**2. Materials and methods**

Submersible vehicles require control systems to guide the vehicle around obstacles that can present dangers to vehicle health and safety in the presence of ocean currents. The challenge addressed here is to navigate the Naval Postgraduate School's *Phoenix* submersible vehicle (**Figure 1**) through a minefield whose dimensions are 200 m 5100 m in the presence of 0.5 m/s ocean currents. The field will contain at least 30 mines placed at locations using a random number generator. The resulting controller structure has an inner-outer loop structure, and several technologies will be described including pole-placement designs, linear-optimal (quadratic) Gaussian techniques, full and partial order observers for online disturbance identification for ocean currents (both constant lateral underwater ocean currents and also sinusoidal varying currents), tracking systems and feedforward control designed to counter open ocean currents, in addition to integral control. The outer loop controller uses Line-of-Site (LOS)

**Figure 1.** Submersible vehicle sample and notional minefield [1]: (a) field of randomly placed submersed mines to be avoided by autonomous vehicle and (b) *Aries* submersible in open ocean.

guidance to provide a heading command to the inner loop. The inner loop controller uses output heading feedback to track heading commands. The vehicle is simulated to traverse the minefield and successfully travels no closer than 5 m from any mine and arrive within one half meter from the commanded destination autonomously.
