Near Space Vehicle Research Articles

Fault-tolerant control design for near-space vehicles based on a dynamic terminal sliding mode technique

In this paper, a fault-tolerant control scheme based on a second-order dynamic terminal sliding mode is proposed for a near-space vehicle attitude dynamical system in the presence of actuator faults, model parameter uncertainties and external disturbances. The principle of the proposed dynamic terminal sliding mode scheme is firstly introduced. Then, a near-space vehicle attitude faulty model with parameter uncertainty is established. Furthermore, two dynamic terminal sliding mode controllers are designed for the inner and outer loops. It is shown that the proposed algorithm can reduce chattering phenomenon and guarantee system stability and asymptotic state tracking. Finally, simulation results are provided to demonstrate the performance of the proposed fault-tolerant control scheme.

Near-Space Vehicle-Borne SAR With Reflector Antenna for High-Resolution and Wide-Swath Remote Sensing

Near-space is recognized as the atmospheric region from 20 to 100 km above the Earth's surface. Near-space vehicles offer several advantages compared to low earth orbit satellites and airplanes because near-space vehicles are not constrained by orbital mechanics and fuel consumption. These advantages provide potential for future remote sensing applications, but little related work has been published. This paper explains what near-space is and how it should be exploited for remote sensing applications. A near-space vehicle-borne synthetic aperture radar (SAR) with reflector antenna and digital beamforming on receive is proposed for high-resolution and wide-swath (HRWS) remote sensing. The system configuration, signal model, imaging scheme, system performance, and nadir echo suppression are investigated. An example system is conceptually designed, along with its system performance analysis. It is shown that the near-space vehicle-borne SAR with reflector antenna can operate with high flexibility and reconfigurability, thus enabling a satisfactory HRWS remote sensing performance.

A Wide-Beam Scanning Mode for Near-Space Passive SARs

A near-space passive SAR consists of a passive radar receiver placed on a near-space vehicle and another existing radar on a satellite serving as an illuminator. In this paper, we present a wide-beam scanning mode for near-space passive SARs for the purpose of increasing the azimuth scene extension. The receiving distance of a near-space SAR is much shorter than that of a satellite-based SAR, and the synthetic aperture time for a near-space passive SAR is not longer than the time interval during which a target transverses the azimuth beam of a transmitter. We design our novel mode by spreading the azimuth beam of a receiver to match the azimuth footprint of the transmitter. We also synchronize the azimuth beam of the receiver with that of the satellite within seconds during the beam scanning to further increase the scene extension. Furthermore, we formulate the azimuth scene extension and the footprint overlapping time for near-space passive SARs in terms of the possible locations of the involved satellites and receivers. Experimental simulations demonstrate the effectiveness of our proposed mode, especially revealing that the wide-beam scanning mode improves the azimuth scene extension and footprint overlapping time over the wide-beam mode, without decreasing azimuth resolution.

Robust reliable control for a near space vehicle with parametric uncertainties and actuator faults

Based on fuzzy control techniques, this article is concerned with the problem of robust reliable control for a near space vehicle (NSV) with parametric uncertainties and actuator faults. The nonlinear dynamics of a NSV is represented by the Takagi–Sugeno fuzzy models, and then the actuator fault model and fuzzy state-space observer are developed. Next, the fuzzy observer-based robust reliable control strategy is proposed. It is proved that the fuzzy control systems for the NSV is reliable in the sense that the closed-loop system is asymptotically stable and the actuator components can operate well in the presence of some actuator faults. The developed theoretical results are in the form of linear matrix inequalities, which can be readily solved via standard numerical software. Finally, simulation results are given to illustrate the applicability of the proposed approach.

Effect of cavity location on combustion flow field of integrated hypersonic vehicle in near space

The cavity has been widely employed as the flame holder to prolong the residence time of fuel in supersonic flows since it improves the combustion efficiency in the scramjet combustor, and also imposes additional drag on the engine. In this paper, the two-dimensional coupled implicit Reynolds Average Navier–Stokes equations, the RNG k–e turbulence model and the finite-rate/eddy-dissipation reaction model have been employed to numerically simulate the combustion flow field of an integrated hypersonic vehicle. The effect of cavity location on the combustion flow field of the vehicle has been investigated, and the fuel, namely hydrogen, was injected upstream of the cavity on the walls of the first stage combustor. The obtained results show that the viscous lift force, drag force and pitching moment of the vehicle are nearly unchanged by varying the cavity location over the location range and designs considered in this article, namely the configurations with single cavity, double cavities in tandem and double cavities in parallel. The variation of the fuel injection strategy affects the separation of the boundary layer, and the viscous effect on the drag force of the vehicle is remarkable, but the viscous effects on the lift force and the pitching moment are both small and they can be neglected in the design process of hypersonic vehicles. In addition to varying the location of the cavities, three fuel injection configurations were considered. It was found that one particular case can restrict the inlet unstart for the scramjet engine.

Robust fault-tolerant tracking control for a near-space vehicle using a sliding mode approach

In this study, a flight fault-tolerant control scheme based on an adaptive sliding mode technique is proposed. First, a control allocation of a near-space vehicle (NSV) attitude dynamics is analysed, and actuator fault modelling is introduced. Then, a modified sliding model tracking control approach, using a continuous strategy of integral sliding mode control, is designed to improve the position tracking precision. This scheme can solve the chattering problem without loss of robustness and control accuracy. Actuator fault and unmeasurable external disturbances are compensated for by an integral action term. To verify the effectiveness of the proposed control scheme, a numerical simulation is performed for an NSV attitude system, which is a non-linear aircraft model with six degrees of freedom. Simulation results demonstrate that the closed-loop system has good performance in spite of the actuator fault and system disturbances.

Active fault-tolerant tracking control for near-space vehicle attitude dynamics with actuator faults

Based on both adaptive and fuzzy logic techniques, the fault-tolerant tracking problem for near-space vehicle (NSV) with actuator faults is investigated in this paper. First, the nonlinear NSV attitude dynamics is given, which can represent the dynamic characteristics of NSV in both ascent and re-entry phases. The actuator fault under consideration in this study is the loss of effectiveness, and a novel fault detection scheme is presented by designing a nonlinear fault detection observer. In terms of fault detection information and multi-observer technique, a fault isolation scheme is proposed. Taking advantage of a fuzzy logic system (FLS) to approximate the unknown nonlinear function, an adaptive FLS-based fault-tolerant tracking control law is developed to achieve asymptotic output tracking and closed-loop stability of NSV attitude dynamics in spite of the actuator faults. Simulation results are provided to illustrate the feasibility of the proposed fault-tolerant tracking control approach.

Near-space vehicles: Supply a gap between satellites and airplanes for remote sensing

Near-space is defined as the atmospheric region from about 20 kilometer (km) to 100 km above the Earth's surface; near-space vehicles offer several advantages to Low Earth Orbit (LEO) satellites and airplanes because near-space vehicles are not constrained by orbital mechanics and fuel consumption. Some of the near-space vehicle advantages include their potential for some specific radar applications that require persistentiy monitoring or fast-revisiting frequency which are explained herein. The role of near-space vehicles is reviewed in supplying a gap between satellites and airplanes for microwave remote sensing applications. Several potential applications such as passive surveillance, reconnaissance, and high resolution wide swath imaging are described. The novel multiple-input and multiple-output (MIMO)-based multi-aperture in elevation and space-time coding (STC) synthetic aperture radar (SAR) are presented for high resolution wide swath imaging. Therefore, given their operational flexibility, near-space vehicle-borne radars may supply the gap between space-borne and airborne radars which is the reason we appeal to the systems engineering community for more publications and more support on the research and development of near-space vehicle-borne radars.

Fault tolerant control for near space vehicle: A survey and some new results

A review on fault-tolerant control (FTC) for near space vehicle (NSV) is presented. First, the concept of near space is introduced, the background of NSV is emphasized, and the model characteristics of NSV in faulty case are investigated. Then, a comparison of different existing approaches is briefly carried out, and achievements on the current research in this field are also presented in the view of the practical application. Furthermore, several existing advanced FTC results for nonlinear flight control systems are given. Finally, the recent literature of NSV are pre- sented to provide an overall view of future developments in this area.

Fault Tolerant Control for a Class of Nonlinear Systems with Application to Near Space Vehicle

In this paper, a fault tolerant control (FTC) scheme, which is based on backstepping and neural network (NN) methodology, is proposed for a general class of nonlinear systems with known structure and unknown faults. Firstly, the linearly parameterized radial basis function (RBF) NNs are employed to approximate unknown system faults, and the network weights are adapted using adaptive on-line parameter-learning algorithms. Then an adaptive backstepping based FTC is designed to compensate for the effect of system faults. The asymptotical stability of the closed-loop system and uniform boundedness of the state tracking errors are proved according to Lyapunov theory. Finally, the designed strategy is applied to near space vehicle (NSV) attitude dynamics, and simulation results are presented to demonstrate the effectiveness of the proposed approach.

Adaptive Fault-Tolerant Tracking Control of Near-Space Vehicle Using Takagi–Sugeno Fuzzy Models

Based on the adaptive-control technique, this paper deals with the problem of fault-tolerant tracking control for near-space-vehicle (NSV) attitude dynamics. First, Takagi–Sugeno (T–S) fuzzy models are used to describe the NSV attitude dynamics; then, an actuator-fault model is developed. Next, an adaptive fault-tolerant tracking-control scheme is proposed based on the online estimation of actuator faults, in which a compensation control term is introduced in order to reduce the effect of actuator faults. Compared with some existing results of fault-tolerant control (FTC) in nonlinear systems, the technique presented in this paper is not dependent on fault detection and isolation (FDI) mechanism and is easy to implement in aerospace-engineering applications. Finally, simulation results are given to illustrate the effectiveness and potential of the proposed FTC scheme.

Adaptive functional link network control of near-space vehicles with dynamical uncertainties

Adaptive functional link network control of near-space vehicles with dynamical uncertainties

Fault-tolerant control for a near space vehicle with a stuck actuator fault based on a Takagi-Sugeno fuzzy model

Based on both adaptive and fuzzy control techniques, this paper proposes a fault-tolerant control (FTC) approach for near space vehicle (NSV) re-entry attitude dynamics with a stuck actuator fault. A Takagi-Sugeno fuzzy model is used to describe complex NSV attitude dynamics. The principle of this FTC approach is to design an iterative learning observer, which is used to estimate the system state and produce control input adjustment and then to reconfigure the control law to compensate for the effect of the stuck actuator. The FTC scheme ensures that the NSV output dynamics asymptotically track that of a reference model under both fault-free conditions and with a stuck actuator. The boundedness of the error dynamics is analysed using the Lyapunov stability theory. Finally, simulation results are given to illustrate the effectiveness and potential of the proposed FTC technique.

SMDO-Based NGPC Control for Uncertain Nonlinear Systems

As the velocity of near-space vehicle (NSV) is hypersonic, the system should be influenced by strong disturbance and uncertainty. It is difficult to design the flight control system. Nonlinear Generalized Predictive Control (NGPC) method is investigated based on the mechanism model. However, the control performance of NGPC method based on nominal model will be degraded for uncertain systems. Therefore, concerning about a class of uncertain nonlinear systems, the ideal NGPC law based on uncertain model is raised first in this paper. Then a sliding mode disturbance observer (SMDO) is designed to estimate the compound disturbance which includes internal uncertainty, modeling error, and external disturbance. On the other hand, the outputs of SMDO are integrated with nominal NGPC law to eliminate the hybrid disturbance. Furthermore, the stability of the close-loop system is analyzed using the Lyapunov method. Finally, the developed control strategy is used in a hypersonic NSV attitude control system, and simulation results show good robustness and disturbance attenuation ability of this strategy.

Conceptual design of near-space synthetic aperture radar for high-resolution and wide-swath imaging

Airborne synthetic aperture radar (SAR) has the capability of high-resolution, and spaceborne SAR has the capability of wide-swath. Inspired by recent advances in near-space defined as the region between 20 km and 100 km, this paper conceptually designed near-space vehicle-borne SAR. The near-space vehicle-borne SAR has the synthetical advantages of the satellite and airplane platforms. By placing SAR transmitter or receiver in near-space vehicles, many functions that are currently performed with satellites or airplanes could be performed in low cost way. These advantages make simultaneous high-resolution and wide-swath SAR imaging possible. As such, this paper focuses on the role of near-space vehicle for high-resolution and wide-swath SAR imaging, and deals with conceptual performance, as opposed to technological implementation. The concepts, models and processing algorithms are provided. To further suppress the azimuth ambiguities and extend swath width, multiple beams in azimuth is applied. Furthermore, an example near-space vehicle-borne SAR is designed. It is shown that the use of cost effective near-space vehicles can provide the solutions that were previously thought to be out of reach for remote sensing scientists and customers.

Near-Space Wide-Swath Radar Imaging With Multiaperture Antenna

Near-space, defined as the altitude region between 20 and 100 km, offers many capabilities that are not accessible for low Earth-orbit (LEO) satellites or airplanes because it is above storm and not constrained by orbital mechanics and high fuel consumption. Hence, a high flying speed can be obtained for the maneuvering vehicles operating in near-space. This offers a promising solution to simultaneous high-resolution and wide-swath synthetic aperture radar (SAR) imaging. As such, one near-space wide-swath SAR imaging technique is presented in this letter. The system configuration, signal model, and imaging scheme are described. An example near-space SAR system is designed, and its imaging performance is analyzed. Simulation results show that near-space maneuvering vehicle SAR indeed seems to be a promising solution to wide-swath SAR imaging.

Prospects for the use of thermionic nuclear power plants for interorbital transfers of space vehicles in near space

Prospects for the use of thermionic nuclear power plants for interorbital transfers of space vehicles in near space