Lowest-Technical-Merit Design Methodology Of Hypersonic Cruise Vehicle

Hypersonic cruise vehicle(HCV)adopts airbreathing propulsion system,and cruises at a Ma ? 5 in the nearspace.Its high speed could remarkably shorten the flight duration,which is beneficial to time-sensitive missions such as emergency transportation,highspeed airliner,and prompt global strike.Since its propulsion system could provide higher efficiency than rocket engines do,HCV has better potential in range/payload performance.Thus it could be used as a common flight carrying platform or a support for S/TSTO systems.Besides,since the near space is outside the working points of most aerial/space vehicles,HCV has well penetration ability.These characteristics endow HCV with a vast potential and great strategic value,and make it a focus of long-range-high-speed flights.However,the development of HCV is challenged by all the subsystems/disciplines.From the perspective of development roadmap of hypersonic vehicle technologies,HCV is based on the boost-glide vehicle,and provides the basis for SSTO aerospace plane.At present,the boost-glide technology is approximately mature,and HCV becomes the focus.The technical levels of involved subsystems could still not support the design or manufacture of HCV,and the interactions among these subsystems make their developments more difficult.Under this background,the primary problem of integrated design is early realization,to seize the initiative of market or fighting capacity.Therefore,the dominant contradiction of HCV is no longer an economical concern,but a conflict between demanded vehicle performances and insufficient subsystem performances.This contradiction brings with the infeasible problem of HCV design.To resolve this problem,one approach is to improve the performances and technical readiness levels of subsystems,and the other is to improve the feasibility by integrated design.By the latter way,this research proposed two technical routes: 1)allocate subsystem performances by lowest-technical-merit design methodology,to achieve the most feasible design;2)design/optimize a periodic cruise trajectory,to reduce the requirements for subsystem performances.The contents of this study are detailed as follows:(1)With the contradiction of system design and development law of subsystems/disciplines studied,a lowest-technical-merit(LTM)design methodology has been proposed,to coordinate the developments of subsystems.By this methodology,a most feasible design could be achieved.With range/payload performance and subsystems of HCV considered,a LTM suitable for HCV has also been proposed.(2)With couplings among aerodynamics,propulsion,aerothermodynamics,flight dynamics,and thermodynamics studied,a multi-disciplinary dynamic model is built,to describe the coupled dynamics of HCV.With dynamic analyses of normalized flight dynamics,a 3Do F model is proposed,to resolve the motion of equilibrium point caused by fuel consumption.Hence the design problem of multiple periods could be converted to one of single period.(3)With the optimal periodic control of HCV studied,an optimal periodic control theory with constraints is proposed.By this theory,three important features of optimal periodic cruise trajectory have been found,namely 1)bang-singular-bang control of equivalent ratio,2)consistency between singular arc of active cooling and boundary arc of inner wall temperature,and 3)discontinuity of costate and control inputs caused by pure state constraints of velocity.(4)With the mechanism of optimal periodic cruise and the stability of normalized flightpath-density closed orbit studied,a design approach of stable/suboptimal periodic cruise trajectory has been proposed.By this approach,the instability problem of optimal periodic cruise could be resolved;meanwhile,the advantages of periodic cruise in performances could be succeeded.(5)With the technical merit of periodic cruise studied,a design methodology of periodically cruising HCV has been proposed.By this methodology,periodic cruise and LTM are considered together,and the effectiveness of periodic cruise to reduce system-gross technical merit has been verified.This study is focused on the problem to improve the design feasibility of HCV from the perspective of system.A lowest-technical-merit design methodology and an applicable periodic cruise trajectory design approach have been proposed,and the influences of steady/periodic cruises on subsystem technical merits have been compared.This study could help to suggest the future development focus of HCV,and to coordinate the consequent advances,thus leading to a higher feasibility of a HCV design.