Robust approach and landing trajectory generation for reusable launch vehicles in winds

When a reusable launch vehicle (RLV) experiences a failure, it is crucial to recover the vehicle from such failure in real time. Our previous works proposed a scheme of motion primitives (MPs) and neighboring optimal control (NOC) to deal with on-line trajectory reshaping on approach and landing (A&L). Furthermore, a robustifying term was introduced to robustify NOC when the failures are severe. Wind speed especially wind shear has been shown to be a greater hazard than had been appreciated, however, the flight safety during A&L has to be treated more seriously when wind effect is included. In this paper, wind effects on robust A&L trajectory generation for RLVs are discussed based on our prior works, namely, neighboring feasible trajectory existence theorem (NFTET) and trajectory robustness theorem (TRT). A straightforward wind effect theorem (WET) will then be investigated. According to WET, the modifications to the NOC approach and robustification can on-line recover those vehicles in winds from some failures even if they are severe. The simulation results verified the conclusions.