a number of devices. Using standalone GENRAY simulations, we find that efficient EBW current drive is possible on NSTX-U if the injection angle is shifted below the midplane and aimed towards the top half of the vacuum vessel. However, collisional damping of the EBW is projected to be significant, in some cases accounting for up to 97% of the absorbed EBW power.

Satellite design for demise thermal characterisation in early re-entry for dismantlement mechanisms

Preliminary analyses at ESA have shown that space objects in LEO with masses above 500 kg might already imply an on-ground casualty risk higher than 1E-4 in case of uncontrolled re-entry. Compliance to this casualty risk requirement may be achieved through controlled re-entry, but this solution has a major impact at system level. Sometime it requires a full re-design of the spacecraft and may involve switching to a completely different launcher performance (consequently a significant mission cost impact).This option may be avoided with achievement of compliant ablation (demise) of the spacecraft upon uncontrolled atmospheric re-entry. The so-called Design-for-Demise discipline (D4D) is a highly multidisciplinary approach that can bring significant benefits in the future missions in the medium to long term. (Klinkrad, 2006; Johnson, 2012) [1,2].ESA created in 2012 the “Cleanspace” initiative and team to promote actions on green aspects and debris remediation (ESA Clean Space Team, 2015) [3]. Recently ALTRAN was involved inside THALES ALENIA Space consortium in those ESA activities on S/C D4D techniques and proposed several D4D concepts. This ESA D4D study had the objective to find D4D solutions for the Sentinel-1 study case (around 2 tons). This objective were about to be theoretically achieved.[4].The outcomes of those D4D studies performed in parallel at level of 3 LSI (Large System Integrator) were concluded in early 2016 [4,5] and used mainly ESA Sentinels S/C as study cases. Those studies all demonstrated that S/C dismantlement (controlled and earlier to natural break-up) has a major benefit in reduction of S/C Debris Casualty Area (DCA). Then this technique has to be considered with high priority in a global approach for D4D improvement. (ESA, 2015; CleanSat Workshop presentations, 2015) [6,7].The proposed ALTRAN/NIMESIS study CLEANSAT Building Block 10: Shape Memory Alloys (SMA) Dismantlement Mechanisms has investigated several technological devices and SMA material options for their suitability to be implemented in LEO satellite H/W of main European LSI for dismantlement during atmospheric re-entry.

The Effect of Salt-water Corrosion on Copper Alloy Rail Claddings in a Small Railgun

As the U.S. Navy gets closer to fielding shipboard railguns; there is an increasing concern with how surface corrosion of the rail claddings will affect launcher performance and lifetime. It is intuitive to hypothesize that corrosion on the rail surface will negatively affect both the performance and lifetime since significant surface oxide formation on the rail surface will increase the rail/armature contact resistance and surface pitting will reduce the rail/armature contact area. Negative effects from surface corrosion could include increase arcing contact between the armature and the rails, also known as transition, decreasing the launcher efficiency, muzzle velocity, and enhance the rate of rail erosion. In the experiments discussed here, the University of Texas at Arlington has performed two unique sets of experiments. In the first, 6.35-mm diameter C18150 copper rods were pulsed with high current while immersed in a salt fog environment to study how pulsed currents affect surface corrosion. In the second set of experiments, a 1-m-long railgun was used to evaluate the impact of rail corrosion on the launcher operation. A controlled corrosion process was used to induce damage on rail sections positioned at two locations within the gun, the startup and peak current regions, respectively. The launcher has a peak current of roughly 120 kA and a muzzle energy of 1.8 kJ when 14 g launch packages, fabricated from 6061-T6 aluminum, are used. The rail sections, which have dimensions of 1” $\times4$ ” $\times1$ /8,” are fabricated of C18150 and were corroded using a using potentiostatic polarization to drive oxide formation and growth. Railgun performance was evaluated using the standard measurements of armature current, breech voltage, muzzle voltage, and velocity interpolated through b-dots. The rail sections were characterized at the material surface level prior to and after a shot series using scanning electron microscope imagery and x-ray diffraction. Three different sets of samples were tested and include, baseline samples, i.e., no corrosion, samples corroded with a potentiostatic polarization of −0.1 V saturated calomel reference electrode (SCE) for 20 $\text {k}\cdot \text {s}$ in 3.5% NaCl, and samples corroded with a potentiostatic polarization of −0.2 V SCE for 28.8 $\text {k}\cdot \text {s}$ in 3.5% NaCl. Each set of samples were subjected to a series of five railgun shots with a 10-min rest between each shot. The aim of these experiments was to study the surface corrosion induced by the high ohmic heating and pulsed magnetic fields while immersed in a salt fog. The results of both respective types of experiments will be presented here.

Impact of Corroded Copper Rails on the Performance of a Miniature Electromagnetic Launcher

The U.S. Navy is getting much closer to fielding shipboard railguns. As they get closer, there is increasing concern with how corrosion of the rail surface will affect launcher performance and lifetime, with it intuitively hypothesized that corrosion will negatively affect both. It is anticipated that significant surface-oxide formation on the rail surface will increase the rail/armature contact resistance, and surface pitting/deposition will further affect the rail/armature contact area. There are several negative effects that could arise from surface corrosion on the rails. One includes an increased probability of armature transition occurring that can significantly decrease launcher efficiency and muzzle velocity, and enhance the rate of rail erosion. In the experiments discussed here, the University of Texas at Arlington has performed two sets of experiments aimed at better understanding how corrosion impacts the performance of a 1-m long railgun with muzzle energies of roughly 1.8 kJ (14 g to roughly 450 m/s). In the first experiment, virgin C11000 rails were shot on five times, and after the shots, the rails were segmented and characterized using an optical microscope and X-Ray diffraction. In the second set of experiments, bare C11000 rails were corroded, using a custom salt fog chamber for 96 h, before being shot on five times and then surface characterized in the same manner. The launcher has a peak current of roughly 100 kA, and launch packages fabricated from 6061-T6 aluminum are used. The rail claddings studied have dimensions of 1 in $\times 39.4$ in $\times 1$ /8 in. The railgun performance was evaluated using the standard measurements of armature current and muzzle voltage. The results of both experimental test series will be presented here.

Investigating the velocity envelope of laser-driven micro-flyers for hypervelocity impact experiments

Protection materials are continuously facing higher velocity threats; characterizing their response to these threats is necessary to improve performance. We have previously examined failure of boron carbide and magnesium systems at strain rates of up to 105 per second [12,13]. To study dynamic deformation at higher strain rates closer to the hypervelocity regime, we use micro-flyers to impact target materials. Over the last two decades, pulsed lasers have proven to be effective drivers for micro-flyers when achieving hypervelocity impacts. However, control of the experiment requires good characterization of the flyer behavior [11] and velocities. Here, we explore the velocity regime for a tabletop laser-driven flyer system as a function of laser pulse conditioning (fluence, pulse duration, etc.),and launch package materials. We modify an established model to inform the selection of launch package substrates and configuration in a lens-coupled micro-flyer apparatus. We use Photon Doppler Velocimetry (PDV) to obtain velocity histories of the flyers [10]. Comparisons between flyer data from our launcher system and the model predictions uncover the important parameters controlling launcher performance.

Transverse circular-polarized Bessel beam generation by inward cylindrical aperture distribution.

In this paper the focusing capability of a radiating aperture implementing an inward cylindrical traveling wave tangential electric field distribution directed along a fixed polarization unit vector is investigated. In particular, it is shown that such an aperture distribution generates a non-diffractive Bessel beam whose transverse component (with respect to the normal of the radiating aperture) of the electric field takes the form of a zero-th order Bessel function. As a practical implementation of the theoretical analysis, a circular-polarized Bessel beam launcher, made by a radial parallel plate waveguide loaded with several slot pairs, arranged on a spiral pattern, is designed and optimized. The proposed launcher performance agrees with the theoretical model and exhibits an excellent polarization purity.

R&D activities on RF contacts for the ITER ion cyclotron resonance heating launcher

Embedded RF contacts are integrated within the ITER ICRH launcher to allow assembling, sliding and to lower the thermo-mechanical stress. They have to withstand a peak RF current up to 2.5kA at 55MHz in steady-state conditions, in the vacuum environment of the machine. The contacts have to sustain a temperature up to 250°C during several days in baking operations and have to be reliable during the whole life of the launcher without degradation. The RF contacts are critical components for the launcher performance and intensive R&D is therefore required, since no RF contacts have so far been qualified at these specifications. In order to test and validate the anticipated RF contacts in operational conditions, CEA has prepared a test platform consisting of a steady-state vacuum pumped RF resonator. In collaboration with ITER Organization and the CYCLE consortium (CYclotron CLuster for Europe), an R&D program has been conducted to develop RF contacts that meet the ITER ICRH launcher specifications. A design proposed by CYCLE consortium, using brazed lamellas supported by a spring to improve thermal exchange efficiency while guaranteeing high contact force, was tested successfully in the T-resonator up to 1.7kA during 1200s, but failed for larger current values due to a degradation of the contacts. Details concerning the manufacturing of the brazed contacts on its titanium holder, the RF tests results performed on the resonator and the non-destructive tests analysis of the contacts are given in this paper.

Assessment of the ITER EC Upper Launcher Performance

The 24 MW ITER Electron Cyclotron (EC) Heating and Current Drive (HC) system, operating at 170 GHz, consists of one Equatorial (EL) and four Upper Launchers (UL). The main task of the UL will be the control of Magneto-Hydrodynamic (MHD) activity such as Neoclassical Tearing Modes (NTMs) at the q=3/2 and q=2 surfaces, but it will also be needed for current profile tailoring in advanced scenarios and to assist plasma break-down and L-to H-mode transition. Moreover, it is required to be effective both when ITER will operate at nominal and reduced magnetic field magnitude. Here the performance of the UL is assessed through the study of the full temporal evolution of different scenarios, including the reference ITER 15MA H-mode plasma, a half-field case at 2.65T, and a steady state scenario. The ECCD efficiency has been evaluated for a wide range of injection angles, deriving the optimal angles and the power required for NTMs stabilization, as well as the steering range necessary to reach the rational surfaces during all the phases of the discharge. The steering sensitivity to shifts of the target or aiming errors has been estimated too. The result is an assessment of the UL design requirements to achieve the desired functionalities, which, together with the engineering limits, will be used to drive the optimization and finalization of the UL design.

Effects of Limitation of Nozzle Flow Separation on Launcher Performance

Limitations induced by flow separation at liftoff of launcher core engines can be overcome with the use of a new nozzle concept recently proposed. This device is able to prevent separation in an overexpanded nozzle. Consequently, a lower nozzle-exit pressure is possible at sea level and low altitudes, allowing for engine throttling or for the use of a nozzle with larger nozzle expansion-area ratios. To assess the actual potential of payload growth given by the application of such a device, the ascent trajectory must be evaluated and possibly optimized. A fast and reliable in-house code, based on the optimal-control theory, is used to optimize the ascent trajectory. Results show that the ideal velocity gain can be increased with throttling. However, ascent losses offset this benefit and reduce the actual payload; in any case, the launcher experiences lower dynamical loads and gains flexibility. On the other hand, payload improvements from the increase in the nozzle expansion-area ratio of the core engine may be obtained, depending on how large the penalty of the increased nozzle weight is.

액체로켓 연소기 노즐확장부 제작 및 재료 기술 동향

The combustion chamber and nozzle of a liquid rocket engine should be protected from the high temperature combustion gas generated by the chamber. An upper-stage nozzle extension has a large expansion ratio, therefore, The light-weight refractory materials have been used since the weight impact on the launcher performance is crucial. Gas film cooling method was used before, but was not applicable nowadays. Ablative cooling method and radiative cooling method with niobium alloy, Ni-based superalloy and ceramic based composite have been used to this day.

A12 ローラ式バドミントンマシンの発射性能に関する研究(空力,計測システム)

A12 ローラ式バドミントンマシンの発射性能に関する研究(空力,計測システム)

Influence of the critical velocity on deformation of launcher components

Abstract This paper is related to the dynamics of hypervelocity electromagnetic launchers. A projectile accelerating along launcher rails may cross a range of critical velocities and induce structural resonance. As a result, the rails and other components exhibit increased displacements and stress that may affect launcher performance and lead to premature launcher failure. This work is a continuation of our previous studies of the critical velocity and resulting transient resonance that was performed for a notional hypervelocity launcher [Nechitailo NV, Lewis KB. Critical velocity for rails in hypervelocity launchers. In: Proceedings of the 2005 hypervelocity impact symposium. International Journal of Impact Engineering Dec. 2006; 33: 485–495; Lewis KB, Nechitailo NV. Transient resonance in hypervelocity launchers at critical velocities [Selected papers from the 13th Electromagnetic Launch Technology (EML) Symposium, Potsdam, Germany, May 22–25, 2006]. IEEE Transactions on Magnetics Jan. 2007; 43 (No. 1, Part II): 157–162 [1,2]]. Analytical models including Bernoulli–Euler model of a beam resting on an elastic foundation and the Timoshenko and Flugge tube models as well as finite element tools helped to better understand the transient resonant regimes in launcher components and offered insight on how to alter the launching device materials and geometry to reduce the critical-velocity effects. Analysis showed that the various components of a launcher can have different critical velocities and there is a possibility of enhanced group resonance in the assemblies. The resonance in the launcher assembly can be reduced by controlling the bending stiffness of the individual components. Finite element models were used to illustrate the influence of variations in materials of launcher components on the resulting critical velocities, intensity of the group resonance, and resulting maximum displacements and stress.