This paper introduces a method to minimize norms on nonlinear trajectory sensitivities
during open-loop trajectory optimization. Specifically, we derive new parametric
sensitivity terms that measure the variation in nonlinear (continuous-time)
trajectories due to variations in model parameters, and hybrid
sensitivities, which account for variations in trajectory caused by sudden
transitions from nominal dynamics to alternative dynamic modes. We adapt continuous
trajectory optimization to minimize these sensitivities while only minimally changing a
nominal trajectory. We provide appended states, cost, and linearizations, required so that
existing open-loop optimization methods can generate minimally sensitive feedforward
trajectories. Although there are several applications for sensitivity optimization, this
paper focuses on robot motion planning, where popular sample-based planners rely on local
trajectory generation to expand tree/graph structures. While such planners often use
stochastic uncertainty propagation to model and reduce uncertainty, this paper shows that
trajectory uncertainty can be reduced by minimizing first-order sensitivities. Simulated
vehicle examples show parametric sensitivity optimization generates trajectories optimally
insensitive to parametric model uncertainty. Similarly, minimizing hybrid sensitivities
reduces uncertainty in crossing mobility hazards (e.g. rough terrain, sand, ice). Examples
demonstrate the process yields a planner that uses approximate hazard models to
automatically and optimally choose when to avoid hazardous terrain and when controls can
be adjusted to traverse hazards with reduced uncertainty. Sensitivity optimization offers
a simple alternative to stochastic simulation and complicated uncertainty modeling for
nonlinear systems.