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Typical flight motion simulation (FMS) systems for missiles with infrared (IR) seekers include missile and target simulation subsystems. The seeker “flies” a three-axis table – the missile simulator – whereas a simulation computer “flies” a two-axis positioner – the evading target. When the costs of this process became unmanageable for one aerospace company, they sought help from Ideal Aerosmith and the result was an ingenious and cost-effective solution.
How we solved it.
FMS systems with five-axis hardware-in-the-loop (HIL) control tend to be very expensive, and for one customer, such a solution exceeded the budget. Due to unit under test (UUT) characteristics such as mass, inertia, and mechanical interface, no substantial cost savings could be achieved on the three-axis missile simulator subsystem.
That meant that a substantially different implementation was needed for the target simulator to achieve the desired cost savings. Notwithstanding its anticipated drastic design change, the control of the new target simulator was not allowed to impose an additional computational burden on the simulation computer.
The solution represents a significant paradigm shift in target simulation. The optical scene is created by a stationary projector and then manipulated by two mirrors to cause it to appear as if coming from various angles to the UUT. The simulation computer uses the scene incident angle as input and generates the control angles for the two mirrors.
Although each mirror is manipulated by a small, two-axis positioning table, this approach is substantially less expensive than a traditional two-axis scene positioner because it maintains the target dynamics using lower cost hardware with significantly reduced power requirements. Additionally, this setup has a substantially smaller footprint than the conventional one.
Mapping the scene incident angle on the UUT to specific mirror control angles would normally require solving a system of nonlinear equations in real-time. No closed-form solutions exist for these equations and solving them through numerical algorithms would violate the real-time requirement, whereas using look-up tables, as suggested by the customer, would have an extremely large memory footprint. However, Ideal Aerosmith provided a solution that exceeded all expectations on positioning accuracy, memory footprint, and computational burden: approximation through multivariate polynomials.
A similar polynomial approximation was also provided for the in-plane scene rotation compensation, leading to an overall optimal solution.
Ideal Aerosmith’s engineering ingenuity – coupled with a scientific approach to tackling difficult problems – led to a nonconventional and cost-effective FMS solution. The “evading target” is simulated with a fixed projector and two optical mirrors, drastically reducing the dynamic requirements for the positioner. Additional benefits of this approach included a substantially smaller footprint and overall target cost savings.