Explicit guidance law for manned spacecraft

The paper presents a closed loop guidance law for the sxoatmospheric trajectory of a launch vehicle. This algorithm has been especially developped for manned misson. The main objectives of this investigation were optimization, accuracy and reliability. Another great issue was to reduce the mission analysis. The explicit guidance generates onboard the optimal path to the desired orbit while optimizing fuel consumption, and respecting some constraints. The computation of the steering law is based on an analytical integration of the trajectory which is divided in a little number of segments. Intermediate constraints such as thermal flux, stage footprint, radar visibility, are applied at the end of the segments. At the final point five orbital parameters are targetted. The steering law parameters are updated at each guidance cycle to cancel predicted constraint errors, using a linear differential correction method. Simulations tested this algorithm with respect to accuracy, optimization, reconfiguration capability. Results are very good compared with off-line ii optimization. NOMENCLATURE to. tf U Global control vector Y Global constraints vector AK Predicted constraints errors vector r Sensitivity matrix of constraints w.r.t. control parameters AU Control vector wrrection %,vi Initial and final velocity of vehicle on a segment 6,g Initial and final position of vehicle on a segment Vih-Rth First and second integrals of thNst effect on a segment vt,,c First and second integrals 01 gravity effect on a segment V, Ejected gas velocity 7 zero mass time l o h J o . J n xo. xi Initial and final dates of a segment.