Trajectory Optimization And Entry Guidance For Clipper Vehicle

Lifting entry vehicle has advantages of high lift-to-drag ratio, small entry overload,large motorized range, and high landing accuracy, so it has enormous appeal anddevelopment prospects. The United States, Russia and EU have invested a lot ofmanpower, material and financial resources on the research of lifting entrytransportation vehicle. But the history has proved that the system reliability and thereusable technology which is necessary in the development of transportation vehicle arefar from the expected level.While announcing the retired of the space shuttle, the United States starts adevelopment program of new generation of launch vehicle and spacecraft. During thesame period, Russia discloses a new transportation vehicle Clippers, which between thetraditional manned spacecraft and the space shuttle. With two configuration designs, theClippers vehicle has the potential to meet the technical and reliability requirements, andit is considered to be the represent of the new generation transportation vehicle. Thispaper summed up the technology development path and analyzes the technology trendsof the transportation vehicle in the world. It takes the Clippers-type vehicle as theresearch object and focuses on its entry force environment, trajectory characteristics,and autonomous entry guidance method for lifting entry. The study includes thefollowing aspects.First, according to the overall design phase of the mission and features of the twotypical configurations of the Clippers vehicle, engineering calculation methods andnumerical methods were used from the perspective of system balancing in thecalculation and analysis of longitudinal aerodynamic characteristics. The results showthat the longitudinal aerodynamic coefficient Clippers vehicle having remarkableregularity with the change of angle of attack and Mach number. In the range of smallangle of attack, the aerodynamic coefficient changes gently. While the angle of attackcontinues to increase, the shock interaction induced flow separation, and it then formedseparation vortices, which led to complex changes in the vehicle surface pressure loaddistribution, this phenomenon manifests as the nonlinear changes in the aerodynamiccoefficients.Secondly, this paper studies the specific applications of the SG-R algorithm in thetrajectory optimization of lifting entry vehicle, and formed an improved SG-Roptimization method. Through the conversion of the general mathematical model of thecontrol constraints and process constraints, the augmented entry equations of motionand control variables are constructed. In order to reduce the nonlinear effects inherent inthe motion model, a full state integral-update method is introduced. The influence onthe results of numerical optimization of different conditions, such as the initial updatemethod, atmospheric model, constraint processing method, is analyzed by the algorithmsimulation. Based on the numerical optimization results of entry trajectory, various design factors of angle of attack in the initial entry phase, equilibrium glide phase andTerminal Area Energy Management are considered. This paper proposed the program ofconstant high angle of attack and maximum lift-drag ratio angle of attack for differenttasks backgrounds, the specific profile function of the angle of attack is designed andused for entry guidance algorithm design.Thirdly, a new online three-dimensional trajectory planning and trajectory trackingentry guidance method is designed based on drag acceleration versus energy profile isproposed. The trajectory planning is based on two sub-line updating policy. In eachplanning stage, the bank angle reverses only once. The reference drag accelerationenergy profile is matched to the target range by adjusting the parameters, and nominaltrajectory is tracked using the bank angle as the main tracking control variables. Sincethe trajectory planning taking into account the vertical and horizontal movement of thevehicle, it does not need to specifically regulate the bank reverse in lateral channel. Thealgorithm program simulation results show that, online planning reference dragacceleration profile shows the trend of slightly fluctuating by the balanced gliderboundary, which keep the entry trajectory to meet process constraints, decent along thebalanced glider border steadily until the end of the entry phase. Monte Carlo analysisshows that, the method is able to independent planning three-dimensional entrytrajectory quickly and efficiently. It has high guidance precision, strong task adaptabilityand the potential of online application.Finally, in the framework of predictor-corrector guidance, a numerical predictioncorrection entry guidance which based on virtual target strategy is present. By using thebalance gliding conditions, the method transformed the process constraints into the bankangle velocity corridor under the condition of the angle of attack profile is given, whichis used as the design constraints of the nominal bank profile and the output truncatedboundary of quasi-guidance commands. In lateral guidance logic, a virtual targetstrategy is introduced. It makes full use of the time cumulative effect of high-levelatmospheric damping. By regulating the bank angle of initial decrease phase, guidingthe vehicle flight a considerable lateral offset, which is used to offset the impact of thenon-inertial force in the department of earth, and the guidance burden of thequasi-equilibrium glide phase will be reduced. The program simulation analysis showsthat, the method overcomes the contradiction of insufficient accuracy of entry guidancedue to the limited trajectory tracking capability. The algorithm has strong taskadaptability and high stability. Monte Carlo analysis shows that, the bias targetingstrategy has enhanced and ensured the entry terminal guidance accuracy. Especially inthe long range and large orbital inclination entry conditions, the effect is more obvious,and it has a simple and easy maneuverability.