Optimal ballistic coefficient control for Mars aerocapture
Taking advantage of the aerodynamic force to capture the vehicle from hyperbolic orbit to planetary orbit is a preferable approach because of the lower fuel consumption. This paper aims to research the Mars aerocapture process using the ballistic coefficient as control variable, and the inflatable deceleration device is used to change the ballistic coefficient. Firstly, the corridor is described in detail considering the different ballistic coefficients. Besides, the optimal aerocapture trajectories are analyzed, which show that they have bang-bang control structures. Additionally, the optimal results are showed under the different control structures, and the corresponding performances are presented. Finally, the optimal constant control problem is analyzed through the statistical results with the different initial conditions, and the change rules of the peak heating rate and the ballistic coefficient are given.
Rapid planning for aerocapture trajectory via convex optimization
Abstract Aerocapture, which usually refers to delivering a vehicle from hyperbolic orbit to planetary orbit using the aerodynamic force, can potentially lower fuel consumption. By controlling the direction and magnitude of the aerodynamic force, the vehicle can be accurately transferred to the target orbit. This paper mainly focuses on developing a convex algorithm for the constrained trajectory planning of aerocapture. For nonlinear aerocapture problem, the main task is to convert this problem into a convex sub-problem, and then the solution of the original problem can be efficiently obtained by solving a sequence of such sub-problems with convex optimization. In order to formulate a highly constrained aerocapture trajectory-planning problem into a convex-form one, all non-convex items in aerocapture problem are turned into convex functions by successive linearization, variable equivalent replacement and control variable relaxation. The simulation results of the optimal aerocapture, represented by minimum impulse, flight time and heat load, indicate that the proposed method is highly efficient and can be potentially applied for on-board trajectory planning method.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.