Prediction-Correction Guidance Algorithm for High Velocity Reentry Capsules

Spacecraft returning from lunar or interplanetary missions reenter the Earth’ s atmosphere with velocities that can approach 11 km/s. The landing position accuracy on the Earth is severely affected by small errors in the vehicle ’ s position and velocity, unforeseen variations in the atmospheric density and imperfect vehicle modeling. An adaptive guidance control approach is presented to ensure precision of the landing location. The algorithm is a multi-step predictor-corrector iterative approach. A self-adaptive control law, composed of two quantities termed the gross error adjustment and the fine error adjustment, is developed. The gross error adjustment effectively reduces the vehicle cross range error. The guidance law continuously adjusts the capsule’ s bank angle until the bias in the capsule’ s cruising range is less than a prescribed value at which point the fine adjustment reduces the capsule’ s landing position error. The algorithm’ s adaptability is applied to the deep space mission reentry profile for a variety of initial conditions. Results demonstrate adaptability to the bias ranges of -0.6 ° to +0.25° in reentry angle, -25% to +25% in lift-drag ratio, and -80% to +100% in atmospheric density. Additionally, it is shown that the algorithm has the capability to remove a reentry insertion error of more than 100 km.