SITUATION: As the an independent third party reviewer for oversight on Navy programs, JHUAPL was tasked to ensure mission requirements were being met with the SM-6 product line being produced by Raytheon. Derived from the prime contractor's prior SM-2 Block IV product line, the SM-6 contained some additional add-on features including a gimbaled active seeker for targeting over-the-horizon threats. Part of the seeker responsibility was to track the target it sensed and part of this tracking involved a guidance estimation filter that estimated the kinematic state of the target, such as line-of-sight (LOS) to the target, the rate of change of the LOS, and the acceleration of the target.
TASK: Due to the nature of the gimballed seeker that allowed it to rotate independently of the SM-6 vehicle body when tracking target, the algorithm utilized by the seeker software to propagate forward in time the system model of the discrete guidance estimation filter had several ways to implement the propagation. The task commenced with the question what is the best way to implement the propagation step of the filter.
ACTIONS: The answer to this question could not be identified as a closed form solution due to the high fidelity and complex nature of the problem. First, several methods on how the propagation step of the filter were identified. Next, these methods were coded as separate executable options into guidance estimation filter code of the SM-6 6-DOF simulation that was used to assess performance of the missile. Monte Carlo simulations were executed of each method to determine how the filter propagation methods performed in the face of missile parameter variations that were external to the guidance estimation filter
RESULTS: Comparison of the 6-DOF simulation results showed that one particular method allowed the missile to outperform all other methods. This method was communicated to the the prime who performed their own assessment of the method to decide to eventually implement the method on the missile flight software.
Photo courtesy U.S. Navy