SRAAM5—Short-Range Air-to-Air Missile

SRAAM5 is a good example of how far a five-DoF simulation can grow in so­phistication and still maintain the simple pseudo structure of the dynamic equations of motion. Figure 9.54 shows the structure with the shaded modules indicating new

elements. The A1 and A2 Modules are specific to the SRAAM concept, while the guidance loop is expanded by a midcourse and a terminal mode. In midcourse the shooter aircraft sends target data over data link to the missile INS navigator, which in turn delivers the kinematic LOS rates to the pro-nav guidance law. In the terminal phase the LOS rates are provided by an imaging infrared seeker. A brief description of the new modules follows.

The G1 Target Module implements realistic engagement scenarios are imple­mented. They are known by special designations, like Pre-Merge (shooter cen­tered), One Circle Fight, Two Circle Fight, Lufbery Circle, Target Centered En­gagement, Chase Circle, Head-On Circle, and Twin Circle. You just need to set the flag MTARG and thus invoke the preprogrammed initial conditions for target and shooter aircraft.

SI Seeker Module uses imaging IR sensors as the current state of the art for short-range air-to-air missiles. Although only generic data are used, the roll/pitch gimbals and the coordinate systems are quite realistic. The description of the seeker is at an advanced level and is therefore deferred to Sec. 10.2.6.

The S2 Air Intercept Radar is a simple kinematic model of an acquisition and tracking radar, located in the shooter aircraft. It is used to acquire and track the target and transmit that information to the missile at launch and during an optional midcourse phase.

S4 INS Module is used in midcourse only. The nine error state equations (three positions, three velocities, and three tilts) bring realism to the fly-out accuracy. The derivation of the error equations is postponed until Sec. 10.2.4.

The Cl Guidance Module provides a midcourse and terminal guidance phase. In midcourse a simple pro-nav law is implemented (see Sec. 9.2.4.1), whereas the terminal phase relies on an advanced formulation of the pro-nav law, described in Sec. 10.2.5.1.

The A1 Aerodynamics Module uses trimmed aerodynamic lift and drag coeffi­cients of a generic short-range air-to-air missile expressed in tables as a function of Mach and angle of attack, for power on/off, and three c. m. locations. The length of the missile is 2.95 m, and its diameter 0.1524 m.

The A2 Propulsion Module gives the thrust of a single-pulse rocket motor as a table of thrust vs time with backpressure corrections. Vehicle mass and c. m. shifts are also updated. Launch mass is 91.7 kg, and the motor fuel is 35.3 kg.

To your chagrin, the discussion of several features are postponed until the next chapter because of their advanced nature. Actually, I built the six-DoF version of SRAAM6 first and then converted the inner loop (equations of motion, aerody­namics and autopilot) to the five-DoF model. The outer (guidance) loop transferred with only minor modifications to the SRAAM5 simulation. If resources permit, I recommend this approach from six-DoF to five-DoF modeling because in the process we can validate our simplified model with the six-DoF truth model.

The AIM5 and SRAAM5 simulations are representative of highly maneuver – able missiles with tetragonal symmetry executing skid-to-tum maneuvers. Cruise missiles, requiring long range performance, are designed with high-aspect-ratio wings for efficient cruise. They are steered like airplanes by bank-to-tum maneu­vers. We turn now to the CRUISE5 simulation and all of the attributes of a typical cruise missile.

Fig. 9.55 CADAC CRUISE5 pseudo-flve-DoF simulation.